Study on characterization of SrO Aerosols Generated by Optimized Thermal Plasma Torch Aerosol Generator

Study on characterization of SrO Aerosols Generated by Optimized Thermal Plasma Torch Aerosol Generator | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Study on characterization of SrO Aerosols Generated by Optimized Thermal Plasma Torch Aerosol Generator Amit Kumar, P. Usha This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-4007909/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 07 Nov, 2024 Read the published version in Aerosol Science and Engineering → Version 1 posted 6 You are reading this latest preprint version Abstract Plasma Torch Aerosol Generation System (PTAGS) has been employed to generate nano aerosols with desirable characteristics. The operational parameters of PTAGS installed in the aerosol test facility have been optimized, and aerosols are generated using non-radioactive SrO 2 powder. The current-voltage characteristics, electro-thermal efficiency and torch power are studied as a function of the flow rate of the plasma-generating gas (mixture of argon and nitrogen) and the arc current of the plasma torch. The arc characteristics relation is determined using the Nottingham formulation. Based on this, torch parameters are evolved and optimized as 20 kW power, 70% electro-thermal efficiency, 25 L min − 1 flow rate of plasma forming gas, 5 mg min − 1 powder feed rate and for 4–5 min torch operation towards the generation of SrO nano aerosols to achieve 10 12 m − 3 and ~ 25 mg m − 3 for the count and mass concentration of aerosol respectively. The initial size distribution of the aerosols is in the few tens of nanometre range (10–40 nm) with a mean diameter of 26 nm (σ g = 1.45). SEM and EDAX analysis reveal that the morphology of nano aerosols was nearly spherical and the formation of SrO nanoparticles. A set of operational parameters of PTAGS has been standardized to perform further experiments related to reactor safety analysis. PTAGS shall be tuned for aerosol generation in a large facility to achieve the characteristics equivalent to reactor accidental conditions. I-V characteristics electro-thermal efficiency plasma torch aerosol generator aerosols characterization Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 Figure 12 Figure 13 Figure 14 Figure 15 1.0 Introduction Today thermal technology covers a broad spectrum of applications, which are classified as coating including spraying (Samal, 2017 ), chemical vapour deposition (Rao et al., 1998 ), waste destruction (Chang et al., 1997 ), densification of powders, metallurgy, synthesis of fine powders, material cutting in air and water (Steiner et al., 1988 ; Windelberg et al., 1987 ), generating nanoparticles and many more (LF Pfender, 2000 ). The nanoparticles are formed by plasma synthesis through gas/ vapour to particle conversion. The high temperature of the plasma state is used for the interaction of plasma with solids and gases, which is the basis for plasma-enabled material processing called plasma synthesis and material processing (Young and Pfender, 1985 ). The materials introduced into the plasma flame zone are evaporated while plasma-forming gas provides an inert atmosphere to prevent undesirable reactions. Condensable molecules produced by these processes are self-nucleated to form nanoparticles. The advantages of plasma spray torch in material processing (N. Venkatramani, 2002 ) consist of (i) high enthalpy to increase the kinetics of the reaction, (ii) sharp temperature gradient that enables quick quenching and (iii) the clean or varying reaction atmosphere. These processes, in tandem, can produce several effects in material processing to manufacture high-purity materials of ultra-fine powders (Kruis et al., 1998 ). The plasma torch parameters, such as power, type of plasma generating gas, and flow rates, vary depending on the material processing and synthesis. Noble gases like argon and helium are the most used gases to form plasma. In some cases, nitrogen, hydrogen, air, oxygen, carbon monoxide, steam, methane, and their mixtures are also used (Glocker et al., 2000 ). In general, N 2 or H 2 is used as a plasma-forming gas since the energy content of nitrogen and hydrogen is higher than that of argon and helium due to its diatomic nature. Non-reactive gases are advantageous for several applications where chemical reactions between plasma gas and substrate have been avoided. If oxidizing gases are used in conventional plasma torches, a high electrode erosion occurs, thus limiting the lifetime and contaminating the plasma torch with electrode material. Nevertheless, argon is usually favoured as a plasma-generating gas to have an inert reaction environment. Based on the temperatures of the electrons, ions, and neutrals, plasmas are categorized as thermal or non-thermal. Thermal plasmas have electrons and heavy particles/ ions at the same temperature, i.e., in thermal equilibrium. On the other hand, non-thermal plasmas have ions and neutrals at much lower temperatures (sometimes room temperature), whereas electrons are at higher temperatures (Samal, 2017 ). Thermal plasma torches generate the plasma by Direct Current (DC), Alternating Current (AC), Radiofrequency (RF) and other discharges. DC torches are the most used and researched than AC torches as there is less flicker generation and noise, give a more stable operation and better control, operate with a minimum of two electrodes, lower electrode erosion, low power consumption and slightly lower heat wear (Gomez et al., 2009 ). In a DC torch, the electric arc is formed between the electrodes (made of copper, tungsten, graphite, molybdenum, silver etc.), and the thermal plasma is formed from the continual input of carrier gas. Furthermore, the flow rate of the carrier gas can be raised to promote a larger, more projecting plasma jet if the arc current is sufficiently increased and vice versa. It is important to note that there are two types of DC plasma torches viz. (i) non-transferred arc: electrode inside the torch body, arc is formed inside the body and low electrical to thermal efficiency and (ii) transferred arc: one electrode outside the torch body, arc is formed outside the body and high electrical to thermal efficiency. Many researchers have used atmospheric transferred arc thermal plasma torches for synthesis of metal oxide particles (Balasubramaniam et al., 2004 ; Banerjee et al., 2006 ; Praburam and Goree, 1996 ; Prodi et al., 1988 ). The quality of plasma generated is a function of density (pressure), temperature and torch power, i.e., the greater the torch power, the better the plasma. The efficiency of the plasma torch can vary among manufacturers, design, and torch technology (Leal-Quirós, 2004 ). The thermal efficiency of the torch varies over a wide range of 10–90 %. The thermal plama temperature is 10 4 K, so solid powder (metal, metal oxide, and ceramic) can be evaporated quickly, and nanoparticles form upon cooling while exiting the plasma region. The thermal plasma torches that produce nanoparticles are mainly based on DC plasma jets, DC arc plasmas, and radio frequency (RF) induction plasmas. In the arc plasma torch, an electric arc formed between the anode and the cathode provides the necessary energy for evaporation. Different plasma torches were used for various purposes; generally, rod-type cathode and nozzle shape (conical) anode and torch power ranges from 2 to 6000 kW. The Plasma Torch Aerosol Generation System (PTAGS) consist of a rod-type cathode and nozzle shape (conical) anode and gives an intense and prolonged plasma flame for the contentious aerosol source from metal, ceramic, and composites (Baskaran et al., 2004 ; Krasenbrink et al., 1995 ). The concentration of nanoparticles can be achieved as high as 10 13 /m 3 by this kind of aerosol generator. As a part of reactor safety studies, the Indira Gandhi Centre for Atomic Research (IGCAR) is involved in aerosol studies pertaining to severe accident conditions of sodium-cooled Fast Reactors (SFR). Out of the different aerosol generation techniques, the plasma torch is most preferred and used for generating metal aerosols in experimental facilities (Baskaran et al., 2004 ; Suckow and Guentay, 2008 ). PTAGS best simulates the characteristics of the aerosol generated during severe nuclear reactor accidents. Towards this, a non-transferred DC arc, atmospheric pressure, thermal plasma torch with a suitable power supply, control system and water-cooling system were installed in the Aerosol Test Facility (ATF). PTAGS generates nanoparticles of non-radioactive fission products and fuel equivalent, metals, ceramics, and composites. This paper focuses on optimizing the working parameters of PTAGS for generating aerosols and studying the characteristics (number and mass concentration, size distribution, and initial aerosol size) of generated aerosols. The torch characterization allowed scoping operative ranges based on minimum voltage fluctuations and maximum thermal efficiency for different gas flow rates, arc current and process gases. The current study uses a mixture of nitrogen and argon gas as plasma process gas; the PTAGS was operated at different powers and various gas flow rates, and the current-voltage characteristics and electro-thermal efficiency are studied under atmospheric pressure conditions. The powder feeder used for feeding the test material for aerosol generation is calibrated concerning mass flow rate for various feed rates. The aerosols that are generated are characterized using a filter paper sampler, Sequential Mobility Particle Sizer (SMPS), Energy dispersive X-ray (EDAX) spectroscopy, Scanning Electron Microscopy (SEM) and Mastersizer − 2000. The optimized working parameters of PTAGS and aerosol characteristics are analyzed and would be a crucial database for future nuclear reactor safety analysis studies. The detailed characterization of PTAGS and generated nano aerosol is reported in this paper. 2.0 Background and Theory The primary operational characteristics of a plasma torch are its current voltage, electro-thermal characteristics, and torch power. The generalized characteristics of plasma torch are experimentally introduced hyperbolic characteristics related to arc voltage, current and arc length (Mosleh et al., 1994 ; Ramasamy and Selvarajan, 2000 ). However, the characteristics are valid only for carbon electrodes in air with a few millimetres of arc length. Nottingham proposed an arc characteristics relation, which is much broader in application (Nottingham, 1926 , 1923 ). Eberhart and Seban have studied the characteristics of a high-intensity argon arc with a water-cooled anode to develop an empirical relation between the arc voltage, current, and arc length (Eberhart and Seban, 1966 ). The applicability of the Nottingham relation to stabilize a non-transferred plasma torch by correlating the electrode heat losses, input power and arc current under different gas flow rates and a mixture of argon and nitrogen gas has been evaluated (Das et al., 1993 ). Detailed studies on the characteristics of a non-transferred and transferred arc plasma torch, the internal diameter of the electrode for different gas flow rates and different mixture ratios of argon and nitrogen gas have been performed using dimensionless analysis (Venkatramani and Ray, 1997 ). Brilhac et al. studied DC vortex plasma torch dynamic and static behaviour with well and button type cathode (Brilhac et al., 1995a , b ). Planche et al. reported the I-V characteristics of the DC plasma torch, such as gas flow rate and nozzle diameter (Planche et al., 1998 ). The preceding review shows that only a few works focused on establishing a relation connecting the arc voltage, arc current and plasma forming gas flow rates (Ramasamy et al., 2000 ). 2.1 Current-Voltage Characteristics of the Torch The relationship between arc voltage (V) , current (I) and arc length (l) is given by the Nottingham equation (Das et al., 1993 ; Nottingham, 1926 ). $$V=\left(A+B*l\right)+\left(C+D*l\right)*{I}^{-n}$$ 1 Where A, B, C and D are constants depending on the nature of the plasma torch, plasma generating gas, flow rate, gas pressure, electrode material etc. (Ramasamy and Selvarajan, 2000 ). The exponent' n' depends on the anode material and type of plasma generating gas. The typical value of n is 1 for carbon and 0.65–0.67 for copper electrodes (Das et al., 1993 ) and depends on some degree of intensity of anode cooling. For the constant length of arc, Eq. ( 1 ) can be written as: $$V= {K}_{1}+ {K}_{2}*{I}^{{\prime }}$$ 2 $$\text{H}\text{e}\text{r}\text{e}, {K}_{1}= A+B*l, {K}_{2}= C+D*l \text{a}\text{n}\text{d} {I}^{{\prime }}={I}^{-n}$$ Similarly, if plasma-generating gas flow rates are known, then the above relation can be modified and written as $$V=\left(A+B*{f}_{t}\right)+\left(C+D*{f}_{t}\right)* {I}^{{\prime }}$$ 3 Where f t is the total flow rate of plasma generating gas. For constant gas flow rate, Eq. ( 3 ) become like Eq. ( 2 ). The value of coefficients K 1 and K 2 are determined by solving Eq. ( 2 ) using the least square method. Once the values of coefficients K 1 and K 2 are known, a suitable system of equations is formulated from which constants A, B, C and D are determined. The system of equations is in the following forms: $$A+B*{{(f}_{t})}_{i}= {{(K}_{1})}_{i}$$ 4a $$C+D*{{(f}_{t})}_{i}= {{(K}_{2})}_{i}$$ 4b Where i ranges from 1 to N and N is the number of experiments. The Eq. (4a) and (4b) can be written in matrix form as: $${M}_{Nx2}*{X}_{2x1}= {K}_{Nx1}$$ 5 The solution of the above matrix is calculated as: $$\left[X\right]= {\left[{M}^{{\prime }}*M\right]}^{-1}*\left[K*{M}^{{\prime }}\right]$$ 6 The empirical relation has been derived for V as a function of I and total gas flow rate ( f t ), which is suitable for a plasma torch under investigation with defined electrode dimensions and input parameters. 2.2 Electro-thermal Efficiency of the Torch The electro-thermal efficiency of the plasma torch is one of the essential parameters that need to be derived. Electro-thermal efficiency is the capability of the torch to convert electrical energy into thermal energy, i.e., the percentage of the input electric power contained as thermal power in the plasma torch. The electro-thermal efficiency depends on parameters such as torch design, flow rate of plasma gas, nature of plasma gas, torch input power etc. The electro-thermal efficiency (η) of the non-transfer arc plasma torch is calculated using the energy balance equation and given below (Bokari and Boulos, 1980 ), $$\eta =\frac{P-{Q}_{loss}}{P}$$ 7 Where P is the input power to the torch (arc power), Q loss is the total power loss from the cathode, anode, torch body and plenum chamber i.e., the total power dissipated through cooling water from the surface of the torch body along with plenum chamber, and it is given as: $${Q}_{loss}=4.18*{C}_{p}*\dot{m}*({T}_{2}- {T}_{1})$$ 8 Where 4.18 is the conversion factor for converting calories into watts, c p is the specific heat of water (1 calorie cm − 3 ), is the amount of cooling water supplied (cm 3 s − 1 ), T 1 is the inlet water temperature entered into the torch, and T 2 is the temperature of the water coming out from the plenum chamber. The electro-thermal efficiency (η) is given in Eq. ( 7 ) becomes: $$\eta =\frac{P - m*\varDelta T}{P}$$ 9 $$\text{W}\text{h}\text{e}\text{r}\text{e}, \varDelta T ={T}_{2}- {T}_{1} \text{a}\text{n}\text{d} m =4.18*{C}_{p}*\dot{m}$$ $$\eta =-m*\left(\frac{1}{\frac{ P}{\varDelta T}}\right)+1$$ 10 Eq. ( 10 ) represents a straight line with a negative gradient, where P/ΔT is the torch's efficiency factor (ηf). The efficiency factor is defined as the ratio of input power to the temperature difference between the torch's inlet and the plenum chamber's outlet. $$P={\eta }_{f}*\varDelta T$$ 11 It is clear from Eq. ( 11 ) that the input power is directly proportional to the temperature difference between the inlet of the torch and outlet of the plenum chamber i.e., the variation of temperature difference between the inlet of the torch and outlet of the plenum chamber is linear with input power of the torch. 3.0 Materials and Methods 3.1 Plasma Torch Aerosol Generation System (PTAGS) A 25 kW (100 V and 100–250 A) dc non-transfer arc PTAGS has been installed at ATF, RESD for the generation of nanoparticles. The PTAGS consists of the following sub-systems viz. (i) plasma torch, (ii) main power supply and HV/ HF power supply, (iii) water and gas control panel, (iv) cooling water supply system, (v) plasma/ sheath gas supply system and (vi) PLC automation. 3.1.1 Plasma torch The schematic presentation of the thermal plasma torch is shown in Fig. 1 . The plasma torch consists of a rod-type cathode made of copper with a 16 mm diameter and conical shape tungsten tip at the end portion made of thoria for better thermionic emission and copper anode in the form of convergence nozzle with conical shape. The plasma torch is operated in non-transferred arc mode and atmospheric pressure. The total lengths of the cathode and anode are 126 mm and 49 mm, respectively. The electric arc inside the torch is initiated between the tip of the cathode and the anode. The arc generated by plasma torches strongly depends on many parameters, like the design of the cathode and anode, the current and voltage of the arc, and the gas mass flow rate. The structure of plasma arcs also depends on the type of gas used, such as plasma-generating gas, as different gases have different specific heat, thermal conductivity, radical production, and power requirements. The entire plasma torch (cathode and anode) is cooled by De-mineralised (DM) water from a separate chilling unit through a closed-loop circulation pump. The present plasma torch (custom fabricated) can be operated with a mixture of nitrogen and argon as plasma-generating gas for various flow rates. The plasma-forming gas is introduced axially across the cathode region. The gas flow forces the anodic arc root to stride into the nozzle, and plasma is initiated when electrons are accelerated from the cathode to the anode. The electron collides and ionizes the atoms or molecules in the gas. The additional electrons generated by the ionization cause further ionization, giving a multiple effect, and collision transfers the kinetic energy of the gas molecules. The high-velocity ions and electrons in the path of the arc further dissociate the gas molecules that flow along the cathode length and produce the plasma. The gas is heated when the arc originates as a plasma jet from the torch orifice (the diameter of the torch orifice is 6 mm). The arc stability is accomplished in the plasma torch by magnetic arc rotation. A permanent magnet is provided inside the torch body (anode side), giving the magnetic field parallel to both the cathode and anode axis (along the discharge axis). The arc route at the anode side (i.e., the current carried by the arc at the location where it touches the anode) is perpendicular to the magnetic field. Hence, the tip of the arc rotates along the axis due to tangential force without continuously touching the anode surface at the same location. It reduces the rate of electrode erosion and increases the life of electrodes. 3.1.2 Main power supply and HV/ HF power supply The arc of the plasma torch is initiated between the cathode and anode using a high voltage high-frequency source (HVHF) and then transferred to the copper anode. The power supply is made from an un-controlled bridge rectifier, a controlled half-bridge thyristor and a diode. DC power coming from the transformer through thyristor circuits energizes and sustains the arc. The open circuit voltage is around 470 V (depending on the input AC three-phase voltage). The HV/ HF power supply (3 kV – 3 MHz) initiates the start pulse to produce the arc between the cathode and anode. This arc exists only for a second (set time), and the DC power from the power supply is used to sustain the arc for a long time and increase the arc power. The sustainability of the arc flow depends on the flow rate of plasma gas and the electric power to the torch for the fixed electrode design. 3.1.3 Water and gas control panel The torch body and plenum chamber portions are subjected to extreme temperature or heat flux. A cooling water system is provided to sustain the system's integrity against thermal, electrical, and mechanical stress. It consists of a water cooler, pump, PVC, PU, and headers. A closed loop of water line is connected from the chiller unit of 400 L capacity to the torch body and the plenum chamber through the motor and control panel. The water chiller unit cools the water down to a minimum of 18 ⁰ C. The hot water comes back to the cooler unit and gets cooled. For the stable operation of the plasma torch, the electric power to the torch and the plasma gas flow rate must be properly balanced. The choice of plasma-generating gas is generally based on the energy it can carry, reactivity and cost. A gas line made of PU pipe from the nitrogen and argon cylinder to the torch body is mounted through the control panel, which is used for gas mixing and flow control. Water and gas flow meters relate to flow control valves to the panel. The temperature controller mounted on the panel displays the torch inlet and outlet water temperatures. Panel continuously sends temperature and flow rate data to PLC using wireless data transmission. 3.1.4 Programmable Logic Controller (PLC) Automation A programmable logic controller (PLC) is used to automate the process parameters of the plasma torch operation. It is provided with a digital display to monitor the system's status, PF bank switches and the arc power parameters (voltage and current) during operation. The control panel continuously sends temperature and flow rate data to PLC using wireless data transmission. The main screen will display the arc current, voltage, and system status. When PLC starts, it should show 'system healthy'. For safe operation of the system and attaining the sustained arc, some parameters are set to the range as given in Table 1 . Whenever any interlock parameter crosses the set values of the system during the process, this screen automatically displays the status as 'check interlock'. Table 1 Interlocks and the corresponding set points. Interlock parameters Inference Set value Water Flow Water is not flowing in Plasma Torch 7 L min − 1 Water Temperature Inlet water Temperature is high 30 ⁰ C Check Gas Flow Gas is not flowing in the Plasma Torch 10–25 L min − 1 Stack Temperature High Thyristor heat sink temperature is high 40 ⁰ C Over Current Arc current value is crossed to set the value 95–300 A Over Voltage Arc volts value crossed to set value Set Value: 30–600 V 3.2 Experimental Setup All the experiments are performed in the Aerosols Test Facility (ATF), which consists of a 1 m 3 cylindrical chamber (diameter 150 cm and height 60 cm) made of Stainless Steel (SS) with multiple ports on the wall of the chamber. More details on ATF can be found elsewhere (Baskaran et al., 2004 ; KUMAR, 2010 ; Subramanian et al., 2017 ). The experimental setup consists of PTAGS, material feeder, aerosol chamber, Data Acquisition System (DAS), and aerosol diagnostic instruments. The detailed schematic diagram of the experimental setup and PTAGS is shown in Fig. 2 . The coaxial SS cylindrical plenum chamber of 0.5 m length is used to transport the generated aerosol to the chamber by opening the gate valve. The plenum chamber is cooled with water to prevent excessive heating and restrict the damage to the O-rings, flowing in a closed loop from the torch body to the plenum chamber to the back chiller unit. K-type thermocouples, pressure transducers (M/s Gems Sensors, UK) and humidity sensors (M/s Rotronics, INC, USA – HC2 series) were used inside the aerosol chamber for measurement of temperature, pressure, and relative humidity during the experiment, respectively. The measuring range and error in measuring pressure, temperature and relative humidity are 0.5 to 400 ± 0.25% bar, − 200 to 1370 ± 1 ⁰ C and 0 to 100 ± 1.5%, respectively. The pneumatic gate valve between the aerosol chamber and plenum chamber can be closed and opened with the help of an air compressor (Make and model: Whitestar and KND-SPTC-9). 3.2.1 Aerosol Characterization Techniques The aerosol generated by PTAGS is characterized using real-time aerosol diagnostic instruments such as SMPS (Make and Model: M/s Grimm Aerosol Technik, Germany and 5416 CPC based), Mastersizer (Make and Model: M/s Malvern, UK and 2000) and an offline filter paper sampler. The SMPS is a combination of Differential Mobility Analyser (DMA), Condensation Particle Counter (CPC) and 64-bit Personal Computer (PC) based operating software. SMPS gives the number size distribution and number concentration of aerosols in the size range of 0.01–1.1 µm based on the electrical mobility principle (Baskaran et al., 2009 ). The flow rate of the SMPS instrument is 0.3 lpm, and the time interval for single data recording is 3.5 minutes. Mastersizer gives volume/ mass size distribution of aerosols suspended in liquid (size ranges from 0.02–2000 µm) and air medium (size ranges from 0.5–2000 µm) based on the ensemble diffraction technique (Kumar et al., 2015 , 2014 ). The uncertainty in the size distribution measurement by SMPS and Mastersizer ranges from 0.8–3 % and 2–3 %, respectively (Kumar et al., 2019 ). The suspended aerool mass conentration is measured using a filter paper sampler at one port of the aerosol chamber. A closed-face type filter paper sampler (47 mm diameter), a rotary pump with a maximum 25 lpm flow rate capacity and a rotameter to measure the flow rate are used for sampling. A microbalance with an accuracy of 0.01 mg (Sartorius make, Secura 26 Model and Design 1) is used for the gravimetric analysis of the glass fibre filter (M/s Whatman). The flow rate measurement and sampling time uncertainty are ± 2% and ± 1 second, respectively. Further, a fluctuation in flow rate is observed during experiments due to the loading of aerosol on the filter paper. This leads to the total uncertainty in the sampled volume is about ± 1%. Considering all uncertainties, the calculated uncertainty in measured mass concentration is approximately 5% (Narayanam et al., 2020 ). The microchemistry and morphology of aerosol generated by plasma torch were analyzed by Energy dispersive X-ray (EDAX) spectroscopy and Scanning Electron Microscopy (SEM), respectively. The EDAX is used for determining the crystalline phase, diffraction pattern and qualitative chemical information, while SEM (make and model: Philips and XL 30) is used to obtain the shape and size of aerosols deposited on the surface of the chamber. 3.2.2 Materials used for aerosol generation The material used for aerosol generation is strontium peroxide (SrO 2 ) powder. Since SrO 2 is the most stable compound of strontium, it is one of the fission products with a high fission yield (5%) and has more radiological and biological half-life, leading to a high effective half-life (Subramanian et al., 2017 ), its non-radioactive form of material is chosen for present studies. The volume size distribution of SrO 2 powder (M/s Alfa Aesar, USA) is measured using Mastersizer-2000 with liquid dispersion method and water as dispersant medium. The volume size distribution of SrO 2 powder is presented in Fig. 3 . The grain size of SrO 2 powder particles ranges from 0.5 to 70 µm with peak distribution at 15 µm. The volume size distribution of SrO 2 powder particles is a mono-model with Mass Median Diameter (MMD), and Standard Deviation (SD) of 12.2 µm and 2.49, respectively. 2.2.2 Powder, wire, and pellet feeder For the generation of aerosols, the material can be fed in the form of powder, wire or tube, and pellet into the plasma flame zone (Subramanian et al., 2009 ). The powder feeder (Make and Model: M/s Metallizing Equipment Co. Pvt. Ltd., India, and PF-700), which works on pressurization and constant volumetric feed principle, was used for injecting the metal oxide powder towards the plasma flame at a constant feed rate. The powder feeder consists of a pressurized canister (capacity 700 cm 3 ) where the powder is stored, and a slotted rotating metal disc mounted off-centre concerning the canister. The pressurized canister can withstand a backpressure of 7.5 bar. The given mass of powder is fed into the slot of the rotating disc by gravity, and the disc rotates past the exit port, where the carrier gas passes through the disc and carries the powder to the plasma torch. The feed rate of powder (mass of powder fed to the torch per unit of time) is governed by the speed of the rotating disc, i.e., the powder feed rate is proportional to the disc rpm, which can be controlled. The powder feeder can be operated manually and automatically with the help of a programmable logic controller system. In the other method, the feed material in the form of wire or tube of 6 mm diameter can be fed in the plasma flame at the required rate. In the pellet feed mode, a known powder weight is pelletized, and then the pellet is rigidly fixed in the feeder tube and kept in front of the plasma flame. In the pellet mode feed, the percentage of conversion to aerosols from the pellet is less. In all forms of feeding, the feed material can be fed by powder/ wire/ pellet oriented perpendicular to the plasma flame axis. 3.3 Experimental procedure The experiments are performed in two phases. In the first phase, the operational characterization parameters of PTAGS, like I-V characteristics, electro-thermal efficiency, and torch power, have been optimized for various combinations of argon and nitrogen mixture gas flow rates. The experimental parameters for the characterization of PTAGS and the generation of aerosols are given in Table 2 . The flow rate of argon gas is kept constant at 10 L min − 1 while that of nitrogen gas is varied over 5–20 L min − 1 in steps of 5 L min − 1 . The total flow rates of a mixture of gases are 15, 20, 25 and 30 L min − 1 . The PTAGS is tested for each flow rate while increasing the current of the torch from 100–250 A. All experimental runs keep the cooling water flow rate constant (7 L min − 1 ). The inlet water temperature ranges from 20–22 ⁰ C, and the outlet temperature is 24–40 ⁰ C with the rise in temperature 2–20 ⁰ C. In the second phase, experiments were performed to generate SrO with the optimized torch parameters. The range of operating parameters of PTAGS for the generation of aerosols is included in Table 2 . The nitrogen gas flow rate was kept at more than 10 L min − 1 for a fixed argon gas flow rate (10 L min − 1 ) to achieve high PTAGS power. The range of torch arc current and voltages are set between 200–250 A and 70–90 V, respectively. At the start of each experiment, the aerosol and plenum chamber were opened and cleaned using a wet cloth followed by alcohol spray and wiped with tissue paper to remove the deposited particles. The clean air was blown inside the chamber with the help of HEPA filters, and chamber air was flushed out using an air displacement pump to minimize background aerosol concentration. The argon was used as powder feeder gas to transport the powder inside the canister into the plasma flame. The powder feeder was turned on after the plasma torch was switched on, and the power of the torch was ensured to be at the desired value (18–20 kW) with an arc in the stabilized condition. In this scenario, the aerosols generated by PTAGS are filled in the aerosol chamber and all ports, resulting in homogeneous aerosol distribution. The gate valve between the aerosol and plenum chamber is closed after the plasma torch is switched off. Table 2 The experimental parameters for characterization of PTAGS and aerosol generation. Operating Parameters Range of Optimisation Parameters for aerosol generation Torch Power (kW) 5–25 More than 15 Arc voltage (V) 55–95 70–90 Arc current (A) 100–250 200–250 Nitrogen gas flow rate (L min − 1 ) 5–20 10–20 Argon gas flow rate (L min − 1 ) 10 10 Cooling water flow rate (L min − 1 ) 7 7 Rise in water temperature ( ⁰ C) 2–20 10–16 4.0 Results and Discussion 4.1 Effect of Arc Current and Gas Flow Rates on I - V Characteristics The dependence of current-voltage characteristics of plasma torch on the various mixtures of gas flow rates of argon and nitrogen have been studied. The tests are performed by varying the nitrogen gas flow rates from 5–20 L min − 1 at a constant argon gas flow rate of 10 L min − 1 . The variation of arc voltage as a function of current and gas flow rates is given in Fig. 4 . The torch's arc voltage decreases with increasing current for an offered total gas flow rate. At constant current, the arc voltage is higher for the large flow rate of plasma-generating gas. This is due to increased plasma conductivity with an increase in temperature. The decreasing I - V characteristics trend was found in order with other works (Glocker et al., 2000 ; Ramasamy and Selvarajan, 2000 ). The variation of arc voltage with a ratio of nitrogen and argon flow rate for different arc currents is shown in Fig. 5 . For a given current, the arc voltage increases with the ratio of nitrogen to argon gas flow rate. An increase in the flow ratio of nitrogen to argon gas decreases plasma conductivity; hence, the arc voltage increases. At a higher current, the arc voltage is lower; for example, at 240 A current and ratio of nitrogen to argon gas flow rate 2, the arc voltage is 87.5 V, and at a current of 100 A and the same gas flow ratio, the voltage is 97 V. The increase in the ratio of the gas flow rate causes the lengthening of the arc and thermal pinch due to a decrease in the plasma conductivity (Planche et al., 1998 ). Further, as the gas flow rate increases, more thermionic electrons are emitted from the torch's cathode, which lowers the voltage drop near the electrodes. 4.1.1 Empirical relation The relationship between arc voltage ( V ), current ( I ) and total gas flow rate ( f t ) is derived based on the Nottingham equation given in section 2.0 . The value of coefficients K 1 and K 2 are determined using the least square method and presented in Table 3 . Table 3 Calculated values of K 1 and K 2 for argon and nitrogen gas mixtures. S. N. f Ar (L min − 1 ) f N2 (L min − 1 ) f t (L min − 1 ) K 1 K 2 1 10 5 15 53.57 267.09 2 10 10 20 62.59 520.73 3 10 15 25 69.15 369.28 4 10 20 30 74.94 533.66 The f Ar , f N2 and f t flow rates of argon, nitrogen and total gas (argon + nitrogen). The empirical relation for V has been derived as a function of total gas flow rate ( f t ) and I by using derived constant K 1 and K 2 and from Eqs. 5 and 6 . The derived empirical relation is given as follows: $$V=\left(33.245+0.9949*{f}_{t}\right)+(130.973+12.965*{f}_{t})*{I}^{-n}$$ 12 The total gas flow rate of argon and nitrogen is in L min − 1 . The measured and predicted voltage as a function of arc current for various gas flow rates is compared in Fig. 4 . The deviation between measured and predicted arc voltage for different arc current and gas flow rates does not exceed ± 8.78%. The error analysis shows that the experimentally measured values are in fair agreement with the predicted values. The I-V characteristics curve is in the form of hyperbolic and asymptotic towards zero voltage. 4.2 Power of the Plasma Torch The power of the plasma torch is calculated from arc current and voltage. The variation of arc power with the current for a mixture of argon and nitrogen gas is plotted in Fig. 6 . The arc power increases linearly with increasing the arc current for all gas flow rates. The net change of torch power is 7.56 kW when the current changes from 100 to 240 A for the flow rate of 5 L min − 1 , whereas the change of torch power is 11.3 kW for 20 L min − 1 for the exact current change. Further, for a given current, the net torch power increases from 6.5 to 9.7 kW at 100 A when the flow rate changes from 5 to 20 L min − 1 , while it is 14.1 to 21 kW at 240 A. The total power transferred to the plasma increases with increased gas flow rate. Various earlier studies also obtained similar results (Capetti and Pfender, 1989 ; Ramasamy and Selvarajan, 2000 ). The variation of torch power with temperature difference (ΔT) between the inlet and outlet of the torch is illustrated in Fig. 7 . At constant temperature difference, the torch power is more prominent for higher gas flow rates. It is noted that when the power is maintained constant even after reducing the gas flow rate, the ΔT is high. The variation of the temperature difference between the inlet and outlet of the torch with power is also linear. 4.3 Electro-thermal efficiency of the torch The electro-thermal efficiency (η) of the plasma torch for various flow rates of argon and nitrogen gas mixtures was determined by using Eq. ( 7 ). The calculated η of the torch for gas mixtures (flow rate of Ar + N 2 :10 + 5 L min − 1 ) is given in Table 4 . The η of the torch decreases with the increase of torch power. Similarly, η for other gas flow rates is determined and shown in Fig. 8 . The η reduces with increased torch power for experimented gas flow rates (25, 20, 25, 30 L min − 1 ). The η is larger for higher gas flow rates at constant torch power. Further, the η also decreased with an increase in the current intensity of the torch. Table 4 Electro-thermal efficiency of the plasma torch for argon-nitrogen gas mixture. Gas flow rate: Ar: N 2 (10:5 L min − 1 ) and Inlet temperature (T 1 = 22 ⁰ C) P (kW) T 2 ( ⁰ C) ΔT = (T 2 - T 1 ) Q loss (kW) η η (%) 1/ η f 6.48 24 2 0.98 0.85 84.95 0.31 7.91 26 4 1.95 0.75 75.33 0.51 9.20 28 6 2.93 0.68 68.19 0.65 11.34 30 8 3.90 0.66 65.60 0.71 12.16 32 10 4.88 0.60 59.90 0.82 13.27 34 12 5.85 0.56 55.89 0.91 14.04 36 14 6.83 0.51 51.38 0.99 Similarly, the variation of η with the temperature difference ( ΔT ) between the inlet and outlet of the torch is given in Fig. 9 . The η decreases with increase of ΔT between the inlet and outlet of the torch for all gas flow rates. Bokhari et al. have reported a similar observation that the η of the torch increases as convective and radiative heat losses decrease by decreasing the size of the anode (Bokari and Boulos, 1980 ). The variation of η with the reciprocal of efficiency factor ( η f ) is shown in Fig. 10 . The η decreases linearly with the increase of η f for all gas flow rates. There is an inverse linearity relation between the η and η f , i.e., the η decreases with an increase in input power and found that the efficiency increased with increased gas flow rate. Similar observations have been reported previously; there is an increase in the thermal efficiency with an increase in the gas flow rates and a decrease in the thermal efficiency with an increase in the torch power. The flow rate of plasma forming gas and current intensity are found to influence the torch efficiency and power for fixed nozzle diameter and length. It has been found that properly distributed gas injection increases the torch power and η. At low torch power (less than 10 kW) of PTAGS, the torch's flame was unstable, while at high torch power (more than 15 kW), the plasma flame was stabilized. Based on the above investigation, the regulation of the PTAGS operational parameters was standardized and operational stability was ensured. The PTAGS is operated at 18–20 kW power, 60–80% electro-thermal efficiency and 20–30 L min − 1 flow rate plasma forming gas for generation of aerosols. 4.4 Calibration of Powder Feeder The powder feeder was calibrated using SrO 2 powder for a constant flow rate (8 L min − 1 ) of argon gas. Figure 11 represents the relation between the feed rate (mg min − 1 ) and revolution per minute (RPM) of the rotating disc of the powder feeder. The powder feed rate (powder obtained) varies linearly with RPM within experimental uncertainty. Since the expected mass concentration of fuel and non-volatile fission product aerosols in containment during severe accident conditions of a nuclear reactor are in the range of 10–40 mg m − 3 (Baskaran et al., 2004 ), the powder feeder was operated at 5 RPM in all experiments for the generation of aerosols to generate few tens of mg m − 3 concentration. However, generation rate and mass concentration can be increased with the increase of powder feed rate, i.e., RPM of powder feeder and duration of torch operation. 4.5 Characterization of aerosols generated by a plasma torch It was found that at less than 10 kW of torch power, the torch's flame was not stable, and this led to the metal powder not aerosolizing correctly, resulting in the falling of metal powder at the bottom of the plenum chamber region. At more than 15 kW, the plasma flame was stabilized, and effective vaporization of metal powder was observed due to the high temperature and the length of the torch flame. Hence, the PTAGS is operated at 20 kW power, and the total flow rate of plasma-generating gas is kept at 25 L min − 1 . The powder feed rate is maintained at 10 mg min − 1 at a fixed 5 RPM. The torch is operated continuously for 4–5 min. The suspended total mass concentration of aerosols is measured by using a filter paper sampler connected to one of the ports of the aerosol chamber. The aerosol sampling is carried out for 1 min at 10 L min − 1 flow rate. The measured total mass concentration of aerosol ranges from 20.9 ± 1.1 to 29.5 ± 1.5 mg m − 3 with an average concentration of 24.9 ± 1.3 mg m − 3 in various sets of performed experiments. The suspended number concentration and size distribution of the generated aerosol were continuously monitored by using SMPS before the start of the experiment. The evolution of the number concentration of SrO aerosol for experiments is shown in Fig. 12 . The aerosol concentration increases during generation time and reaches a maximum value of 6.0*10 6 cm − 3 at 7 min; thereafter, aerosol concentration starts decaying by coagulation and various settling processes inside the aerosol chamber. The concentration of SrO aerosol was reduced by almost one order in one hour inside the aerosol chamber. The aerosol size distribution at various time intervals for a typical experiment is presented in Fig. 13 . The aerosol size distribution measured at different time intervals (3, 7, 10, 14, 21, 42 and 70 min) is mono-model and polydisperse. The initial size distribution (up to 3 min) of SrO aerosol generated by PTAGS ranges from 10–40 nm with Count Geometric Mean Diameter (CGMD), Geometric Standard Deviation (GSD) is 26.5 nm and 1.45 respectively, and the maximum number concentration is 2.99*10 5 cm − 3 . The number concentration of aerosols increases (6.08*10 6 cm − 3 ) up to aerosol generation time (5 minutes). After that, the size distribution of aerosol shifted, and particle size was found to range from 11 to 310 nm in 7 minutes due to the rapid aggregation of aerosol. Then, with the progress of time, the number concentration progressively reduced until 70 min, and the concentration became one order less (4.97*10 5 cm − 3 ) due to coagulation and various settling processes. The evolution of CGMD and GSD for the experiment period has been presented in Fig. 14 . The CGMD increases from 26.5 to 190 nm for 70 min, and GSD values rise marginally from 1.45 to 1.59 in the first 25 min, then remain nearly the same (~ 1.57) up to 70 min. The increase in aerosol CGMD is attributed to the agglomeration process, which is dominated by the high concentration of aerosols. The initial GSD increases due to various aerosol processes, viz., source accumulation, coagulation, and agglomeration. At a later period, with the progress of time, as the concentration began to reduce one order less (after 25 min), it remained almost constant due to negligible agglomeration. The number concentration and initial size distribution of aerosols generated by PTAGS are in agreement with values measured by other works (Misra et al., 2013 ; Subramanian et al., 2009 ). The experiments were repeated a few times to check the results reproducibility and data presented in Table 5 . The total aerosol concentration measured using SMPS ranges from 4–6*106 cm-3 with an average value of 4.8*10 6 cm − 3 . The CGMD during generation time ranges from 26.5–33.0 nm (GSD ranges from 1.12–1.45) and increases to a value 119.6–140.3 nm (GSD ranges from 1.29–1.46). Average CGMD and Standard Deviation (SD) during and after the generation of SrO aerosols for all four experiments are 29.28 ± 3.1 nm and 130.2 ± 9.3 nm, respectively. The formation of metal aerosols in a very high-temperature gradient through rapid cooling favours homogeneous condensation rather than heterogeneous, resulting in aerosol sizes as small as 10 nm (Oxtoby and Evans, 1998 ). Table 5 Aerosol number concentration, CGMD with GSD of aerosols during and after generation. Exp. runs Aerosol number Concentration (cm − 3 ) CGMD (nm), GSD during generation (3rd min) CGMD (nm), GSD after generation (7th min) 1. 6.08*10 6 26.5 (1.45) 119.6 (1.46) 2. 5.12*10 6 27.1 (1.22) 126.2 (1.39) 3. 3.89*10 6 33.0 (1.32) 135.8 (1.35) 4. 4.09*10 6 30.5 (1.12) 140.3 (1.29) Further, the calculated Mass Median Diameter (MMD) using CGMD and GSD by applying the Hatch-Choate equation after aerosol generation (7th min) is found to be in the range of 170–185 nm with an average diameter of 175 nm. The calculated MMD of SrO aerosol generated by PTAGS aligns with other synthesis methods (Gungor et al., 2019). 4.6 EDAX and SEM analysis The aerosols deposited on the floor surface of the aerosol chamber were collected on aluminium foil kept at the bottom surface of the chamber and analyzed for microchemistry and morphological properties by using Energy dispersive X-ray (EDAX) spectroscopy and Scanning Electron Microscopy (SEM). Figure 15 (a) and (b) show the SEM micrograph and EDAX spectrum of SrO aerosol particles deposited on aluminium foil. The EDAX spectrum of deposited aerosols on the bottom surface of the chamber contains peaks corresponding to strontium and oxygen, which says that only SrO aerosols are present on the aluminium foil. The SEM analysis shows that most of the aerosols are in the sub-micrometre range, and many nanometre-sized aerosols agglomerated and collected in a single place due to settling on the surface of the aluminium foil. The deposited aerosols are found to be polydisperse with sub-micrometre-sized particles, and the shape is nearly spherical. 5.0 Summary and Conclusion The operational characteristics of PTAGS installed in our laboratory are studied to obtain suitable optimized operational parameters for proposed experiments for safety studies related to sodium and fission product aerosols generated during accident conditions in large volumes. The Nottingham coefficients were calculated using the least-square method, and an empirical relation for arc voltage as a function of arc current and flow rate of plasma forming gas is derived. The relation developed strictly applies to the torch under investigation, but the same methodology can be applied to any other plasma torch. The predicted and measured arc voltages are in good agreement. The electro-thermal efficiency is derived from an analytical expression using an energy balance equation for different flow rates of a mixture of argon-nitrogen gases (5–20 L min − 1 for nitrogen and 10 L min − 1 for argon) and other torch power (8–24 kW) levels. Based on the above investigation, the regulation of the PTAGS operational parameters was standardized and operational stability was ensured. The PTAGS is operated at 18–20 kW power, 60–80% electro-thermal efficiency and 20–30 L min − 1 flow rate plasma forming gas for generation of aerosols. SrO aerosols are generated by using a powder feeder and PTAGS. The desired mass flow rate of powder was obtained at the speed of a rotating disc ranging from 5 to 35 RPM. The average aerosol mass concentration and maximum number concentration are 24.9 mg m − 3 and 4.8*10 6 cm − 3, respectively. The average measured CMD and calculated MMD are 130.2 nm and 175 nm after generation. Aerosol size distribution becomes broader, and number concentration increases with time (5 minutes) due to coagulation and various settling processes. The SEM analysis of the deposited aerosols reveals that the shape of the aerosol is primarily spherical, and the size of aerosols deposited on the surface is sub-micrometre but polydisperse. The interpretation from the experiments could be helpful for the safety analysis of severe accidents of nuclear reactor codes. The operational parameters of the torch shall be tuned to achieve desired aerosol characteristics for future works like aerosol dispersion in large buildings and retention factor in a liquid pool. Declarations Conflict of interest statement On behalf of all authors, the corresponding author states that there is no conflict of interest that could have appeared to influence the work reported in this paper. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-4007909","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":284324210,"identity":"66a880ee-15e4-4f9c-a280-8151d84a6016","order_by":0,"name":"Amit Kumar","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA3ElEQVRIiWNgGAWjYLCCBwY1PIztDUCWgQUx6pkZGBIqjskx9xwAaZEgVssZZmP2GQkgHhFazNnPH3yQ2MaW2Dvz+dUNPwokGPjbuxPwarHsSWY2SGyTSZw5O6fsZg/QYRJnzm7Aq8XgQDKbBMiWjbNz0m7wALUYSOQS0HL+MfuPxDbmxP03z6Td/EOUlhvJbGDvM85gP3abKFssZzw2lgAFMmNPDtttGQMJHoJ+MedPfPjhAzgqjz+7+eaPjRx/ey8BhyGYPGA2D17laFrYHxBUPQpGwSgYBSMTAABNs0o4YsQuNQAAAABJRU5ErkJggg==","orcid":"https://orcid.org/0000-0002-4160-4586","institution":"Indira Gandhi Centre for Atomic Research","correspondingAuthor":true,"prefix":"","firstName":"Amit","middleName":"","lastName":"Kumar","suffix":""},{"id":284324211,"identity":"5a54e159-1657-4f62-953f-6c8c8857bf51","order_by":1,"name":"P. Usha","email":"","orcid":"","institution":"Indira Gandhi Centre for Atomic Research","correspondingAuthor":false,"prefix":"","firstName":"P.","middleName":"","lastName":"Usha","suffix":""}],"badges":[],"createdAt":"2024-03-03 07:54:53","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-4007909/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-4007909/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1007/s41810-024-00267-z","type":"published","date":"2024-11-07T15:58:19+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":53706176,"identity":"be926d4c-0c39-401d-8873-ea660394f133","added_by":"auto","created_at":"2024-03-29 06:54:16","extension":"jpg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":221042,"visible":true,"origin":"","legend":"\u003cp\u003eSchematic diagram of thermal plasma torch.\u003c/p\u003e","description":"","filename":"floatimage1.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4007909/v1/df5c12067cb3ed6aa1755837.jpg"},{"id":53706175,"identity":"7d5efd98-654a-49b5-aec6-a9ad1afd8134","added_by":"auto","created_at":"2024-03-29 06:54:16","extension":"jpg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":355759,"visible":true,"origin":"","legend":"\u003cp\u003eThe schematic diagram of the experimental setup.\u003c/p\u003e","description":"","filename":"floatimage2.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4007909/v1/0fa10ecbab06091664bb6ca4.jpg"},{"id":53706660,"identity":"9799629f-d5e9-4b4e-b5ba-9597e749552c","added_by":"auto","created_at":"2024-03-29 07:02:16","extension":"jpg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":49271,"visible":true,"origin":"","legend":"\u003cp\u003eVolume-size distribution of SrO\u003csub\u003e2 \u003c/sub\u003epowder grain size.\u003c/p\u003e","description":"","filename":"floatimage3.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4007909/v1/3e8fda7c4a926e0658654c86.jpg"},{"id":53706173,"identity":"ae29c17f-2baf-4d86-9afd-ccab332508e1","added_by":"auto","created_at":"2024-03-29 06:54:16","extension":"jpg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":113653,"visible":true,"origin":"","legend":"\u003cp\u003eMeasured and calculated I - V characteristics of torch for various gas flow rate mixtures.\u003c/p\u003e","description":"","filename":"floatimage4.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4007909/v1/963400eb829775fc0b96761b.jpg"},{"id":53706177,"identity":"dc94053e-629b-48e9-b455-3ec650499f1d","added_by":"auto","created_at":"2024-03-29 06:54:16","extension":"jpg","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":85153,"visible":true,"origin":"","legend":"\u003cp\u003eVariation of arc voltage with nitrogen to argon flow rate ratio for different arc currents\u003c/p\u003e","description":"","filename":"floatimage5.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4007909/v1/c82ffb524e9d6a9a2a178475.jpg"},{"id":53706181,"identity":"70e8ea37-9b51-4fa5-841c-c1e379920098","added_by":"auto","created_at":"2024-03-29 06:54:16","extension":"jpg","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":270049,"visible":true,"origin":"","legend":"\u003cp\u003eVariation of torch power with arc current at various gas flow rates\u003c/p\u003e","description":"","filename":"floatimage6.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4007909/v1/1aeff8e94dad00bb29c53ba3.jpg"},{"id":53706661,"identity":"d4f8a884-4988-437b-81ce-5c69600735a2","added_by":"auto","created_at":"2024-03-29 07:02:16","extension":"jpg","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":112688,"visible":true,"origin":"","legend":"\u003cp\u003eVariation of torch power with ΔT between the inlet and outlet of the torch.\u003c/p\u003e","description":"","filename":"floatimage7.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4007909/v1/c60fbbca2f24a8098ee36bc4.jpg"},{"id":53706180,"identity":"22f140f4-abbb-410c-a1fb-245477426ff1","added_by":"auto","created_at":"2024-03-29 06:54:16","extension":"jpg","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":83323,"visible":true,"origin":"","legend":"\u003cp\u003eVariation of η with torch power for various gas flow rates.\u003c/p\u003e","description":"","filename":"floatimage8.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4007909/v1/9ab05a3414bad0d35018c94d.jpg"},{"id":53706185,"identity":"60ed3fb0-3de7-4c87-9f96-fd2d3e46468c","added_by":"auto","created_at":"2024-03-29 06:54:17","extension":"jpg","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":444308,"visible":true,"origin":"","legend":"\u003cp\u003eVariation of η of the torch with \u003cem\u003eΔT\u003c/em\u003e between the inlet and outlet of the torch.\u003c/p\u003e","description":"","filename":"floatimage9.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4007909/v1/7ec67c577f90a59313ee1dd1.jpg"},{"id":53706178,"identity":"6b5a676c-777f-4b0c-9d63-c9c9cbeebc6a","added_by":"auto","created_at":"2024-03-29 06:54:16","extension":"jpg","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":353318,"visible":true,"origin":"","legend":"\u003cp\u003eVariation of η of the torch with reciprocal of efficiency factor.\u003c/p\u003e","description":"","filename":"floatimage10.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4007909/v1/db933d8d242722683baa2171.jpg"},{"id":53706662,"identity":"77db15f5-f384-476e-b8be-c7cb3ad5afea","added_by":"auto","created_at":"2024-03-29 07:02:17","extension":"jpg","order_by":11,"title":"Figure 11","display":"","copyAsset":false,"role":"figure","size":324881,"visible":true,"origin":"","legend":"\u003cp\u003ePowder feed rate vs RPM for SrO\u003csub\u003e2 \u003c/sub\u003epowder.\u003c/p\u003e","description":"","filename":"floatimage11.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4007909/v1/81f24b5a4c8d1b780cc6fa1a.jpg"},{"id":53706183,"identity":"31949fc6-b39b-4020-8441-7e9f3162ed32","added_by":"auto","created_at":"2024-03-29 06:54:17","extension":"jpg","order_by":12,"title":"Figure 12","display":"","copyAsset":false,"role":"figure","size":69199,"visible":true,"origin":"","legend":"\u003cp\u003eEvolution of SrO aerosol number concentration.\u003c/p\u003e","description":"","filename":"floatimage12.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4007909/v1/3dc50a570bee69806c0914e4.jpg"},{"id":53706182,"identity":"843d5313-ad3e-49b2-84a8-a2a594a4d422","added_by":"auto","created_at":"2024-03-29 06:54:16","extension":"jpg","order_by":13,"title":"Figure 13","display":"","copyAsset":false,"role":"figure","size":555563,"visible":true,"origin":"","legend":"\u003cp\u003eThe log–normal size distribution of aerosols at various times\u003c/p\u003e","description":"","filename":"floatimage13.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4007909/v1/4a6a9ecc499c87469c1ad792.jpg"},{"id":53706187,"identity":"1a09044e-8c46-4de4-9a82-a7dba309cc0d","added_by":"auto","created_at":"2024-03-29 06:54:17","extension":"jpg","order_by":14,"title":"Figure 14","display":"","copyAsset":false,"role":"figure","size":384015,"visible":true,"origin":"","legend":"\u003cp\u003eEvolution of CGMD and GSD.\u003c/p\u003e","description":"","filename":"floatimage14.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4007909/v1/b548347247bd5f322aadcc7b.jpg"},{"id":53706186,"identity":"08dc4117-1876-4906-9e8e-3ddf9352b6f0","added_by":"auto","created_at":"2024-03-29 06:54:17","extension":"jpg","order_by":15,"title":"Figure 15","display":"","copyAsset":false,"role":"figure","size":240385,"visible":true,"origin":"","legend":"\u003cp\u003e(a) SEM micrograph and (b) EDAX spectrum of SrO aerosols.\u003c/p\u003e","description":"","filename":"floatimage15.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4007909/v1/6ead77fea3521ab98eb83711.jpg"},{"id":68751115,"identity":"48603457-ecba-429a-ac30-515bd249fdf1","added_by":"auto","created_at":"2024-11-11 16:12:59","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":4552844,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4007909/v1/debfa4fa-8551-4f53-b36e-2e5f00b2ec96.pdf"}],"financialInterests":"","formattedTitle":"Study on characterization of SrO Aerosols Generated by Optimized Thermal Plasma Torch Aerosol Generator","fulltext":[{"header":"1.0 Introduction","content":"\u003cp\u003eToday thermal technology covers a broad spectrum of applications, which are classified as coating including spraying (Samal, \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e2017\u003c/span\u003e), chemical vapour deposition (Rao et al., \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e1998\u003c/span\u003e), waste destruction (Chang et al., \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e1997\u003c/span\u003e), densification of powders, metallurgy, synthesis of fine powders, material cutting in air and water (Steiner et al., \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e1988\u003c/span\u003e; Windelberg et al., \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e1987\u003c/span\u003e), generating nanoparticles and many more (LF Pfender, \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2000\u003c/span\u003e). The nanoparticles are formed by plasma synthesis through gas/ vapour to particle conversion. The high temperature of the plasma state is used for the interaction of plasma with solids and gases, which is the basis for plasma-enabled material processing called plasma synthesis and material processing (Young and Pfender, \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e1985\u003c/span\u003e). The materials introduced into the plasma flame zone are evaporated while plasma-forming gas provides an inert atmosphere to prevent undesirable reactions. Condensable molecules produced by these processes are self-nucleated to form nanoparticles. The advantages of plasma spray torch in material processing (N. Venkatramani, \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2002\u003c/span\u003e) consist of (i) high enthalpy to increase the kinetics of the reaction, (ii) sharp temperature gradient that enables quick quenching and (iii) the clean or varying reaction atmosphere. These processes, in tandem, can produce several effects in material processing to manufacture high-purity materials of ultra-fine powders (Kruis et al., \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e1998\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eThe plasma torch parameters, such as power, type of plasma generating gas, and flow rates, vary depending on the material processing and synthesis. Noble gases like argon and helium are the most used gases to form plasma. In some cases, nitrogen, hydrogen, air, oxygen, carbon monoxide, steam, methane, and their mixtures are also used (Glocker et al., \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2000\u003c/span\u003e). In general, N\u003csub\u003e2\u003c/sub\u003e or H\u003csub\u003e2\u003c/sub\u003e is used as a plasma-forming gas since the energy content of nitrogen and hydrogen is higher than that of argon and helium due to its diatomic nature. Non-reactive gases are advantageous for several applications where chemical reactions between plasma gas and substrate have been avoided. If oxidizing gases are used in conventional plasma torches, a high electrode erosion occurs, thus limiting the lifetime and contaminating the plasma torch with electrode material. Nevertheless, argon is usually favoured as a plasma-generating gas to have an inert reaction environment.\u003c/p\u003e\u003cp\u003eBased on the temperatures of the electrons, ions, and neutrals, plasmas are categorized as thermal or non-thermal. Thermal plasmas have electrons and heavy particles/ ions at the same temperature, i.e., in thermal equilibrium. On the other hand, non-thermal plasmas have ions and neutrals at much lower temperatures (sometimes room temperature), whereas electrons are at higher temperatures (Samal, \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). Thermal plasma torches generate the plasma by Direct Current (DC), Alternating Current (AC), Radiofrequency (RF) and other discharges. DC torches are the most used and researched than AC torches as there is less flicker generation and noise, give a more stable operation and better control, operate with a minimum of two electrodes, lower electrode erosion, low power consumption and slightly lower heat wear (Gomez et al., \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2009\u003c/span\u003e). In a DC torch, the electric arc is formed between the electrodes (made of copper, tungsten, graphite, molybdenum, silver etc.), and the thermal plasma is formed from the continual input of carrier gas. Furthermore, the flow rate of the carrier gas can be raised to promote a larger, more projecting plasma jet if the arc current is sufficiently increased and vice versa. It is important to note that there are two types of DC plasma torches viz. (i) non-transferred arc: electrode inside the torch body, arc is formed inside the body and low electrical to thermal efficiency and (ii) transferred arc: one electrode outside the torch body, arc is formed outside the body and high electrical to thermal efficiency. Many researchers have used atmospheric transferred arc thermal plasma torches for synthesis of metal oxide particles (Balasubramaniam et al., \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2004\u003c/span\u003e; Banerjee et al., \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2006\u003c/span\u003e; Praburam and Goree, \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e1996\u003c/span\u003e; Prodi et al., \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e1988\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eThe quality of plasma generated is a function of density (pressure), temperature and torch power, i.e., the greater the torch power, the better the plasma. The efficiency of the plasma torch can vary among manufacturers, design, and torch technology (Leal-Quir\u0026oacute;s, \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2004\u003c/span\u003e). The thermal efficiency of the torch varies over a wide range of 10\u0026ndash;90 %. The thermal plama temperature is 10\u003csup\u003e4\u003c/sup\u003e K, so solid powder (metal, metal oxide, and ceramic) can be evaporated quickly, and nanoparticles form upon cooling while exiting the plasma region. The thermal plasma torches that produce nanoparticles are mainly based on DC plasma jets, DC arc plasmas, and radio frequency (RF) induction plasmas. In the arc plasma torch, an electric arc formed between the anode and the cathode provides the necessary energy for evaporation. Different plasma torches were used for various purposes; generally, rod-type cathode and nozzle shape (conical) anode and torch power ranges from 2 to 6000 kW. The Plasma Torch Aerosol Generation System (PTAGS) consist of a rod-type cathode and nozzle shape (conical) anode and gives an intense and prolonged plasma flame for the contentious aerosol source from metal, ceramic, and composites (Baskaran et al., \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2004\u003c/span\u003e; Krasenbrink et al., \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e1995\u003c/span\u003e). The concentration of nanoparticles can be achieved as high as 10\u003csup\u003e13\u003c/sup\u003e/m\u003csup\u003e3\u003c/sup\u003e by this kind of aerosol generator.\u003c/p\u003e\u003cp\u003eAs a part of reactor safety studies, the Indira Gandhi Centre for Atomic Research (IGCAR) is involved in aerosol studies pertaining to severe accident conditions of sodium-cooled Fast Reactors (SFR). Out of the different aerosol generation techniques, the plasma torch is most preferred and used for generating metal aerosols in experimental facilities (Baskaran et al., \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2004\u003c/span\u003e; Suckow and Guentay, \u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e2008\u003c/span\u003e). PTAGS best simulates the characteristics of the aerosol generated during severe nuclear reactor accidents. Towards this, a non-transferred DC arc, atmospheric pressure, thermal plasma torch with a suitable power supply, control system and water-cooling system were installed in the Aerosol Test Facility (ATF). PTAGS generates nanoparticles of non-radioactive fission products and fuel equivalent, metals, ceramics, and composites. This paper focuses on optimizing the working parameters of PTAGS for generating aerosols and studying the characteristics (number and mass concentration, size distribution, and initial aerosol size) of generated aerosols. The torch characterization allowed scoping operative ranges based on minimum voltage fluctuations and maximum thermal efficiency for different gas flow rates, arc current and process gases. The current study uses a mixture of nitrogen and argon gas as plasma process gas; the PTAGS was operated at different powers and various gas flow rates, and the current-voltage characteristics and electro-thermal efficiency are studied under atmospheric pressure conditions. The powder feeder used for feeding the test material for aerosol generation is calibrated concerning mass flow rate for various feed rates. The aerosols that are generated are characterized using a filter paper sampler, Sequential Mobility Particle Sizer (SMPS), Energy dispersive X-ray (EDAX) spectroscopy, Scanning Electron Microscopy (SEM) and Mastersizer \u0026minus;\u0026thinsp;2000. The optimized working parameters of PTAGS and aerosol characteristics are analyzed and would be a crucial database for future nuclear reactor safety analysis studies. The detailed characterization of PTAGS and generated nano aerosol is reported in this paper.\u003c/p\u003e"},{"header":"2.0 Background and Theory","content":"\u003cp\u003eThe primary operational characteristics of a plasma torch are its current voltage, electro-thermal characteristics, and torch power. The generalized characteristics of plasma torch are experimentally introduced hyperbolic characteristics related to arc voltage, current and arc length (Mosleh et al., \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e1994\u003c/span\u003e; Ramasamy and Selvarajan, \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e2000\u003c/span\u003e). However, the characteristics are valid only for carbon electrodes in air with a few millimetres of arc length. Nottingham proposed an arc characteristics relation, which is much broader in application (Nottingham, \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e1926\u003c/span\u003e, \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e1923\u003c/span\u003e). Eberhart and Seban have studied the characteristics of a high-intensity argon arc with a water-cooled anode to develop an empirical relation between the arc voltage, current, and arc length (Eberhart and Seban, \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e1966\u003c/span\u003e). The applicability of the Nottingham relation to stabilize a non-transferred plasma torch by correlating the electrode heat losses, input power and arc current under different gas flow rates and a mixture of argon and nitrogen gas has been evaluated (Das et al., \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e1993\u003c/span\u003e). Detailed studies on the characteristics of a non-transferred and transferred arc plasma torch, the internal diameter of the electrode for different gas flow rates and different mixture ratios of argon and nitrogen gas have been performed using dimensionless analysis (Venkatramani and Ray, \u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e1997\u003c/span\u003e). Brilhac et al. studied DC vortex plasma torch dynamic and static behaviour with well and button type cathode (Brilhac et al., \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e1995a\u003c/span\u003e, \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003eb\u003c/span\u003e). Planche et al. reported the I-V characteristics of the DC plasma torch, such as gas flow rate and nozzle diameter (Planche et al., \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e1998\u003c/span\u003e). The preceding review shows that only a few works focused on establishing a relation connecting the arc voltage, arc current and plasma forming gas flow rates (Ramasamy et al., \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e2000\u003c/span\u003e).\u003c/p\u003e \u003cdiv id=\"Sec2\" class=\"Section2\"\u003e \u003ch2\u003e2.1 Current-Voltage Characteristics of the Torch\u003c/h2\u003e \u003cp\u003eThe relationship between arc voltage \u003cem\u003e(V)\u003c/em\u003e, current \u003cem\u003e(I)\u003c/em\u003e and arc length \u003cem\u003e(l)\u003c/em\u003e is given by the Nottingham equation (Das et al., \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e1993\u003c/span\u003e; Nottingham, \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e1926\u003c/span\u003e).\u003cdiv id=\"Equ1\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ1\" name=\"EquationSource\"\u003e\n$$V=\\left(A+B*l\\right)+\\left(C+D*l\\right)*{I}^{-n}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e1\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eWhere \u003cem\u003eA, B, C\u003c/em\u003e and \u003cem\u003eD\u003c/em\u003e are constants depending on the nature of the plasma torch, plasma generating gas, flow rate, gas pressure, electrode material etc. (Ramasamy and Selvarajan, \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e2000\u003c/span\u003e). The exponent' \u003cem\u003en'\u003c/em\u003e depends on the anode material and type of plasma generating gas. The typical value of \u003cem\u003en\u003c/em\u003e is 1 for carbon and 0.65\u0026ndash;0.67 for copper electrodes (Das et al., \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e1993\u003c/span\u003e) and depends on some degree of intensity of anode cooling. For the constant length of arc, Eq.\u0026nbsp;(\u003cspan refid=\"Equ1\" class=\"InternalRef\"\u003e1\u003c/span\u003e) can be written as:\u003cdiv id=\"Equ2\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ2\" name=\"EquationSource\"\u003e\n$$V= {K}_{1}+ {K}_{2}*{I}^{{\\prime }}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e2\u003c/div\u003e\u003c/div\u003e\u003cdiv id=\"Equa\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equa\" name=\"EquationSource\"\u003e\n$$\\text{H}\\text{e}\\text{r}\\text{e}, {K}_{1}= A+B*l, {K}_{2}= C+D*l \\text{a}\\text{n}\\text{d} {I}^{{\\prime }}={I}^{-n}$$\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eSimilarly, if plasma-generating gas flow rates are known, then the above relation can be modified and written as\u003cdiv id=\"Equ3\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ3\" name=\"EquationSource\"\u003e\n$$V=\\left(A+B*{f}_{t}\\right)+\\left(C+D*{f}_{t}\\right)* {I}^{{\\prime }}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e3\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eWhere \u003cem\u003ef\u003c/em\u003e\u003csub\u003e\u003cem\u003et\u003c/em\u003e\u003c/sub\u003e is the total flow rate of plasma generating gas. For constant gas flow rate, Eq.\u0026nbsp;(\u003cspan refid=\"Equ3\" class=\"InternalRef\"\u003e3\u003c/span\u003e) become like Eq.\u0026nbsp;(\u003cspan refid=\"Equ2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). The value of coefficients \u003cem\u003eK\u003c/em\u003e\u003csub\u003e\u003cem\u003e1\u003c/em\u003e\u003c/sub\u003e and \u003cem\u003eK\u003c/em\u003e\u003csub\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sub\u003e are determined by solving Eq.\u0026nbsp;(\u003cspan refid=\"Equ2\" class=\"InternalRef\"\u003e2\u003c/span\u003e) using the least square method. Once the values of coefficients \u003cem\u003eK\u003c/em\u003e\u003csub\u003e\u003cem\u003e1\u003c/em\u003e\u003c/sub\u003e and \u003cem\u003eK\u003c/em\u003e\u003csub\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sub\u003e are known, a suitable system of equations is formulated from which constants \u003cem\u003eA, B, C\u003c/em\u003e and \u003cem\u003eD\u003c/em\u003e are determined. The system of equations is in the following forms:\u003cdiv id=\"Equ4\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ4\" name=\"EquationSource\"\u003e\n$$A+B*{{(f}_{t})}_{i}= {{(K}_{1})}_{i}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e4a\u003c/div\u003e\u003c/div\u003e\u003cdiv id=\"Equ5\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ5\" name=\"EquationSource\"\u003e\n$$C+D*{{(f}_{t})}_{i}= {{(K}_{2})}_{i}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e4b\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eWhere i ranges from 1 to \u003cem\u003eN\u003c/em\u003e and \u003cem\u003eN\u003c/em\u003e is the number of experiments. The Eq.\u0026nbsp;(4a) and (4b) can be written in matrix form as:\u003cdiv id=\"Equ6\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ6\" name=\"EquationSource\"\u003e\n$${M}_{Nx2}*{X}_{2x1}= {K}_{Nx1}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e5\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eThe solution of the above matrix is calculated as:\u003cdiv id=\"Equ7\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ7\" name=\"EquationSource\"\u003e\n$$\\left[X\\right]= {\\left[{M}^{{\\prime }}*M\\right]}^{-1}*\\left[K*{M}^{{\\prime }}\\right]$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e6\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eThe empirical relation has been derived for \u003cem\u003eV\u003c/em\u003e as a function of \u003cem\u003eI\u003c/em\u003e and total gas flow rate (\u003cem\u003ef\u003c/em\u003e\u003csub\u003e\u003cem\u003et\u003c/em\u003e\u003c/sub\u003e), which is suitable for a plasma torch under investigation with defined electrode dimensions and input parameters.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.2 Electro-thermal Efficiency of the Torch\u003c/h2\u003e \u003cp\u003eThe electro-thermal efficiency of the plasma torch is one of the essential parameters that need to be derived. Electro-thermal efficiency is the capability of the torch to convert electrical energy into thermal energy, i.e., the percentage of the input electric power contained as thermal power in the plasma torch. The electro-thermal efficiency depends on parameters such as torch design, flow rate of plasma gas, nature of plasma gas, torch input power etc. The electro-thermal efficiency \u003cem\u003e(η)\u003c/em\u003e of the non-transfer arc plasma torch is calculated using the energy balance equation and given below (Bokari and Boulos, \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e1980\u003c/span\u003e),\u003cdiv id=\"Equ8\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ8\" name=\"EquationSource\"\u003e\n$$\\eta =\\frac{P-{Q}_{loss}}{P}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e7\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eWhere \u003cem\u003eP\u003c/em\u003e is the input power to the torch (arc power), \u003cem\u003eQ\u003c/em\u003e\u003csub\u003e\u003cem\u003eloss\u003c/em\u003e\u003c/sub\u003e is the total power loss from the cathode, anode, torch body and plenum chamber i.e., the total power dissipated through cooling water from the surface of the torch body along with plenum chamber, and it is given as:\u003cdiv id=\"Equ9\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ9\" name=\"EquationSource\"\u003e\n$${Q}_{loss}=4.18*{C}_{p}*\\dot{m}*({T}_{2}- {T}_{1})$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e8\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eWhere 4.18 is the conversion factor for converting calories into watts, \u003cem\u003ec\u003c/em\u003e\u003csub\u003e\u003cem\u003ep\u003c/em\u003e\u003c/sub\u003e is the specific heat of water (1 calorie cm\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e), is the amount of cooling water supplied (cm\u003csup\u003e3\u003c/sup\u003e s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e), \u003cem\u003eT\u003c/em\u003e\u003csub\u003e\u003cem\u003e1\u003c/em\u003e\u003c/sub\u003e is the inlet water temperature entered into the torch, and \u003cem\u003eT\u003c/em\u003e\u003csub\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sub\u003e is the temperature of the water coming out from the plenum chamber.\u003c/p\u003e \u003cp\u003eThe electro-thermal efficiency (η) is given in Eq.\u0026nbsp;(\u003cspan refid=\"Equ8\" class=\"InternalRef\"\u003e7\u003c/span\u003e) becomes:\u003cdiv id=\"Equ10\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ10\" name=\"EquationSource\"\u003e\n$$\\eta =\\frac{P - m*\\varDelta T}{P}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e9\u003c/div\u003e\u003c/div\u003e\u003cdiv id=\"Equb\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equb\" name=\"EquationSource\"\u003e\n$$\\text{W}\\text{h}\\text{e}\\text{r}\\text{e}, \\varDelta T ={T}_{2}- {T}_{1} \\text{a}\\text{n}\\text{d} m =4.18*{C}_{p}*\\dot{m}$$\u003c/div\u003e\u003c/div\u003e\u003cdiv id=\"Equ11\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ11\" name=\"EquationSource\"\u003e\n$$\\eta =-m*\\left(\\frac{1}{\\frac{ P}{\\varDelta T}}\\right)+1$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e10\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eEq.\u0026nbsp;(\u003cspan refid=\"Equ11\" class=\"InternalRef\"\u003e10\u003c/span\u003e) represents a straight line with a negative gradient, where \u003cem\u003eP/ΔT\u003c/em\u003e is the torch's efficiency factor (ηf). The efficiency factor is defined as the ratio of input power to the temperature difference between the torch's inlet and the plenum chamber's outlet.\u003cdiv id=\"Equ12\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ12\" name=\"EquationSource\"\u003e\n$$P={\\eta }_{f}*\\varDelta T$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e11\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eIt is clear from Eq.\u0026nbsp;(\u003cspan refid=\"Equ12\" class=\"InternalRef\"\u003e11\u003c/span\u003e) that the input power is directly proportional to the temperature difference between the inlet of the torch and outlet of the plenum chamber i.e., the variation of temperature difference between the inlet of the torch and outlet of the plenum chamber is linear with input power of the torch.\u003c/p\u003e \u003c/div\u003e"},{"header":"3.0 Materials and Methods","content":"\u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e3.1 Plasma Torch Aerosol Generation System (PTAGS)\u003c/h2\u003e \u003cp\u003eA 25 kW (100 V and 100\u0026ndash;250 A) dc non-transfer arc PTAGS has been installed at ATF, RESD for the generation of nanoparticles. The PTAGS consists of the following sub-systems viz. (i) plasma torch, (ii) main power supply and HV/ HF power supply, (iii) water and gas control panel, (iv) cooling water supply system, (v) plasma/ sheath gas supply system and (vi) PLC automation.\u003c/p\u003e \u003cdiv id=\"Sec6\" class=\"Section3\"\u003e \u003ch2\u003e3.1.1 Plasma torch\u003c/h2\u003e \u003cp\u003eThe schematic presentation of the thermal plasma torch is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. The plasma torch consists of a rod-type cathode made of copper with a 16 mm diameter and conical shape tungsten tip at the end portion made of thoria for better thermionic emission and copper anode in the form of convergence nozzle with conical shape. The plasma torch is operated in non-transferred arc mode and atmospheric pressure. The total lengths of the cathode and anode are 126 mm and 49 mm, respectively. The electric arc inside the torch is initiated between the tip of the cathode and the anode.\u003c/p\u003e\u003cp\u003eThe arc generated by plasma torches strongly depends on many parameters, like the design of the cathode and anode, the current and voltage of the arc, and the gas mass flow rate. The structure of plasma arcs also depends on the type of gas used, such as plasma-generating gas, as different gases have different specific heat, thermal conductivity, radical production, and power requirements. The entire plasma torch (cathode and anode) is cooled by De-mineralised (DM) water from a separate chilling unit through a closed-loop circulation pump. The present plasma torch (custom fabricated) can be operated with a mixture of nitrogen and argon as plasma-generating gas for various flow rates. The plasma-forming gas is introduced axially across the cathode region. The gas flow forces the anodic arc root to stride into the nozzle, and plasma is initiated when electrons are accelerated from the cathode to the anode. The electron collides and ionizes the atoms or molecules in the gas. The additional electrons generated by the ionization cause further ionization, giving a multiple effect, and collision transfers the kinetic energy of the gas molecules. The high-velocity ions and electrons in the path of the arc further dissociate the gas molecules that flow along the cathode length and produce the plasma. The gas is heated when the arc originates as a plasma jet from the torch orifice (the diameter of the torch orifice is 6 mm).\u003c/p\u003e \u003cp\u003eThe arc stability is accomplished in the plasma torch by magnetic arc rotation. A permanent magnet is provided inside the torch body (anode side), giving the magnetic field parallel to both the cathode and anode axis (along the discharge axis). The arc route at the anode side (i.e., the current carried by the arc at the location where it touches the anode) is perpendicular to the magnetic field. Hence, the tip of the arc rotates along the axis due to tangential force without continuously touching the anode surface at the same location. It reduces the rate of electrode erosion and increases the life of electrodes.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec7\" class=\"Section3\"\u003e \u003ch2\u003e3.1.2 Main power supply and HV/ HF power supply\u003c/h2\u003e \u003cp\u003eThe arc of the plasma torch is initiated between the cathode and anode using a high voltage high-frequency source (HVHF) and then transferred to the copper anode. The power supply is made from an un-controlled bridge rectifier, a controlled half-bridge thyristor and a diode. DC power coming from the transformer through thyristor circuits energizes and sustains the arc. The open circuit voltage is around 470 V (depending on the input AC three-phase voltage). The HV/ HF power supply (3 kV \u0026ndash; 3 MHz) initiates the start pulse to produce the arc between the cathode and anode. This arc exists only for a second (set time), and the DC power from the power supply is used to sustain the arc for a long time and increase the arc power. The sustainability of the arc flow depends on the flow rate of plasma gas and the electric power to the torch for the fixed electrode design.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec8\" class=\"Section3\"\u003e \u003ch2\u003e3.1.3 Water and gas control panel\u003c/h2\u003e \u003cp\u003eThe torch body and plenum chamber portions are subjected to extreme temperature or heat flux. A cooling water system is provided to sustain the system's integrity against thermal, electrical, and mechanical stress. It consists of a water cooler, pump, PVC, PU, and headers. A closed loop of water line is connected from the chiller unit of 400 L capacity to the torch body and the plenum chamber through the motor and control panel. The water chiller unit cools the water down to a minimum of 18 \u003csup\u003e⁰\u003c/sup\u003eC. The hot water comes back to the cooler unit and gets cooled. For the stable operation of the plasma torch, the electric power to the torch and the plasma gas flow rate must be properly balanced. The choice of plasma-generating gas is generally based on the energy it can carry, reactivity and cost. A gas line made of PU pipe from the nitrogen and argon cylinder to the torch body is mounted through the control panel, which is used for gas mixing and flow control. Water and gas flow meters relate to flow control valves to the panel. The temperature controller mounted on the panel displays the torch inlet and outlet water temperatures. Panel continuously sends temperature and flow rate data to PLC using wireless data transmission.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec9\" class=\"Section3\"\u003e \u003ch2\u003e3.1.4 Programmable Logic Controller (PLC) Automation\u003c/h2\u003e \u003cp\u003eA programmable logic controller (PLC) is used to automate the process parameters of the plasma torch operation. It is provided with a digital display to monitor the system's status, PF bank switches and the arc power parameters (voltage and current) during operation. The control panel continuously sends temperature and flow rate data to PLC using wireless data transmission. The main screen will display the arc current, voltage, and system status. When PLC starts, it should show 'system healthy'. For safe operation of the system and attaining the sustained arc, some parameters are set to the range as given in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. Whenever any interlock parameter crosses the set values of the system during the process, this screen automatically displays the status as 'check interlock'.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eInterlocks and the corresponding set points.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"3\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eInterlock parameters\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eInference\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eSet value\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eWater Flow\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eWater is not flowing in Plasma Torch\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e7 L min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eWater Temperature\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eInlet water Temperature is high\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e30 \u003csup\u003e⁰\u003c/sup\u003eC\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCheck Gas Flow\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eGas is not flowing in the Plasma Torch\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e10\u0026ndash;25 L min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eStack Temperature High\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eThyristor heat sink temperature is high\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e40 \u003csup\u003e⁰\u003c/sup\u003eC\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eOver Current\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eArc current value is crossed to set the value\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e95\u0026ndash;300 A\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eOver Voltage\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eArc volts value crossed to set value\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eSet Value: 30\u0026ndash;600 V\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Sec10\" class=\"Section2\"\u003e \u003ch2\u003e3.2 Experimental Setup\u003c/h2\u003e \u003cp\u003eAll the experiments are performed in the Aerosols Test Facility (ATF), which consists of a 1 m\u003csup\u003e3\u003c/sup\u003e cylindrical chamber (diameter 150 cm and height 60 cm) made of Stainless Steel (SS) with multiple ports on the wall of the chamber. More details on ATF can be found elsewhere (Baskaran et al., \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2004\u003c/span\u003e; KUMAR, \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2010\u003c/span\u003e; Subramanian et al., \u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). The experimental setup consists of PTAGS, material feeder, aerosol chamber, Data Acquisition System (DAS), and aerosol diagnostic instruments. The detailed schematic diagram of the experimental setup and PTAGS is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e. The coaxial SS cylindrical plenum chamber of 0.5 m length is used to transport the generated aerosol to the chamber by opening the gate valve. The plenum chamber is cooled with water to prevent excessive heating and restrict the damage to the O-rings, flowing in a closed loop from the torch body to the plenum chamber to the back chiller unit.\u003c/p\u003e \u003cp\u003eK-type thermocouples, pressure transducers (M/s Gems Sensors, UK) and humidity sensors (M/s Rotronics, INC, USA \u0026ndash; HC2 series) were used inside the aerosol chamber for measurement of temperature, pressure, and relative humidity during the experiment, respectively. The measuring range and error in measuring pressure, temperature and relative humidity are 0.5 to 400\u0026thinsp;\u0026plusmn;\u0026thinsp;0.25% bar, \u0026minus;\u0026thinsp;200 to 1370\u0026thinsp;\u0026plusmn;\u0026thinsp;1 \u003csup\u003e⁰\u003c/sup\u003eC and 0 to 100\u0026thinsp;\u0026plusmn;\u0026thinsp;1.5%, respectively. The pneumatic gate valve between the aerosol chamber and plenum chamber can be closed and opened with the help of an air compressor (Make and model: Whitestar and KND-SPTC-9).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cdiv id=\"Sec11\" class=\"Section3\"\u003e \u003ch2\u003e3.2.1 Aerosol Characterization Techniques\u003c/h2\u003e \u003cp\u003eThe aerosol generated by PTAGS is characterized using real-time aerosol diagnostic instruments such as SMPS (Make and Model: M/s Grimm Aerosol Technik, Germany and 5416 CPC based), Mastersizer (Make and Model: M/s Malvern, UK and 2000) and an offline filter paper sampler. The SMPS is a combination of Differential Mobility Analyser (DMA), Condensation Particle Counter (CPC) and 64-bit Personal Computer (PC) based operating software. SMPS gives the number size distribution and number concentration of aerosols in the size range of 0.01\u0026ndash;1.1 \u0026micro;m based on the electrical mobility principle (Baskaran et al., \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2009\u003c/span\u003e). The flow rate of the SMPS instrument is 0.3 lpm, and the time interval for single data recording is 3.5 minutes. Mastersizer gives volume/ mass size distribution of aerosols suspended in liquid (size ranges from 0.02\u0026ndash;2000 \u0026micro;m) and air medium (size ranges from 0.5\u0026ndash;2000 \u0026micro;m) based on the ensemble diffraction technique (Kumar et al., \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2015\u003c/span\u003e, \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). The uncertainty in the size distribution measurement by SMPS and Mastersizer ranges from 0.8\u0026ndash;3 % and 2\u0026ndash;3 %, respectively (Kumar et al., \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). The suspended aerool mass conentration is measured using a filter paper sampler at one port of the aerosol chamber. A closed-face type filter paper sampler (47 mm diameter), a rotary pump with a maximum 25 lpm flow rate capacity and a rotameter to measure the flow rate are used for sampling. A microbalance with an accuracy of 0.01 mg (Sartorius make, Secura 26 Model and Design 1) is used for the gravimetric analysis of the glass fibre filter (M/s Whatman). The flow rate measurement and sampling time uncertainty are \u0026plusmn;\u0026thinsp;2% and \u0026plusmn;\u0026thinsp;1 second, respectively. Further, a fluctuation in flow rate is observed during experiments due to the loading of aerosol on the filter paper. This leads to the total uncertainty in the sampled volume is about\u0026thinsp;\u0026plusmn;\u0026thinsp;1%. Considering all uncertainties, the calculated uncertainty in measured mass concentration is approximately 5% (Narayanam et al., \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). The microchemistry and morphology of aerosol generated by plasma torch were analyzed by Energy dispersive X-ray (EDAX) spectroscopy and Scanning Electron Microscopy (SEM), respectively. The EDAX is used for determining the crystalline phase, diffraction pattern and qualitative chemical information, while SEM (make and model: Philips and XL 30) is used to obtain the shape and size of aerosols deposited on the surface of the chamber.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section3\"\u003e \u003ch2\u003e3.2.2 Materials used for aerosol generation\u003c/h2\u003e \u003cp\u003eThe material used for aerosol generation is strontium peroxide (SrO\u003csub\u003e2\u003c/sub\u003e) powder. Since SrO\u003csub\u003e2\u003c/sub\u003e is the most stable compound of strontium, it is one of the fission products with a high fission yield (5%) and has more radiological and biological half-life, leading to a high effective half-life (Subramanian et al., \u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e2017\u003c/span\u003e), its non-radioactive form of material is chosen for present studies. The volume size distribution of SrO\u003csub\u003e2\u003c/sub\u003e powder (M/s Alfa Aesar, USA) is measured using Mastersizer-2000 with liquid dispersion method and water as dispersant medium. The volume size distribution of SrO\u003csub\u003e2\u003c/sub\u003e powder is presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe grain size of SrO\u003csub\u003e2\u003c/sub\u003e powder particles ranges from 0.5 to 70 \u0026micro;m with peak distribution at 15 \u0026micro;m. The volume size distribution of SrO\u003csub\u003e2\u003c/sub\u003e powder particles is a mono-model with Mass Median Diameter (MMD), and Standard Deviation (SD) of 12.2 \u0026micro;m and 2.49, respectively.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec13\" class=\"Section3\"\u003e \u003ch2\u003e2.2.2 Powder, wire, and pellet feeder\u003c/h2\u003e \u003cp\u003eFor the generation of aerosols, the material can be fed in the form of powder, wire or tube, and pellet into the plasma flame zone (Subramanian et al., \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e2009\u003c/span\u003e). The powder feeder (Make and Model: M/s Metallizing Equipment Co. Pvt. Ltd., India, and PF-700), which works on pressurization and constant volumetric feed principle, was used for injecting the metal oxide powder towards the plasma flame at a constant feed rate. The powder feeder consists of a pressurized canister (capacity 700 cm\u003csup\u003e3\u003c/sup\u003e) where the powder is stored, and a slotted rotating metal disc mounted off-centre concerning the canister. The pressurized canister can withstand a backpressure of 7.5 bar. The given mass of powder is fed into the slot of the rotating disc by gravity, and the disc rotates past the exit port, where the carrier gas passes through the disc and carries the powder to the plasma torch. The feed rate of powder (mass of powder fed to the torch per unit of time) is governed by the speed of the rotating disc, i.e., the powder feed rate is proportional to the disc rpm, which can be controlled. The powder feeder can be operated manually and automatically with the help of a programmable logic controller system. In the other method, the feed material in the form of wire or tube of 6 mm diameter can be fed in the plasma flame at the required rate. In the pellet feed mode, a known powder weight is pelletized, and then the pellet is rigidly fixed in the feeder tube and kept in front of the plasma flame. In the pellet mode feed, the percentage of conversion to aerosols from the pellet is less. In all forms of feeding, the feed material can be fed by powder/ wire/ pellet oriented perpendicular to the plasma flame axis.\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Sec14\" class=\"Section2\"\u003e \u003ch2\u003e3.3 Experimental procedure\u003c/h2\u003e \u003cp\u003eThe experiments are performed in two phases. In the first phase, the operational characterization parameters of PTAGS, like I-V characteristics, electro-thermal efficiency, and torch power, have been optimized for various combinations of argon and nitrogen mixture gas flow rates. The experimental parameters for the characterization of PTAGS and the generation of aerosols are given in Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e. The flow rate of argon gas is kept constant at 10 L min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e while that of nitrogen gas is varied over 5\u0026ndash;20 L min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e in steps of 5 L min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. The total flow rates of a mixture of gases are 15, 20, 25 and 30 L min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. The PTAGS is tested for each flow rate while increasing the current of the torch from 100\u0026ndash;250 A. All experimental runs keep the cooling water flow rate constant (7 L min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e). The inlet water temperature ranges from 20\u0026ndash;22 \u003csup\u003e⁰\u003c/sup\u003eC, and the outlet temperature is 24\u0026ndash;40 \u003csup\u003e⁰\u003c/sup\u003eC with the rise in temperature 2\u0026ndash;20 \u003csup\u003e⁰\u003c/sup\u003eC. In the second phase, experiments were performed to generate SrO with the optimized torch parameters. The range of operating parameters of PTAGS for the generation of aerosols is included in Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e. The nitrogen gas flow rate was kept at more than 10 L min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e for a fixed argon gas flow rate (10 L min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) to achieve high PTAGS power. The range of torch arc current and voltages are set between 200\u0026ndash;250 A and 70\u0026ndash;90 V, respectively.\u003c/p\u003e \u003cp\u003eAt the start of each experiment, the aerosol and plenum chamber were opened and cleaned using a wet cloth followed by alcohol spray and wiped with tissue paper to remove the deposited particles. The clean air was blown inside the chamber with the help of HEPA filters, and chamber air was flushed out using an air displacement pump to minimize background aerosol concentration. The argon was used as powder feeder gas to transport the powder inside the canister into the plasma flame. The powder feeder was turned on after the plasma torch was switched on, and the power of the torch was ensured to be at the desired value (18\u0026ndash;20 kW) with an arc in the stabilized condition. In this scenario, the aerosols generated by PTAGS are filled in the aerosol chamber and all ports, resulting in homogeneous aerosol distribution. The gate valve between the aerosol and plenum chamber is closed after the plasma torch is switched off.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eThe experimental parameters for characterization of PTAGS and aerosol generation.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"3\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eOperating Parameters\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eRange of Optimisation\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eParameters for aerosol generation\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTorch Power (kW)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e5\u0026ndash;25\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eMore than 15\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eArc voltage (V)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e55\u0026ndash;95\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e70\u0026ndash;90\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eArc current (A)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e100\u0026ndash;250\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e200\u0026ndash;250\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eNitrogen gas flow rate (L min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e5\u0026ndash;20\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e10\u0026ndash;20\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eArgon gas flow rate (L min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e10\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCooling water flow rate (L min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e7\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eRise in water temperature (\u003csup\u003e⁰\u003c/sup\u003eC)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e2\u0026ndash;20\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e10\u0026ndash;16\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"4.0 Results and Discussion","content":"\u003cdiv id=\"Sec16\" class=\"Section2\"\u003e \u003ch2\u003e4.1 Effect of Arc Current and Gas Flow Rates on I - V Characteristics\u003c/h2\u003e \u003cp\u003eThe dependence of current-voltage characteristics of plasma torch on the various mixtures of gas flow rates of argon and nitrogen have been studied. The tests are performed by varying the nitrogen gas flow rates from 5\u0026ndash;20 L min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e at a constant argon gas flow rate of 10 L min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. The variation of arc voltage as a function of current and gas flow rates is given in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e. The torch's arc voltage decreases with increasing current for an offered total gas flow rate. At constant current, the arc voltage is higher for the large flow rate of plasma-generating gas. This is due to increased plasma conductivity with an increase in temperature. The decreasing I - V characteristics trend was found in order with other works (Glocker et al., \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2000\u003c/span\u003e; Ramasamy and Selvarajan, \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e2000\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe variation of arc voltage with a ratio of nitrogen and argon flow rate for different arc currents is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e. For a given current, the arc voltage increases with the ratio of nitrogen to argon gas flow rate.\u003c/p\u003e \u003cp\u003eAn increase in the flow ratio of nitrogen to argon gas decreases plasma conductivity; hence, the arc voltage increases. At a higher current, the arc voltage is lower; for example, at 240 A current and ratio of nitrogen to argon gas flow rate 2, the arc voltage is 87.5 V, and at a current of 100 A and the same gas flow ratio, the voltage is 97 V. The increase in the ratio of the gas flow rate causes the lengthening of the arc and thermal pinch due to a decrease in the plasma conductivity (Planche et al., \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e1998\u003c/span\u003e). Further, as the gas flow rate increases, more thermionic electrons are emitted from the torch's cathode, which lowers the voltage drop near the electrodes.\u003c/p\u003e \u003cdiv id=\"Sec17\" class=\"Section3\"\u003e \u003ch2\u003e4.1.1 Empirical relation\u003c/h2\u003e \u003cp\u003eThe relationship between arc voltage (\u003cem\u003eV\u003c/em\u003e), current (\u003cem\u003eI\u003c/em\u003e) and total gas flow rate (\u003cb\u003ef\u003c/b\u003e\u003csub\u003e\u003cb\u003et\u003c/b\u003e\u003c/sub\u003e) is derived based on the Nottingham equation given in section \u003cspan refid=\"Sec1\" class=\"InternalRef\"\u003e2.0\u003c/span\u003e. The value of coefficients \u003cem\u003eK\u003c/em\u003e\u003csub\u003e\u003cem\u003e1\u003c/em\u003e\u003c/sub\u003e and \u003cem\u003eK\u003c/em\u003e\u003csub\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sub\u003e are determined using the least square method and presented in Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab3\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eCalculated values of \u003cem\u003eK\u003c/em\u003e\u003csub\u003e\u003cem\u003e1\u003c/em\u003e\u003c/sub\u003e and \u003cem\u003eK\u003c/em\u003e\u003csub\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sub\u003e for argon and nitrogen gas mixtures.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"6\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eS. N.\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cem\u003ef\u003c/em\u003e\u003csub\u003e\u003cem\u003eAr\u003c/em\u003e\u003c/sub\u003e (L min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u003cem\u003ef\u003c/em\u003e\u003csub\u003e\u003cem\u003eN2\u003c/em\u003e\u003c/sub\u003e (L min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u003cem\u003ef\u003c/em\u003e\u003csub\u003e\u003cem\u003et\u003c/em\u003e\u003c/sub\u003e (L min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003e\u003cem\u003eK\u003c/em\u003e\u003csub\u003e\u003cem\u003e1\u003c/em\u003e\u003c/sub\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003e\u003cem\u003eK\u003c/em\u003e\u003csub\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sub\u003e\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e15\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e53.57\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e267.09\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e20\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e62.59\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e520.73\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e15\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e25\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e69.15\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e369.28\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e20\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e30\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e74.94\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e533.66\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eThe \u003cb\u003ef\u003c/b\u003e\u003csub\u003e\u003cb\u003eAr\u003c/b\u003e,\u003c/sub\u003e \u003cb\u003ef\u003c/b\u003e\u003csub\u003e\u003cb\u003eN2\u003c/b\u003e\u003c/sub\u003e and \u003cb\u003ef\u003c/b\u003e\u003csub\u003e\u003cb\u003et\u003c/b\u003e\u003c/sub\u003e flow rates of argon, nitrogen and total gas (argon\u0026thinsp;+\u0026thinsp;nitrogen). The empirical relation for \u003cem\u003eV\u003c/em\u003e has been derived as a function of total gas flow rate (\u003cb\u003ef\u003c/b\u003e\u003csub\u003e\u003cb\u003et\u003c/b\u003e\u003c/sub\u003e) and \u003cem\u003eI\u003c/em\u003e by using derived constant \u003cem\u003eK\u003c/em\u003e\u003csub\u003e\u003cem\u003e1\u003c/em\u003e\u003c/sub\u003e and \u003cem\u003eK\u003c/em\u003e\u003csub\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sub\u003e and from Eqs.\u0026nbsp;\u0026lt;link rid=\"eqn\u003cspan refid=\"Equ7\" class=\"InternalRef\"\u003e6\u003c/span\u003e\"\u0026gt;5\u0026lt;/link\u0026gt; and \u003cspan refid=\"Equ7\" class=\"InternalRef\"\u003e6\u003c/span\u003e. The derived empirical relation is given as follows:\u003cdiv id=\"Equ13\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ13\" name=\"EquationSource\"\u003e\n$$V=\\left(33.245+0.9949*{f}_{t}\\right)+(130.973+12.965*{f}_{t})*{I}^{-n}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e12\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eThe total gas flow rate of argon and nitrogen is in L min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. The measured and predicted voltage as a function of arc current for various gas flow rates is compared in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e. The deviation between measured and predicted arc voltage for different arc current and gas flow rates does not exceed\u0026thinsp;\u0026plusmn;\u0026thinsp;8.78%. The error analysis shows that the experimentally measured values are in fair agreement with the predicted values. The I-V characteristics curve is in the form of hyperbolic and asymptotic towards zero voltage.\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Sec18\" class=\"Section2\"\u003e \u003ch2\u003e4.2 Power of the Plasma Torch\u003c/h2\u003e \u003cp\u003eThe power of the plasma torch is calculated from arc current and voltage. The variation of arc power with the current for a mixture of argon and nitrogen gas is plotted in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e. The arc power increases linearly with increasing the arc current for all gas flow rates. The net change of torch power is 7.56 kW when the current changes from 100 to 240 A for the flow rate of 5 L min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, whereas the change of torch power is 11.3 kW for 20 L min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e for the exact current change. Further, for a given current, the net torch power increases from 6.5 to 9.7 kW at 100 A when the flow rate changes from 5 to 20 L min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, while it is 14.1 to 21 kW at 240 A. The total power transferred to the plasma increases with increased gas flow rate. Various earlier studies also obtained similar results (Capetti and Pfender, \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e1989\u003c/span\u003e; Ramasamy and Selvarajan, \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e2000\u003c/span\u003e). The variation of torch power with temperature difference (ΔT) between the inlet and outlet of the torch is illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e. At constant temperature difference, the torch power is more prominent for higher gas flow rates. It is noted that when the power is maintained constant even after reducing the gas flow rate, the ΔT is high. The variation of the temperature difference between the inlet and outlet of the torch with power is also linear.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec19\" class=\"Section2\"\u003e \u003ch2\u003e4.3 Electro-thermal efficiency of the torch\u003c/h2\u003e \u003cp\u003eThe electro-thermal efficiency (η) of the plasma torch for various flow rates of argon and nitrogen gas mixtures was determined by using Eq.\u0026nbsp;(\u003cspan refid=\"Equ8\" class=\"InternalRef\"\u003e7\u003c/span\u003e). The calculated η of the torch for gas mixtures (flow rate of Ar\u0026thinsp;+\u0026thinsp;N\u003csub\u003e2\u003c/sub\u003e:10\u0026thinsp;+\u0026thinsp;5 L min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) is given in Table\u0026nbsp;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e. The η of the torch decreases with the increase of torch power. Similarly, η for other gas flow rates is determined and shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e. The η reduces with increased torch power for experimented gas flow rates (25, 20, 25, 30 L min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e). The η is larger for higher gas flow rates at constant torch power. Further, the η also decreased with an increase in the current intensity of the torch.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab4\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 4\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eElectro-thermal efficiency of the plasma torch for argon-nitrogen gas mixture.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"7\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colspan=\"7\" nameend=\"c7\" namest=\"c1\"\u003e \u003cp\u003eGas flow rate: Ar: N\u003csub\u003e2\u003c/sub\u003e (10:5 L min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) and Inlet temperature (T\u003csub\u003e1\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;22 \u003csup\u003e⁰\u003c/sup\u003eC)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eP (kW)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eT\u003csub\u003e2\u003c/sub\u003e (\u003csup\u003e⁰\u003c/sup\u003eC)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eΔT = (T\u003csub\u003e2\u003c/sub\u003e - T\u003csub\u003e1\u003c/sub\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eQ\u003csub\u003eloss\u003c/sub\u003e (kW)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eη\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eη (%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e1/ η\u003csub\u003ef\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e6.48\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e24\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.98\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.85\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e84.95\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e0.31\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e7.91\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e26\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1.95\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.75\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e75.33\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e0.51\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e9.20\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e28\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e2.93\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.68\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e68.19\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e0.65\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e11.34\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e30\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e3.90\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.66\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e65.60\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e0.71\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e12.16\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e32\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e4.88\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.60\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e59.90\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e0.82\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e13.27\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e34\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e12\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e5.85\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.56\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e55.89\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e0.91\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e14.04\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e36\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e14\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e6.83\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.51\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e51.38\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e0.99\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eSimilarly, the variation of η with the temperature difference (\u003cem\u003eΔT\u003c/em\u003e) between the inlet and outlet of the torch is given in Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e. The η decreases with increase of \u003cem\u003eΔT\u003c/em\u003e between the inlet and outlet of the torch for all gas flow rates. Bokhari et al. have reported a similar observation that the η of the torch increases as convective and radiative heat losses decrease by decreasing the size of the anode (Bokari and Boulos, \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e1980\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe variation of η with the reciprocal of efficiency factor (\u003cem\u003eη\u003c/em\u003e\u003csub\u003e\u003cem\u003ef\u003c/em\u003e\u003c/sub\u003e) is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003e. The η decreases linearly with the increase of \u003cem\u003eη\u003c/em\u003e\u003csub\u003e\u003cem\u003ef\u003c/em\u003e\u003c/sub\u003e for all gas flow rates. There is an inverse linearity relation between the η and \u003cem\u003eη\u003c/em\u003e\u003csub\u003e\u003cem\u003ef\u003c/em\u003e,\u003c/sub\u003e i.e., the η decreases with an increase in input power and found that the efficiency increased with increased gas flow rate. Similar observations have been reported previously; there is an increase in the thermal efficiency with an increase in the gas flow rates and a decrease in the thermal efficiency with an increase in the torch power. The flow rate of plasma forming gas and current intensity are found to influence the torch efficiency and power for fixed nozzle diameter and length. It has been found that properly distributed gas injection increases the torch power and η.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eAt low torch power (less than 10 kW) of PTAGS, the torch's flame was unstable, while at high torch power (more than 15 kW), the plasma flame was stabilized. Based on the above investigation, the regulation of the PTAGS operational parameters was standardized and operational stability was ensured. The PTAGS is operated at 18\u0026ndash;20 kW power, 60\u0026ndash;80% electro-thermal efficiency and 20\u0026ndash;30 L min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e flow rate plasma forming gas for generation of aerosols.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec20\" class=\"Section2\"\u003e \u003ch2\u003e4.4 Calibration of Powder Feeder\u003c/h2\u003e \u003cp\u003eThe powder feeder was calibrated using SrO\u003csub\u003e2\u003c/sub\u003e powder for a constant flow rate (8 L min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) of argon gas. Figure\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e11\u003c/span\u003e represents the relation between the feed rate (mg min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) and revolution per minute (RPM) of the rotating disc of the powder feeder. The powder feed rate (powder obtained) varies linearly with RPM within experimental uncertainty. Since the expected mass concentration of fuel and non-volatile fission product aerosols in containment during severe accident conditions of a nuclear reactor are in the range of 10\u0026ndash;40 mg m\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e (Baskaran et al., \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2004\u003c/span\u003e), the powder feeder was operated at 5 RPM in all experiments for the generation of aerosols to generate few tens of mg m\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e concentration. However, generation rate and mass concentration can be increased with the increase of powder feed rate, i.e., RPM of powder feeder and duration of torch operation.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec21\" class=\"Section2\"\u003e \u003ch2\u003e4.5 Characterization of aerosols generated by a plasma torch\u003c/h2\u003e \u003cp\u003eIt was found that at less than 10 kW of torch power, the torch's flame was not stable, and this led to the metal powder not aerosolizing correctly, resulting in the falling of metal powder at the bottom of the plenum chamber region. At more than 15 kW, the plasma flame was stabilized, and effective vaporization of metal powder was observed due to the high temperature and the length of the torch flame. Hence, the PTAGS is operated at 20 kW power, and the total flow rate of plasma-generating gas is kept at 25 L min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. The powder feed rate is maintained at 10 mg min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e at a fixed 5 RPM. The torch is operated continuously for 4\u0026ndash;5 min. The suspended total mass concentration of aerosols is measured by using a filter paper sampler connected to one of the ports of the aerosol chamber. The aerosol sampling is carried out for 1 min at 10 L min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e flow rate. The measured total mass concentration of aerosol ranges from 20.9\u0026thinsp;\u003cb\u003e\u0026plusmn;\u003c/b\u003e\u0026thinsp;1.1 to 29.5\u0026thinsp;\u003cb\u003e\u0026plusmn;\u003c/b\u003e\u0026thinsp;1.5 mg m\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e with an average concentration of 24.9\u0026thinsp;\u003cb\u003e\u0026plusmn;\u003c/b\u003e\u0026thinsp;1.3 mg m\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e in various sets of performed experiments. The suspended number concentration and size distribution of the generated aerosol were continuously monitored by using SMPS before the start of the experiment. The evolution of the number concentration of SrO aerosol for experiments is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig12\" class=\"InternalRef\"\u003e12\u003c/span\u003e. The aerosol concentration increases during generation time and reaches a maximum value of 6.0*10\u003csup\u003e6\u003c/sup\u003e cm\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e at 7 min; thereafter, aerosol concentration starts decaying by coagulation and various settling processes inside the aerosol chamber. The concentration of SrO aerosol was reduced by almost one order in one hour inside the aerosol chamber.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe aerosol size distribution at various time intervals for a typical experiment is presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig13\" class=\"InternalRef\"\u003e13\u003c/span\u003e. The aerosol size distribution measured at different time intervals (3, 7, 10, 14, 21, 42 and 70 min) is mono-model and polydisperse. The initial size distribution (up to 3 min) of SrO aerosol generated by PTAGS ranges from 10\u0026ndash;40 nm with Count Geometric Mean Diameter (CGMD), Geometric Standard Deviation (GSD) is 26.5 nm and 1.45 respectively, and the maximum number concentration is 2.99*10\u003csup\u003e5\u003c/sup\u003e cm\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e. The number concentration of aerosols increases (6.08*10\u003csup\u003e6\u003c/sup\u003e cm\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e) up to aerosol generation time (5 minutes). After that, the size distribution of aerosol shifted, and particle size was found to range from 11 to 310 nm in 7 minutes due to the rapid aggregation of aerosol. Then, with the progress of time, the number concentration progressively reduced until 70 min, and the concentration became one order less (4.97*10\u003csup\u003e5\u003c/sup\u003e cm\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e) due to coagulation and various settling processes.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe evolution of CGMD and GSD for the experiment period has been presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig14\" class=\"InternalRef\"\u003e14\u003c/span\u003e. The CGMD increases from 26.5 to 190 nm for 70 min, and GSD values rise marginally from 1.45 to 1.59 in the first 25 min, then remain nearly the same (~\u0026thinsp;1.57) up to 70 min. The increase in aerosol CGMD is attributed to the agglomeration process, which is dominated by the high concentration of aerosols. The initial GSD increases due to various aerosol processes, viz., source accumulation, coagulation, and agglomeration. At a later period, with the progress of time, as the concentration began to reduce one order less (after 25 min), it remained almost constant due to negligible agglomeration. The number concentration and initial size distribution of aerosols generated by PTAGS are in agreement with values measured by other works (Misra et al., \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2013\u003c/span\u003e; Subramanian et al., \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e2009\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe experiments were repeated a few times to check the results reproducibility and data presented in Table\u0026nbsp;\u003cspan refid=\"Tab5\" class=\"InternalRef\"\u003e5\u003c/span\u003e. The total aerosol concentration measured using SMPS ranges from 4\u0026ndash;6*106 cm-3 with an average value of 4.8*10\u003csup\u003e6\u003c/sup\u003e cm\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e. The CGMD during generation time ranges from 26.5\u0026ndash;33.0 nm (GSD ranges from 1.12\u0026ndash;1.45) and increases to a value 119.6\u0026ndash;140.3 nm (GSD ranges from 1.29\u0026ndash;1.46). Average CGMD and Standard Deviation (SD) during and after the generation of SrO aerosols for all four experiments are 29.28\u0026thinsp;\u0026plusmn;\u0026thinsp;3.1 nm and 130.2\u0026thinsp;\u0026plusmn;\u0026thinsp;9.3 nm, respectively. The formation of metal aerosols in a very high-temperature gradient through rapid cooling favours homogeneous condensation rather than heterogeneous, resulting in aerosol sizes as small as 10 nm (Oxtoby and Evans, \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e1998\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab5\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 5\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eAerosol number concentration, CGMD with GSD of aerosols during and after generation.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"4\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eExp. runs\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eAerosol number Concentration (cm\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eCGMD (nm), GSD during generation (3rd min)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eCGMD (nm), GSD after generation (7th min)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003e1.\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e6.08*10\u003csup\u003e6\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e26.5 (1.45)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e119.6 (1.46)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003e2.\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e5.12*10\u003csup\u003e6\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e27.1 (1.22)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e126.2 (1.39)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003e3.\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e3.89*10\u003csup\u003e6\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e33.0 (1.32)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e135.8 (1.35)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003e4.\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e4.09*10\u003csup\u003e6\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e30.5 (1.12)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e140.3 (1.29)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eFurther, the calculated Mass Median Diameter (MMD) using CGMD and GSD by applying the Hatch-Choate equation after aerosol generation (7th min) is found to be in the range of 170\u0026ndash;185 nm with an average diameter of 175 nm. The calculated MMD of SrO aerosol generated by PTAGS aligns with other synthesis methods (Gungor et al., 2019).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec22\" class=\"Section2\"\u003e \u003ch2\u003e4.6 EDAX and SEM analysis\u003c/h2\u003e \u003cp\u003eThe aerosols deposited on the floor surface of the aerosol chamber were collected on aluminium foil kept at the bottom surface of the chamber and analyzed for microchemistry and morphological properties by using Energy dispersive X-ray (EDAX) spectroscopy and Scanning Electron Microscopy (SEM). Figure\u0026nbsp;\u003cspan refid=\"Fig15\" class=\"InternalRef\"\u003e15\u003c/span\u003e (a) and (b) show the SEM micrograph and EDAX spectrum of SrO aerosol particles deposited on aluminium foil. The EDAX spectrum of deposited aerosols on the bottom surface of the chamber contains peaks corresponding to strontium and oxygen, which says that only SrO aerosols are present on the aluminium foil.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe SEM analysis shows that most of the aerosols are in the sub-micrometre range, and many nanometre-sized aerosols agglomerated and collected in a single place due to settling on the surface of the aluminium foil. The deposited aerosols are found to be polydisperse with sub-micrometre-sized particles, and the shape is nearly spherical.\u003c/p\u003e \u003c/div\u003e"},{"header":"5.0 Summary and Conclusion","content":"\u003cp\u003eThe operational characteristics of PTAGS installed in our laboratory are studied to obtain suitable optimized operational parameters for proposed experiments for safety studies related to sodium and fission product aerosols generated during accident conditions in large volumes. The Nottingham coefficients were calculated using the least-square method, and an empirical relation for arc voltage as a function of arc current and flow rate of plasma forming gas is derived. The relation developed strictly applies to the torch under investigation, but the same methodology can be applied to any other plasma torch. The predicted and measured arc voltages are in good agreement. The electro-thermal efficiency is derived from an analytical expression using an energy balance equation for different flow rates of a mixture of argon-nitrogen gases (5\u0026ndash;20 L min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e for nitrogen and 10 L min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e for argon) and other torch power (8\u0026ndash;24 kW) levels. Based on the above investigation, the regulation of the PTAGS operational parameters was standardized and operational stability was ensured. The PTAGS is operated at 18\u0026ndash;20 kW power, 60\u0026ndash;80% electro-thermal efficiency and 20\u0026ndash;30 L min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e flow rate plasma forming gas for generation of aerosols.\u003c/p\u003e \u003cp\u003eSrO aerosols are generated by using a powder feeder and PTAGS. The desired mass flow rate of powder was obtained at the speed of a rotating disc ranging from 5 to 35 RPM. The average aerosol mass concentration and maximum number concentration are 24.9 mg m\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e and 4.8*10\u003csup\u003e6\u003c/sup\u003e cm\u003csup\u003e\u0026minus;\u0026thinsp;3,\u003c/sup\u003e respectively. The average measured CMD and calculated MMD are 130.2 nm and 175 nm after generation. Aerosol size distribution becomes broader, and number concentration increases with time (5 minutes) due to coagulation and various settling processes. The SEM analysis of the deposited aerosols reveals that the shape of the aerosol is primarily spherical, and the size of aerosols deposited on the surface is sub-micrometre but polydisperse. The interpretation from the experiments could be helpful for the safety analysis of severe accidents of nuclear reactor codes. The operational parameters of the torch shall be tuned to achieve desired aerosol characteristics for future works like aerosol dispersion in large buildings and retention factor in a liquid pool.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e \u003ch2\u003e Conflict of interest statement\u003c/h2\u003e \u003cp\u003eOn behalf of all authors, the corresponding author states that there is no conflict of interest that could have appeared to influence the work reported in this paper.\u003c/p\u003e \u003c/p\u003e\u003ch2\u003eAcknowledgement\u003c/h2\u003e \u003cp\u003eThe authors are thankful to Dr. Parameswaran P., Head, XRDSES, PMD, for facilitating the EDAX and SEM analysis of the samples.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eBalasubramaniam, C., Khollam, Y.B., Banerjee, I., Bakare, P.P., Date, S.K., Das, A.K., Bhoraskar, S. v. (2004). 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Plasma Chemistry and Plasma Processing 1985 5:1 5, 1\u0026ndash;37. https://doi.org/10.1007/BF00567907\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":true,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"aerosol-science-and-engineering","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"asen","sideBox":"Learn more about [Aerosol Science and Engineering](https://link.springer.com/journal/41810)","snPcode":"41810","submissionUrl":"https://www.editorialmanager.com/asen/default2.aspx","title":"Aerosol Science and Engineering","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"I-V characteristics, electro-thermal efficiency, plasma torch aerosol generator, aerosols characterization","lastPublishedDoi":"10.21203/rs.3.rs-4007909/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4007909/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003ePlasma Torch Aerosol Generation System (PTAGS) has been employed to generate nano aerosols with desirable characteristics. The operational parameters of PTAGS installed in the aerosol test facility have been optimized, and aerosols are generated using non-radioactive SrO\u003csub\u003e2\u003c/sub\u003e powder. The current-voltage characteristics, electro-thermal efficiency and torch power are studied as a function of the flow rate of the plasma-generating gas (mixture of argon and nitrogen) and the arc current of the plasma torch. The arc characteristics relation is determined using the Nottingham formulation. Based on this, torch parameters are evolved and optimized as 20 kW power, 70% electro-thermal efficiency, 25 L min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e flow rate of plasma forming gas, 5 mg min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e powder feed rate and for 4\u0026ndash;5 min torch operation towards the generation of SrO nano aerosols to achieve 10\u003csup\u003e12\u003c/sup\u003e m\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e and ~\u0026thinsp;25 mg m\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e for the count and mass concentration of aerosol respectively. The initial size distribution of the aerosols is in the few tens of nanometre range (10\u0026ndash;40 nm) with a mean diameter of 26 nm (σ\u003csub\u003eg\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;1.45). SEM and EDAX analysis reveal that the morphology of nano aerosols was nearly spherical and the formation of SrO nanoparticles. A set of operational parameters of PTAGS has been standardized to perform further experiments related to reactor safety analysis. PTAGS shall be tuned for aerosol generation in a large facility to achieve the characteristics equivalent to reactor accidental conditions.\u003c/p\u003e","manuscriptTitle":"Study on characterization of SrO Aerosols Generated by Optimized Thermal Plasma Torch Aerosol Generator","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-03-29 06:54:11","doi":"10.21203/rs.3.rs-4007909/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Major revisions","date":"2024-08-04T04:09:28+00:00","index":"","fulltext":""},{"type":"reviewerAgreed","content":"","date":"2024-03-27T03:54:28+00:00","index":0,"fulltext":""},{"type":"reviewersInvited","content":"","date":"2024-03-27T03:15:16+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"Aerosol Science and Engineering","date":"2024-03-12T07:07:54+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2024-03-11T02:36:00+00:00","index":"","fulltext":""},{"type":"submitted","content":"Aerosol Science and Engineering","date":"2024-03-03T02:54:41+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"aerosol-science-and-engineering","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"asen","sideBox":"Learn more about [Aerosol Science and Engineering](https://link.springer.com/journal/41810)","snPcode":"41810","submissionUrl":"https://www.editorialmanager.com/asen/default2.aspx","title":"Aerosol Science and Engineering","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"ffc9fc6a-c126-4ae1-b489-12bdd849b4a6","owner":[],"postedDate":"March 29th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2024-11-11T16:11:33+00:00","versionOfRecord":{"articleIdentity":"rs-4007909","link":"https://doi.org/10.1007/s41810-024-00267-z","journal":{"identity":"aerosol-science-and-engineering","isVorOnly":false,"title":"Aerosol Science and Engineering"},"publishedOn":"2024-11-07 15:58:19","publishedOnDateReadable":"November 7th, 2024"},"versionCreatedAt":"2024-03-29 06:54:11","video":"","vorDoi":"10.1007/s41810-024-00267-z","vorDoiUrl":"https://doi.org/10.1007/s41810-024-00267-z","workflowStages":[]},"version":"v1","identity":"rs-4007909","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4007909","identity":"rs-4007909","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}