Experimental Study of an Optimized Evacuated Tube Collector with Wavy Tape and Phase Change Material for Hot Water Production

Experimental Study of an Optimized Evacuated Tube Collector with Wavy Tape and Phase Change Material for Hot Water Production | 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 Experimental Study of an Optimized Evacuated Tube Collector with Wavy Tape and Phase Change Material for Hot Water Production Punam Kumar Agade This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-6252758/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract This study evaluates the performance of four configurations of an evacuated tube solar collector (ETSC): conventional ETSC, ETSC with wavy tape (WT), ETSC with phase change material (PCM), and ETSC with a combination of PCM and WT. The novelty of this research lies in integrating a binary eutectic PCM and analysing the combined effects of PCM and WT on ETSC performance. The results indicate that the highest hourly efficiency, 71.75%, is achieved with the ETSC incorporating both PCM and WT, followed by 67.63% for ETSC with WT, 65.5% for ETSC with PCM, and 60.61% for the conventional ETSC. The daily average efficiency for these cases is 35.17%, 39.90%, 40.32%, and 45.92%, respectively. Similarly, exergy efficiency follows the same trend, with the ETSC featuring both WT and PCM achieving the highest average exergy efficiency of 6.11%, compared to 3.48% for the conventional ETSC, 4.43% for ETSC with WT, and 5.09% for ETSC with PCM. An environmental analysis based on energy and exergy approaches further reveals that the ETSC with PCM and WT mitigates the highest amount of CO₂ emissions per ton compared to the other configurations. Thermodynamics and statistical mechanics Evacuated tube Solar collector Phase change material Wavy tape Energy efficiency Exergy efficiency 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 Figure 16 Figure 17 1. INTRODUCTION The increasing energy demand, driven by rising consumption across residential and industrial sectors, continues to grow daily (Boafo et al., 2017 ; Karthick et al., 2020a ). Energy is essential for various applications, including heating, transportation, lighting, and air conditioning. According to Reddy et al. ( 2020 ), heat production accounts for nearly half of global energy consumption. The reliance on conventional fuels contributes to environmental degradation, leading to issues such as global warming and ozone layer depletion. In India, heat generation constitutes two-thirds of total energy consumption, highlighting the need for sustainable alternatives. Solar energy, particularly for heat collection, presents a viable solution by reducing dependence on conventional energy sources. Rooftop solar systems, including photovoltaic (PV) modules and solar water heaters, have emerged as innovative, cost-effective, and sustainable solutions for harnessing solar energy (Ram et al., 2024). Among these, solar water heating systems are widely adopted due to their low maintenance requirements, ease of manufacturing, and operational simplicity. The efficiency of such systems is largely determined by the performance of the collector, which is often regarded as the "heart" of the solar water heater. Most research in this field focuses on improving the thermal performance of collectors. Traditionally, water has been the primary heat transfer fluid (HTF) in flat plate solar collectors (FPSC). However, its poor heat transfer properties pose a challenge in enhancing system efficiency. Two commonly used solar collectors are flat plate collectors (FPC) and evacuated tube solar collectors (ETSC) (Henein et al., 2022). Compared to FPCs, ETSCs offer higher thermal efficiency, lower maintenance costs, and reduced thermal losses. The cylindrical shape of ETSCs allows for passive solar tracking, further improving performance (Papadimitratos et al., 2016 ). As a result, ETSCs have gained popularity, surpassing FPCs in solar applications. According to the International Energy Agency (IEA), ETSCs currently dominate the global market, accounting for over 70% of solar thermal applications, including air, water, and space heating (Solar Heat Worldwide, 2024). ETSCs are well-suited for diverse climatic conditions and are categorized into heat pipe-based and U-tube-based systems, depending on their heat transfer mechanisms (Pathak et al., 2022). U-tube ETSCs facilitate heat transfer through conduction and convection, enhancing thermal efficiency (Deshmukh et al., 2023 ; Shafieian et al., 2019 ). Several factors influence FPSC performance, including HTF properties, absorber tube design, inlet fluid temperature, ambient conditions, solar radiation, wind speed, humidity, absorber coating, collector angle, and insulation. Conventional FPSCs, featuring smooth copper tubes, exhibit poor thermal transport due to a low convective heat transfer coefficient (Sakhaei et al., 2019). Various active and passive techniques have been explored to enhance heat transfer efficiency, with passive methods being particularly attractive due to their ability to improve thermal performance without additional energy input (Fan et al., 2019). Passive techniques, such as modifying absorber tubes, enhance convective heat transfer by increasing velocity gradients and reducing thermal boundary layers (Poongavanam et al., 2019; Pandey et al., 2017; Farhana et al., 2019; Arunkumar et al., 2018; Patil et al., 2018; Zhang et al., 2017; Methods et al., 2019 ; Sheikholeslami et al., 2019 ). Absorber tube modifications play a crucial role in improving solar thermal system efficiency due to their cost-effectiveness and ease of implementation. Various thermal performance enhancement techniques have been reported, including spiral tapes (Sheikholeslami et al., 2019 ; Milani et al., 2016; Farshad et al., 2019; Eiamsa-Ard et al., 2013 , 2010 ), coiled wires (Ponnada et al., 2019 ), ribbed pipes (Zhang et al., 2019 ), micro-fin structures (Promvonge et al., 2007), barriers, swirl producers (Wongcharee et al., 2012), and concentric rings. Tse et al. (2015) modified conventional solar water heaters by incorporating a ring-type heat exchanger, reducing frictional losses, and improving system performance compared to helical coil designs. Ghoneim et al. (2005) utilized double-glazing with a sputter-deposited low-emission layer and low-iron glass with honeycomb insertion, increasing transmittance to 85%. Similarly, Wang et al. ( 2015 ) applied SiO₂ antireflection coatings on all-glass evacuated tubes, raising solar transmittance to 0.94 and achieving 50.2% thermal efficiency at 150°C. Wongcharee and Eiamsa-Ard ( 2011 ) examined heat transfer performance using alternating clockwise and counterclockwise twisted tapes, finding that a lower twist ratio (3) resulted in optimal heat transfer enhancement. Kumar et al. ( 2024 ) investigated the effect of perforated wavy tapes in FPSCs, reporting heat transfer improvements of 20.83%, 14.85%, and 6.25% for systems without wavy tape, with WT, and with 9mm perforated wavy tape (PWT), respectively. However, one major drawback of solar water heaters is their reliance on solar availability, leading to reduced performance at night and increased thermal losses (Papadimitratos et al., 2016 ; Karthick et al., 2020b ). Nocturnal flow redirection in evacuated tubes exacerbates these losses (Tang et al., 2014). Recent studies suggest incorporating thermal storage media to mitigate this issue. Thermal storage can be integrated into storage tanks (Gurturk et al., 2017 ) or collector tubes (Feliński et al., 2017), enhancing efficiency by storing excess energy during the day and supplying heat when sunlight is unavailable. Two primary forms of thermal storage—sensible heat and latent heat—have been extensively studied (Alva et al., 2017 ). Latent heat storage is preferred in modern applications due to its higher energy density, superior thermal characteristics, and minimal volume changes (Cunha et al., 2016; Kumar et al., 2020a ). The integration of phase change materials (PCM) in solar thermal systems has gained significant attention for its potential to improve thermal storage and overall efficiency. Al-Hinti et al. ( 2010 ) investigated the effectiveness of solar collectors by incorporating paraffin wax as a phase change material (PCM) within a water storage tank. Their study demonstrated that this setup could maintain a hot water temperature of 55°C throughout the day, including during draw-off periods, and a warm water temperature of 30°C the following morning. Similarly, Canbazoglu et al. ( 2005 ) examined a 190-liter storage tank filled with plastic bottles containing salt hydrates as PCM. Their findings indicated that the heat storage capacity in the PCM-integrated tank was approximately 2.59–3.45 times higher than that of a conventional solar water heating system. Mehla and Yadav ( 2017 ) conducted an experimental study on an evacuated tube solar collector (ETSC) integrated with thermal storage for hot air production. Their results showed that the combination of ETSC and PCM enabled continuous hot air generation for up to 24 hours and improved system efficiency from 14.43–17.65%. Additionally, Xue et al. (2016) found that an ETSC integrated with PCM outperformed conventional ETSC systems. Abokersh et al. ( 2017 ) carried out a similar study, enhancing the heat retention capability of U-tube collectors by incorporating aluminium fins. To accurately assess the impact of integrating PCM with an ETSC system, it is essential to analyse the system under different operating conditions. Each PCM exhibits distinct thermal properties, such as melting point and latent heat capacity, which may not be suitable for all climatic conditions. To overcome this limitation, eutectic PCMs are developed by blending two or more organic PCMs, thereby enhancing their thermophysical properties for specific applications. In this study, a binary eutectic PCM is formulated by optimizing the weight ratio of palmitic and stearic acid. Its applicability in an ETSC system is evaluated by incorporating it into the storage tank. Additionally, to enhance the daytime efficiency of the ETSC, wavy tapes are introduced into the evacuated tubes. The system is analysed in four configurations: conventional ETSC, ETSC with wavy tape, ETSC with PCM, and ETSC with PCM + wavy tape. Various types of passive thermal enhancement devices used in riser tubes are illustrated in Fig. 1 . 2. METHODOLOGY This section is divided into three key parts: material selection and characterization, experimental setup development, and testing with data analysis. The first part involves selecting appropriate materials based on thermal and physical properties, followed by their preparation and characterization to assess parameters such as thermal conductivity and phase change behavior. The second part focuses on assembling the experimental setup, integrating essential components such as the evacuated tube solar collector, phase change materials, and thermal enhancement devices, along with installing and calibrating measuring instruments like thermocouples and flow meters to ensure accurate data collection. The final part involves conducting controlled experiments to evaluate system performance under various conditions, analyzing key parameters such as energy and exergy efficiency, heat transfer rates, and thermal storage capacity, followed by systematic data analysis to compare different configurations and derive meaningful conclusions. 2.1 Selection and Procurement of PCMs Stearic acid (SA) and palmitic acid (PA) were selected as the base phase change materials (PCMs) for the experimental study due to their suitable thermal properties for thermal energy storage applications. Stearic acid (SA), with a molar mass of 279.12 g/mol, exhibits a phase transition temperature range of 65–67°C, making it effective for heat storage and release within this temperature range. It was procured from Fischer to ensure high purity and reliability. Similarly, palmitic acid (PA), characterized by a molar mass of 254.32 g/mol and a phase transition temperature range of 59–62°C, was sourced from Himedia Chemicals. These PCMs were carefully selected based on their thermal stability, latent heat capacity, and compatibility with the experimental setup. Figure 2 provides a visual representation of the base PCMs used in the study. 2.2 Development of binary eutectic PCM The eutectic PCM material is synthesized using the impregnation and dispersion technique. Initially, stearic acid (SA) and palmitic acid (PA) are combined in a weight ratio of 36:64 and heated to a temperature of 70°C to ensure complete liquefaction of the PCM components. Once fully melted, the mixture is subjected to continuous stirring using a magnetic stirrer with a hot plate for approximately 30 minutes at a speed of 600 rpm. This process ensures uniform blending and homogeneity of the eutectic PCM. Figure 3 illustrates the preparation of the binary eutectic PCM using a magnetic stirrer with a hot plate. Additionally, Table 1 presents the key properties of the base PCMs (SA and PA) and the synthesized eutectic PCM. Table 1 Characteristics of base and prepared PCMs S. No. Characteristics PA SA Eutectic PCM 1 Melting Point (°C) 57.6 67.32 52.9 2 Latent Heat (KJ/kg) 189.6 201.8 174.29 3 Appearance White White White 2.3 Experimental setup The installed solar water heating system features an evacuated tube solar collector (ETSC) designed for passive operation. It consists of eight evacuated tubes and an integrated 150-liter water reservoir. Cold water enters from the top, ensuring uniform distribution across all tubes. Heated water accumulates in the upper header and remains stored until the inlet and outlet temperatures stabilize. The storage tank is constructed from corrosion-resistant steel and insulated with polyurethane foam to minimize heat loss and maintain water temperature. A top lid facilitates easy access for integrating or removing phase change material (PCM) and wavy tapes, as illustrated in Figs. 4 and 5. The experimental setup was installed on the flat roof of SISTec-R College in Madhya Pradesh, India (latitude 23.2599° N, longitude 77.4126° E). Outdoor experiments were conducted under northern Indian climate conditions during October 2024, with data collected over four separate days: October 1 (Day 1), October 7 (Day 2), October 14 (Day 3), and October 20 (Day 4). The system was oriented southward and inclined at 30° to the horizontal, as shown in Fig. 5. Four different configurations—conventional ETSC, ETSC with wavy tape, ETSC with PCM, and ETSC with PCM + wavy tape—were tested under identical environmental conditions. The physical dimensions of the experimental setup are presented in Table 2. Six copper cylinders, each with a diameter of 6 cm and a height of 24 cm, were used to contain 900 grams of the prepared eutectic PCM. To ensure a secure enclosure, both ends of the cylinders were tightly sealed using gas welding and coated with a sealant. Considering the thermal expansion behavior of the PCM during phase transition, each cylinder was filled to 85% of its total capacity to prevent leakage or structural damage. Additionally, wavy tapes were fabricated using a copper strip with a thickness of 0.3 mm, a width of 16 mm, and a total length of 1200 mm. These tapes were designed by folding the strip at regular 20 mm intervals, with each fold angled at 60° to enhance thermal performance. Figure 6 illustrates the PCM-filled copper cylinders and the wavy tapes utilized in the experimental setup. Figure 6 PCM-Filled Copper Cylinders and Wavy Tapes Used in the Experimental Setup 2.4 Experimental Procedure Observations were systematically recorded over a 10-hour period for each experimental scenario, starting at 8:00 a.m. and ending at 6:00 p.m. (sunset). Temperature measurements were taken at three different positions within the water storage tank, as well as in the PCM cylinder and wavy tapes inside the evacuated tubes. Additionally, ambient parameters such as atmospheric temperature, wind velocity, and solar intensity were recorded hourly. These data points were subsequently used to conduct energetic, exergetic, and environmental analyses for all four configurations of the evacuated tube solar collector (ETSC). To ensure precise thermal monitoring, a total of seven K-type thermocouples were strategically positioned at key locations. Three thermocouples were placed inside the water tank at the top, middle, and bottom to determine the bulk water temperature through an averaged reading. One thermocouple was dedicated to measuring the PCM temperature, another for ambient temperature, and two additional thermocouples were installed inside the evacuated tubes to capture the temperature of the wavy tape. A data logger was employed to continuously record and store these temperature readings. Solar radiation levels were measured using a solar power meter with a reading accuracy of ± 10.0 W/m². To ensure reproducibility and reliability of the collected data, each experiment was conducted over at least five clear-sky solar days. Following this, readings from solar days exhibiting similar radiation patterns were analysed to accurately evaluate the thermal performance and efficiency of the ETSC system. Table 2 Physical dimension of experimental setup S. No Design material/parameters Specification 1 Glass inclination angle 30° towards south 2 Aperture area 1.5 m 2 3 Evacuated tube (8 No.s) 1.5 m length 4 Collection tank 0.4 m diameter and 1.020 m length 5 Insulating material (PUF) 50 mm thickness 6 Sealing Material Silicone gel and rubber 7 Evacuated tubes material Borosilicate glass 8 Absorptance 91% 9 Transmittance 93% 93% 10 Wavy tapes Strip having dimensions of 0.3 mm thickness, 16 mm width, and a length (l) of 1200 mm. 11 Thermocouple K type thermocouple 12 Solar radiation measurement device Solar power metre 13 Temperature measurement device Data logger 3. DATA REDUCTION 3.1 Energy Analysis This section presents the mathematical formulations necessary for evaluating the key performance parameters of the current system. A comprehensive daily energy and exergy analysis is conducted to estimate critical factors such as the total solar energy collected, the useful heat gain, and the overall daily thermal efficiency of the system. The primary focus of the energy analysis is based on the First Law of Thermodynamics, which assesses the efficiency of energy conversion within the system. The First Law states that energy cannot be created or destroyed but can only be transferred or converted from one form to another. In this context, system efficiency is determined by calculating the ratio of useful energy output to the total solar energy input. The efficiency of the system, as derived from the First Law, is expressed mathematically as follows (Bracamonte et al., 2015 ). $$\:{{\eta\:}}_{\text{e}\text{n}\text{e}\text{r}\text{g}\text{y}}=\frac{{\text{Q}}_{\text{s}\text{y}\text{s}}}{{\text{Q}}_{\text{i}\text{n}}}$$ 1 The system's accumulated energy is expressed as; $$\:{\text{Q}}_{\text{s}\text{y}\text{s}}={\text{Q}}_{\text{w}\:}\:+\:{\text{Q}}_{\text{P}\text{C}\text{M}}$$ 2 Where, Q w is the energy contained within the water, Q PCM is the amount of energy stored by the PCM and Q in represent the amount of solar energy acquired by the tubes. $$\:{\text{Q}}_{\text{P}\text{C}\text{M}}={{\text{m}}_{\text{P}\text{C}\text{M}}{[\text{C}}_{\text{P},\text{P}\text{C}\text{M}}({\text{T}}_{\text{P}\text{C}\text{M},\text{f}}-\:{\text{T}}_{\text{P}\text{C}\text{M},\text{i}})\:+\text{A}}_{\text{m}}{\:\varDelta\:\text{h}}_{\text{P}\text{C}\text{M}}$$ 3 Moreover, the energy contained within the water can be computed using the equations provided by (Kumar and Mylsamy 2019) $$\:{\text{Q}}_{\text{w}}=\:{{\text{m}}_{\text{w}}\text{c}}_{\text{p},\text{w}}\left({\text{T}}_{\text{W}\text{o}\text{u}\text{t}}-{\text{T}}_{\text{W}\text{i}\text{n}}\right)$$ 4 m w and C p,w is the mass (kg/s) and specific heat values of water in the collection tank whereas T Wout and T Win is the water temperature at outlet and inlet section in ℃. The thermal energy absorbed by evacuated tubes during a specific period has been derived from the below equation $$\:{\text{Q}}_{\text{i}\text{n}}=\:{{\text{A}}_{\text{c}}\:\:\times\:\:\text{I}}_{\text{t}}$$ 5 Where A c (m 2 ) is the aperture area and I t is the amount of solar radiation incident on the tubes in W/m 2 3.2 Exergy Analysis The readily accessible energy in a thermodynamic system may be accurately determined using the second law analysis. It takes into consideration different kinds of irreversibilities while concentrating on the quality of energy conversion. Exergy efficiency, which is described by the second law of thermodynamics, can be written as follows $$\:{{\eta\:}}_{\text{e}\text{x}\text{e}}=\:\frac{{\text{E}}_{\text{x},\:\text{o}\text{u}\text{t}}\:}{{\text{E}}_{\text{x},\:\text{i}\text{n}\text{p}}}$$ 6 Ex,out stands for the water's usable exergy and is computed as (Petela et al. 2003) $$\:{\text{E}}_{\text{x},\:\text{o}\text{u}\text{t}}=\:{{\text{m}}_{\text{w}}\:\times\:\text{c}}_{\text{p},\text{w}}\:[\left({\text{T}}_{\text{W}\text{o}\text{u}\text{t}}-{\text{T}}_{\text{W}\text{i}\text{n}}\right)\:-\:{\text{T}}_{\text{a}}\:\text{l}\text{n}\left(\frac{{\text{T}}_{\text{W}\text{o}\text{u}\text{t}}}{{\text{T}}_{\text{W}\text{i}\text{n}}}\right)]$$ 7 The exergy absorbed is given by 53 $$\:{\:\text{E}}_{\text{x},\:\text{i}\text{n}\text{p}}={\text{A}}_{\text{c}\:}\times\:{\text{I}}_{\text{t}\:}[1\:+\:\frac{1}{3}\times\:{\left(\frac{{\text{T}}_{\text{a}}}{{\text{T}}_{\text{s}}}\right)}^{4}-\:\frac{4}{3}\:\times\:\left(\frac{{\text{T}}_{\text{a}}}{{\text{T}}_{\text{s}}}\right)]$$ 8 Where T s represents the sun’s temperature and equal to 5760 K. 3.3 Environmental Analysis Maurya A. et al., in their investigation, determined that environmental analysis is primarily based on the rate of CO₂ emissions released into the atmosphere. Their study established that approximately 2 kg of CO₂ is emitted per kWh of conventional energy consumption. Consequently, the annual CO₂ mitigation achieved by utilizing a solar still can be calculated using the following expression: $$\:{{\varnothing}}_{{\text{c}\text{o}}_{2}}=\:\frac{{(\text{E}}_{\text{e}\text{n},\text{o}\text{u}\text{t}\:}\times\:\text{n})\:\times\:2}{1000}\:$$ 9 $$\:{\:{\varnothing}}_{{\text{e}\text{x},\:\text{c}\text{o}}_{2}}=\:\frac{{(\text{E}}_{\text{e}\text{x},\text{o}\text{u}\text{t}\:}\times\:\text{n})\:\times\:2}{1000}\:$$ 10 4. RESULTS AND DISCUSSIONS 4.1 DSC Analysis The Differential Scanning Calorimetry (DSC) technique was utilized to determine the latent heat and melting point of the formulated eutectic PCM. Figure 7 presents the DSC results, including the melting point and thermal characteristics. During the heating phase, a single endothermic peak was observed, indicating a uniform phase transition. The pure eutectic PCM (PA-SA) demonstrated a latent heat capacity of 174.21 kJ/kg and a melting point of 53°C, confirming its suitability for thermal energy storage applications. 4.2 Thermal Conductivity The thermal conductivity (TC) of a storage system plays a crucial role in determining its heat storage and transfer efficiency. Higher thermal conductivity enhances heat transfer rates, thereby accelerating both the melting and solidification processes, which ultimately reduces the phase transition duration. To evaluate the thermal conductivity of the prepared eutectic PCM, measurements were conducted at a temperature of 35°C, which is below its phase transition temperature, as illustrated in Fig. 8 . The Laser Flash Analysis (LFA 467) method was utilized to precisely assess the thermal conductivity of the eutectic PCM. The results indicated that the pure eutectic PCM (PA-SA-B) exhibited a thermal conductivity value of 0.22 W/mK, demonstrating its potential for thermal energy storage applications. 4.3 Meteorological Parameters To ensure the accuracy and reliability of the observations, experiments were repeated on multiple days using the same experimental setup for each scenario. Additionally, the thermodynamic analysis was conducted by selecting days with similar atmospheric conditions and solar insolation trends. As depicted in Fig. 9 , solar radiation followed a typical diurnal pattern, gradually increasing from morning until midday before declining toward evening. During the trial days, the peak radiation levels were recorded in the early afternoon, with the highest solar intensity reaching 960 W/m² at 13:00. This parabolic trend in solar radiation highlights the natural variations in energy availability throughout the day, which directly impacts the performance of the experimental setup. Furthermore, Fig. 10 illustrates the variation in atmospheric temperature throughout the day. The temperature starts at 18°C at 08:00, gradually rising to its peak of 34°C at 15:00, before declining to approximately 26°C by 18:00. Additionally, Fig. 11 presents the fluctuation in wind velocity over time, showing a maximum recorded velocity of 2.2 m/s² at 14:00. These environmental factors play a crucial role in influencing the overall performance and efficiency of the experimental setup. 4.4 Variation in HTF temperature The changes in the water's outflow temperature (T wo ) in each of the four scenarios for every day under consideration are shown in Fig. 12 . During the initial 10-hour period, the outlet temperature of all ETSC configurations remains similar, around 36°C, due to the uniform absorption of solar radiation through the evacuated tubes, following the same trend as solar radiation. Temperature measurements were taken at three locations within the storage tank—top, center, and bottom— with their average considered as the outlet temperature for analysis. Among the different configurations, the highest outlet water temperature was recorded in the ETSC with both wavy tape and PCM (74.4°C), outperforming the ETSC with PCM alone (73.5°C), ETSC with wavy tape (71.2°C), and the conventional ETSC system (67°C). The inclusion of wavy tape enhances the outlet water temperature by 7%, demonstrating that the induced turbulence within the evacuated tubes promotes better mixing of water, maximizing solar energy utilization. However, in configurations with PCM in the storage tank, a significant portion of the absorbed solar heat is initially utilized for the sensible and latent heating of the PCM, delaying heat transfer to the heat transfer fluid (HTF). Consequently, during the early hours, the HTF experiences a slower temperature rise compared to cases without PCM. Overall, the outlet temperature enhancement in ETSC with PCM and ETSC with PCM + wavy tape is 9.7% and 12%, respectively, compared to the conventional ETSC system. 4.5 Energy Efficiency The daily thermal efficiency (η) is a crucial metric for assessing the overall thermal performance of solar collectors throughout the day. As defined in Eq. 1 , η represents the ratio of the total solar energy collected to the usable heat gain. While all configurations receive the same amount of solar radiation, their usable heat gain differs due to variations in heat absorption and retention. The efficiency of each collector setup fluctuates over time, reflecting the impact of design modifications such as wavy tape and PCM integration. Figure 13 illustrates the time-dependent variation in collector efficiency across all tested cases, providing insights into their comparative performance. Based on the observed trends in the graph, the integration of wavy tape (WT) and phase change material (PCM) significantly enhances the daily efficiency of the evacuated tube solar collector (ETSC). The conventional ETSC, without PCM, achieved a maximum efficiency of 58%. However, incorporating eutectic PCM and nano-PCM led to efficiency improvements of 63% and 67%, respectively, highlighting the beneficial impact of thermal energy storage materials. During the experimental trials, the highest hourly efficiency was recorded around 14:00, marking the peak energy absorption phase of the ETSC with PCM and PCM + WT. The maximum hourly efficiency was 71.75% for the PCM + WT configuration, followed by 67.63% for WT, 65.5% for PCM, and 60.61% for the conventional ETSC. In the first two cases (without PCM), efficiency steadily increased until midday before gradually declining. However, in the latter two cases (with PCM and PCM + WT), the system retained a higher efficiency for an extended period. This suggests that the presence of PCM significantly improves heat retention and transfer capabilities, reducing thermal losses and prolonging the effective energy utilization phase. Figure 14 presents the daily average efficiency of all the developed ETSC configurations. The results indicate that the conventional ETSC achieved an efficiency of 35.17%, while the ETSC with wavy tape (WT) showed an improved efficiency of 39.90%. Further enhancement was observed in the ETSC with PCM, which attained an efficiency of 40.32%. The highest efficiency, 45.92%, was recorded for the ETSC with both WT and PCM, demonstrating the combined effect of enhanced heat transfer and thermal energy storage in improving system performance. 4.6 Exergy Efficiency The second law efficiency was determined based on the energy content of the thermodynamic system and the reference air conditions, emphasizing the quality of the energy supply. In thermal systems, while energy is conserved, exergy represents the useful work potential and is often accumulated. A higher second law efficiency indicates better utilization of available energy, signifying superior system performance by minimizing irreversible losses and enhancing the effectiveness of energy conversion processes. Figure 15 illustrates the hourly fluctuation of exergy efficiency for all four experimental scenarios. The exergy efficiency increased gradually throughout the day, reaching its peak around 14:00, before sharply declining. This trend indicates that as the PCM absorbed heat, the system's energy content increased, but once the PCM was fully charged, the efficiency started to drop. Among the four scenarios, the highest hourly exergy efficiency was recorded for the ETSC with PCM and wavy tape (PCM + WT) at 11.43%. In comparison, the efficiency values for the conventional ETSC, ETSC with WT, and ETSC with PCM were 9.45%, 8.91%, and 7.2%, respectively. As highlighted by Gurturk et al. ( 2017 ), similar trends were observed in AGSWH systems, where the integration of PCM or hybrid nano-PCM (HNCPCM) led to an improvement in both exergy and energy efficiency. The relatively low exergy efficiency values observed in this study highlight the system’s low exergy content and significant irreversibilities, which are inherent to thermal energy storage and conversion processes. Figure 16 illustrates the daily exergy efficiency achieved for different experimental cases. The results indicate that the integration of wavy tape and PCM significantly enhances the exergy efficiency of the ETSC system. The highest average exergy efficiency of 6.11% was observed in the ETSC with PCM and wavy tape (WT + PCM), surpassing the values recorded for the conventional ETSC (3.48%), ETSC with plain wavy tape (4.43%), and ETSC with PCM (5.09%). Additionally, the exergy efficiency of the ETSC with (WT + PCM) was found to be 75.5% higher than that of the conventional ETSC, 37.9% higher than ETSC with plain wavy tape, and 20.1% higher than ETSC with PCM alone. This improvement highlights the combined effect of wavy tape-induced turbulence and the latent heat storage capability of PCM, which enhances thermal energy utilization and minimizes exergy destruction. 4.7 Environmental Analysis The environmental analysis of the ETSC system is conducted using both energetic and exergetic approaches. The energy-based environmental analysis evaluates the system’s impact based on its annual energy output and the expected lifespan of the ETSC, whereas the exergy-based environmental analysis assesses the impact using the annual exergy output over the same duration. These analyses provide insights into the environmental implications of energy conversion processes, highlighting the influence of each component on overall system sustainability. A comprehensive energy and exergy analysis is performed to quantify the environmental impact of the ETSC system. This evaluation considers annual energy and exergy outputs as well as the carbon emissions reduction (in tons per year) resulting from the system’s operation. By understanding these parameters, the study aims to assess the effectiveness of ETSC technology in reducing greenhouse gas emissions and promoting cleaner energy utilization. Based on the findings of the experimental investigation, the CO₂ mitigation potential was analyzed using both energy and exergy outputs for different configurations of the Evacuated Tube Solar Collector (ETSC). The results revealed that the annual CO₂ reduction based on energy output was 31.58 tons/year for the conventional ETSC, 35.8 tons/year for ETSC with plain wavy tape (WT), 38.4 tons/year for ETSC with PCM, and 42.81 tons/year for ETSC with PCM + WT. Similarly, the CO₂ mitigation potential based on exergy output was recorded as 3.6 tons/year, 4.9 tons/year, 6.3 tons/year, and 6.9 tons/year for the conventional ETSC, ETSC with plain WT, ETSC with PCM, and ETSC with PCM + WT, respectively, as illustrated in Fig. 17 . Considering a 15-year operational lifespan for the ETSC systems, the findings indicate that ETSC with PCM + WT exhibits the highest CO₂ mitigation potential, significantly surpassing other configurations. This superior environmental performance is attributed to the enhanced energy and exergy efficiency of the system, leading to greater overall sustainability. The integration of PCM and wavy tape not only improves thermal energy storage and heat transfer characteristics but also extends the effective operational duration of the system, thereby contributing to a substantial reduction in carbon emissions over its lifetime. 5. CONCLUSION This study presents a comprehensive experimental analysis of an Evacuated Tube Solar Collector (ETSC) integrated with wavy tape (WT) in the tubes and eutectic Phase Change Material (PCM) in the storage tank. The performance assessment was conducted based on heat transfer characteristics, energy and exergy efficiencies, and environmental impact, comparing the ETSC with WT and PCM to the conventional ETSC system. The key findings from this investigation are summarized as follows: The combination of wavy tape and PCM significantly improved the heat transfer efficiency compared to the use of plain wavy tape or the absence of wavy tape. The WT + PCM configuration demonstrated superior heat transfer capacity throughout the experiment. The highest recorded outlet water temperature was 74.4°C for the ETSC with WT + PCM, surpassing the ETSC with PCM (73.5°C), ETSC with WT (71.2°C), and conventional ETSC (67°C). This confirms the effectiveness of PCM and wavy tape in enhancing thermal energy absorption and storage. The maximum hourly energy efficiency was achieved with ETSC (WT + PCM) at 71.75%, which was higher than ETSC with plain WT (67.63%), ETSC with PCM (65.5%), and conventional ETSC (60.61%). The daily thermal efficiency for the various ETSC configurations was found to be 35.17% (conventional ETSC), 39.90% (ETSC with WT), 40.32% (ETSC with PCM), and 45.92% (ETSC with WT + PCM). The ETSC with WT + PCM exhibited a 30.56%, 15.08%, and 13.88% improvement in daily energy efficiency over the conventional ETSC, ETSC with WT, and ETSC with PCM, respectively. The ETSC with WT + PCM demonstrated a higher average exergy efficiency, exceeding conventional ETSC by 75.5%, ETSC with plain WT by 37.9%, and ETSC with PCM by 20.1%. The CO₂ mitigation potential based on energy output was calculated as 31.58 tons/year (conventional ETSC), 35.8 tons/year (ETSC with WT), 38.4 tons/year (ETSC with PCM), and 42.81 tons/year (ETSC with WT + PCM). Similarly, based on exergy output, the corresponding values were 3.6, 4.9, 6.3, and 6.9 tons/year, respectively. These findings highlight the superior environmental benefits of ETSC with WT + PCM, which exhibited the highest CO₂ reduction potential over its operational lifespan. Declarations Author Contributions Punam Kumar Agade : Writing – original draft, Supervision, Investigation, Data curation, Conceptualization, Project administration. Nitin Dubey : Writing – review & editing, Formal analysis. Rahul Agrawal : Writing – review & editing, Visualization, Validation. Declaration of Competing Interests The authors declare that they have no known competing financial interests or personal relationships that could have influenced the work reported in this paper. Ethical Statement The authors confirm that this study adheres to the ethical policies of the journal and maintains integrity in scientific research and publication. No form of malpractice was involved in the publication process. Compliance with Human and Animal Rights This study does not involve human or animal subjects. The authors affirm that there were no violations of ethical standards concerning animal rights in the research conducted. References Boafo, F. E., J. T. Kim, and J. H. Kim. 2017. 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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-6252758","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":430467138,"identity":"8ba627cd-15c3-4dd3-ac84-87e126b1c137","order_by":0,"name":"Punam Kumar 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cases\u003c/p\u003e","description":"","filename":"floatimage14.png","url":"https://assets-eu.researchsquare.com/files/rs-6252758/v1/ba73d758f54a677148366516.png"},{"id":78888087,"identity":"723c465f-3620-4489-8e8c-bd8c4672941a","added_by":"auto","created_at":"2025-03-20 09:56:29","extension":"png","order_by":14,"title":"Figure 14","display":"","copyAsset":false,"role":"figure","size":14508,"visible":true,"origin":"","legend":"\u003cp\u003eComparison of daily energy efficiency of different cases\u003c/p\u003e","description":"","filename":"floatimage15.png","url":"https://assets-eu.researchsquare.com/files/rs-6252758/v1/b7c2202948c744bd94c754f1.png"},{"id":78888083,"identity":"c6e9bb43-3d5a-46db-8f03-b8f5b70d26f1","added_by":"auto","created_at":"2025-03-20 09:56:29","extension":"png","order_by":15,"title":"Figure 15","display":"","copyAsset":false,"role":"figure","size":58943,"visible":true,"origin":"","legend":"\u003cp\u003eTime wise variation of energy efficiency of different cases\u003c/p\u003e","description":"","filename":"floatimage16.png","url":"https://assets-eu.researchsquare.com/files/rs-6252758/v1/05ccb41df9cfacb9700393ca.png"},{"id":78888622,"identity":"b36ce6a7-5010-4ad7-b53b-922ec0e1f235","added_by":"auto","created_at":"2025-03-20 10:04:30","extension":"png","order_by":16,"title":"Figure 16","display":"","copyAsset":false,"role":"figure","size":14301,"visible":true,"origin":"","legend":"\u003cp\u003eComparison of daily exergy efficiency of different cases\u003c/p\u003e","description":"","filename":"floatimage17.png","url":"https://assets-eu.researchsquare.com/files/rs-6252758/v1/84dc03a3731064eefdf0dfcb.png"},{"id":78888104,"identity":"389239c8-fd44-4a5a-a222-8358ccf97990","added_by":"auto","created_at":"2025-03-20 09:56:30","extension":"png","order_by":17,"title":"Figure 17","display":"","copyAsset":false,"role":"figure","size":77105,"visible":true,"origin":"","legend":"\u003cp\u003eComparison of environmental factors of different cases\u003c/p\u003e","description":"","filename":"17.png","url":"https://assets-eu.researchsquare.com/files/rs-6252758/v1/9ab4afd49c1e03403ed3bf09.png"},{"id":78890043,"identity":"539db973-dc8a-416b-907b-fa31fd75df98","added_by":"auto","created_at":"2025-03-20 10:28:34","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":8386959,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6252758/v1/8a8cf7f9-2984-4471-9d46-21a2b10c238f.pdf"}],"financialInterests":"The authors declare no competing interests.","formattedTitle":"\u003cp\u003e\u003cstrong\u003eExperimental Study of an Optimized Evacuated Tube Collector with Wavy Tape and Phase Change Material for Hot Water Production\u003c/strong\u003e\u003c/p\u003e","fulltext":[{"header":"1. INTRODUCTION","content":"\u003cp\u003eThe increasing energy demand, driven by rising consumption across residential and industrial sectors, continues to grow daily (Boafo et al., \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2017\u003c/span\u003e; Karthick et al., \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2020a\u003c/span\u003e). Energy is essential for various applications, including heating, transportation, lighting, and air conditioning. According to Reddy et al. (\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2020\u003c/span\u003e), heat production accounts for nearly half of global energy consumption. The reliance on conventional fuels contributes to environmental degradation, leading to issues such as global warming and ozone layer depletion. In India, heat generation constitutes two-thirds of total energy consumption, highlighting the need for sustainable alternatives. Solar energy, particularly for heat collection, presents a viable solution by reducing dependence on conventional energy sources.\u003c/p\u003e \u003cp\u003eRooftop solar systems, including photovoltaic (PV) modules and solar water heaters, have emerged as innovative, cost-effective, and sustainable solutions for harnessing solar energy (Ram et al., 2024). Among these, solar water heating systems are widely adopted due to their low maintenance requirements, ease of manufacturing, and operational simplicity. The efficiency of such systems is largely determined by the performance of the collector, which is often regarded as the \"heart\" of the solar water heater. Most research in this field focuses on improving the thermal performance of collectors.\u003c/p\u003e \u003cp\u003eTraditionally, water has been the primary heat transfer fluid (HTF) in flat plate solar collectors (FPSC). However, its poor heat transfer properties pose a challenge in enhancing system efficiency. Two commonly used solar collectors are flat plate collectors (FPC) and evacuated tube solar collectors (ETSC) (Henein et al., 2022). Compared to FPCs, ETSCs offer higher thermal efficiency, lower maintenance costs, and reduced thermal losses. The cylindrical shape of ETSCs allows for passive solar tracking, further improving performance (Papadimitratos et al., \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2016\u003c/span\u003e). As a result, ETSCs have gained popularity, surpassing FPCs in solar applications. According to the International Energy Agency (IEA), ETSCs currently dominate the global market, accounting for over 70% of solar thermal applications, including air, water, and space heating (Solar Heat Worldwide, 2024). ETSCs are well-suited for diverse climatic conditions and are categorized into heat pipe-based and U-tube-based systems, depending on their heat transfer mechanisms (Pathak et al., 2022). U-tube ETSCs facilitate heat transfer through conduction and convection, enhancing thermal efficiency (Deshmukh et al., \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2023\u003c/span\u003e; Shafieian et al., \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2019\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eSeveral factors influence FPSC performance, including HTF properties, absorber tube design, inlet fluid temperature, ambient conditions, solar radiation, wind speed, humidity, absorber coating, collector angle, and insulation. Conventional FPSCs, featuring smooth copper tubes, exhibit poor thermal transport due to a low convective heat transfer coefficient (Sakhaei et al., 2019). Various active and passive techniques have been explored to enhance heat transfer efficiency, with passive methods being particularly attractive due to their ability to improve thermal performance without additional energy input (Fan et al., 2019). Passive techniques, such as modifying absorber tubes, enhance convective heat transfer by increasing velocity gradients and reducing thermal boundary layers (Poongavanam et al., 2019; Pandey et al., 2017; Farhana et al., 2019; Arunkumar et al., 2018; Patil et al., 2018; Zhang et al., 2017; Methods et al., \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Sheikholeslami et al., \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2019\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eAbsorber tube modifications play a crucial role in improving solar thermal system efficiency due to their cost-effectiveness and ease of implementation. Various thermal performance enhancement techniques have been reported, including spiral tapes (Sheikholeslami et al., \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Milani et al., 2016; Farshad et al., 2019; Eiamsa-Ard et al., \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2013\u003c/span\u003e, \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2010\u003c/span\u003e), coiled wires (Ponnada et al., \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2019\u003c/span\u003e), ribbed pipes (Zhang et al., \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2019\u003c/span\u003e), micro-fin structures (Promvonge et al., 2007), barriers, swirl producers (Wongcharee et al., 2012), and concentric rings. Tse et al. (2015) modified conventional solar water heaters by incorporating a ring-type heat exchanger, reducing frictional losses, and improving system performance compared to helical coil designs. Ghoneim et al. (2005) utilized double-glazing with a sputter-deposited low-emission layer and low-iron glass with honeycomb insertion, increasing transmittance to 85%. Similarly, Wang et al. (\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e2015\u003c/span\u003e) applied SiO₂ antireflection coatings on all-glass evacuated tubes, raising solar transmittance to 0.94 and achieving 50.2% thermal efficiency at 150\u0026deg;C. Wongcharee and Eiamsa-Ard (\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2011\u003c/span\u003e) examined heat transfer performance using alternating clockwise and counterclockwise twisted tapes, finding that a lower twist ratio (3) resulted in optimal heat transfer enhancement.\u003c/p\u003e \u003cp\u003eKumar et al. (\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e2024\u003c/span\u003e) investigated the effect of perforated wavy tapes in FPSCs, reporting heat transfer improvements of 20.83%, 14.85%, and 6.25% for systems without wavy tape, with WT, and with 9mm perforated wavy tape (PWT), respectively. However, one major drawback of solar water heaters is their reliance on solar availability, leading to reduced performance at night and increased thermal losses (Papadimitratos et al., \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2016\u003c/span\u003e; Karthick et al., \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e2020b\u003c/span\u003e). Nocturnal flow redirection in evacuated tubes exacerbates these losses (Tang et al., 2014). Recent studies suggest incorporating thermal storage media to mitigate this issue. Thermal storage can be integrated into storage tanks (Gurturk et al., \u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e2017\u003c/span\u003e) or collector tubes (Feliński et al., 2017), enhancing efficiency by storing excess energy during the day and supplying heat when sunlight is unavailable.\u003c/p\u003e \u003cp\u003eTwo primary forms of thermal storage\u0026mdash;sensible heat and latent heat\u0026mdash;have been extensively studied (Alva et al., \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). Latent heat storage is preferred in modern applications due to its higher energy density, superior thermal characteristics, and minimal volume changes (Cunha et al., 2016; Kumar et al., \u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e2020a\u003c/span\u003e). The integration of phase change materials (PCM) in solar thermal systems has gained significant attention for its potential to improve thermal storage and overall efficiency.\u003c/p\u003e \u003cp\u003eAl-Hinti et al. (\u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e2010\u003c/span\u003e) investigated the effectiveness of solar collectors by incorporating paraffin wax as a phase change material (PCM) within a water storage tank. Their study demonstrated that this setup could maintain a hot water temperature of 55\u0026deg;C throughout the day, including during draw-off periods, and a warm water temperature of 30\u0026deg;C the following morning. Similarly, Canbazoglu et al. (\u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e2005\u003c/span\u003e) examined a 190-liter storage tank filled with plastic bottles containing salt hydrates as PCM. Their findings indicated that the heat storage capacity in the PCM-integrated tank was approximately 2.59\u0026ndash;3.45 times higher than that of a conventional solar water heating system.\u003c/p\u003e \u003cp\u003eMehla and Yadav (\u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e2017\u003c/span\u003e) conducted an experimental study on an evacuated tube solar collector (ETSC) integrated with thermal storage for hot air production. Their results showed that the combination of ETSC and PCM enabled continuous hot air generation for up to 24 hours and improved system efficiency from 14.43\u0026ndash;17.65%. Additionally, Xue et al. (2016) found that an ETSC integrated with PCM outperformed conventional ETSC systems. Abokersh et al. (\u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e2017\u003c/span\u003e) carried out a similar study, enhancing the heat retention capability of U-tube collectors by incorporating aluminium fins.\u003c/p\u003e \u003cp\u003eTo accurately assess the impact of integrating PCM with an ETSC system, it is essential to analyse the system under different operating conditions. Each PCM exhibits distinct thermal properties, such as melting point and latent heat capacity, which may not be suitable for all climatic conditions. To overcome this limitation, eutectic PCMs are developed by blending two or more organic PCMs, thereby enhancing their thermophysical properties for specific applications. In this study, a binary eutectic PCM is formulated by optimizing the weight ratio of palmitic and stearic acid. Its applicability in an ETSC system is evaluated by incorporating it into the storage tank. Additionally, to enhance the daytime efficiency of the ETSC, wavy tapes are introduced into the evacuated tubes. The system is analysed in four configurations: conventional ETSC, ETSC with wavy tape, ETSC with PCM, and ETSC with PCM\u0026thinsp;+\u0026thinsp;wavy tape. Various types of passive thermal enhancement devices used in riser tubes are illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e"},{"header":"2. METHODOLOGY","content":"\u003cp\u003eThis section is divided into three key parts: material selection and characterization, experimental setup development, and testing with data analysis. The first part involves selecting appropriate materials based on thermal and physical properties, followed by their preparation and characterization to assess parameters such as thermal conductivity and phase change behavior. The second part focuses on assembling the experimental setup, integrating essential components such as the evacuated tube solar collector, phase change materials, and thermal enhancement devices, along with installing and calibrating measuring instruments like thermocouples and flow meters to ensure accurate data collection. The final part involves conducting controlled experiments to evaluate system performance under various conditions, analyzing key parameters such as energy and exergy efficiency, heat transfer rates, and thermal storage capacity, followed by systematic data analysis to compare different configurations and derive meaningful conclusions.\u003c/p\u003e\n\u003cdiv id=\"Sec3\"\u003e\n \u003ch2\u003e2.1 Selection and Procurement of PCMs\u003c/h2\u003e\n \u003cp\u003eStearic acid (SA) and palmitic acid (PA) were selected as the base phase change materials (PCMs) for the experimental study due to their suitable thermal properties for thermal energy storage applications. Stearic acid (SA), with a molar mass of 279.12 g/mol, exhibits a phase transition temperature range of 65–67°C, making it effective for heat storage and release within this temperature range. It was procured from Fischer to ensure high purity and reliability. Similarly, palmitic acid (PA), characterized by a molar mass of 254.32 g/mol and a phase transition temperature range of 59–62°C, was sourced from Himedia Chemicals. These PCMs were carefully selected based on their thermal stability, latent heat capacity, and compatibility with the experimental setup. Figure 2 provides a visual representation of the base PCMs used in the study.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec4\"\u003e\n \u003ch2\u003e2.2 Development of binary eutectic PCM\u003c/h2\u003e\n \u003cp\u003eThe eutectic PCM material is synthesized using the impregnation and dispersion technique. Initially, stearic acid (SA) and palmitic acid (PA) are combined in a weight ratio of 36:64 and heated to a temperature of 70°C to ensure complete liquefaction of the PCM components. Once fully melted, the mixture is subjected to continuous stirring using a magnetic stirrer with a hot plate for approximately 30 minutes at a speed of 600 rpm. This process ensures uniform blending and homogeneity of the eutectic PCM. Figure 3 illustrates the preparation of the binary eutectic PCM using a magnetic stirrer with a hot plate. Additionally, Table 1 presents the key properties of the base PCMs (SA and PA) and the synthesized eutectic PCM.\u003c/p\u003e\n \u003cdiv\u003e\n \u003ctable id=\"Tab1\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv\u003eTable 1\u003c/div\u003e\n \u003cdiv\u003e\n \u003cp\u003eCharacteristics of base and prepared PCMs\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eS. No.\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eCharacteristics\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003ePA\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eSA\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eEutectic PCM\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eMelting Point (°C)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e57.6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e67.32\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e52.9\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eLatent Heat (KJ/kg)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e189.6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e201.8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e174.29\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eAppearance\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eWhite\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eWhite\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eWhite\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n \u003c/div\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec5\"\u003e\n \u003ch2\u003e2.3 Experimental setup\u003c/h2\u003e\n \u003cp\u003eThe installed solar water heating system features an evacuated tube solar collector (ETSC) designed for passive operation. It consists of eight evacuated tubes and an integrated 150-liter water reservoir. Cold water enters from the top, ensuring uniform distribution across all tubes. Heated water accumulates in the upper header and remains stored until the inlet and outlet temperatures stabilize. The storage tank is constructed from corrosion-resistant steel and insulated with polyurethane foam to minimize heat loss and maintain water temperature. A top lid facilitates easy access for integrating or removing phase change material (PCM) and wavy tapes, as illustrated in Figs. 4 and 5.\u003c/p\u003e\n \u003cp\u003eThe experimental setup was installed on the flat roof of SISTec-R College in Madhya Pradesh, India (latitude 23.2599° N, longitude 77.4126° E). Outdoor experiments were conducted under northern Indian climate conditions during October 2024, with data collected over four separate days: October 1 (Day 1), October 7 (Day 2), October 14 (Day 3), and October 20 (Day 4). The system was oriented southward and inclined at 30° to the horizontal, as shown in Fig. 5.\u003c/p\u003e\n \u003cp\u003eFour different configurations—conventional ETSC, ETSC with wavy tape, ETSC with PCM, and ETSC with PCM + wavy tape—were tested under identical environmental conditions. The physical dimensions of the experimental setup are presented in Table 2.\u003c/p\u003e\n \u003cp\u003eSix copper cylinders, each with a diameter of 6 cm and a height of 24 cm, were used to contain 900 grams of the prepared eutectic PCM. To ensure a secure enclosure, both ends of the cylinders were tightly sealed using gas welding and coated with a sealant. Considering the thermal expansion behavior of the PCM during phase transition, each cylinder was filled to 85% of its total capacity to prevent leakage or structural damage. Additionally, wavy tapes were fabricated using a copper strip with a thickness of 0.3 mm, a width of 16 mm, and a total length of 1200 mm. These tapes were designed by folding the strip at regular 20 mm intervals, with each fold angled at 60° to enhance thermal performance. Figure 6 illustrates the PCM-filled copper cylinders and the wavy tapes utilized in the experimental setup.\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003eFigure\u0026nbsp;6\u003c/strong\u003e\u003c/p\u003e\n \u003cp\u003ePCM-Filled Copper Cylinders and Wavy Tapes Used in the Experimental Setup\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec6\"\u003e\n \u003ch2\u003e2.4 Experimental Procedure\u003c/h2\u003e\n \u003cp\u003eObservations were systematically recorded over a 10-hour period for each experimental scenario, starting at 8:00 a.m. and ending at 6:00 p.m. (sunset). Temperature measurements were taken at three different positions within the water storage tank, as well as in the PCM cylinder and wavy tapes inside the evacuated tubes. Additionally, ambient parameters such as atmospheric temperature, wind velocity, and solar intensity were recorded hourly. These data points were subsequently used to conduct energetic, exergetic, and environmental analyses for all four configurations of the evacuated tube solar collector (ETSC).\u003c/p\u003e\n \u003cp\u003eTo ensure precise thermal monitoring, a total of seven K-type thermocouples were strategically positioned at key locations. Three thermocouples were placed inside the water tank at the top, middle, and bottom to determine the bulk water temperature through an averaged reading. One thermocouple was dedicated to measuring the PCM temperature, another for ambient temperature, and two additional thermocouples were installed inside the evacuated tubes to capture the temperature of the wavy tape. A data logger was employed to continuously record and store these temperature readings.\u003c/p\u003e\n \u003cp\u003eSolar radiation levels were measured using a solar power meter with a reading accuracy of ± 10.0 W/m². To ensure reproducibility and reliability of the collected data, each experiment was conducted over at least five clear-sky solar days. Following this, readings from solar days exhibiting similar radiation patterns were analysed to accurately evaluate the thermal performance and efficiency of the ETSC system.\u003c/p\u003e\n \u003cdiv\u003e\n \u003ctable id=\"Tab2\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv\u003eTable 2\u003c/div\u003e\n \u003cdiv\u003e\n \u003cp\u003ePhysical dimension of experimental setup\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eS. No\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eDesign material/parameters\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eSpecification\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003e1\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eGlass inclination angle\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e30° towards south\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eAperture area\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.5 m\u003csup\u003e2\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003e3\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eEvacuated tube (8 No.s)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.5 m length\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003e4\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eCollection tank\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.4 m diameter and 1.020 m length\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003e5\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eInsulating material (PUF)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e50 mm thickness\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003e6\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eSealing Material\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eSilicone gel and rubber\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003e7\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eEvacuated tubes material\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eBorosilicate glass\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003e8\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eAbsorptance\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e91%\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003e9\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eTransmittance 93%\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e93%\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003e10\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eWavy tapes\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eStrip having dimensions of 0.3 mm thickness, 16 mm width, and a length (l) of 1200 mm.\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003e11\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eThermocouple\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eK type thermocouple\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003e12\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eSolar radiation measurement device\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eSolar power metre\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003e13\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eTemperature measurement device\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eData logger\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n \u003c/div\u003e\n\u003c/div\u003e"},{"header":"3. DATA REDUCTION","content":"\u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003e3.1 Energy Analysis\u003c/h2\u003e \u003cp\u003eThis section presents the mathematical formulations necessary for evaluating the key performance parameters of the current system. A comprehensive daily energy and exergy analysis is conducted to estimate critical factors such as the total solar energy collected, the useful heat gain, and the overall daily thermal efficiency of the system. The primary focus of the energy analysis is based on the First Law of Thermodynamics, which assesses the efficiency of energy conversion within the system. The First Law states that energy cannot be created or destroyed but can only be transferred or converted from one form to another. In this context, system efficiency is determined by calculating the ratio of useful energy output to the total solar energy input. The efficiency of the system, as derived from the First Law, is expressed mathematically as follows (Bracamonte et al., \u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e2015\u003c/span\u003e).\u003cdiv id=\"Equ1\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ1\" name=\"EquationSource\"\u003e\n$$\\:{{\\eta\\:}}_{\\text{e}\\text{n}\\text{e}\\text{r}\\text{g}\\text{y}}=\\frac{{\\text{Q}}_{\\text{s}\\text{y}\\text{s}}}{{\\text{Q}}_{\\text{i}\\text{n}}}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e1\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eThe system's accumulated energy is expressed as;\u003cdiv id=\"Equ2\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ2\" name=\"EquationSource\"\u003e\n$$\\:{\\text{Q}}_{\\text{s}\\text{y}\\text{s}}={\\text{Q}}_{\\text{w}\\:}\\:+\\:{\\text{Q}}_{\\text{P}\\text{C}\\text{M}}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e2\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eWhere, Q\u003csub\u003ew\u003c/sub\u003e is the energy contained within the water, Q\u003csub\u003ePCM\u003c/sub\u003e is the amount of energy stored by the PCM and Q\u003csub\u003ein\u003c/sub\u003e represent the amount of solar energy acquired by the tubes.\u003cdiv id=\"Equ3\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ3\" name=\"EquationSource\"\u003e\n$$\\:{\\text{Q}}_{\\text{P}\\text{C}\\text{M}}={{\\text{m}}_{\\text{P}\\text{C}\\text{M}}{[\\text{C}}_{\\text{P},\\text{P}\\text{C}\\text{M}}({\\text{T}}_{\\text{P}\\text{C}\\text{M},\\text{f}}-\\:{\\text{T}}_{\\text{P}\\text{C}\\text{M},\\text{i}})\\:+\\text{A}}_{\\text{m}}{\\:\\varDelta\\:\\text{h}}_{\\text{P}\\text{C}\\text{M}}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e3\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eMoreover, the energy contained within the water can be computed using the equations provided by (Kumar and Mylsamy 2019)\u003cdiv id=\"Equ4\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ4\" name=\"EquationSource\"\u003e\n$$\\:{\\text{Q}}_{\\text{w}}=\\:{{\\text{m}}_{\\text{w}}\\text{c}}_{\\text{p},\\text{w}}\\left({\\text{T}}_{\\text{W}\\text{o}\\text{u}\\text{t}}-{\\text{T}}_{\\text{W}\\text{i}\\text{n}}\\right)$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e4\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003em\u003csub\u003ew\u003c/sub\u003e and C\u003csub\u003ep,w\u003c/sub\u003e is the mass (kg/s) and specific heat values of water in the collection tank whereas T\u003csub\u003eWout\u003c/sub\u003e and T\u003csub\u003eWin\u003c/sub\u003e is the water temperature at outlet and inlet section in ℃.\u003c/p\u003e \u003cp\u003eThe thermal energy absorbed by evacuated tubes during a specific period has been derived from the below equation\u003cdiv id=\"Equ5\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ5\" name=\"EquationSource\"\u003e\n$$\\:{\\text{Q}}_{\\text{i}\\text{n}}=\\:{{\\text{A}}_{\\text{c}}\\:\\:\\times\\:\\:\\text{I}}_{\\text{t}}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e5\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eWhere A\u003csub\u003e\u003cem\u003ec\u003c/em\u003e\u003c/sub\u003e (m\u003csup\u003e2\u003c/sup\u003e) is the aperture area and I\u003csub\u003e\u003cem\u003et\u003c/em\u003e\u003c/sub\u003e is the amount of solar radiation incident on the tubes in W/m\u003csup\u003e2\u003c/sup\u003e\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec9\" class=\"Section2\"\u003e \u003ch2\u003e3.2 Exergy Analysis\u003c/h2\u003e \u003cp\u003eThe readily accessible energy in a thermodynamic system may be accurately determined using the second law analysis. It takes into consideration different kinds of irreversibilities while concentrating on the quality of energy conversion. Exergy efficiency, which is described by the second law of thermodynamics, can be written as follows\u003cdiv id=\"Equ6\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ6\" name=\"EquationSource\"\u003e\n$$\\:{{\\eta\\:}}_{\\text{e}\\text{x}\\text{e}}=\\:\\frac{{\\text{E}}_{\\text{x},\\:\\text{o}\\text{u}\\text{t}}\\:}{{\\text{E}}_{\\text{x},\\:\\text{i}\\text{n}\\text{p}}}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e6\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eEx,out stands for the water's usable exergy and is computed as (Petela et al. 2003)\u003cdiv id=\"Equ7\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ7\" name=\"EquationSource\"\u003e\n$$\\:{\\text{E}}_{\\text{x},\\:\\text{o}\\text{u}\\text{t}}=\\:{{\\text{m}}_{\\text{w}}\\:\\times\\:\\text{c}}_{\\text{p},\\text{w}}\\:[\\left({\\text{T}}_{\\text{W}\\text{o}\\text{u}\\text{t}}-{\\text{T}}_{\\text{W}\\text{i}\\text{n}}\\right)\\:-\\:{\\text{T}}_{\\text{a}}\\:\\text{l}\\text{n}\\left(\\frac{{\\text{T}}_{\\text{W}\\text{o}\\text{u}\\text{t}}}{{\\text{T}}_{\\text{W}\\text{i}\\text{n}}}\\right)]$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e7\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eThe exergy absorbed is given by\u003csup\u003e53\u003c/sup\u003e\u003cdiv id=\"Equ8\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ8\" name=\"EquationSource\"\u003e\n$$\\:{\\:\\text{E}}_{\\text{x},\\:\\text{i}\\text{n}\\text{p}}={\\text{A}}_{\\text{c}\\:}\\times\\:{\\text{I}}_{\\text{t}\\:}[1\\:+\\:\\frac{1}{3}\\times\\:{\\left(\\frac{{\\text{T}}_{\\text{a}}}{{\\text{T}}_{\\text{s}}}\\right)}^{4}-\\:\\frac{4}{3}\\:\\times\\:\\left(\\frac{{\\text{T}}_{\\text{a}}}{{\\text{T}}_{\\text{s}}}\\right)]$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e8\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eWhere T\u003csub\u003es\u003c/sub\u003e represents the sun\u0026rsquo;s temperature and equal to 5760 K.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec10\" class=\"Section2\"\u003e \u003ch2\u003e3.3 Environmental Analysis\u003c/h2\u003e \u003cp\u003eMaurya A. et al., in their investigation, determined that environmental analysis is primarily based on the rate of CO₂ emissions released into the atmosphere. Their study established that approximately 2 kg of CO₂ is emitted per kWh of conventional energy consumption. Consequently, the annual CO₂ mitigation achieved by utilizing a solar still can be calculated using the following expression:\u003cdiv id=\"Equ9\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ9\" name=\"EquationSource\"\u003e\n$$\\:{{\\varnothing}}_{{\\text{c}\\text{o}}_{2}}=\\:\\frac{{(\\text{E}}_{\\text{e}\\text{n},\\text{o}\\text{u}\\text{t}\\:}\\times\\:\\text{n})\\:\\times\\:2}{1000}\\:$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e9\u003c/div\u003e\u003c/div\u003e\u003cdiv id=\"Equ10\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ10\" name=\"EquationSource\"\u003e\n$$\\:{\\:{\\varnothing}}_{{\\text{e}\\text{x},\\:\\text{c}\\text{o}}_{2}}=\\:\\frac{{(\\text{E}}_{\\text{e}\\text{x},\\text{o}\\text{u}\\text{t}\\:}\\times\\:\\text{n})\\:\\times\\:2}{1000}\\:$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e10\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003c/div\u003e"},{"header":"4. RESULTS AND DISCUSSIONS","content":"\u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003e4.1 DSC Analysis\u003c/h2\u003e \u003cp\u003eThe Differential Scanning Calorimetry (DSC) technique was utilized to determine the latent heat and melting point of the formulated eutectic PCM. Figure\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e7\u003c/span\u003e presents the DSC results, including the melting point and thermal characteristics. During the heating phase, a single endothermic peak was observed, indicating a uniform phase transition. The pure eutectic PCM (PA-SA) demonstrated a latent heat capacity of 174.21 kJ/kg and a melting point of 53\u0026deg;C, confirming its suitability for thermal energy storage applications.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec13\" class=\"Section2\"\u003e \u003ch2\u003e4.2 Thermal Conductivity\u003c/h2\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe thermal conductivity (TC) of a storage system plays a crucial role in determining its heat storage and transfer efficiency. Higher thermal conductivity enhances heat transfer rates, thereby accelerating both the melting and solidification processes, which ultimately reduces the phase transition duration. To evaluate the thermal conductivity of the prepared eutectic PCM, measurements were conducted at a temperature of 35\u0026deg;C, which is below its phase transition temperature, as illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e8\u003c/span\u003e. The Laser Flash Analysis (LFA 467) method was utilized to precisely assess the thermal conductivity of the eutectic PCM. The results indicated that the pure eutectic PCM (PA-SA-B) exhibited a thermal conductivity value of 0.22 W/mK, demonstrating its potential for thermal energy storage applications.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec14\" class=\"Section2\"\u003e \u003ch2\u003e4.3 Meteorological Parameters\u003c/h2\u003e \u003cp\u003eTo ensure the accuracy and reliability of the observations, experiments were repeated on multiple days using the same experimental setup for each scenario. Additionally, the thermodynamic analysis was conducted by selecting days with similar atmospheric conditions and solar insolation trends. As depicted in Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e9\u003c/span\u003e, solar radiation followed a typical diurnal pattern, gradually increasing from morning until midday before declining toward evening. During the trial days, the peak radiation levels were recorded in the early afternoon, with the highest solar intensity reaching 960 W/m\u0026sup2; at 13:00. This parabolic trend in solar radiation highlights the natural variations in energy availability throughout the day, which directly impacts the performance of the experimental setup.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFurthermore, Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e10\u003c/span\u003e illustrates the variation in atmospheric temperature throughout the day. The temperature starts at 18\u0026deg;C at 08:00, gradually rising to its peak of 34\u0026deg;C at 15:00, before declining to approximately 26\u0026deg;C by 18:00.\u003c/p\u003e \u003cp\u003eAdditionally, Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e11\u003c/span\u003e presents the fluctuation in wind velocity over time, showing a maximum recorded velocity of 2.2 m/s\u0026sup2; at 14:00. These environmental factors play a crucial role in influencing the overall performance and efficiency of the experimental setup.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec15\" class=\"Section2\"\u003e \u003ch2\u003e4.4 Variation in HTF temperature\u003c/h2\u003e \u003cp\u003eThe changes in the water's outflow temperature (T\u003csub\u003ewo\u003c/sub\u003e) in each of the four scenarios for every day under consideration are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e12\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eDuring the initial 10-hour period, the outlet temperature of all ETSC configurations remains similar, around 36\u0026deg;C, due to the uniform absorption of solar radiation through the evacuated tubes, following the same trend as solar radiation. Temperature measurements were taken at three locations within the storage tank\u0026mdash;top, center, and bottom\u0026mdash; with their average considered as the outlet temperature for analysis. Among the different configurations, the highest outlet water temperature was recorded in the ETSC with both wavy tape and PCM (74.4\u0026deg;C), outperforming the ETSC with PCM alone (73.5\u0026deg;C), ETSC with wavy tape (71.2\u0026deg;C), and the conventional ETSC system (67\u0026deg;C). The inclusion of wavy tape enhances the outlet water temperature by 7%, demonstrating that the induced turbulence within the evacuated tubes promotes better mixing of water, maximizing solar energy utilization. However, in configurations with PCM in the storage tank, a significant portion of the absorbed solar heat is initially utilized for the sensible and latent heating of the PCM, delaying heat transfer to the heat transfer fluid (HTF). Consequently, during the early hours, the HTF experiences a slower temperature rise compared to cases without PCM. Overall, the outlet temperature enhancement in ETSC with PCM and ETSC with PCM\u0026thinsp;+\u0026thinsp;wavy tape is 9.7% and 12%, respectively, compared to the conventional ETSC system.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec16\" class=\"Section2\"\u003e \u003ch2\u003e4.5 Energy Efficiency\u003c/h2\u003e \u003cp\u003eThe daily thermal efficiency (η) is a crucial metric for assessing the overall thermal performance of solar collectors throughout the day. As defined in Eq.\u0026nbsp;\u003cspan refid=\"Equ1\" class=\"InternalRef\"\u003e1\u003c/span\u003e, η represents the ratio of the total solar energy collected to the usable heat gain. While all configurations receive the same amount of solar radiation, their usable heat gain differs due to variations in heat absorption and retention. The efficiency of each collector setup fluctuates over time, reflecting the impact of design modifications such as wavy tape and PCM integration. Figure\u0026nbsp;\u003cspan refid=\"Fig12\" class=\"InternalRef\"\u003e13\u003c/span\u003e illustrates the time-dependent variation in collector efficiency across all tested cases, providing insights into their comparative performance.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eBased on the observed trends in the graph, the integration of wavy tape (WT) and phase change material (PCM) significantly enhances the daily efficiency of the evacuated tube solar collector (ETSC). The conventional ETSC, without PCM, achieved a maximum efficiency of 58%. However, incorporating eutectic PCM and nano-PCM led to efficiency improvements of 63% and 67%, respectively, highlighting the beneficial impact of thermal energy storage materials.\u003c/p\u003e \u003cp\u003eDuring the experimental trials, the highest hourly efficiency was recorded around 14:00, marking the peak energy absorption phase of the ETSC with PCM and PCM\u0026thinsp;+\u0026thinsp;WT. The maximum hourly efficiency was 71.75% for the PCM\u0026thinsp;+\u0026thinsp;WT configuration, followed by 67.63% for WT, 65.5% for PCM, and 60.61% for the conventional ETSC. In the first two cases (without PCM), efficiency steadily increased until midday before gradually declining. However, in the latter two cases (with PCM and PCM\u0026thinsp;+\u0026thinsp;WT), the system retained a higher efficiency for an extended period. This suggests that the presence of PCM significantly improves heat retention and transfer capabilities, reducing thermal losses and prolonging the effective energy utilization phase.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig13\" class=\"InternalRef\"\u003e14\u003c/span\u003e presents the daily average efficiency of all the developed ETSC configurations. The results indicate that the conventional ETSC achieved an efficiency of 35.17%, while the ETSC with wavy tape (WT) showed an improved efficiency of 39.90%. Further enhancement was observed in the ETSC with PCM, which attained an efficiency of 40.32%. The highest efficiency, 45.92%, was recorded for the ETSC with both WT and PCM, demonstrating the combined effect of enhanced heat transfer and thermal energy storage in improving system performance.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec17\" class=\"Section2\"\u003e \u003ch2\u003e4.6 Exergy Efficiency\u003c/h2\u003e \u003cp\u003eThe second law efficiency was determined based on the energy content of the thermodynamic system and the reference air conditions, emphasizing the quality of the energy supply. In thermal systems, while energy is conserved, exergy represents the useful work potential and is often accumulated. A higher second law efficiency indicates better utilization of available energy, signifying superior system performance by minimizing irreversible losses and enhancing the effectiveness of energy conversion processes.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig14\" class=\"InternalRef\"\u003e15\u003c/span\u003e illustrates the hourly fluctuation of exergy efficiency for all four experimental scenarios. The exergy efficiency increased gradually throughout the day, reaching its peak around 14:00, before sharply declining. This trend indicates that as the PCM absorbed heat, the system's energy content increased, but once the PCM was fully charged, the efficiency started to drop.\u003c/p\u003e \u003cp\u003eAmong the four scenarios, the highest hourly exergy efficiency was recorded for the ETSC with PCM and wavy tape (PCM\u0026thinsp;+\u0026thinsp;WT) at 11.43%. In comparison, the efficiency values for the conventional ETSC, ETSC with WT, and ETSC with PCM were 9.45%, 8.91%, and 7.2%, respectively. As highlighted by Gurturk et al. (\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e2017\u003c/span\u003e), similar trends were observed in AGSWH systems, where the integration of PCM or hybrid nano-PCM (HNCPCM) led to an improvement in both exergy and energy efficiency. The relatively low exergy efficiency values observed in this study highlight the system\u0026rsquo;s low exergy content and significant irreversibilities, which are inherent to thermal energy storage and conversion processes.\u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig15\" class=\"InternalRef\"\u003e16\u003c/span\u003e illustrates the daily exergy efficiency achieved for different experimental cases. The results indicate that the integration of wavy tape and PCM significantly enhances the exergy efficiency of the ETSC system. The highest average exergy efficiency of 6.11% was observed in the ETSC with PCM and wavy tape (WT\u0026thinsp;+\u0026thinsp;PCM), surpassing the values recorded for the conventional ETSC (3.48%), ETSC with plain wavy tape (4.43%), and ETSC with PCM (5.09%).\u003c/p\u003e \u003cp\u003eAdditionally, the exergy efficiency of the ETSC with (WT\u0026thinsp;+\u0026thinsp;PCM) was found to be 75.5% higher than that of the conventional ETSC, 37.9% higher than ETSC with plain wavy tape, and 20.1% higher than ETSC with PCM alone. This improvement highlights the combined effect of wavy tape-induced turbulence and the latent heat storage capability of PCM, which enhances thermal energy utilization and minimizes exergy destruction.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec18\" class=\"Section2\"\u003e \u003ch2\u003e4.7 Environmental Analysis\u003c/h2\u003e \u003cp\u003eThe environmental analysis of the ETSC system is conducted using both energetic and exergetic approaches. The energy-based environmental analysis evaluates the system\u0026rsquo;s impact based on its annual energy output and the expected lifespan of the ETSC, whereas the exergy-based environmental analysis assesses the impact using the annual exergy output over the same duration. These analyses provide insights into the environmental implications of energy conversion processes, highlighting the influence of each component on overall system sustainability.\u003c/p\u003e \u003cp\u003eA comprehensive energy and exergy analysis is performed to quantify the environmental impact of the ETSC system. This evaluation considers annual energy and exergy outputs as well as the carbon emissions reduction (in tons per year) resulting from the system\u0026rsquo;s operation. By understanding these parameters, the study aims to assess the effectiveness of ETSC technology in reducing greenhouse gas emissions and promoting cleaner energy utilization.\u003c/p\u003e \u003cp\u003eBased on the findings of the experimental investigation, the CO₂ mitigation potential was analyzed using both energy and exergy outputs for different configurations of the Evacuated Tube Solar Collector (ETSC). The results revealed that the annual CO₂ reduction based on energy output was 31.58 tons/year for the conventional ETSC, 35.8 tons/year for ETSC with plain wavy tape (WT), 38.4 tons/year for ETSC with PCM, and 42.81 tons/year for ETSC with PCM\u0026thinsp;+\u0026thinsp;WT. Similarly, the CO₂ mitigation potential based on exergy output was recorded as 3.6 tons/year, 4.9 tons/year, 6.3 tons/year, and 6.9 tons/year for the conventional ETSC, ETSC with plain WT, ETSC with PCM, and ETSC with PCM\u0026thinsp;+\u0026thinsp;WT, respectively, as illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig16\" class=\"InternalRef\"\u003e17\u003c/span\u003e.\u003c/p\u003e \u003cp\u003eConsidering a 15-year operational lifespan for the ETSC systems, the findings indicate that ETSC with PCM\u0026thinsp;+\u0026thinsp;WT exhibits the highest CO₂ mitigation potential, significantly surpassing other configurations. This superior environmental performance is attributed to the enhanced energy and exergy efficiency of the system, leading to greater overall sustainability. The integration of PCM and wavy tape not only improves thermal energy storage and heat transfer characteristics but also extends the effective operational duration of the system, thereby contributing to a substantial reduction in carbon emissions over its lifetime.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"5. CONCLUSION","content":"\u003cp\u003eThis study presents a comprehensive experimental analysis of an Evacuated Tube Solar Collector (ETSC) integrated with wavy tape (WT) in the tubes and eutectic Phase Change Material (PCM) in the storage tank. The performance assessment was conducted based on heat transfer characteristics, energy and exergy efficiencies, and environmental impact, comparing the ETSC with WT and PCM to the conventional ETSC system. The key findings from this investigation are summarized as follows:\u003c/p\u003e \u003cp\u003e \u003col\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003eThe combination of wavy tape and PCM significantly improved the heat transfer efficiency compared to the use of plain wavy tape or the absence of wavy tape. The WT\u0026thinsp;+\u0026thinsp;PCM configuration demonstrated superior heat transfer capacity throughout the experiment.\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003eThe highest recorded outlet water temperature was 74.4\u0026deg;C for the ETSC with WT\u0026thinsp;+\u0026thinsp;PCM, surpassing the ETSC with PCM (73.5\u0026deg;C), ETSC with WT (71.2\u0026deg;C), and conventional ETSC (67\u0026deg;C). This confirms the effectiveness of PCM and wavy tape in enhancing thermal energy absorption and storage.\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003eThe maximum hourly energy efficiency was achieved with ETSC (WT\u0026thinsp;+\u0026thinsp;PCM) at 71.75%, which was higher than ETSC with plain WT (67.63%), ETSC with PCM (65.5%), and conventional ETSC (60.61%).\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003eThe daily thermal efficiency for the various ETSC configurations was found to be 35.17% (conventional ETSC), 39.90% (ETSC with WT), 40.32% (ETSC with PCM), and 45.92% (ETSC with WT\u0026thinsp;+\u0026thinsp;PCM).\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003eThe ETSC with WT\u0026thinsp;+\u0026thinsp;PCM exhibited a 30.56%, 15.08%, and 13.88% improvement in daily energy efficiency over the conventional ETSC, ETSC with WT, and ETSC with PCM, respectively.\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003eThe ETSC with WT\u0026thinsp;+\u0026thinsp;PCM demonstrated a higher average exergy efficiency, exceeding conventional ETSC by 75.5%, ETSC with plain WT by 37.9%, and ETSC with PCM by 20.1%.\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003eThe CO₂ mitigation potential based on energy output was calculated as 31.58 tons/year (conventional ETSC), 35.8 tons/year (ETSC with WT), 38.4 tons/year (ETSC with PCM), and 42.81 tons/year (ETSC with WT\u0026thinsp;+\u0026thinsp;PCM). Similarly, based on exergy output, the corresponding values were 3.6, 4.9, 6.3, and 6.9 tons/year, respectively. These findings highlight the superior environmental benefits of ETSC with WT\u0026thinsp;+\u0026thinsp;PCM, which exhibited the highest CO₂ reduction potential over its operational lifespan.\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003c/ol\u003e \u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAuthor Contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cul type=\"disc\"\u003e\n \u003cli\u003e\u003cstrong\u003ePunam Kumar Agade\u003c/strong\u003e: Writing \u0026ndash; original draft, Supervision, Investigation, Data curation, Conceptualization, Project administration.\u003c/li\u003e\n \u003cli\u003e\u003cstrong\u003eNitin Dubey\u003c/strong\u003e: Writing \u0026ndash; review \u0026amp; editing, Formal analysis.\u003c/li\u003e\n \u003cli\u003e\u003cstrong\u003eRahul Agrawal\u003c/strong\u003e: Writing \u0026ndash; review \u0026amp; editing, Visualization, Validation.\u003c/li\u003e\n\u003c/ul\u003e\n\u003cp\u003e\u003cstrong\u003eDeclaration of Competing Interests\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare that they have no known competing financial interests or personal relationships that could have influenced the work reported in this paper.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEthical Statement\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors confirm that this study adheres to the ethical policies of the journal and maintains integrity in scientific research and publication. No form of malpractice was involved in the publication process.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompliance with Human and Animal Rights\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis study does not involve human or animal subjects. The authors affirm that there were no violations of ethical standards concerning animal rights in the research conducted.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eBoafo, F. E., J. T. Kim, and J. H. Kim. 2017. Evaluating the impact of green roof evapotranspiration on annual building energy performance. International Journal of Green Energy 14 (5):479\u0026ndash;89. doi:10.1080/ 15435075.2016.1278375.\u003c/li\u003e\n\u003cli\u003eKarthick, A., M. Manokar Athikesavan, M. K. Pasupathi, N. Manoj Kumar, S. S. Chopra, and A. Ghosh. 2020a. Investigation of inorganic phase change material for a semi-transparent photovoltaic (STPV) module. 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Int J Green Energy. 2017;14(12):1073-80. doi: 10.1080/15435075.2017.1358625.\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Evacuated tube, Solar collector, Phase change material, Wavy tape, Energy efficiency, Exergy efficiency","lastPublishedDoi":"10.21203/rs.3.rs-6252758/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-6252758/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThis study evaluates the performance of four configurations of an evacuated tube solar collector (ETSC): conventional ETSC, ETSC with wavy tape (WT), ETSC with phase change material (PCM), and ETSC with a combination of PCM and WT. The novelty of this research lies in integrating a binary eutectic PCM and analysing the combined effects of PCM and WT on ETSC performance. The results indicate that the highest hourly efficiency, 71.75%, is achieved with the ETSC incorporating both PCM and WT, followed by 67.63% for ETSC with WT, 65.5% for ETSC with PCM, and 60.61% for the conventional ETSC. The daily average efficiency for these cases is 35.17%, 39.90%, 40.32%, and 45.92%, respectively. Similarly, exergy efficiency follows the same trend, with the ETSC featuring both WT and PCM achieving the highest average exergy efficiency of 6.11%, compared to 3.48% for the conventional ETSC, 4.43% for ETSC with WT, and 5.09% for ETSC with PCM. An environmental analysis based on energy and exergy approaches further reveals that the ETSC with PCM and WT mitigates the highest amount of CO₂ emissions per ton compared to the other configurations.\u003c/p\u003e","manuscriptTitle":"Experimental Study of an Optimized Evacuated Tube Collector with Wavy Tape and Phase Change Material for Hot Water Production","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-03-20 09:56:24","doi":"10.21203/rs.3.rs-6252758/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"fd7ecb2c-62d2-42cb-a3cd-5fc436970044","owner":[],"postedDate":"March 20th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[{"id":45847232,"name":"Thermodynamics and statistical mechanics"}],"tags":[],"updatedAt":"2025-03-28T15:23:27+00:00","versionOfRecord":[],"versionCreatedAt":"2025-03-20 09:56:24","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-6252758","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-6252758","identity":"rs-6252758","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}