Experimental study of condensation heat transfer in tubes under centrifugal force

Experimental study of condensation heat transfer in tubes under centrifugal force | 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 condensation heat transfer in tubes under centrifugal force Leigang Zhang, Meng Ru, Yonghai Zhang, Guopei Li, Zhenqian Chen, and 2 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-5175333/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 06 Jan, 2025 Read the published version in Microgravity Science and Technology → Version 1 posted 9 You are reading this latest preprint version Abstract In this study, fluid flow during condensation in a tube under different gravity conditions is simulated by utilizing centrifugal force to offset gravitational effects. The role of fins, tube diameter, and vapor mass on the two-phase flow pattern, temperature distribution, and pressure drop is investigated. The results show that gravity, pipe diameter, and steam quality have a significant effect on the flow pattern. The flow characteristics were also significantly affected by the operating parameters, with undulating and laminar flow dominating, while bubbling flow emerges under specific conditions. In microgravity environments, as vapor mass decreases, the temperature drop diminishes progressively compared to normal gravity conditions. Under normal gravity and low flow conditions, the average temperature of finned tubes increased by 7°C to 16.4°C relative to bare tube temperatures, and the pressure drop escalated by up to 56%. The introduction of fins notably enhanced heat transfer efficiency and facilitated a more uniform temperature distribution. However, this enhancement in heat transfer was accompanied by an increase in pressure drop due to the heightened resistance to fluid flow caused by the presence of fins. These experimental insights offer a deeper comprehension of fluid behavior under diverse gravity conditions and lay a scientific foundation for designing future thermal management systems. centrifugal force condensation flow pattern gravity 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 1. Introduction In recent years, the advancement of space exploration technology has increasingly focused attention on condensation research conducted in microgravity environments. Compared with the traditional condensation process under Earth gravity, condensation in microgravity environment has many different characteristics and challenges. First, the flow and heat transfer characteristics under microgravity conditions are significantly different from those under Earth gravity. For example, liquid film thickness [ 1 ] heat transfer efficiency [ 2 , 3 ] and hydrodynamic behaviors [ 4 , 5 ] exhibit different patterns in microgravity. These differences are critical for a deeper understanding of the effects of gravity on condenser operating mechanisms and for the design of thermal management systems for space applications. The effect of gravity, in a broader perspective, is the effect of acceleration. There are two common ways to alter the acceleration of gravity: parabolic flight and centrifuges. Under standard gravity conditions (the surface of the Earth), fluid flow is predominantly driven by gravity. However, in microgravity environments, due to the absence of gravity, the interactions between inertial, viscous, and surface tension reach a new equilibrium [ 6 ] . This shift results in changes to the interfacial mechanisms of action. Consequently, this alteration gives rise to unique manifestations in both flow properties and heat transfer characteristics. Brendel et al. [ 7 , 8 ] conducted an experimental study on the stability and performance of the R134a vapor compression cycle under microgravity conditions, which were simulated using a parabolic flight. The results indicated that during the initial phase of exposure to microgravity, there was a notable increase in condensation pressure, amounting to a 3% rise. The rise in pressure is primarily attributed to a reduction in the volume of liquid exiting the wall and a diminished heat transfer coefficient, presenting a stark contrast to thermodynamic behavior observed on Earth. Reinarts et al. [ 9 , 10 ] carried out condensation experiments using R12 within a pipe of 8.7 mm internal diameter aboard NASA KC-135 aircraft, with the objective of investigating heat transfer efficiency in microgravity conditions. The experiment observed a slight increase in temperature and pressure of the working fluid at the inlet of the condensing test section during the transition from hypergravity to microgravity conditions. More importantly, it was found that the condensation heat transfer efficiency under microgravity conditions showed a significant decrease of about 26% compared to Earth conditions. The deterioration of the condensation heat transfer under weightlessness conditions was exhaustively documented in the study by Azzolin [ 11 ] et al. Convective condensation in a horizontally placed inner diameter (ID) 3.38 mm channel of HFE-7000 at mass fluxes of G = 70–170 kg m − 2 s − 1 was investigated in the 62nd European Space Agency (ESA) parabolic flight experiment. The test section device consists of two countercurrent heat exchangers designed to accurately measure the local heat transfer coefficient and to visualize the flow through a borosilicate glass window. The ratio of the heat transfer coefficient under microgravity to that under normal gravity conditions decreases with increasing steam mass for a mass flux of G = 130 kg m − 2 s − 1 . For higher mass fluxes (G = 170 kg m − 2 s − 1 ), the difference between the heat transfer coefficients measured under microgravity and normal gravity conditions is negligible. However, at lower mass fluxes (G = 70 kg m − 2 s − 1 ), the difference in heat transfer coefficients reaches 20%. Similar conclusions were reached by Lee et al. in parabolic flight experiments on the local heat transfer coefficients and visualized flow patterns of FC-72 within an internal diameter (ID) of 7.1 mm [ 12 , 13 ] . These experiments included microgravity, lunar gravity (0.17g), and Martian gravity (0.377g), with mass fluxes of G = 129–341 kg m − 2 s − 1 and saturation temperatures of 60-63.4°C. It was found that the effect of gravity on flow-type and condensation heat transfer is particularly significant at low mass fluxes. Specifically, the gravity conditions on the Moon and Mars resulted in a thicker liquid film at the bottom of the pipe and a thinner one at the top, and this inhomogeneous distribution increased the condensation heat transfer rate compared to microgravity conditions. To further extend the experimental dataset of Azzolin et al., Berto et al. [ 14 ] investigated the condensation process at low mass fluxes (30–50 kg m − 2 s − 1 ) during the 70th ESA parabolic flight campaign using the same experimental setup at a saturation temperature of 38–41°C. In agreement with previous studies, the results show that gravity has an enhancing effect on condensation heat transfer, especially at low mass fluxes. Specifically, at G = 50 kg m − 2 s − 1 , the heat transfer coefficients under normal gravity conditions were 33–56% higher than those under microgravity, while at G = 30 kg m − 2 s − 1 , the enhancement of heat transfer due to gravity effects increased from 52% to a range of 77%. Additionally, the heat transfer performance in the microgravity environment was less degraded at high vapor mass conditions for all mass flow rates tested. By increasing the mass flux of the working fluid, the effect of gravity can be completely counteracted. Through meticulous experimental observation of the formation and evolution of liquid films, coupled with rigorous computational simulations of two-phase flow condensation processes [ 15 , 16 ] , researchers have employed a diverse array of methodologies and techniques. These comprehensive studies have yielded invaluable data and profound insights into the subject matter. Among the current platforms for microgravity experiments—including parabolic flights, drop towers, sounding rockets, and the International Space Station (ISS)—parabolic flights have been widely used due to their reasonable cost, the ability to carry large experimental setups, and the allowance for manual interaction. Despite the low level of residual gravity achieved in parabolic flights (± 0.01 g s ), the experimental data are well reproducible. A number of experimental and theoretical studies have been carried out under adiabatic conditions with the aim of investigating the effect of gravity on the characteristics of two-phase flow [ 17 – 19 ] . These studies have usually been conducted in conventionally sized pipes (internal diameters greater than 10 mm). According to existing literature, there is no consensus on the effect of gravity on liquid film thickness and interface wave characteristics. Some researchers have found that the effect of gravity is negligible, while others consider it significant [ 20 , 21 ] . This contradictory result suggests that further experimental work is needed in the study of two-phase flows under both adiabatic and non-adiabatic conditions, particularly to develop reliable prediction tools suitable for weightless environments or to update existing correlations obtained based on ground experiments. This paper simulates different gravity conditions by using centrifugal force to offset gravity and discusses the influence of these conditions on the fluid flow and heat transfer characteristics during the condensation process in tubes. 1 Experimental setup and methods 1.1 Experimental setup As illustrated in Fig. 1 , 2 , the condensation experimental apparatus is primarily constituted by three fundamental components: a steam generation system, an examination zone, and a data acquisition mechanism. Throughout the experimental procedure, distilled water from the liquid reservoir is conveyed to the steam generator via a peristaltic pump. This generator possesses a nominal output power of 3000W and its output can be modulated using a frequency converter, thereby altering its power output. The steam produced within the generator is subsequently channeled into the condensation chamber through stainless steel conduits, which are encased with electrical heating tape to mitigate thermal losses. Within the designated test segment, the condensation of the steam transpires. Furthermore, airbags have been incorporated into the circulatory system with the objective of sustaining a systemic pressure approximating 0.1 MPa. Upon assembling the apparatus as illustrated in Fig. 1 , 2 , the experiment commenced with the activation of the motor, which initiated rotation of the test section. With an increase in motor speed, the centrifugal force acting upon the test section progressively counterbalances gravity's influence. A state of equilibrium between centrifugal force and gravity is achieved at a particular rotational velocity, thereby simulating zero-gravity conditions for the test section. Following this, the steam generator undergoes preheating, with temperature monitoring facilitated by the data acquisition instrumentation. Subsequently, a peristaltic pump is engaged to introduce distilled water into the steam generator at a controlled rate, generating a consistent steam flow. To mitigate the impact of non-condensable gases on experimental outcomes, the exhaust valve is opened, directing freshly generated steam to expel these gases from the system. By manipulating the motor's rotational speed, one can modulate the magnitude of the centrifugal force, thus simulating diverse gravitational environments ranging from microgravity to terrestrial conditions. This approach enables a comprehensive examination of gravity's impact on the condensation heat transfer process. Throughout the experiment, meticulous control was exercised to maintain the steam generator's output power at a steady 1500 W. Based on this setting, steam flow rates were systematically varied at 30, 40, and 50mL/min, with the objective of modifying steam quality. This methodology further facilitated the exploration of condensation phenomena under varying operational parameters. 1.2 Data processing The different gravitational forces in the experiment were generated by simulating the motor rotation, so the centrifugal acceleration a c was: a c = ω 2 R (1) where ω is the angular velocity, m/s; R is the radius of rotation of the copper tube, m. n = 30ω/π (2) n is the motor speed, r/min. The combined acceleration in the experiment is the synthesis of centrifugal acceleration and gravitational acceleration, a h =g-a c (3) The centrifugal acceleration ac in the experiment was 0g, 25%g, 63%g and 1g, so ah was 1g, 75%g, 37%g and 0g. Q = m(h 2 -h 1 ) (4) Where Q is the heating power, W; h 2 is the outlet enthalpy, J/kg; h 1 is the inlet enthalpy, J/kg. $$\:X=\frac{{h}_{2}-{h}_{l}}{{h}_{v}-{h}_{l}}$$ 5 where hl denotes the specific enthalpy of saturated liquid and hv denotes the specific enthalpy of saturated vapor. The average density of the two-phase fluid \(\:{\rho\:}_{\text{t}\text{p}}\) is $$\:{\rho\:}_{tp}={\left[\frac{x}{{\rho\:}_{v}}+\frac{\left(1-x\right)}{{\rho\:}_{1}}\right]}^{-1}$$ 6 where \(\:{\rho\:}_{\text{v}}\) denotes the density of saturated steam and \(\:{\rho\:}_{1}\) denotes the density of saturated water. The average kinematic viscosity of the two-phase fluid \(\:{\mu\:}_{\text{t}\text{p}}\) is $$\:\frac{1}{{\mu\:}_{tp}}=\frac{x}{{\mu\:}_{v}}+\frac{\left(1-x\right)}{{\mu\:}_{1}}$$ 7 where µ v is the dynamic viscosity of saturated steam and µ l is the dynamic viscosity of saturated water. The average Reynolds number of two-phase flow, Retp , is a dimensionless parameter of the ratio of fluid inertial force to viscous force. $$\:{Re}_{tp}=\frac{{\rho\:}_{tp}u{D}_{h}}{{\mu\:}_{tp}}$$ 8 where \(\:u\) is the velocity of the fluid and D h is the hydraulic diameter of the channel. 2 Visualization In the realm of two-phase flow investigations, the significance of flow patterns cannot be overstated, as they dictate the intricate distribution of liquid and gas phases throughout the conduit. This distribution, in turn, exerts a profound influence on the pressure drop characteristics inherent to the system. The present study meticulously documented these flow patterns under a variety of experimental conditions, employing a high-resolution video camera strategically positioned above the test section to capture every nuance. It is imperative to note that, irrespective of whether the environment is subject to conventional gravity or microgravity conditions, the mass of vapor emerges as a pivotal determinant in shaping its flow behavior within the confines of the pipe. Figure 3 illustrates the flow characteristics observed under conventional gravity for varying pipe diameters and vapor masses. Owing to the influence of gravity, gas-liquid two-phase flow within a horizontal pipe demonstrates significant phase distribution inhomogeneity, with the liquid phase predominantly accumulating along the bottom of the pipe. The prevalent flow patterns in horizontal pipes encompass smooth laminar flow and bubble flow. Figure 4 and 5 illustrate the flow behavior under microgravity conditions. For pipes with a large diameter (OD 12 mm), the vapor flow rate can reach up to 0.01 m/s. In a normal gravity environment, the density difference within the fluid due to gravitational forces results in phase separation, where denser liquids settle at the lower portion of the pipe, while lighter gases occupy the upper region. This stratification gives rise to laminar flow, which is characterized by a relatively smooth and well-defined interface between the liquid and gas phases. Conversely, in microgravity environments, where the influence of gravity is significantly diminished, differences in fluid density are insufficient to drive fluid stratification. Instead, surface tension and inertial forces dominate. The interaction of these forces leads to undulatory flow patterns, characterized by fluctuations at the gas-liquid interface. Additionally, rotational motion introduces Coriolis forces, which affect the direction of fluid flow. When fluid moves through a rotating pipe, the Coriolis force induces a deflection in the fluid trajectory, causing deformation and fluctuations at the fluid interface, ultimately resulting in wavy flow formation. As shown in Fig. 5, within a 10 mm diameter pipe, the diminution of the pipe's width facilitates an escalation in the steam's maximum speed to 0.016 m/s. This increase in flow rate enables faster removal of the formed condensate compared to a 12 mm pipe. It is particularly noteworthy that at X = 1, the relatively small amount of condensation produced due to the complete vaporization of the steam, coupled with the higher steam flow rate, results in the inability to form a continuous liquid film. At lower vapor flow rates, the distribution of the liquid film is significantly affected by gravity, as evidenced by a thicker liquid film at the bottom of the pipe and almost no liquid present at the top. As the vapor flow rate increases, the shear perturbation of the liquid film at the bottom increases. However, even with the increase in shear, most of the condensate is still deposited at the bottom of the pipe by gravity as the amount of condensate increases. Several flow patterns have been observed under various operating conditions: undulating, stratified, and bubbling flows. Annular flow occurs when the liquid is distributed circumferentially along the inner wall of the pipe. If most of the liquid is concentrated at the bottom of the pipe with only a thin film of liquid present at the top, it exhibits stratified flow. Bubbly flow, observed in a 12 mm pipe under normal gravity conditions with a quality of X = 0.85, is characterized by the liquid being the continuous phase and the gas being dispersed in the liquid in the form of tiny bubbles. The change in vapor mass significantly affects the transition between flow patterns. As the vapor mass decreases, the degree of turbulence in the fluid increases, which influences not only the formation of the flow pattern but also the transition between flow patterns. The transition between flow patterns is a continuous process influenced by factors such as the size of the pipe and gravity. For different vapor qualities, the flow can be wavy and stratified, depending on the gravity conditions, and the influence of the pipe diameter. As gravity decreases, the pressure gradient within the fluid changes, and this change destabilizes the original flow, causing the flow to shift from a steady state to an unsteady state. This phenomenon is especially obvious in the transition between laminar and undulating flow. In the microgravity environment, the originally stable laminar flow will be destabilized, and then transformed into a wavy flow. As shown in Fig. 4, when the steam mass is low (X = 0.65), the momentum of the steam is relatively large, which can inhibit the effect of surface tension to a certain extent, thus making the characteristics of the wavy flow less obvious. With a higher vapor mass (X = 1), there is less liquid, and the wavy flow is also less pronounced at this time. At a vapor mass of X = 0.85, under 75%g gravity, the liquid film thickness is neither too thin to cause the fluctuations to be insignificant nor too thick to impede the propagation of the fluctuations, and the wavy flow is most pronounced. Under the same gravity conditions, the decrease in vapor mass means an increase in the water content in the vapor, which leads to more condensate production during condensation. In rotating piping, an increase in centrifugal force acts on the liquid film to flatten its distribution, thus affecting the thickness and uniformity of the liquid film. The increase in centrifugal force causes the film to flatten out in the pipe, ultimately reducing fluctuations and instabilities in the flow. Gravity significantly impacts the behavior of fluids within pipes, particularly influencing the flow dynamics of liquid films, but it is not the only influence. Within a tube, the movement of a condensate film is governed by multiple factors, encompassing gravitational pull, surface tension, viscosity-induced forces, among others. Specifically, gravity induces a downward motion along the tube's inner walls for the liquid film. Conversely, surface tension causes liquid molecules to aggregate on the surface of the liquid film to form a uniform film, thus resisting gravity and maintaining the stability of the film. Meanwhile, viscous forces act as impediments to fluid motion, typically resulting in the manifestation of laminar flow characteristics. Over time, regardless of gravity conditions, the condensate film inside the tube will eventually tend to form a laminar flow state. For small tube diameters (10 mm), the case shown in Fig. 5, the increase in vapor flow rate causes the liquid film to become discontinuous. The flow characteristics are more sensitive to the vapor quality. At 75% g, the surface tension and viscous forces of the liquid are relatively small, so the liquid is more likely to form a continuous liquid film as the vapor mass decreases. Gravity is the dominant factor, while surface tension and viscous force are relatively minor. In contrast, at 37%g and 0g microgravity, the surface tension and viscous force of the liquid become the dominant factors due to the reduction of gravity. Consequently, as vapor mass declines, condensation is more prone to result in droplet formation, driven by surface tension which prompts the liquid to adopt a spherical or near-spherical configuration to minimize surface area. This flow pattern is quite different from the liquid film formed by gravity. 3 Temperature Distribution Under the earth's normal gravity conditions, condensate droplets flow down the pipe wall and are effectively removed from the pipe. This droplet removal process is critical to maintaining effective heat exchange between the vapor and condensate. However, in microgravity or zero-gravity environments, droplet flow is impeded due to the lack of gravity, resulting in droplets that are more likely to accumulate or be suspended on the pipe wall. This buildup reduces the contact area between the vapor and the cooling surface, thereby decreasing the heat exchange efficiency. In exploring the effect of different tube diameters (12 mm and 10 mm) on the temperature distribution of the vapor condensation process under normal gravity and microgravity conditions, some interesting phenomena were observed. Figure 6 demonstrates that, in a 12 mm tube, the temperature drop is 2℃ when X = 1 in normal gravity, while in weightlessness (0g), the temperature drop increases to 2.3℃. For X = 0.85, the corresponding temperature drop changes from 2.9℃ to 2.8℃, while for X = 0.65, it decreases from 3.1℃ to 2.7℃. Similarly, in the 10 mm tube, the temperature drop at X = 1 in normal gravity is 3℃, while it rises to 3.2℃ in weightlessness. For X = 0.85, the temperature drop varied from 2.2℃ to 1.8℃, while for X = 0.65, it decreased from 2.1℃ to 1.9℃. In weightlessness, the temperature drop increases compared to the normal gravity condition. This results from the weakening of natural convection in microgravity environments. The increase in temperature drop is associated with a change in the stability of the liquid-gas interface. In a microgravity environment, the surface tension between the liquid and gas phases is enhanced, resulting in reduced mixing and heat exchange between the liquid and gas, leading to an increase in temperature drop. Under different gravity conditions, the temperature drop at high vapor masses increases with decreasing gravity because less condensate is produced, resulting in droplets that are more likely to adhere to the upper portion of the pipe. Conversely, the temperature drop at low vapor masses decreases with decreasing gravity due to the fact that condensate is produced more rapidly at low vapor masses. This inverse relationship is attributed to the accelerated production of condensate under these conditions, a process that is particularly pronounced in zero-gravity environments. Consequently, the condensate becomes more homogeneously dispersed throughout the upper section of the piping, thereby mitigating the temperature drop. $$\:{j}_{G}^{\text{*}}=\frac{xG}{{\left[gD{\rho\:}_{G}\left({\rho\:}_{L}-{\rho\:}_{G}\right)\right]}^{0.5}}$$ 9 As in Eq. 9 , the correlation of shear with respect to gravity is expected to increase as the diameter dimension D decreases or the mass flux G increases; moreover, it must be noted that during condensation, the vapor mass X is gradually decreasing and therefore the correlation of gravity increases in relation to the shear stresses. A criterion has been developed by Cavallini [ 22 , 23 ] et al. from a database dealing with macroscopic scale pipes. The criterion is based on Wallis' uncaused gas velocities and Martinelli's parameters to predict the transition to gravity-dominated condensation in horizontal channels. At the lowest diameter size considered in their work (ie., D = 3mm), R134a condensation at a saturation temperature of 40℃ is gravity-independent for G ≥ 300 kg m − 2 s − 1 , and for G ≤ 100 kg m − 2 s − 1 the entire tube length is gravity-dominated; between these two mass flux values, the transition to gravity-dependent heat transfer is expected to occur at some intermediate point between the vapor masses x = 1 and x = 0. In analyzing the effect of tube diameter on the temperature distribution of the steam condensation process, some key phenomena were noted. Under the condition of maintaining a constant steam mass, it was observed that the steam flow rate increased with decreasing pipe diameter. Within the pipe, this increased vapor flow rate had a beneficial effect by rapidly removing more condensate, thereby reducing liquid accumulation within the pipe and promoting a more uniform temperature distribution. The experimental results show that for all gravity conditions considered, the decrease in pipe diameter is accompanied by a decrease in temperature drop. 4 Effect of fins In order to strengthen the heat transfer performance of the circular tube in the test section, it can be seen from the basic equation of heat transfer Q = hAΔT that the heat transfer capacity of the test section can be increased by increasing the heat transfer area on one hand; on the other hand, the heat transfer coefficient can be improved. Increase the heat transfer area does not mean simply by expanding the volume of the equipment to increase the heat transfer area, but by changing the structure of the heat transfer surface to increase the effective heat transfer area per unit volume, increasing the amount of heat transfer. At present, fins are usually added outside the round tube, and the effect of fins of different materials on the test section of the round tube is not the same. Galvanized iron and copper fins are selected for this experiment. In subsequent studies, galvanized iron and copper will be used as materials for the fins. Figure 6, 7, and 8 show the steady-state along-track temperature distributions for the light tube and the tube with fins, respectively, with the horizontal coordinates indicating the position of each thermocouple from the test section. By analyzing the data in Figs. 6 and 7 and 8, it can be observed that the temperature of the tube with fins increases significantly under the same conditions. Specifically, the average temperature of the light tube was 35.3°C under normal gravity at 30 mL/min, while the average temperature of the copper finned tube reached 50.2°C, an increase of 14.9°C compared to the light tube, and the average temperature of the galvanized iron finned tube was 44.6°C, an increase of 9.3°C. This indicates a greater increase in temperature for copper finned tubes. As the volume flow rate increases, it means that more heat source is involved in the heat transfer process. When the flow rate was increased to 50 mL/min, the temperature changes under different gravity conditions were as follows: the temperature drop of the copper finned tube under normal gravity was 1.3°C, while under 75%g, 37%g and 0g gravity, the temperature drops were 1°C, 1°C and 0.8°C, respectively; the temperature drop of the galvanized iron finned tube under normal gravity was 2.7°C, while under 75%g, 37%g and 0g gravity, the temperature drops were 2°C, 1.2°C and 1.2°C. When the volume flow rate increases, the temperature drop decreases under normal microgravity. These data clearly show that copper finned tubes perform better in terms of temperature rise and their temperature drop is also relatively small. Moreover, as the gravity decreases, the temperature drop of the finned tube decreases gradually as compared to the light tube. This phenomenon indicates that the addition of fins effectively compensates for the uneven temperature distribution due to the lack of gravity. The choice of fin material and the variation of gravity conditions have a significant effect on the temperature characteristics. Copper finned tubes are hotter under the same condensing conditions. This is because copper has a much higher thermal conductivity than galvanized iron, which means that copper finned tubes conduct heat faster under the same conditions. Due to the high thermal conductivity of copper, it is able to transfer heat more quickly from the round tube to the fins, but the air carries less heat away, causing the heat to collect in the fins in turn the heat from the fins acts on the round tube to eventually reach equilibrium, resulting in higher temperatures for round tubes with fins than for bare tubes. Under the same heating power condition, as the mass of steam decreases, the corresponding volume flow rate increases. In Fig. 7, comparing the pipes with outer diameters of 12 mm and 10 mm, it can be found that the temperature of the outer diameter of 10 mm is higher than that of the outer diameter of 12 mm. This phenomenon is especially significant at high volumetric flow rates, indicating that the effect of gravity on heat transfer in a pipe with a diameter of 12 mm is more significant. The effect of thermophysical properties, especially surface tension, on heat transfer becomes more pronounced when the pipe diameter decreases. The effect of surface tension leads to a more uniform distribution of the liquid film around the pipe, resulting in a thinning of the liquid film thickness at the bottom of the pipe and an increase in the liquid film thickness at the top of the pipe. This effect of surface tension helps to increase the heat transfer coefficient at higher mass flow rates and vice versa. Thus, both mass flux and flow pattern play a vital role in the condensation heat transfer process. Thermal imaging results for the same heating power condition in a normal gravity environment, considering the case of X = 1, are shown in Figs. 9 and 10, demonstrating the effect of the fins on the temperature distribution.P1, P2, and P3 represent the temperatures of the center gas core, the upper wall, and the lower wall, respectively. In the bare tube, the unevenness of the temperature distribution is mainly manifested in the higher temperature in the upper part and lower temperature in the lower part. This phenomenon is mainly due to the effect of gravity, which causes the condensed liquid to collect in the lower part of the pipe and form a thicker liquid film, thus increasing the thermal resistance to heat transfer. As a result, in the light tube configuration, P1 (center air core temperature) is relatively high while P3 (lower wall temperature) is relatively low. Comparatively, in finned tubes, the presence of fins significantly alters the distribution of the temperature field. The fins facilitate the heat exchange between the surrounding area and the air by increasing the effective heat transfer area, which helps to reduce the uneven temperature distribution due to gravity. In addition, the maximum temperature of the finned tube is higher than that of the light tube, which indicates that the addition of fins effectively enhances the heat transfer efficiency. The presence of fins not only enhances the heat exchange in the tube, but also equalizes the temperature distribution to some extent. As the diameter of the tube decreases, the temperature at the same position also shows an increasing trend. The reduction in tube diameter means that the cross-sectional area of the fluid flow is reduced, which leads to an increase in the fluid flow rate. At higher flow rates, the interaction between the fluid and the pipe wall is increased, and the increased flow rate also helps to improve the mixing within the fluid. When the fluids are more thoroughly mixed with each other, heat can be more evenly distributed throughout the fluid, which promotes more efficient heat exchange, reduces temperature gradients, and thus improves temperature uniformity. 5 Effect of Re on pressure drop As the microgravity increases the pressure drop increases. As the vapor velocity increases, it carries more droplets along with it, increasing the kinetic energy of the fluid mixture. In addition, changes in temperature affect pressure. In normal gravity and microgravity environments, the temperature drop is insignificant, meaning that the thermal energy of the fluid remains relatively constant. However, an increase in vapor velocity leads to an increase in temperature, indicating that a portion of the fluid's kinetic energy is converted to thermal energy, which in turn leads to a change in pressure. When the gravitational conditions are equal, the pressure drop increases as the steam mass decreases. The decrease in vapor mass results in a faster rate of vapor condensation and a faster rate of condensate formation, which further results in the formation of a thicker liquid film. These droplets not only occupy a certain amount of space, thereby reducing the steam flow area, but also cause turbulence and instability in the steam flow, increasing the resistance of the steam as it passes through the piping. This results in greater pressure loss in the piping. As shown in Fig. 11, the pressure drop in the channel increases with decreasing microgravity. The fluid distribution in a microgravity environment is not uniform. This inhomogeneity leads to an increase or decrease in the local flow rate, which in turn affects the pressure drop across the system. The pressure drop increases with increase in Re tp as shown in Fig. 12. When Re tp increases, the friction between steam and condensate increases. At the same time, the friction between the condensate and the channel wall increases. As a result, the two-phase flow pressure drop in the channel increases with increasing Re tp Figure 12 illustrates the relationship between pressure drop Δp and Re tp for finned tube. As the Re tp increases, the pressure drop Δp increases significantly. Further analysis shows that for the same Re tp , the pressure drop Δp of finned tube is 20–56% of that of bare tube. This range of ratios reveals that finned tubes bring higher flow resistance along with enhanced heat transfer efficiency. The fins increase the surface area of the tube, thereby increasing the contact area with the fluid, which, while contributing to the heat transfer efficiency, also increases the frictional resistance to fluid flow. This increased resistance results in a greater pressure differential to overcome as the fluid flows through the pipe, and therefore the pressure drop increases. 5 Conclusion In this experiment, the condensing heat transfer characteristics of steam in a rotating channel were investigated in depth using centrifugal force to simulate a microgravity environment. It aims to understand the effects of gravity, steam mass, fins, and tube diameter on the heat transfer performance, with a view to supporting the optimization of thermal management systems in space applications, and draws the following conclusions: (1) The dependence of the flow pattern on steam mass increases with decreasing tube diameter. In addition, the flow is undulating in the 12-mm tube in a microgravity environment, and a continuous liquid film cannot be formed in the 10-mm tube. (2) In the microgravity environment, as the vapor mass decreases, the magnitude of the temperature drop decreases gradually compared to the normal gravity condition. The uneven temperature distribution is reduced by decreasing the pipe diameter and increasing the volume flow rate of the fluid. (3) Under normal and microgravity environments, the temperature average temperature of the finned tube is increased compared to the average temperature of the smooth tube. This phenomenon was particularly significant under normal gravity conditions, where the temperature inside the 12 mm tube was elevated by 9.3°C to 16.4°C, while the temperature inside the 10 mm tube was elevated by 7.0°C to 15.5°C. In addition, copper finned tubes exhibited higher temperature values compared to galvanized iron fins. The finned tube exhibits a smaller temperature drop and more uniform temperature distribution. (4) Pressure drop during vapor condensation increases with decreasing gravity. The pressure drop increases with increasing Re tp . Specifically, the pressure drop during steam condensation shows a clear increasing trend with the weakening of gravity conditions., the transition from a normal gravity environment to a microgravity environment. Due to the change in convective heat transfer mode under microgravity conditions, it leads to an increase in flow resistance. Higher Re tp tends to be accompanied by the emergence of more complex flow structures such as turbulence, and these flow characteristics increase the friction between the fluid and the inner wall of the pipeline, which induces greater energy loss and pressure drop. Declarations Ethical Approval This article does not contain any studies with human participants and/ or animals performed by any of the authors. Informed consent This article does not contain any studies with human participants and/ or animals performed by any of the authors. Competing interests The authors declare no conflict of interest. Authors' contributions Leigang Zhang conducted preliminary research, designed the experimental system, monitored the experimental process, and supervised the writing of the paper. Meng Ru conducted the experiments, organized the experimental data, and wrote the main manuscript text. Yonghai Zhang guided the implementation of the experiments and monitored the experimental process. Guopei Li optimized the design of the figures and tables in the manuscript and provided improvement suggestions for the entire text. Zhenqian Chen reviewed the experimental methods and data analysis section, offering modification suggestions. Gang Chen reviewed the paper for format details and provided suggestions for revisions. Xuehong Wu was responsible for supervising the overall framework of the manuscript and revising the text. All authors reviewed the manuscript. Funding The authors gratefully acknowledge the support provided by National Natural Science Foundation of China (52106116, 52106115 and 52106212), Key projects of Science and Technology of Henan Province (242102221021), Key scientific research project of Higher Education of Henan Province (22A470011). Availability of data and materials Data will be made available on request. References Igor Marchuk·Oleg Kabov: Vapor Condensation on Curvilinear Disk-Shaped Fin at Microgravity[J]. Microgravity Sci. Technol. 20 , 165–169 (2008) Stéphane Lips, J.P., Meyer: Effect of Gravity Forces on Heat Transfer and Pressure Drop During Condensation of R134a[J]. Microgravity Sci. Technol. 24 , 157–164 (2012) Bai, C., Qiu, Y., Leng, X., et al.: Diverging/converging small channel for condensation heat transfer enhancement under different gravity conditions[J]. Int. Commun. Heat Mass Transfer. 116 , 10471 (2020) Stefano Bortolin, G.E., Achkar, M., Kostoglou, et al.: Experimental Investigations on Condensation in the Framework of ENhanced COndensers in Microgravity (ENCOM-2) Project[J]. Microgravity Sci. Technol. 26 , 335–349 (2014) RYAN M. M ACGILLIVRAY, KAMIEL S. GABRIEL. Annular Flow Film Characteristics in Variable Gravity[J]. New York Academy of Sciences, 974: 306–315 (2002) Wang Weicheng, L., Yuke, Z., Lining, et al.: Study on performance of condensation heat transfer in tubes under microgravity[J]. J. Tsinghua Univ. (Natural Sci. Edition). 2 , 1–5 (1997) Brendel, L.P.M., Caskey, S.L., Ewert, M.K., et al.: Vapor compression refrigeration testing on parabolic flights: Part1-cycle stability[J]. Int. J. Refrig. 136 , 152–161 (2022) Brendel, L., Caskey, S., Braun, J., et al.: Vapor Compression Refrigeration Testing on Parabolic Flights:Part2-Heat Exchanger Performance[J]. Int. J. Refrig. 135 , 254–260 (2022) Reinarts, T.R., Best, F.R., Hill, W.S.: Definition of condensation two phase flow behaviors for spacecraft design[C]. AIP Conference. Proceedings, 246(1): 1216–1225 (1992) Reinarts, T.R., Ochterbeck, J., Lebaigue, O., et al.: A review of flow regimes,pressure drops, convective boiling, and condensation in microgravity environments[C]. In: Proceeding 31st AIAA Thermophysics Conference (1996), American Institute of Aeronautics and Astronautics. 246(1): 1216–1225 (1992) Azzolin, M., Bortolin, S., Nguyen, L.P.L., et al.: Experimental investigation of in-tube condensation in microgravity[J]. Int. Commun. Heat Mass Transfer. 96 , 69–79 (2018) Lee, H., Park, I., Konishi, C., et al.: Experimental Investigation of Flow Condensation in Microgravity[J]. J. Heat Transfer. 136 (2), 021502 (2014) Lee, H., Mudawar, I., Hasan, M.M.: Experimental and theoretical investigation of annular flow condensation in microgravity[J]. Int. J. Heat Mass Transf. 61 , 293–309 (2013) Berto, A., Azzolin, M., Lavieille, P., et al.: Experimental investigation of liquid film thickness and heat transfer during condensation in microgravity[J]. Int. J. Heat Mass Transf. 199 , 123467 (2022) Prasenjit Dey, D., Raj, S.K.: Saha. A Numerical Study on Condensation Heat Transfer Characteristics of R134a in Microchannel Under Varying Gravity Conditions[J]. Microgravity Sci. Technol. 33 , 34 (2021) Zhang, J., Li, W., Minkowycz, W.J.: Numerical simulation of condensation for R410A at varying saturation temperatures in mini/micro tubes. Int. J. Comput. Methodology[J] Int. J. Comput. Methodol. 69 (5), 464–478 (2016) Narcy, M., Colin, C.: Two-Phase Pipe Flow in Microgravity with and without Phase Change: recent progress and future prospects[J]. Interfacial Phenom. Heat. Transf. 3 (1), 1–17 (2015) Macgillivray, R.M., Gabriel, K.S.: A study of annular flow film characteristics in microgravity and hypergravity conditions[J]. Acta Astronaut. 53 (4/10), 289–297 (2003) Choi, B., Fujii, T., Asano, H., et al.: A Study of the Flow Characteristics in Air-Water Two-Phase Flow under Microgravity (Results of Flight Experiments)[J]. JSME Int. J. Ser. B Fluids Therm. Eng. 46 , 262–269 (2003) Wang, Z.L., Gabriel, K.S., Zhu, Z.F.: The effects of gravity on the features of the interfacial waves in annular two-phase flow[J]. Microgravity Sci. Technol. 15 (3), 19–27 (2004) Han, H., Gabriel, K.S.: The influence of flow pressure gradient on interfacial wave properties in annular two-phase flow at microgravity and normal gravity conditions[J]. Fluid Dynamics Mater. Process. 2 , 287–295 (2006) Cavallini, A., Censi, G., Del Col, D., et al.: Condensation in horizontal smooth tubes: a new heat transfer model for heat exchanger design[J]. Heat Transfer Eng. 27 , 31–38 (2006) Cavallini, A., Del Col, D., Doretti, L., Rossetto, C., Zilio, et al.: Condensation heat transfer and pressure gradient inside multiport minichannels[J]. Heat Transfer Eng. 26 (3), 45–55 (2005) Additional Declarations No competing interests reported. Cite Share Download PDF Status: Published Journal Publication published 06 Jan, 2025 Read the published version in Microgravity Science and Technology → Version 1 posted Editorial decision: Revision requested 03 Dec, 2024 Reviews received at journal 02 Dec, 2024 Reviews received at journal 30 Nov, 2024 Reviewers agreed at journal 12 Nov, 2024 Reviewers agreed at journal 11 Nov, 2024 Reviewers invited by journal 06 Oct, 2024 Editor assigned by journal 30 Sep, 2024 Submission checks completed at journal 30 Sep, 2024 First submitted to journal 29 Sep, 2024 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. 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-5175333","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":385529460,"identity":"1f379f74-13e8-4753-a02d-1b92187707be","order_by":0,"name":"Leigang Zhang","email":"","orcid":"","institution":"Zhengzhou University of Light Industry","correspondingAuthor":false,"prefix":"","firstName":"Leigang","middleName":"","lastName":"Zhang","suffix":""},{"id":385529466,"identity":"dfd671da-e239-4428-9990-2c7d2d077f3a","order_by":1,"name":"Meng Ru","email":"","orcid":"","institution":"Zhengzhou University of Light Industry","correspondingAuthor":false,"prefix":"","firstName":"Meng","middleName":"","lastName":"Ru","suffix":""},{"id":385529468,"identity":"9b506d47-d116-4fad-bea2-f7a0ab223f17","order_by":2,"name":"Yonghai Zhang","email":"","orcid":"","institution":"Zhengzhou University of Light Industry","correspondingAuthor":false,"prefix":"","firstName":"Yonghai","middleName":"","lastName":"Zhang","suffix":""},{"id":385529469,"identity":"12c06e1f-b06b-4a1c-b546-6258d21acd06","order_by":3,"name":"Guopei Li","email":"","orcid":"","institution":"Zhengzhou University of Light Industry","correspondingAuthor":false,"prefix":"","firstName":"Guopei","middleName":"","lastName":"Li","suffix":""},{"id":385529470,"identity":"29038fd7-401a-4758-950f-30f413acfe8c","order_by":4,"name":"Zhenqian Chen","email":"","orcid":"","institution":"Southeast University","correspondingAuthor":false,"prefix":"","firstName":"Zhenqian","middleName":"","lastName":"Chen","suffix":""},{"id":385529472,"identity":"2a1ebefb-fba8-4317-b8aa-e6f213b8bca7","order_by":5,"name":"Gang Chen","email":"","orcid":"","institution":"Zhengzhou University of Light Industry","correspondingAuthor":false,"prefix":"","firstName":"Gang","middleName":"","lastName":"Chen","suffix":""},{"id":385529474,"identity":"8e45dd89-8917-4e1c-9a99-d3b1718ef147","order_by":6,"name":"Xuehong Wu","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAxElEQVRIiWNgGAWjYHACNmaGCiDFztgAZBOt5QyQYiZJC2MbSAuYTYR6gxs5Zo8L59XZGxxmbmD4UHaYgX92AyEtaenGM7exMRscZmxgnHHuMIPEnQP4tZjdSD4mzbuNhw2khZm37TCDgUQCIS2JbdK8cyR4wFr+EqcFZEuDgQRYCyMxWuzPPEuT5jmWYCAJ1HKw51w6j8QNAlok23PMpHlq6uz5jrc/fPCjzFqOfwYBLSjgABDzkKB+FIyCUTAKRgEuAACzOTuyNmgwfAAAAABJRU5ErkJggg==","orcid":"","institution":"Zhengzhou University of Light Industry","correspondingAuthor":true,"prefix":"","firstName":"Xuehong","middleName":"","lastName":"Wu","suffix":""}],"badges":[],"createdAt":"2024-09-29 14:08:09","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-5175333/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-5175333/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1007/s12217-024-10159-z","type":"published","date":"2025-01-06T15:58:00+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":71214487,"identity":"7fe255a9-b4ba-4f0d-a93c-4ef33b7715cc","added_by":"auto","created_at":"2024-12-12 08:30:23","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":43821,"visible":true,"origin":"","legend":"\u003cp\u003eSchematic diagram of the experimental setup\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-5175333/v1/f8db5283a13861704934fcae.png"},{"id":71214828,"identity":"20c8924b-b7cc-4762-9c67-e325f1a10d5f","added_by":"auto","created_at":"2024-12-12 08:38:24","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":27512,"visible":true,"origin":"","legend":"\u003cp\u003eSchematic diagram of the test section\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-5175333/v1/05a13b3209c47d9b3fab6121.png"},{"id":71218755,"identity":"186ad49a-a53a-4ee3-a318-6b9f679a9a96","added_by":"auto","created_at":"2024-12-12 09:02:24","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":176074,"visible":true,"origin":"","legend":"\u003cp\u003eVisualization under normal gravity\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-5175333/v1/ef67b1b08054a550fddb8548.png"},{"id":71214488,"identity":"4ce3d834-b9ce-442f-b789-6b69c8756dbf","added_by":"auto","created_at":"2024-12-12 08:30:23","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":124350,"visible":true,"origin":"","legend":"\u003cp\u003eVisualization of pipe diameter 12mm under different gravity\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-5175333/v1/9fcb320c605d285aa5427676.png"},{"id":71217828,"identity":"d63fb038-23bc-49c9-ba38-1fd56ce1700d","added_by":"auto","created_at":"2024-12-12 08:54:24","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":137032,"visible":true,"origin":"","legend":"\u003cp\u003eVisualization of pipe diameter 10mm under different gravity\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-5175333/v1/a376cd4b872cbbc90692a454.png"},{"id":71214491,"identity":"016d07d2-8496-44c8-9c41-af4babda4c06","added_by":"auto","created_at":"2024-12-12 08:30:24","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":45541,"visible":true,"origin":"","legend":"\u003cp\u003eTemperature distribution under different diameters and gravity\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-5175333/v1/1949937c8be2111e2dca86a1.png"},{"id":71214821,"identity":"724ecd76-0a2c-4a0a-852b-a396608d691a","added_by":"auto","created_at":"2024-12-12 08:38:24","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":28411,"visible":true,"origin":"","legend":"\u003cp\u003eTemperature distribution of copper finned tubes under different diameters and gravity\u003c/p\u003e","description":"","filename":"7.png","url":"https://assets-eu.researchsquare.com/files/rs-5175333/v1/c142daa794813ff193aef65e.png"},{"id":71214496,"identity":"d10ac782-35d7-4c7c-a563-0a3a43a168dd","added_by":"auto","created_at":"2024-12-12 08:30:24","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":36056,"visible":true,"origin":"","legend":"\u003cp\u003eTemperature distribution of galvanized iron fins under different diameters and gravity\u003c/p\u003e","description":"","filename":"8.png","url":"https://assets-eu.researchsquare.com/files/rs-5175333/v1/226f3526106ca6b759e7761e.png"},{"id":71216257,"identity":"407136fa-fe4c-4b91-992e-91edfad0c3a8","added_by":"auto","created_at":"2024-12-12 08:46:24","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":277713,"visible":true,"origin":"","legend":"\u003cp\u003eThermal imaging of temperature under normal gravity\u003c/p\u003e","description":"","filename":"9.png","url":"https://assets-eu.researchsquare.com/files/rs-5175333/v1/ead931c948d801477de9f845.png"},{"id":71214824,"identity":"3ee1291e-8989-4320-ae26-4db0ce72028e","added_by":"auto","created_at":"2024-12-12 08:38:24","extension":"png","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":302282,"visible":true,"origin":"","legend":"\u003cp\u003eThermal imaging of temperature under normal gravity\u003c/p\u003e","description":"","filename":"10.png","url":"https://assets-eu.researchsquare.com/files/rs-5175333/v1/870128d06498373abe013327.png"},{"id":71214830,"identity":"fd223c8a-0e39-4450-a6d3-9e740db284c4","added_by":"auto","created_at":"2024-12-12 08:38:24","extension":"png","order_by":11,"title":"Figure 11","display":"","copyAsset":false,"role":"figure","size":13842,"visible":true,"origin":"","legend":"\u003cp\u003ePressure drop under different pipe diameters and gravity\u003c/p\u003e","description":"","filename":"11.png","url":"https://assets-eu.researchsquare.com/files/rs-5175333/v1/df97e43fbb4d292db57ffd5a.png"},{"id":71216254,"identity":"08cb43cb-5122-4232-ba6e-39ea5deb589e","added_by":"auto","created_at":"2024-12-12 08:46:24","extension":"png","order_by":12,"title":"Figure 12","display":"","copyAsset":false,"role":"figure","size":28219,"visible":true,"origin":"","legend":"\u003cp\u003ePressure drop under different Retp\u003c/p\u003e","description":"","filename":"12.png","url":"https://assets-eu.researchsquare.com/files/rs-5175333/v1/1028ec4ac118b9c4c51f6596.png"},{"id":73694491,"identity":"1742f971-e596-4ba6-8481-86b0004feb0f","added_by":"auto","created_at":"2025-01-13 16:13:20","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1792016,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-5175333/v1/642c98c8-28b1-43a2-b96c-6990666e9253.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Experimental study of condensation heat transfer in tubes under centrifugal force","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eIn recent years, the advancement of space exploration technology has increasingly focused attention on condensation research conducted in microgravity environments. Compared with the traditional condensation process under Earth gravity, condensation in microgravity environment has many different characteristics and challenges. First, the flow and heat transfer characteristics under microgravity conditions are significantly different from those under Earth gravity. For example, liquid film thickness\u003csup\u003e[\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]\u003c/sup\u003e heat transfer efficiency\u003csup\u003e[\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e, \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]\u003c/sup\u003e and hydrodynamic behaviors\u003csup\u003e[\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e, \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]\u003c/sup\u003e exhibit different patterns in microgravity. These differences are critical for a deeper understanding of the effects of gravity on condenser operating mechanisms and for the design of thermal management systems for space applications.\u003c/p\u003e \u003cp\u003eThe effect of gravity, in a broader perspective, is the effect of acceleration. There are two common ways to alter the acceleration of gravity: parabolic flight and centrifuges. Under standard gravity conditions (the surface of the Earth), fluid flow is predominantly driven by gravity. However, in microgravity environments, due to the absence of gravity, the interactions between inertial, viscous, and surface tension reach a new equilibrium\u003csup\u003e[\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]\u003c/sup\u003e. This shift results in changes to the interfacial mechanisms of action. Consequently, this alteration gives rise to unique manifestations in both flow properties and heat transfer characteristics.\u003c/p\u003e \u003cp\u003eBrendel et al.\u003csup\u003e[\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e, \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]\u003c/sup\u003e conducted an experimental study on the stability and performance of the R134a vapor compression cycle under microgravity conditions, which were simulated using a parabolic flight. The results indicated that during the initial phase of exposure to microgravity, there was a notable increase in condensation pressure, amounting to a 3% rise. The rise in pressure is primarily attributed to a reduction in the volume of liquid exiting the wall and a diminished heat transfer coefficient, presenting a stark contrast to thermodynamic behavior observed on Earth. Reinarts et al.\u003csup\u003e[\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e, \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]\u003c/sup\u003e carried out condensation experiments using R12 within a pipe of 8.7 mm internal diameter aboard NASA KC-135 aircraft, with the objective of investigating heat transfer efficiency in microgravity conditions. The experiment observed a slight increase in temperature and pressure of the working fluid at the inlet of the condensing test section during the transition from hypergravity to microgravity conditions. More importantly, it was found that the condensation heat transfer efficiency under microgravity conditions showed a significant decrease of about 26% compared to Earth conditions. The deterioration of the condensation heat transfer under weightlessness conditions was exhaustively documented in the study by Azzolin\u003csup\u003e[\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]\u003c/sup\u003e et al. Convective condensation in a horizontally placed inner diameter (ID) 3.38 mm channel of HFE-7000 at mass fluxes of G\u0026thinsp;=\u0026thinsp;70\u0026ndash;170 kg m\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e was investigated in the 62nd European Space Agency (ESA) parabolic flight experiment. The test section device consists of two countercurrent heat exchangers designed to accurately measure the local heat transfer coefficient and to visualize the flow through a borosilicate glass window. The ratio of the heat transfer coefficient under microgravity to that under normal gravity conditions decreases with increasing steam mass for a mass flux of G\u0026thinsp;=\u0026thinsp;130 kg m\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. For higher mass fluxes (G\u0026thinsp;=\u0026thinsp;170 kg m\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e), the difference between the heat transfer coefficients measured under microgravity and normal gravity conditions is negligible. However, at lower mass fluxes (G\u0026thinsp;=\u0026thinsp;70 kg m\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e), the difference in heat transfer coefficients reaches 20%. Similar conclusions were reached by Lee et al. in parabolic flight experiments on the local heat transfer coefficients and visualized flow patterns of FC-72 within an internal diameter (ID) of 7.1 mm\u003csup\u003e[\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e, \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]\u003c/sup\u003e. These experiments included microgravity, lunar gravity (0.17g), and Martian gravity (0.377g), with mass fluxes of G\u0026thinsp;=\u0026thinsp;129\u0026ndash;341 kg m\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and saturation temperatures of 60-63.4\u0026deg;C. It was found that the effect of gravity on flow-type and condensation heat transfer is particularly significant at low mass fluxes. Specifically, the gravity conditions on the Moon and Mars resulted in a thicker liquid film at the bottom of the pipe and a thinner one at the top, and this inhomogeneous distribution increased the condensation heat transfer rate compared to microgravity conditions. To further extend the experimental dataset of Azzolin et al., Berto et al.\u003csup\u003e[\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e]\u003c/sup\u003e investigated the condensation process at low mass fluxes (30\u0026ndash;50 kg m\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) during the 70th ESA parabolic flight campaign using the same experimental setup at a saturation temperature of 38\u0026ndash;41\u0026deg;C. In agreement with previous studies, the results show that gravity has an enhancing effect on condensation heat transfer, especially at low mass fluxes. Specifically, at G\u0026thinsp;=\u0026thinsp;50 kg m\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, the heat transfer coefficients under normal gravity conditions were 33\u0026ndash;56% higher than those under microgravity, while at G\u0026thinsp;=\u0026thinsp;30 kg m\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, the enhancement of heat transfer due to gravity effects increased from 52% to a range of 77%. Additionally, the heat transfer performance in the microgravity environment was less degraded at high vapor mass conditions for all mass flow rates tested. By increasing the mass flux of the working fluid, the effect of gravity can be completely counteracted.\u003c/p\u003e \u003cp\u003eThrough meticulous experimental observation of the formation and evolution of liquid films, coupled with rigorous computational simulations of two-phase flow condensation processes\u003csup\u003e[\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e, \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]\u003c/sup\u003e, researchers have employed a diverse array of methodologies and techniques. These comprehensive studies have yielded invaluable data and profound insights into the subject matter. Among the current platforms for microgravity experiments\u0026mdash;including parabolic flights, drop towers, sounding rockets, and the International Space Station (ISS)\u0026mdash;parabolic flights have been widely used due to their reasonable cost, the ability to carry large experimental setups, and the allowance for manual interaction. Despite the low level of residual gravity achieved in parabolic flights (\u0026plusmn;\u0026thinsp;0.01 g\u003csub\u003es\u003c/sub\u003e), the experimental data are well reproducible. A number of experimental and theoretical studies have been carried out under adiabatic conditions with the aim of investigating the effect of gravity on the characteristics of two-phase flow\u003csup\u003e[\u003cspan additionalcitationids=\"CR18\" citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e]\u003c/sup\u003e. These studies have usually been conducted in conventionally sized pipes (internal diameters greater than 10 mm).\u003c/p\u003e \u003cp\u003eAccording to existing literature, there is no consensus on the effect of gravity on liquid film thickness and interface wave characteristics. Some researchers have found that the effect of gravity is negligible, while others consider it significant\u003csup\u003e[\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e, \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e]\u003c/sup\u003e. This contradictory result suggests that further experimental work is needed in the study of two-phase flows under both adiabatic and non-adiabatic conditions, particularly to develop reliable prediction tools suitable for weightless environments or to update existing correlations obtained based on ground experiments. This paper simulates different gravity conditions by using centrifugal force to offset gravity and discusses the influence of these conditions on the fluid flow and heat transfer characteristics during the condensation process in tubes.\u003c/p\u003e"},{"header":"1 Experimental setup and methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e1.1 Experimental setup\u003c/h2\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eAs illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e,\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e, the condensation experimental apparatus is primarily constituted by three fundamental components: a steam generation system, an examination zone, and a data acquisition mechanism. Throughout the experimental procedure, distilled water from the liquid reservoir is conveyed to the steam generator via a peristaltic pump. This generator possesses a nominal output power of 3000W and its output can be modulated using a frequency converter, thereby altering its power output. The steam produced within the generator is subsequently channeled into the condensation chamber through stainless steel conduits, which are encased with electrical heating tape to mitigate thermal losses. Within the designated test segment, the condensation of the steam transpires. Furthermore, airbags have been incorporated into the circulatory system with the objective of sustaining a systemic pressure approximating 0.1 MPa.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eUpon assembling the apparatus as illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e,\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e, the experiment commenced with the activation of the motor, which initiated rotation of the test section. With an increase in motor speed, the centrifugal force acting upon the test section progressively counterbalances gravity's influence. A state of equilibrium between centrifugal force and gravity is achieved at a particular rotational velocity, thereby simulating zero-gravity conditions for the test section. Following this, the steam generator undergoes preheating, with temperature monitoring facilitated by the data acquisition instrumentation. Subsequently, a peristaltic pump is engaged to introduce distilled water into the steam generator at a controlled rate, generating a consistent steam flow. To mitigate the impact of non-condensable gases on experimental outcomes, the exhaust valve is opened, directing freshly generated steam to expel these gases from the system. By manipulating the motor's rotational speed, one can modulate the magnitude of the centrifugal force, thus simulating diverse gravitational environments ranging from microgravity to terrestrial conditions. This approach enables a comprehensive examination of gravity's impact on the condensation heat transfer process. Throughout the experiment, meticulous control was exercised to maintain the steam generator's output power at a steady 1500 W. Based on this setting, steam flow rates were systematically varied at 30, 40, and 50mL/min, with the objective of modifying steam quality. This methodology further facilitated the exploration of condensation phenomena under varying operational parameters.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e1.2 Data processing\u003c/h2\u003e \u003cp\u003eThe different gravitational forces in the experiment were generated by simulating the motor rotation, so the centrifugal acceleration a\u003csub\u003ec\u003c/sub\u003e was:\u003c/p\u003e \u003cp\u003e \u003cem\u003ea\u003c/em\u003e \u003csub\u003e \u003cem\u003ec\u003c/em\u003e \u003c/sub\u003e\u0026thinsp;\u003cem\u003e=\u0026thinsp;ω\u003c/em\u003e\u003csup\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sup\u003e\u003cem\u003eR\u003c/em\u003e (1)\u003c/p\u003e \u003cp\u003ewhere \u003cem\u003eω\u003c/em\u003e is the angular velocity, m/s; R is the radius of rotation of the copper tube, m.\u003c/p\u003e \u003cp\u003e \u003cem\u003en\u0026thinsp;=\u0026thinsp;30ω/π\u003c/em\u003e (2)\u003c/p\u003e \u003cp\u003en is the motor speed, r/min.\u003c/p\u003e \u003cp\u003eThe combined acceleration in the experiment is the synthesis of centrifugal acceleration and gravitational acceleration,\u003c/p\u003e \u003cp\u003e \u003cem\u003ea\u003c/em\u003e \u003csub\u003e \u003cem\u003eh\u003c/em\u003e \u003c/sub\u003e \u003cem\u003e=g-a\u003c/em\u003e \u003csub\u003e \u003cem\u003ec\u003c/em\u003e \u003c/sub\u003e (3)\u003c/p\u003e \u003cp\u003eThe centrifugal acceleration ac in the experiment was 0g, 25%g, 63%g and 1g, so ah was 1g, 75%g, 37%g and 0g.\u003c/p\u003e \u003cp\u003e \u003cem\u003eQ\u0026thinsp;=\u0026thinsp;m(h\u003c/em\u003e \u003csub\u003e \u003cem\u003e2\u003c/em\u003e \u003c/sub\u003e \u003cem\u003e-h\u003c/em\u003e \u003csub\u003e \u003cem\u003e1\u003c/em\u003e \u003c/sub\u003e \u003cem\u003e)\u003c/em\u003e (4)\u003c/p\u003e \u003cp\u003eWhere Q is the heating power, W; h\u003csub\u003e2\u003c/sub\u003e is the outlet enthalpy, J/kg; h\u003csub\u003e1\u003c/sub\u003e is the inlet enthalpy, J/kg.\u003cdiv id=\"Equ1\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ1\" name=\"EquationSource\"\u003e\n$$\\:X=\\frac{{h}_{2}-{h}_{l}}{{h}_{v}-{h}_{l}}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e5\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003ewhere hl denotes the specific enthalpy of saturated liquid and hv denotes the specific enthalpy of saturated vapor.\u003c/p\u003e \u003cp\u003eThe average density of the two-phase fluid \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\rho\\:}_{\\text{t}\\text{p}}\\)\u003c/span\u003e\u003c/span\u003e is\u003cdiv id=\"Equ2\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ2\" name=\"EquationSource\"\u003e\n$$\\:{\\rho\\:}_{tp}={\\left[\\frac{x}{{\\rho\\:}_{v}}+\\frac{\\left(1-x\\right)}{{\\rho\\:}_{1}}\\right]}^{-1}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e6\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003ewhere \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\rho\\:}_{\\text{v}}\\)\u003c/span\u003e\u003c/span\u003e denotes the density of saturated steam and \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\rho\\:}_{1}\\)\u003c/span\u003e\u003c/span\u003e denotes the density of saturated water.\u003c/p\u003e \u003cp\u003eThe average kinematic viscosity of the two-phase fluid \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\mu\\:}_{\\text{t}\\text{p}}\\)\u003c/span\u003e\u003c/span\u003e is\u003cdiv id=\"Equ3\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ3\" name=\"EquationSource\"\u003e\n$$\\:\\frac{1}{{\\mu\\:}_{tp}}=\\frac{x}{{\\mu\\:}_{v}}+\\frac{\\left(1-x\\right)}{{\\mu\\:}_{1}}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e7\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003ewhere \u003cem\u003e\u0026micro;\u003c/em\u003e\u003csub\u003e\u003cem\u003ev\u003c/em\u003e\u003c/sub\u003e is the dynamic viscosity of saturated steam and \u003cem\u003e\u0026micro;\u003c/em\u003e\u003csub\u003e\u003cem\u003el\u003c/em\u003e\u003c/sub\u003e is the dynamic viscosity of saturated water.\u003c/p\u003e \u003cp\u003eThe average Reynolds number of two-phase flow, \u003cem\u003eRetp\u003c/em\u003e, is a dimensionless parameter of the ratio of fluid inertial force to viscous force.\u003cdiv id=\"Equ4\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ4\" name=\"EquationSource\"\u003e\n$$\\:{Re}_{tp}=\\frac{{\\rho\\:}_{tp}u{D}_{h}}{{\\mu\\:}_{tp}}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e8\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003ewhere \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:u\\)\u003c/span\u003e\u003c/span\u003e is the velocity of the fluid and \u003cem\u003eD\u003c/em\u003e\u003csub\u003e\u003cem\u003eh\u003c/em\u003e\u003c/sub\u003e is the hydraulic diameter of the channel.\u003c/p\u003e \u003c/div\u003e"},{"header":"2 Visualization","content":"\u003cp\u003eIn the realm of two-phase flow investigations, the significance of flow patterns cannot be overstated, as they dictate the intricate distribution of liquid and gas phases throughout the conduit. This distribution, in turn, exerts a profound influence on the pressure drop characteristics inherent to the system. The present study meticulously documented these flow patterns under a variety of experimental conditions, employing a high-resolution video camera strategically positioned above the test section to capture every nuance. It is imperative to note that, irrespective of whether the environment is subject to conventional gravity or microgravity conditions, the mass of vapor emerges as a pivotal determinant in shaping its flow behavior within the confines of the pipe.\u003c/p\u003e \u003cp\u003eFigure\u0026nbsp;3 illustrates the flow characteristics observed under conventional gravity for varying pipe diameters and vapor masses. Owing to the influence of gravity, gas-liquid two-phase flow within a horizontal pipe demonstrates significant phase distribution inhomogeneity, with the liquid phase predominantly accumulating along the bottom of the pipe. The prevalent flow patterns in horizontal pipes encompass smooth laminar flow and bubble flow.\u003c/p\u003e \u003cp\u003eFigure\u0026nbsp;4 and 5 illustrate the flow behavior under microgravity conditions. For pipes with a large diameter (OD 12 mm), the vapor flow rate can reach up to 0.01 m/s. In a normal gravity environment, the density difference within the fluid due to gravitational forces results in phase separation, where denser liquids settle at the lower portion of the pipe, while lighter gases occupy the upper region. This stratification gives rise to laminar flow, which is characterized by a relatively smooth and well-defined interface between the liquid and gas phases. Conversely, in microgravity environments, where the influence of gravity is significantly diminished, differences in fluid density are insufficient to drive fluid stratification. Instead, surface tension and inertial forces dominate. The interaction of these forces leads to undulatory flow patterns, characterized by fluctuations at the gas-liquid interface. Additionally, rotational motion introduces Coriolis forces, which affect the direction of fluid flow. When fluid moves through a rotating pipe, the Coriolis force induces a deflection in the fluid trajectory, causing deformation and fluctuations at the fluid interface, ultimately resulting in wavy flow formation.\u003c/p\u003e \u003cp\u003eAs shown in Fig.\u0026nbsp;5, within a 10 mm diameter pipe, the diminution of the pipe's width facilitates an escalation in the steam's maximum speed to 0.016 m/s. This increase in flow rate enables faster removal of the formed condensate compared to a 12 mm pipe. It is particularly noteworthy that at X\u0026thinsp;=\u0026thinsp;1, the relatively small amount of condensation produced due to the complete vaporization of the steam, coupled with the higher steam flow rate, results in the inability to form a continuous liquid film. At lower vapor flow rates, the distribution of the liquid film is significantly affected by gravity, as evidenced by a thicker liquid film at the bottom of the pipe and almost no liquid present at the top. As the vapor flow rate increases, the shear perturbation of the liquid film at the bottom increases. However, even with the increase in shear, most of the condensate is still deposited at the bottom of the pipe by gravity as the amount of condensate increases.\u003c/p\u003e \u003cp\u003eSeveral flow patterns have been observed under various operating conditions: undulating, stratified, and bubbling flows. Annular flow occurs when the liquid is distributed circumferentially along the inner wall of the pipe. If most of the liquid is concentrated at the bottom of the pipe with only a thin film of liquid present at the top, it exhibits stratified flow. Bubbly flow, observed in a 12 mm pipe under normal gravity conditions with a quality of X\u0026thinsp;=\u0026thinsp;0.85, is characterized by the liquid being the continuous phase and the gas being dispersed in the liquid in the form of tiny bubbles. The change in vapor mass significantly affects the transition between flow patterns. As the vapor mass decreases, the degree of turbulence in the fluid increases, which influences not only the formation of the flow pattern but also the transition between flow patterns. The transition between flow patterns is a continuous process influenced by factors such as the size of the pipe and gravity.\u003c/p\u003e \u003cp\u003eFor different vapor qualities, the flow can be wavy and stratified, depending on the gravity conditions, and the influence of the pipe diameter. As gravity decreases, the pressure gradient within the fluid changes, and this change destabilizes the original flow, causing the flow to shift from a steady state to an unsteady state. This phenomenon is especially obvious in the transition between laminar and undulating flow.\u003c/p\u003e \u003cp\u003eIn the microgravity environment, the originally stable laminar flow will be destabilized, and then transformed into a wavy flow. As shown in Fig.\u0026nbsp;4, when the steam mass is low (X\u0026thinsp;=\u0026thinsp;0.65), the momentum of the steam is relatively large, which can inhibit the effect of surface tension to a certain extent, thus making the characteristics of the wavy flow less obvious. With a higher vapor mass (X\u0026thinsp;=\u0026thinsp;1), there is less liquid, and the wavy flow is also less pronounced at this time. At a vapor mass of X\u0026thinsp;=\u0026thinsp;0.85, under 75%g gravity, the liquid film thickness is neither too thin to cause the fluctuations to be insignificant nor too thick to impede the propagation of the fluctuations, and the wavy flow is most pronounced.\u003c/p\u003e \u003cp\u003eUnder the same gravity conditions, the decrease in vapor mass means an increase in the water content in the vapor, which leads to more condensate production during condensation. In rotating piping, an increase in centrifugal force acts on the liquid film to flatten its distribution, thus affecting the thickness and uniformity of the liquid film. The increase in centrifugal force causes the film to flatten out in the pipe, ultimately reducing fluctuations and instabilities in the flow.\u003c/p\u003e \u003cp\u003eGravity significantly impacts the behavior of fluids within pipes, particularly influencing the flow dynamics of liquid films, but it is not the only influence. Within a tube, the movement of a condensate film is governed by multiple factors, encompassing gravitational pull, surface tension, viscosity-induced forces, among others. Specifically, gravity induces a downward motion along the tube's inner walls for the liquid film. Conversely, surface tension causes liquid molecules to aggregate on the surface of the liquid film to form a uniform film, thus resisting gravity and maintaining the stability of the film. Meanwhile, viscous forces act as impediments to fluid motion, typically resulting in the manifestation of laminar flow characteristics. Over time, regardless of gravity conditions, the condensate film inside the tube will eventually tend to form a laminar flow state.\u003c/p\u003e \u003cp\u003eFor small tube diameters (10 mm), the case shown in Fig.\u0026nbsp;5, the increase in vapor flow rate causes the liquid film to become discontinuous. The flow characteristics are more sensitive to the vapor quality. At 75% g, the surface tension and viscous forces of the liquid are relatively small, so the liquid is more likely to form a continuous liquid film as the vapor mass decreases. Gravity is the dominant factor, while surface tension and viscous force are relatively minor. In contrast, at 37%g and 0g microgravity, the surface tension and viscous force of the liquid become the dominant factors due to the reduction of gravity. Consequently, as vapor mass declines, condensation is more prone to result in droplet formation, driven by surface tension which prompts the liquid to adopt a spherical or near-spherical configuration to minimize surface area. This flow pattern is quite different from the liquid film formed by gravity.\u003c/p\u003e"},{"header":"3 Temperature Distribution","content":"\u003cp\u003eUnder the earth's normal gravity conditions, condensate droplets flow down the pipe wall and are effectively removed from the pipe. This droplet removal process is critical to maintaining effective heat exchange between the vapor and condensate. However, in microgravity or zero-gravity environments, droplet flow is impeded due to the lack of gravity, resulting in droplets that are more likely to accumulate or be suspended on the pipe wall. This buildup reduces the contact area between the vapor and the cooling surface, thereby decreasing the heat exchange efficiency.\u003c/p\u003e \u003cp\u003eIn exploring the effect of different tube diameters (12 mm and 10 mm) on the temperature distribution of the vapor condensation process under normal gravity and microgravity conditions, some interesting phenomena were observed. Figure\u0026nbsp;6 demonstrates that, in a 12 mm tube, the temperature drop is 2℃ when X\u0026thinsp;=\u0026thinsp;1 in normal gravity, while in weightlessness (0g), the temperature drop increases to 2.3℃. For X\u0026thinsp;=\u0026thinsp;0.85, the corresponding temperature drop changes from 2.9℃ to 2.8℃, while for X\u0026thinsp;=\u0026thinsp;0.65, it decreases from 3.1℃ to 2.7℃. Similarly, in the 10 mm tube, the temperature drop at X\u0026thinsp;=\u0026thinsp;1 in normal gravity is 3℃, while it rises to 3.2℃ in weightlessness. For X\u0026thinsp;=\u0026thinsp;0.85, the temperature drop varied from 2.2℃ to 1.8℃, while for X\u0026thinsp;=\u0026thinsp;0.65, it decreased from 2.1℃ to 1.9℃. In weightlessness, the temperature drop increases compared to the normal gravity condition. This results from the weakening of natural convection in microgravity environments. The increase in temperature drop is associated with a change in the stability of the liquid-gas interface. In a microgravity environment, the surface tension between the liquid and gas phases is enhanced, resulting in reduced mixing and heat exchange between the liquid and gas, leading to an increase in temperature drop.\u003c/p\u003e \u003cp\u003eUnder different gravity conditions, the temperature drop at high vapor masses increases with decreasing gravity because less condensate is produced, resulting in droplets that are more likely to adhere to the upper portion of the pipe. Conversely, the temperature drop at low vapor masses decreases with decreasing gravity due to the fact that condensate is produced more rapidly at low vapor masses. This inverse relationship is attributed to the accelerated production of condensate under these conditions, a process that is particularly pronounced in zero-gravity environments. Consequently, the condensate becomes more homogeneously dispersed throughout the upper section of the piping, thereby mitigating the temperature drop.\u003c/p\u003e \u003cdiv id=\"Equ5\" class=\"Equation\"\u003e \u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ5\" name=\"EquationSource\"\u003e\n$$\\:{j}_{G}^{\\text{*}}=\\frac{xG}{{\\left[gD{\\rho\\:}_{G}\\left({\\rho\\:}_{L}-{\\rho\\:}_{G}\\right)\\right]}^{0.5}}$$\u003c/div\u003e \u003cdiv class=\"EquationNumber\"\u003e9\u003c/div\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eAs in Eq.\u0026nbsp;\u003cspan refid=\"Equ5\" class=\"InternalRef\"\u003e9\u003c/span\u003e, the correlation of shear with respect to gravity is expected to increase as the diameter dimension D decreases or the mass flux G increases; moreover, it must be noted that during condensation, the vapor mass X is gradually decreasing and therefore the correlation of gravity increases in relation to the shear stresses. A criterion has been developed by Cavallini \u003csup\u003e[\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e, \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e]\u003c/sup\u003e et al. from a database dealing with macroscopic scale pipes. The criterion is based on Wallis' uncaused gas velocities and Martinelli's parameters to predict the transition to gravity-dominated condensation in horizontal channels. At the lowest diameter size considered in their work (ie., D\u0026thinsp;=\u0026thinsp;3mm), R134a condensation at a saturation temperature of 40℃ is gravity-independent for G\u0026thinsp;\u0026ge;\u0026thinsp;300 kg m\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, and for G\u0026thinsp;\u0026le;\u0026thinsp;100 kg m\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e the entire tube length is gravity-dominated; between these two mass flux values, the transition to gravity-dependent heat transfer is expected to occur at some intermediate point between the vapor masses x\u0026thinsp;=\u0026thinsp;1 and x\u0026thinsp;=\u0026thinsp;0.\u003c/p\u003e \u003cp\u003eIn analyzing the effect of tube diameter on the temperature distribution of the steam condensation process, some key phenomena were noted. Under the condition of maintaining a constant steam mass, it was observed that the steam flow rate increased with decreasing pipe diameter. Within the pipe, this increased vapor flow rate had a beneficial effect by rapidly removing more condensate, thereby reducing liquid accumulation within the pipe and promoting a more uniform temperature distribution. The experimental results show that for all gravity conditions considered, the decrease in pipe diameter is accompanied by a decrease in temperature drop.\u003c/p\u003e"},{"header":"4 Effect of fins","content":"\u003cp\u003eIn order to strengthen the heat transfer performance of the circular tube in the test section, it can be seen from the basic equation of heat transfer Q\u0026thinsp;=\u0026thinsp;hAΔT that the heat transfer capacity of the test section can be increased by increasing the heat transfer area on one hand; on the other hand, the heat transfer coefficient can be improved. Increase the heat transfer area does not mean simply by expanding the volume of the equipment to increase the heat transfer area, but by changing the structure of the heat transfer surface to increase the effective heat transfer area per unit volume, increasing the amount of heat transfer. At present, fins are usually added outside the round tube, and the effect of fins of different materials on the test section of the round tube is not the same. Galvanized iron and copper fins are selected for this experiment.\u003c/p\u003e \u003cp\u003eIn subsequent studies, galvanized iron and copper will be used as materials for the fins. Figure\u0026nbsp;6, 7, and 8 show the steady-state along-track temperature distributions for the light tube and the tube with fins, respectively, with the horizontal coordinates indicating the position of each thermocouple from the test section. By analyzing the data in Figs.\u0026nbsp;6 and 7 and 8, it can be observed that the temperature of the tube with fins increases significantly under the same conditions. Specifically, the average temperature of the light tube was 35.3\u0026deg;C under normal gravity at 30 mL/min, while the average temperature of the copper finned tube reached 50.2\u0026deg;C, an increase of 14.9\u0026deg;C compared to the light tube, and the average temperature of the galvanized iron finned tube was 44.6\u0026deg;C, an increase of 9.3\u0026deg;C. This indicates a greater increase in temperature for copper finned tubes. As the volume flow rate increases, it means that more heat source is involved in the heat transfer process. When the flow rate was increased to 50 mL/min, the temperature changes under different gravity conditions were as follows: the temperature drop of the copper finned tube under normal gravity was 1.3\u0026deg;C, while under 75%g, 37%g and 0g gravity, the temperature drops were 1\u0026deg;C, 1\u0026deg;C and 0.8\u0026deg;C, respectively; the temperature drop of the galvanized iron finned tube under normal gravity was 2.7\u0026deg;C, while under 75%g, 37%g and 0g gravity, the temperature drops were 2\u0026deg;C, 1.2\u0026deg;C and 1.2\u0026deg;C. When the volume flow rate increases, the temperature drop decreases under normal microgravity. These data clearly show that copper finned tubes perform better in terms of temperature rise and their temperature drop is also relatively small. Moreover, as the gravity decreases, the temperature drop of the finned tube decreases gradually as compared to the light tube. This phenomenon indicates that the addition of fins effectively compensates for the uneven temperature distribution due to the lack of gravity. The choice of fin material and the variation of gravity conditions have a significant effect on the temperature characteristics.\u003c/p\u003e \u003cp\u003eCopper finned tubes are hotter under the same condensing conditions. This is because copper has a much higher thermal conductivity than galvanized iron, which means that copper finned tubes conduct heat faster under the same conditions. Due to the high thermal conductivity of copper, it is able to transfer heat more quickly from the round tube to the fins, but the air carries less heat away, causing the heat to collect in the fins in turn the heat from the fins acts on the round tube to eventually reach equilibrium, resulting in higher temperatures for round tubes with fins than for bare tubes.\u003c/p\u003e \u003cp\u003eUnder the same heating power condition, as the mass of steam decreases, the corresponding volume flow rate increases. In Fig.\u0026nbsp;7, comparing the pipes with outer diameters of 12 mm and 10 mm, it can be found that the temperature of the outer diameter of 10 mm is higher than that of the outer diameter of 12 mm. This phenomenon is especially significant at high volumetric flow rates, indicating that the effect of gravity on heat transfer in a pipe with a diameter of 12 mm is more significant. The effect of thermophysical properties, especially surface tension, on heat transfer becomes more pronounced when the pipe diameter decreases. The effect of surface tension leads to a more uniform distribution of the liquid film around the pipe, resulting in a thinning of the liquid film thickness at the bottom of the pipe and an increase in the liquid film thickness at the top of the pipe. This effect of surface tension helps to increase the heat transfer coefficient at higher mass flow rates and vice versa. Thus, both mass flux and flow pattern play a vital role in the condensation heat transfer process.\u003c/p\u003e \u003cp\u003eThermal imaging results for the same heating power condition in a normal gravity environment, considering the case of X\u0026thinsp;=\u0026thinsp;1, are shown in Figs.\u0026nbsp;9 and 10, demonstrating the effect of the fins on the temperature distribution.P1, P2, and P3 represent the temperatures of the center gas core, the upper wall, and the lower wall, respectively.\u003c/p\u003e \u003cp\u003eIn the bare tube, the unevenness of the temperature distribution is mainly manifested in the higher temperature in the upper part and lower temperature in the lower part. This phenomenon is mainly due to the effect of gravity, which causes the condensed liquid to collect in the lower part of the pipe and form a thicker liquid film, thus increasing the thermal resistance to heat transfer. As a result, in the light tube configuration, P1 (center air core temperature) is relatively high while P3 (lower wall temperature) is relatively low. Comparatively, in finned tubes, the presence of fins significantly alters the distribution of the temperature field. The fins facilitate the heat exchange between the surrounding area and the air by increasing the effective heat transfer area, which helps to reduce the uneven temperature distribution due to gravity. In addition, the maximum temperature of the finned tube is higher than that of the light tube, which indicates that the addition of fins effectively enhances the heat transfer efficiency. The presence of fins not only enhances the heat exchange in the tube, but also equalizes the temperature distribution to some extent. As the diameter of the tube decreases, the temperature at the same position also shows an increasing trend. The reduction in tube diameter means that the cross-sectional area of the fluid flow is reduced, which leads to an increase in the fluid flow rate. At higher flow rates, the interaction between the fluid and the pipe wall is increased, and the increased flow rate also helps to improve the mixing within the fluid. When the fluids are more thoroughly mixed with each other, heat can be more evenly distributed throughout the fluid, which promotes more efficient heat exchange, reduces temperature gradients, and thus improves temperature uniformity.\u003c/p\u003e "},{"header":"5 Effect of Re on pressure drop","content":"\u003cp\u003eAs the microgravity increases the pressure drop increases. As the vapor velocity increases, it carries more droplets along with it, increasing the kinetic energy of the fluid mixture. In addition, changes in temperature affect pressure. In normal gravity and microgravity environments, the temperature drop is insignificant, meaning that the thermal energy of the fluid remains relatively constant. However, an increase in vapor velocity leads to an increase in temperature, indicating that a portion of the fluid's kinetic energy is converted to thermal energy, which in turn leads to a change in pressure.\u003c/p\u003e \u003cp\u003eWhen the gravitational conditions are equal, the pressure drop increases as the steam mass decreases. The decrease in vapor mass results in a faster rate of vapor condensation and a faster rate of condensate formation, which further results in the formation of a thicker liquid film. These droplets not only occupy a certain amount of space, thereby reducing the steam flow area, but also cause turbulence and instability in the steam flow, increasing the resistance of the steam as it passes through the piping. This results in greater pressure loss in the piping. As shown in Fig.\u0026nbsp;11, the pressure drop in the channel increases with decreasing microgravity. The fluid distribution in a microgravity environment is not uniform. This inhomogeneity leads to an increase or decrease in the local flow rate, which in turn affects the pressure drop across the system. The pressure drop increases with increase in Re\u003csub\u003etp\u003c/sub\u003e as shown in Fig.\u0026nbsp;12. When Re\u003csub\u003etp\u003c/sub\u003e increases, the friction between steam and condensate increases. At the same time, the friction between the condensate and the channel wall increases. As a result, the two-phase flow pressure drop in the channel increases with increasing Re\u003csub\u003etp\u003c/sub\u003e\u003c/p\u003e \u003cp\u003eFigure\u0026nbsp;12 illustrates the relationship between pressure drop Δp and Re\u003csub\u003etp\u003c/sub\u003e for finned tube. As the Re\u003csub\u003etp\u003c/sub\u003e increases, the pressure drop Δp increases significantly. Further analysis shows that for the same Re\u003csub\u003etp\u003c/sub\u003e, the pressure drop Δp of finned tube is 20\u0026ndash;56% of that of bare tube. This range of ratios reveals that finned tubes bring higher flow resistance along with enhanced heat transfer efficiency. The fins increase the surface area of the tube, thereby increasing the contact area with the fluid, which, while contributing to the heat transfer efficiency, also increases the frictional resistance to fluid flow. This increased resistance results in a greater pressure differential to overcome as the fluid flows through the pipe, and therefore the pressure drop increases.\u003c/p\u003e"},{"header":"5 Conclusion","content":"\u003cp\u003eIn this experiment, the condensing heat transfer characteristics of steam in a rotating channel were investigated in depth using centrifugal force to simulate a microgravity environment. It aims to understand the effects of gravity, steam mass, fins, and tube diameter on the heat transfer performance, with a view to supporting the optimization of thermal management systems in space applications, and draws the following conclusions:\u003c/p\u003e \u003cp\u003e(1) The dependence of the flow pattern on steam mass increases with decreasing tube diameter. In addition, the flow is undulating in the 12-mm tube in a microgravity environment, and a continuous liquid film cannot be formed in the 10-mm tube.\u003c/p\u003e \u003cp\u003e(2) In the microgravity environment, as the vapor mass decreases, the magnitude of the temperature drop decreases gradually compared to the normal gravity condition. The uneven temperature distribution is reduced by decreasing the pipe diameter and increasing the volume flow rate of the fluid.\u003c/p\u003e \u003cp\u003e(3) Under normal and microgravity environments, the temperature average temperature of the finned tube is increased compared to the average temperature of the smooth tube. This phenomenon was particularly significant under normal gravity conditions, where the temperature inside the 12 mm tube was elevated by 9.3\u0026deg;C to 16.4\u0026deg;C, while the temperature inside the 10 mm tube was elevated by 7.0\u0026deg;C to 15.5\u0026deg;C. In addition, copper finned tubes exhibited higher temperature values compared to galvanized iron fins. The finned tube exhibits a smaller temperature drop and more uniform temperature distribution.\u003c/p\u003e \u003cp\u003e(4) Pressure drop during vapor condensation increases with decreasing gravity. The pressure drop increases with increasing Re\u003csub\u003etp\u003c/sub\u003e. Specifically, the pressure drop during steam condensation shows a clear increasing trend with the weakening of gravity conditions., the transition from a normal gravity environment to a microgravity environment. Due to the change in convective heat transfer mode under microgravity conditions, it leads to an increase in flow resistance. Higher Re\u003csub\u003etp\u003c/sub\u003e tends to be accompanied by the emergence of more complex flow structures such as turbulence, and these flow characteristics increase the friction between the fluid and the inner wall of the pipeline, which induces greater energy loss and pressure drop.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003eEthical Approval\u003c/p\u003e\n\u003cp\u003eThis article does not contain any studies with human participants and/ or animals performed by any of the authors.\u003c/p\u003e\n\u003cp\u003eInformed consent\u003c/p\u003e\n\u003cp\u003eThis article does not contain any studies with human participants and/ or animals performed by any of the authors.\u003c/p\u003e\n\u003cp\u003eCompeting interests\u003c/p\u003e\n\u003cp\u003eThe authors declare no conflict of interest.\u003c/p\u003e\n\u003cp\u003eAuthors' contributions\u003c/p\u003e\n\u003cp\u003eLeigang Zhang conducted preliminary research, designed the experimental system, monitored the experimental process, and supervised the writing of the paper. Meng Ru conducted the experiments, organized the experimental data, and wrote the main manuscript text. Yonghai Zhang guided the implementation of the experiments and monitored the experimental process. Guopei Li optimized the design of the figures and tables in the manuscript and provided improvement suggestions for the entire text. Zhenqian Chen reviewed the experimental methods and data analysis section, offering modification suggestions. Gang Chen reviewed the paper for format details and provided suggestions for revisions. Xuehong Wu was responsible for supervising the overall framework of the manuscript and revising the text. All authors reviewed the manuscript.\u003c/p\u003e\n\u003cp\u003eFunding\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe authors gratefully acknowledge the support provided by National Natural Science Foundation of China (52106116, 52106115 and 52106212), Key projects of Science and Technology of Henan Province (242102221021), Key scientific research project of Higher Education of Henan Province (22A470011).\u003c/p\u003e\n\u003cp\u003eAvailability of data and materials\u003c/p\u003e\n\u003cp\u003eData will be made available on request.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eIgor Marchuk\u0026middot;Oleg Kabov: Vapor Condensation on Curvilinear Disk-Shaped Fin at Microgravity[J]. Microgravity Sci. Technol. \u003cb\u003e20\u003c/b\u003e, 165\u0026ndash;169 (2008)\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSt\u0026eacute;phane Lips, J.P., Meyer: Effect of Gravity Forces on Heat Transfer and Pressure Drop During Condensation of R134a[J]. Microgravity Sci. Technol. \u003cb\u003e24\u003c/b\u003e, 157\u0026ndash;164 (2012)\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBai, C., Qiu, Y., Leng, X., et al.: Diverging/converging small channel for condensation heat transfer enhancement under different gravity conditions[J]. Int. Commun. Heat Mass Transfer. \u003cb\u003e116\u003c/b\u003e, 10471 (2020)\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eStefano Bortolin, G.E., Achkar, M., Kostoglou, et al.: Experimental Investigations on Condensation in the Framework of ENhanced COndensers in Microgravity (ENCOM-2) Project[J]. Microgravity Sci. Technol. \u003cb\u003e26\u003c/b\u003e, 335\u0026ndash;349 (2014)\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eRYAN M. M ACGILLIVRAY, KAMIEL S. GABRIEL. Annular Flow Film Characteristics in Variable Gravity[J]. New York Academy of Sciences, 974: 306\u0026ndash;315 (2002)\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWang Weicheng, L., Yuke, Z., Lining, et al.: Study on performance of condensation heat transfer in tubes under microgravity[J]. J. Tsinghua Univ. (Natural Sci. Edition). \u003cb\u003e2\u003c/b\u003e, 1\u0026ndash;5 (1997)\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBrendel, L.P.M., Caskey, S.L., Ewert, M.K., et al.: Vapor compression refrigeration testing on parabolic flights: Part1-cycle stability[J]. Int. J. Refrig. \u003cb\u003e136\u003c/b\u003e, 152\u0026ndash;161 (2022)\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBrendel, L., Caskey, S., Braun, J., et al.: Vapor Compression Refrigeration Testing on Parabolic Flights:Part2-Heat Exchanger Performance[J]. Int. J. Refrig. \u003cb\u003e135\u003c/b\u003e, 254\u0026ndash;260 (2022)\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eReinarts, T.R., Best, F.R., Hill, W.S.: Definition of condensation two phase flow behaviors for spacecraft design[C]. AIP Conference. Proceedings, 246(1): 1216\u0026ndash;1225 (1992)\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eReinarts, T.R., Ochterbeck, J., Lebaigue, O., et al.: A review of flow regimes,pressure drops, convective boiling, and condensation in microgravity environments[C]. In: Proceeding 31st AIAA Thermophysics Conference (1996), American Institute of Aeronautics and Astronautics. 246(1): 1216\u0026ndash;1225 (1992)\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAzzolin, M., Bortolin, S., Nguyen, L.P.L., et al.: Experimental investigation of in-tube condensation in microgravity[J]. Int. Commun. Heat Mass Transfer. \u003cb\u003e96\u003c/b\u003e, 69\u0026ndash;79 (2018)\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLee, H., Park, I., Konishi, C., et al.: Experimental Investigation of Flow Condensation in Microgravity[J]. J. Heat Transfer. \u003cb\u003e136\u003c/b\u003e(2), 021502 (2014)\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLee, H., Mudawar, I., Hasan, M.M.: Experimental and theoretical investigation of annular flow condensation in microgravity[J]. Int. J. Heat Mass Transf. \u003cb\u003e61\u003c/b\u003e, 293\u0026ndash;309 (2013)\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBerto, A., Azzolin, M., Lavieille, P., et al.: Experimental investigation of liquid film thickness and heat transfer during condensation in microgravity[J]. Int. J. Heat Mass Transf. \u003cb\u003e199\u003c/b\u003e, 123467 (2022)\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003ePrasenjit Dey, D., Raj, S.K.: Saha. A Numerical Study on Condensation Heat Transfer Characteristics of R134a in Microchannel Under Varying Gravity Conditions[J]. Microgravity Sci. Technol. \u003cb\u003e33\u003c/b\u003e, 34 (2021)\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eZhang, J., Li, W., Minkowycz, W.J.: Numerical simulation of condensation for R410A at varying saturation temperatures in mini/micro tubes. Int. J. Comput. Methodology[J] Int. J. Comput. Methodol. \u003cb\u003e69\u003c/b\u003e(5), 464\u0026ndash;478 (2016)\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eNarcy, M., Colin, C.: Two-Phase Pipe Flow in Microgravity with and without Phase Change: recent progress and future prospects[J]. Interfacial Phenom. Heat. Transf. \u003cb\u003e3\u003c/b\u003e(1), 1\u0026ndash;17 (2015)\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMacgillivray, R.M., Gabriel, K.S.: A study of annular flow film characteristics in microgravity and hypergravity conditions[J]. Acta Astronaut. \u003cb\u003e53\u003c/b\u003e(4/10), 289\u0026ndash;297 (2003)\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eChoi, B., Fujii, T., Asano, H., et al.: A Study of the Flow Characteristics in Air-Water Two-Phase Flow under Microgravity (Results of Flight Experiments)[J]. JSME Int. J. Ser. B Fluids Therm. Eng. \u003cb\u003e46\u003c/b\u003e, 262\u0026ndash;269 (2003)\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWang, Z.L., Gabriel, K.S., Zhu, Z.F.: The effects of gravity on the features of the interfacial waves in annular two-phase flow[J]. Microgravity Sci. Technol. \u003cb\u003e15\u003c/b\u003e(3), 19\u0026ndash;27 (2004)\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eHan, H., Gabriel, K.S.: The influence of flow pressure gradient on interfacial wave properties in annular two-phase flow at microgravity and normal gravity conditions[J]. Fluid Dynamics Mater. Process. \u003cb\u003e2\u003c/b\u003e, 287\u0026ndash;295 (2006)\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eCavallini, A., Censi, G., Del Col, D., et al.: Condensation in horizontal smooth tubes: a new heat transfer model for heat exchanger design[J]. Heat Transfer Eng. \u003cb\u003e27\u003c/b\u003e, 31\u0026ndash;38 (2006)\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eCavallini, A., Del Col, D., Doretti, L., Rossetto, C., Zilio, et al.: Condensation heat transfer and pressure gradient inside multiport minichannels[J]. Heat Transfer Eng. \u003cb\u003e26\u003c/b\u003e(3), 45\u0026ndash;55 (2005)\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"microgravity-science-and-technology","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"mgst","sideBox":"Learn more about [Microgravity Science and Technology](http://link.springer.com/journal/12215)","snPcode":"12217","submissionUrl":"https://submission.nature.com/new-submission/12217/3","title":"Microgravity Science and Technology","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"centrifugal force, condensation, flow pattern, gravity","lastPublishedDoi":"10.21203/rs.3.rs-5175333/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-5175333/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eIn this study, fluid flow during condensation in a tube under different gravity conditions is simulated by utilizing centrifugal force to offset gravitational effects. The role of fins, tube diameter, and vapor mass on the two-phase flow pattern, temperature distribution, and pressure drop is investigated. The results show that gravity, pipe diameter, and steam quality have a significant effect on the flow pattern. The flow characteristics were also significantly affected by the operating parameters, with undulating and laminar flow dominating, while bubbling flow emerges under specific conditions. In microgravity environments, as vapor mass decreases, the temperature drop diminishes progressively compared to normal gravity conditions. Under normal gravity and low flow conditions, the average temperature of finned tubes increased by 7\u0026deg;C to 16.4\u0026deg;C relative to bare tube temperatures, and the pressure drop escalated by up to 56%. The introduction of fins notably enhanced heat transfer efficiency and facilitated a more uniform temperature distribution. However, this enhancement in heat transfer was accompanied by an increase in pressure drop due to the heightened resistance to fluid flow caused by the presence of fins. These experimental insights offer a deeper comprehension of fluid behavior under diverse gravity conditions and lay a scientific foundation for designing future thermal management systems.\u003c/p\u003e","manuscriptTitle":"Experimental study of condensation heat transfer in tubes under centrifugal force","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-12-12 08:30:18","doi":"10.21203/rs.3.rs-5175333/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2024-12-03T07:21:48+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2024-12-02T16:01:37+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2024-11-30T09:35:06+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"132392154108739378142424529081099765536","date":"2024-11-12T10:07:27+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"52633508196393879297984990081718346490","date":"2024-11-11T09:27:06+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2024-10-06T08:04:52+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2024-09-30T04:35:12+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2024-09-30T04:33:39+00:00","index":"","fulltext":""},{"type":"submitted","content":"Microgravity Science and Technology","date":"2024-09-29T13:55:16+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"microgravity-science-and-technology","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"mgst","sideBox":"Learn more about [Microgravity Science and Technology](http://link.springer.com/journal/12215)","snPcode":"12217","submissionUrl":"https://submission.nature.com/new-submission/12217/3","title":"Microgravity Science and Technology","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"83e5a60e-8549-41a6-895d-44d232327347","owner":[],"postedDate":"December 12th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2025-01-13T16:07:54+00:00","versionOfRecord":{"articleIdentity":"rs-5175333","link":"https://doi.org/10.1007/s12217-024-10159-z","journal":{"identity":"microgravity-science-and-technology","isVorOnly":false,"title":"Microgravity Science and Technology"},"publishedOn":"2025-01-06 15:58:00","publishedOnDateReadable":"January 6th, 2025"},"versionCreatedAt":"2024-12-12 08:30:18","video":"","vorDoi":"10.1007/s12217-024-10159-z","vorDoiUrl":"https://doi.org/10.1007/s12217-024-10159-z","workflowStages":[]},"version":"v1","identity":"rs-5175333","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-5175333","identity":"rs-5175333","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}