Condensation Heat Transfer Process Research Articles

Fundamental research on the condensation heat transfer of the hydrocarbon-mixture energy in a spiral tube described by a universal model using flow pattern based and general modes

The transportation of liquefied natural gas (LNG) is a crucial aspect of global energy application and security. However, there are still some challenges in liquefaction. This study establishes systematic experiments to investigate the condensation two-phase flow and heat transfer process of hydrocarbon-mixture energy (methane/ethane/propane/isobutane) in a spiral tube. The main influencing parameters, including mass flux (200–560 kg/(m2·s)), operating pressure (2–4 MPa), and vapor quality (0–1) on the heat transfer intensity and frictional pressure drop were analyzed. Different two-phase flow patterns were observed and categorized them as bubble flow, intermittent flow, stratified-wavy flow, and annular flow. For bubble flow and intermittent flow, vapor quality is found to remarkably affect the heat transfer; regarding stratified-wavy flow and annular flow, gravitational force and inertia force are found to prominently influence the heat transfer, respectively. Additionally, a newly universal model includes split flow patterns mode (SFPM) and the general mode (GM) has been proposed, which is with high-precision for describing the condensation heat transfer coefficients of different flow patterns. Furthermore, the analytical results show the SFPM's root mean square error and mean absolute relative deviation are 97.35 W/(m2·K) and 0.036.

Experimental investigation of thermoelectric system with condensation heat transfer process

The objective of this study was to investigate the impact of vapor temperature, mass flow rate, concentration and turbulating insert on the performance of a thermoelectric generator/module (TEG/TEM) system. The researchers conducted experiments using a thermoelectric setup comprising 32 TEGs. Various experimental conditions were explored, including the electric connection type of the TEGs, inlet saturation steam temperature ranging from 70 °C to 100 °C, steam mass flow rate ranging from 4 kg/h to 16 kg/h, two different types of turbulators (Twisted Tape and Rod), and vapor gas concentration of 1 % to 3 %. The results of the study revealed several key findings. Firstly, the peak power output of the system increased with higher inlet steam temperatures. However, the power output was found to be nearly independent of the mass flow rate and the type of turbulator under the current experimental conditions. Among the different types of TEG module connections, connecting all TEG modules in series yielded the best performance compared to other connection types. Furthermore, the study found that TEMs positioned at different locations within the system produced approximately the same power output due to the high condensation heat transfer coefficient. This was supported by the power uniformity coefficient, which approached unity. Regarding the effect of vapor concentration, the presence of Marangoni effect led to an enhancement in harvested energy by 8 % when the gas phase vapor of the ethanol–water mixture was 1 %. Finally, the highest net efficiency of 1.64 % was achieved at a temperature of 100 °C and a vapor concentration of 1 %.

Modeling analysis of non-azeotropic and immiscible binary mixed vapors condensation under natural convection

A calculation model describing the condensation heat and mass transfer process of non-azeotropic immiscible binary mixed vapors on the vertical wall under natural convection conditions was developed in this study. The model includes the two possible condensation modes of mixed vapors on the vertical wall as well as the conversion conditions between them. Cyclohexane and water were used as non-azeotropic immiscible mixtures. The reliability of the model was verified first, then the influence of vapor mass concentration and wall subcooling on the condensation mode and heat and mass transfer of the mixed vapors were analyzed. The results showed that the maximum deviation between the model results and the experimental results was less than 21%, confirming that the model was reliable. When the mixed vapors mass concentration was nearly eutectic or the wall subcooling was large, the condensation Mode B (Co-condensation) was more likely to occur than Mode A (Single condensation) due to the decrease in vapor-liquid interface temperature. The condensation mode may change from B to A as the wall length increased along the gravity direction of the condensation wall, and the condensation heat transfer coefficient and mass flux decreased. The thermal resistance of the vapor and liquid phases during condensation was also calculated. In Mode A, regulation of the thermal resistance of the vapor-liquid two phases can be achieved by adjusting the vertical length of the condensation wall and the vapor mass concentration. Condensation Mode B can only be realized by adjusting the wall subcooling. The results of this work may provide a workable reference for condensation heat transfer and enhancement of non-azeotropic immiscible mixed vapors in industrial environments.

Phase Change and Heat Transfer Analysis of Different Refrigerants During Condensation in Minichannel Using a Novel Numerical Approach

Abstract This paper analyses the condensation heat transfer phenomena in minichannel using acetone, ammonia, propylene, and R134a as the working fluids used in new-age space applications. A novel numerical model is developed considering the changes in local vapor pressure in the channel established due to shrinking in the flow passage by the gradual formation of the liquid layer. The present developed numerical model is compared with the available numerical and experimental results. The impacts of different inlet mass fluxes (250, 500, and 750 kg/m2 s), channel heights (1, 4, 6, and 8 mm), applied heat loads (10, 100, 250, and 500 W), and channel orientations (0 deg, 30 deg, 45 deg, 60 deg, and 90 deg) on the performance of the condensation heat transfer process are investigated. The formation of the thin liquid film layers and evaluation of the liquid–vapor interface profiles are examined. The study reveals that the channel orientation has a marginal influence on the flow pattern for the considered channel length of 20 mm. The maximum change in pressure loss is found at the channel orientation of 45 deg, and the average heat transfer coefficient is almost the same for all the considered orientations. The flow pattern is affected by the increase in mass flux resulting in the delay of heat transfer coefficient fluctuations. The average heat transfer coefficient decreases with increasing heat load, and the minimum average heat transfer coefficient is obtained for heat load, Q = 500 W.

Experimental study of steam-air mixture thermal stratification during the dropping of containment pressure

The passive containment cooling system (PCCS) as a passive technology has been applied in Generation Ⅲ nuclear power plants. Experiments were conducted in a scale model to analyze the thermal stratification in containment during the containment pressure dropping. Results indicate that the obvious thermal stratification occurs in the containment during the transient-state heat transfer process but not during the steady-state heat transfer process. For the transient-state process, the steam-air mixture temperature increases by 2 °C for each 100 mm increase in the elevation direction of the pressure tank. The nonuniform distribution of air in containment causes thermal stratification, which is more pronounced for lower air mass fraction and higher initial containment pressure. The thermal stratification effect on the condensation heat transfer process is assessed via diffusion layer heat transfer and film heat transfer to evaluate its effect. The diffusion layer heat transfer coefficient (HTC) is strongly affected by thermal stratification, whereas no effect is observed on the film HTC. This leads to the total condensation HTC at the top of the heat exchanger is approximately 3–5 times than that at the bottom in the first 100 s of the containment pressure dropping process. To improve the overall heat transfer performance of PCCS, approaches that enhance the heat transfer capacity at the bottom of the heat exchanger should be considered for prioritization, especially the methods of steam diffusion heat transfer capacity.

Experimental analysis of condensation of zeotropic mixtures from 70 °C to 90 °C in a plate heat exchanger

High temperature condensation is relevant for the heat pump system used for the district heating and the organic Rankine cycle system used for combined heat and power generation. By using a zeotropic mixture as working fluid in such systems, it is possible to achieve a higher system efficiency compared with those of pure fluids. Only two previous studies addressing zeotropic mixture high temperature condensation in plate heat exchangers are available in the open literature, and these studies considered ethanol/water mixtures. The current works present an experimental analysis of high temperature condensation of zeotropic mixtures in a plate heat exchanger. We analyzed the condensation of the hydrofluoroolefin mixture R1234ze(E)/R1233zd(E) and the hydrofluorocarbon mixture R134a/R245fa with different mass compositions at various condensation temperatures and mass fluxes. Based on the experimental results, we analyzed the temperature effects on the condensation heat transfer and identified a convective-dominated condensation heat transfer process. Furthermore, the results suggest that the mixture R1234ze(E)/R1233zd(E) has the up to 8.5% and 4.4% higher heat transfer coefficient and frictional pressure drop, respectively, than the R134a/R245fa mixture. A modified Silver-Bell-Ghaly model predicted the heat transfer data with a 7.1% mean absolute percentage deviation between the predicted and experimental results, and a new pressure drop correlation developed using the mixture test data predicted the pressure drop results with a 6.2% mean absolute percentage deviation.

CONDENSATION PHASE CHANGE BEHAVIORS ON A ROUGH SURFACE CHARACTERIZED BY FRACTAL CANTOR

Understanding the fundamental mechanisms of vapor condensation on rough surfaces is crucial to a wide range of industrial applications. A hybrid thermal lattice Boltzmann model of the condensation heat transfer process on downward-facing rough surfaces characterized by the Cantor fractal is developed and numerically analyzed to investigate the condensation phase change behaviors on rough hydrophobic and hydrophilic surfaces. The dynamic behaviors of vapor condensation, including the evolutions of vapor–liquid interface, heat flux, condensate mass, and temperature distribution, on the hydrophilic and hydrophobic rough surfaces are presented and compared with corresponding smooth surfaces. The results indicate that the rough surface preferred a filmwise condensation under hydrophilic conditions but a hybrid dropwise–filmwise condensation under hydrophobic conditions. On the rough hydrophobic surface, the liquid film can rapidly adsorb droplets, maintaining a high-efficiency dropwise condensation. The absorption of droplets accelerates the liquid film growth and detachment process on the rough hydrophobic surface, which reduces the time-averaged thermal resistance of the filmwise region. These two behaviors together enhance condensation heat transfer on the downward-facing rough hydrophobic surface. Besides, stable dropwise condensation could also be formed on smooth hydrophilic surfaces and has better heat transfer performance than corresponding hydrophobic surfaces under the same heat transfer condition.

Numerical Study on the Heat Transfer Characteristics of Axially Grooved Heat Pipe Assisted by Gravity

The theoretical model of the evaporation and condensation heat transfer process of the axially grooved heat pipe (AGHP) assisted by gravity under small angle inclination is established to investigate the evaporation regimes and the heat transfer characteristics of AGHP. To reveal the heat transfer mechanism of the AGHP, the working state and gas-liquid interface distribution of the AGHP with different input power are analysed. And the influence of the inclination angle and groove structure (length-width ratio), including on the maximum heat transfer of AGHP is also discussed. The numerical simulations indicate that: With the increasing input power, the fin-film evaporation regime transits to the corner-film evaporation regime in the AGHP. The growing inclination angle enhances the gravitational effect on the liquid reflux and increases the critical input power for the evaporation regime transition. As the aspect ratio of the grooves increase, the increasing maximum radius of the meniscus leads to stronger heat transfer capacity of the AGHP.

Heat transfer characteristics of in-tube steam condensation process under stratified flow

For stratified flow condensation process, the heat transfer mechanisms in the film condensation zone above the vapour-liquid interface and the condensate zone below the interface shows significant differences. In the multi-effect evaporation device, due to the high sensitivity of the thermal performance to the variation of the heat transfer parameters, the heat transfer parameters distributions in the film condensation zone and in the condensate zone are worth exploring. In this paper, a validated distributed parameter model was established to simulate the heat transfer and flow process in a single tube of the falling film evaporator. The variation of the heat flux in the condensate zone was presented under various operating conditions. The concept of the effective tube length and the partition map of the in-tube condensation heat transfer process were proposed for the better understanding of the flow and heat transfer process. Results show that the heat transfer in the condensate zone to the total heat transfer can accounts for more than 10% of the total heat transfer, thus cannot be neglected. For the design of falling film evaporator, the condensation heat transfer process in the tube should be located in the high-efficiency heat transfer section. The steam mass flow rate, heat transfer temperature difference and the length of the heat transfer tube should matched to each other to guarantee the condensation heat transfer process be located in the high-efficiency heat transfer zone.

Experimental study of condensation heat-transfer and water-recovery process in a micro-porous ceramic membrane tube bundle

Micro-porous ceramic membrane tube is a new type of condensation material which can synchronously recover both water vapor and its accompanied latent heat from exhausted flue gas. The recovery outcome is helpful to reduce amount of make-up water and enhance boiler efficiency of thermal power plant. In this study, an experiment has been carried out to investigate condensation heat-transfer, water-recovery, and flow-resistance performance of micro-porous ceramic membrane tube bundle (CMTB), respectively. In addition, real exhausted flue gas with inlet flow rate ranging from 390 to 750 m3/h, temperature ranging from 323 K to 373 K was used as experimental feed gas. Results showed that the condensation heat-transfer process got more apparently with increasing of flue gas inlet temperature (from 335.3 K to 364.8 K). In addition, both cooling water flow rate and heat-transfer temperature difference had a remarkable influence on the water-recovery performance of the CMTB, and maximal water-recovery mass flow rate could reach 0.0336 × 103 kg/h. Most of all, velocity drop of flue gas was controlled within an appropriate range (from 28.94 m3/h to 178.78 m3/h). The application analysis on the CMTB gives a good perspective for designing high efficiency membrane-type condenser to recover water vapor from exhausted flue gas and make good use of its latent heat in the thermodynamic system of power plant.

Heat and water recovery from flue gas: Application of micro-porous ceramic membrane tube bundles in gas-fired power plant

Heat and water trans-membrane condenser (HWTMC) consisted of ceramic membrane tube bundles and cooling pathway is a functional apparatus to recover heat and water from flue gas in thermal power plants. In this study, the water and heat-recovery performance of 2 μm HWTMC on a gas-fired power plant was studied theoretically and experimentally. The simultaneous drop-wise/film-wise condensation heat transfer process was proposed in this study, and we investigated them by installing several temperature sensors within the HWTMC. In addition, the heat and water-recovery performance of HWTMC was evaluated respectively under different operational conditions, and the velocity loss of flue gas was also measured to verify its practicability. The experimental results showed that flue gas temperatures change significantly in the first 2/3 of the HWTMC unit, while barely change at end, especially when they are higher than 103.5°C. Compared with other operational conditions, moreover, a moderate cooling water inlet flow rate (0.3 m3/h) would result in a remarkable heat and water-recovery performance. To guarantee the efficiency of the experimental HWTMC with total membrane area of 0.145 m2, flue gas flow rate should be set under 500 m3/h. This paper is useful for membrane type waste heat and water-recovery installation design.

Condensation heat transfer characteristics of the alkali metal thermal to electric converter (AMTEC) porous wick condenser

An axisymmetric 2-D mathematical model was established and the volume of fluid +method was adopted to numerically investigate the condensation heat transfer process of alkali metal in the alkali metal thermal to electric converter (AMTEC) porous wick condenser. The steady-state physical fields of working medium were obtained and the impacts of some relevant parameters including geometrical and operational parameters on condensation heat transfer characteristics were discussed. The results show that the thickness of the liquid sodium increases along the radial direction. The temperature distribution in liquid phase is approximately linear. The condensation rate at the phasechange interface decreases along the radial direction, and the cold end heat flux, q, increases initially and then decreases along the radial direction. The porous wick condenser has very limited self-adaptive ability once the mass flow rate, M , exceeds in some critical value. In addition, there is a corresponding T for a certain M to ensure the w in stable phase-change interface. The performance of AMTEC can be enhanced by reducing the distance between artery and cell wall.

Simulation and experimental studies of R134a flow condensation characteristics in a pump-assisted separate heat pipe

We combine experimental research and numerical simulations to investigate the complex and unknown flow condensation heat transfer process in a pump-assisted separate heat pipe (PASHP) employing R134a. The Chen model and Müller-Steinhagen-Heck model coincide with the experimental pressure drop and heat transfer, respectively, after comparing three correlations of the pressure drop and four correlations of the heat transfer. After analysing the establishment and selection of a model to simulate the flow condensation characteristics in a PASHP, we conclude that the turbulence model, multiphase flow model, and heat and mass transfer model can be described using the SST k-ω model, VOF model, and Lee model, respectively. The phase transformation factor r = 3000, the simulation results and the Chen correlation are all consistent. The pressure drop and heat transfer coefficient increases with increasing mass flow and vapour quality. The simulation results of the pressure drop and heat transfer coefficient are compared with those of the Chen and Muller-Steinhagen-Heck correlations, respectively, showing satisfactory agreement between the simulated and the calculated values. This research provides a theoretical reference for the selection of the pump, design of the heat exchanger, optimization of the system and study of two-phase flow.

Numerical analysis of shell-side thermo-hydraulic performances of submerged combustion vaporizer

Submerged combustion vaporizer belongs to one of the frequently-used and high efficient heat exchanger in the LNG industry chain. In this paper, in order to have a more profound understanding of shell-side thermo-hydraulic performances of submerged combustion vaporizer, an integrated thermal model is built to investigate the direct-contact flue gas and water mixture sweeping across the stagger tube bundle, with the condensation process of superheated water vapor presence. The accuracy of numerical model and method is validated by the experimental test data. On this basis, the unique flow and heat transfer mechanism is firstly analyzed, then variations of the gas hold-up, heat transfer and pressure drop performances with the common operational parameters are systematically studied. Significant results demonstrate that the efficient direct-contact condensation heat transfer process occurs between highly turbulent gas-liquid two-phase flow and tube bundle wall. The distinct and interesting circulating water forms due to the existence of weir, which helps to reduce the fluid boundary layer and strengthens the heat transfer. The water bath efficiently absorbs the sensible heat and latent heat carried by flue gas so that the outlet flue gas temperature almost equals to the water bath temperature. When the gas hold-up is within the scope of 25–45%, the shell-side convective heat transfer ability is obviously enhanced. Finally, in view of the numerical results, a new dimensionless pressure drop correlation and Han model are suggested for the optimum design of submerged combustion vaporizer.

Experimental Study on R245fa Condensation Heat Transfer Properties in Horizontal Tube

Abstract The condenser is widely used in the field of HVAC&R, thermal energy and petrochemical engineering. The improvement of heat transfer efficiency can lead to the overall system energy efficiency increase, so the operating cost is reduced. This study focuses on condensation heat transfer process of R245fa with 4.38 mm horizontal tube. It is shown from test results that the changing rate of heat transfer coefficient for R245fa is normally same in the different condensation temperature. The peak of heat transfer coefficient exists with the quality increasing at the large mass flow condition. And heat transfer coefficient increases with quality increasing at small mass flow conditions. High efficiency of condenser can be designed by the experiment results. In addition, the enhancement of the heat transfer can also reduce the required heat transfer area. And consequently, the initial cost is decreasing.

Dropwise condensation heat transfer process optimisation on superhydrophobic surfaces using a multi-disciplinary approach

Dropwise condensation has superior heat transfer efficiency than filmwise condensation; however condensate evacuation from the surface still remains a significant technological challenge. The process of droplets jumping, against adhesive forces, from a solid surface upon coalescence has been studied using both experimental and Computational Fluid Dynamics (CFD) analysis. Both Lattice Boltzmann (LBM) and Volume of Fluid (VOF) methods have been used to evaluate different kinematic conditions of coalescence inducing a jump velocity. In this paper, an optimisation framework for superhydrophobic surface designs is presented which uses experimentally verified high fidelity CFD analyses to identify optimal combinations of design features which maximise desirable characteristics such as the vertical velocity of the merged jumping droplet from the surface and energy efficiency. A Radial Basis Function (RBF)-based surrogate modelling approach using Design of Experiment (DOE) technique was used to establish near-optimal initial process parameters around which to focus the study. This multidisciplinary approach allows us to evaluate the jumping phenomenon for superhydrophobic surfaces for which several input parameters may be varied, so as to improve the heat transfer exchange rate on the surface during condensation. Reliable conditions were found to occur for droplets within initial radius range of r=20–40μm and static contact angle θs∼160°. Moreover, the jumping phenomenon was observed for droplets with initial radius of up to 500μm. Lastly, our study also reveals that a critical contact angle for droplets to jump upon coalescence is θc∼140°.

An experimental investigation of pure steam and steam–air mixtures condensation outside a vertical pin-fin tube

A set of condensation experiments in the steam–air and pure steam conditions has been conducted to evaluate the heat removal capacity of a vertically pin-fin tube under free convection. Condensation heat transfer coefficient and heat transfer rate have been obtained. The bulk temperature, wall temperature and temperature near tube surface are measured in detail. As a reference, a smooth tube is tested under the same condition. For pure steam case, the pin-fin tube generates restrictions on the condensation heat transfer process in low wall subcooling region. With a higher wall subcooling, the pin-fin tube shows a larger condensation heat transfer coefficient than smooth tube does. For steam–air mixtures case, the result of the temperature measurement demonstrates that there is an air rich region near the pin-fin tube. Compared with the smooth tube, the pin-fin tube generates reduction effect on the condensation heat transfer process under low air mass fraction situation. As air mass fraction increasing, the condensation heat transfer coefficient of the pin-fin tube becomes larger than that of the smooth tube.

Experimental study of steam–air condensation over a vertically longitudinal finned tube

A set of condensation experiments in the pure steam and steam–air conditions have been conducted to evaluate the heat removal capacity of a vertically longitudinal finned tube in natural convection situation. The bulk temperature, wall temperature and temperature near the tube wall were measured in detail. The result of the temperature measurement demonstrated that there was an air rich region near the longitudinal finned tube while gas stratification phenomenon was not found in the mainstream. Condensation heat transfer coefficient and heat transfer rate have been obtained for air mass fraction ranging from 0.07 to 0.95, total pressure ranging from 0.2MPa to 0.7MPa. A smooth tube was also tested under the same condition as a reference. At pure steam case, the longitudinal finned tube played a positive effect on the condensation heat transfer, showing a growth of the condensation heat transfer coefficient by a factor of 3.86–4.89. At the steam–air case, the longitudinal finned tube generated restrictions on the condensation heat transfer process when air mass fraction was below 75%. However, the longitudinal finned tube enhanced the heat transfer process for the air mass fraction in excess of 75%.

A Study on Gas–Liquid Film Thicknesses and Heat Transfer Characteristics of Vapor–Gas Condensation Outside a Horizontal Tube

Noncondensable gases deteriorate heat transfer in the condensation process. It is therefore necessary to study vapor–gas condensation heat transfer process and analyze main factors influencing the process. Based on the double-film theory and the Prandtl boundary layer theory, this investigation developed a mathematical model of gas–liquid film thicknesses and local heat transfer coefficient for studying laminar film condensation in the presence of noncondensable gas over a horizontal tube. Induced velocity in the gas film, gas–liquid interfacial shear stress, and pressure gradient were considered in the study. Importantly, gas–liquid film separations were analyzed in depth in this paper. It obtained the distributions of gas–liquid film thicknesses, local heat transfer coefficient, condensate mass flux, and gas–liquid interfacial temperature along the tube surface, and analyzed the influences of bulk velocity, total pressure, bulk mass concentration of noncondensable gas and wall temperature on them, providing a theoretical guidance for understanding and enhancing vapor–gas condensation heat transfer. Gas film thickness and gas–liquid film separations have certain effects on vapor–gas condensation heat transfer. The average dimensionless heat transfer coefficients are in agreement with the data from related literatures.

Experimental and numerical studies on actual flue gas condensation heat transfer in a left–right symmetric internally finned tube

To improve the thermal efficiency of gas fired equipment, latent heat recovery from the flue gas is a very important concept. Based on the analysis of heat transfer enhancement mechanism in an internally finned tube, in this paper, a new type left–right symmetric internally finned tube is proposed. The heat transfer characteristics of the new type left–right symmetric internally finned tube, the centrosymmetric finned tube and the smooth tube is numerically and experimentally investigated. The numerical simulation results indicate that the left–right symmetric internally finned tube has a promising potential for enhancing the convection heat transfer, in particular, its heat transfer coefficient is 4–8 times higher than that of the reference smooth tube and 1.3–1.8 times higher than that of the centrosymmetric finned tube. The experimental results show that the excess air coefficient, the cooling water flow rate, the water inlet temperature, and the Re number have prominent effects on the convection-condensation heat transfer. The left–right symmetric internally finned tube can effectively decrease the radial temperature gradient, reduce the thickness of the non-condensable gas layer and significantly strengthen the water vapor condensation. The convection-condensation heat transfer coefficient of 10 fins left–right symmetric internally finned tube is about 4.1 times higher than that of the forced convection without condensation. A dimensionless number Tv is derived, which takes into account the effects of the water vapor saturation temperature, the average flue gas temperature, the average internal wall temperature and the inlet water temperature. They are represented in an empirical formula for the condensation heat transfer process.