Condensation Heat Transfer Coefficient Research Articles

Pushing the Limit of Beetle‐Inspired Condensation on Biphilic Quasi‐Liquid Surfaces

AbstractMassive studies concern the development of low‐carbon water and energy systems. Specifically, surfaces with special wettability to promote vapor‐to‐liquid condensation have been widely studied, but current solutions suffer from poor heat transfer performances due to inefficient droplet removal. In this study, the limit of condensation on a beetle‐inspired biphilic quasi‐liquid surface (QLS) in a steam environment is pushed, which provides a heat flux 100 times higher than that in atmospheric condensation. Unlike the beetle‐inspired surfaces that have sticky hydrophilic domains, the biphilic QLS consists of PEGylated and siloxane polymers as hydrophilic and hydrophobic quasi‐liquid patterns with the contact angle hysteresis of 3° and 1°, respectively. More importantly, each hydrophilic slippery pattern behaves like a slippery bridge that accelerates droplet coalescence and removal. As a result, the condensed droplets grow rapidly and shed off. It is demonstrated that the biphilic‐striped QLS shows a 60% higher water harvesting rate in atmospheric condensation and a 170% higher heat transfer coefficient in steam condensation than the conventional beetle‐inspired surface. This study provides a new paradigm to push the limit of condensation heat transfer at a high heat flux, which sheds light on the next‐generation surface design for water and energy sustainability.

Study on heat transfer characteristics of flue gas condensation in narrow gap heat exchangers

Flue gas after wet desulfurization contains a large quantity of water vapor, as well as a small amount of fine particulate matter, acid and other pollutants. Direct emissions will cause haze and environmental pollution. Flue gas condenser can effectively recover latent heat of vaporization and remove these pollutants. However, the traditional flue gas condenser has disadvantages such as large volume, low heat exchange efficiency and easy blockage. To overcome these problems, a new type narrow gap heat exchanger, which is easy to detach and clean, is proposed. Then, the flue gas condensation characteristic is experimentally investigated. The factors including velocity and temperature of flue gas, flow and temperature of cooling water are studied on heat transfer coefficient and the condensation rate. The results indicate that the overall heat transfer coefficient is seven times of convection heat transfer coefficient, and the condensation rate can reach more than 60%. As the cooling water temperature increases, the condensation rate and condensation heat transfer coefficient gradually decrease. With the increasing of the flue gas velocity, condensation rate gradually decreases and condensation heat transfer coefficient gradually increases. Finally, the dimensionless correlation of Nusselt number is carried out, and the error is within 10%.

Novel solid-infused durable nonwetting surfaces for sustained condensation heat transfer enhancement

• Presents novel nonwetting solid-infused surfaces for condensation enhancement. • Solid-infused surfaces demonstrate four-fold larger condensation heat transfer. • Solid-infused surfaces are durable than conventional nonwetting surface. • Solid-infused surfaces overcome the challenges of conventional nonwetting surfaces. In this article, we report novel nonwetting solid-infused surfaces that are easily fabricated using industrially widely adopted methods such as chemical etching or electrodeposition and demonstrate sustained dropwise condensation performance durably than superhydrophobic and lubricant-infused surfaces. Solid-infused surfaces demonstrate four-fold larger condensation heat transfer coefficient and 25% better condensation effectiveness when compared to superhydrophobic surface and conventional filmwise condensation. Although the condensation heat transfer coefficient of lubricant-infused surface initially matches that of solid-infused surface, it is shown through durability studies that the wettability characteristic that underpins the performance of lubricant-infused surfaces degrades quickly with time as the lubricant depletes and lubricant-infused surface transitions to superhydrophobic surface. Solid-infused surface, on the other hand, retains its steadfast superior dropwise condensation effectiveness in the long run, overcoming the challenges of droplet pinning, surface inundation, cloaking, and lubricant depletion that eventually deteriorate condensation on conventional nonwetting superhydrophobic and lubricant-infused surfaces.

Synergistic effect of helically-finned directional tracks and lubricant viscosity on droplet dynamics and condensation heat transfer of bioinspired slippery surfaces

Slippery lubricant-infused porous surfaces (SLIPSs) have been presented herein, developed on helically-fined grooves of copper tubes (HF-SLIPSs). The high viscosity lubricant (GPL 107) has been employed which is firmly locked by the nano-pores of oxidized layer fabricated on helically-finned grooves. The influences of synergistic cooperation of helically-finned grooves and infused lubricant on the condensed droplet dynamics and heat transfer are systematically investigated. Findings demonstrate that HF-SLIPSs not only improve the droplet mobility but also expand the condensing area and provide directional transport tracks where small-sized droplets quickly coalesce on fin surface and slide orderly along the helical grooves, resulting in short renewal time period of 2.99 s. Moreover, the condensation heat transfer on HF-SLIPSs(GPL 107) is better than other test tubes, and condensation heat transfer coefficients are 35.8% and 55.9% higher than that of smooth SLIPSs tubes impregnated with GPL 103 and GPL 107, respectively, and 98.1% and 204.4% higher comparing with smooth hydrophilic and helically-finned hydrophilic tubes, respectively. This indicates that the synergistic cooperation of high viscosity lubricant and helically-finned grooves plays a great role by providing certain directional and stable SLIPSs tracks where droplets are guided and transported faster which ensure the enhanced condensation heat transfer.

Experimental study on condensation heat transfer and pressure drop characteristics of R32 flowing inside an alternating cross-section flattened tube

This work presents the experimental study of two-phase flow inside an alternating cross-section flattened (ACF) tube. The ACF tube was made from a copper circular tube with an inner diameter of 4.31 mm. We conducted the test under the following experimental conditions: a mass flux of 280, 430, and 580 kg/m2s; a saturation temperature of 40, 45, and 50 °C; a heat flux of 10, 15, and 20 kW/m2; and an average vapor quality of 0.1–0.8. Compared to the existing flow pattern maps, most fell into the annular and semi-annular flow regimes. However, the results were found in the transition and intermittent flow regions at low vapor quality. The results from the circular and ACF tubes were examined and discussed. We found that the ACF tube revealed a prominent condensation heat transfer coefficient and a reasonable pressure loss penalty. The heat transfer coefficient and frictional pressure drop of the ACF tube were higher than that of the circular tube by approximately 25.6–111.1% and 4.3–39.9%, respectively. New correlations for the Nusselt number and two-phase friction factor were proposed.

Microgravity two-phase flow research in the context of vapor compression cycle experiments on parabolic flights

Research on two-phase channel flow in microgravity has extensively investigated flow regimes, pressure drop, and heat transfer during evaporation and condensation processes over several decades. This literature has been primarily motivated by the goal of enabling future space applications for two-phase thermal management systems, among them vapor compression refrigeration cycles. However, relative to the number of two-phase channel flow experiments, research on vapor compression cycles in microgravity has been almost non-existent. This paper reviews two-phase flow research and compares key outcomes with those from system-level measurements obtained from recent testing of a vapor compression cycle at varying inclination angles and on parabolic flights. Previous two-phase channel flow experiments have resulted in several microgravity-specific flow regime maps and have also generally found reduced condensation heat transfer coefficients in microgravity as compared to normal gravity. The flow pattern map of Jayawardena et al. (1997) and generally reduced condensation heat transfer are confirmed by the vapor compression cycle experiments. Regarding evaporation heat transfer coefficients and friction factors, there is not a consensus in the literature on the effects of microgravity in two-phase channel flows. Similarly, the system-level experiments do not show repeatable increases or decreases for those parameters. Lastly, the dependence of system-level behavior on orientation with respect to gravity was tested by performing dynamic inclination experiments, where the inclination angle was changed every 2 min by a 90-degree increment. These tests reveal an increased relative dependence of the vapor compression cycle to orientation with decreasing mass fluxes, in line with two-phase channel flow research that has generally shown that increasing the flow inertia acts to mitigate various flow instabilities and dependence on orientation. However, inclination testing with longer locking times per angle showed a constant relative dependence of the vapor compression cycle to orientation changes.

Experimental study on transient heat transfer characteristics during the dropping of containment pressure

The reactor containment integrity and the pressure inside the containment are the most concern in the practical running process. To evaluate the transient heat transfer, non-equilibrium fraction (NEF) is proposed to represent the completed degree of transient condensation. An empirical correlation for NEF is developed and the fit error is within ±25% for 97% of results. Based on this, a simplified calculation model for transient heat transfer rate is also developed, then the transient condensation heat transfer coefficient (HTC) is obtained to characterize the intensity of transient heat transfer. The effect of mixed gas pressure, air mass fraction and temperature of cooling water on NEF and transient condensation HTC are discussed. The result indicates that the initial air mass fraction and initial gas-mixture pressure play an important role in transient-state heat transfer, and the influence of initial cooling water temperature can be ignored. This study aims to improve the understanding of transient-state heat transfer and provide guidance to practical engineering.

Experimental investigation of condensation heat transfer of zeotropic refrigerant/oil mixtures in plate heat exchanger

Plate heat exchanger (PHE) has been wildly used as the condenser of the organic Rankine cycle (ORC). As a potential zeotropic working fluid of ORC system, it is of great significance to study the condensation heat transfer of the mixture of R245fa/R141b and lubricating oil in PHE for the development of ORC system. In this paper, an experimental study on the condensation heat transfer coefficient (HTC) of a mixture of R245fa/R141b (0.5/0.5 by mass) and polyester oil (POE) in a plate heat exchanger (PHE) has been carried out. In addition, the results were compared with those of R245fa and R141b. The parameters in the experiment range from 0 to 0.9 for vapor quality, 0%–4% for oil concentration and 20 to 60 (kg·m−2·s−1) for mass flux. The results showed a 20% reduction in HTC for R245fa/R141b with 4% oil concentration compared to oil-free refrigerant. In addition, the HTC of R245fa/R141b-POE mixture was between that of R245fa/POE and R141b/POE. The oil enhancement factor of different refrigerant/POE mixtures was less than 1.0, which could be well predicted by the Eckels correlation with a maximum mean absolute deviation (MAD) of 13.4%. The product of the predicted enhance factor and HTC predicted by the Jung et al. correlation agreed well with the tested HTC of different refrigerant/POE mixtures in the PHE. The maximum MAD of different refrigerant/POE mixtures was 20.6%, and 96.3% of predicted results were within ±30% deviation. A new correlation with a maximum MAD of 15% was proposed, which predicted the condensed HTC of refrigerant/POE mixture by using its physical properties.

Time-Average Heat Transfer Coefficient for Steam-Air Condensation during the Dropping of Containment Pressure

The passive containment cooling system (PCCS) has been applied in the new generation nuclear power plant. Previous studies mainly focused on steady-state heat transfer, but the actual heat transfer of PCCS is the transient process. Thus, investigating the transient heat transfer during the containment pressure dropping is necessary. The present study proposes a time-average condensation heat transfer coefficient (time-average condensation HTC) to characterize the intensity of transient condensation heat transfer. The time-average condensation HTC is defined as the heat absorbed per unit heat transfer area and per unit wall subcooling in a unit time. Experiments were performed to research the effect of initial gas-mixture pressure and air mass fraction on transient HTC. The result showed that the more significant gas-mixture pressure and lower air mass fraction could promote the transient-state heat transfer, especially the low air mass fraction. Based on the experimental result, a detailed empirical correlation for the time-average heat transfer coefficient is developed with an error of ±20%. Another simplified empirical correlation that only includes air mass fraction is also proposed to predict the transient heat transfer roughly. Besides, research on self-sustaining stability is also conducted to evaluate the stable operation characteristic of PCCS. The system can respond quickly and then run to a new steady state after interference during the long-term operation of PCCS. The phenomenon above implies that PCCS has good self-sustaining stability.

Effect of Marangoni condensation on the heat transfer performance of two-phase closed thermosyphons

A two-phase closed thermosyphon (TPCT) is a heat pipe that effectively transfers heat through a phase change of the working fluid. In the evaporator, the working fluid evaporates and boils, the vaporized fluid is condensed, and the liquid condensate is resupplied by gravity to the evaporator. The thermal performance of the TPCT can be improved by enhancing the heat-transfer ability of the evaporator and condenser. Various studies have been conducted to improve the heat-transfer performance using nanofluids and surface modifications in the TPCT. However, these methods still have durability and economic feasibility limitations. In this study, the Marangoni effect was applied to the TPCT to improve condensation heat transfer by promoting pseudo-dropwise condensation to overcome the limitations of previous studies. Experiments were conducted by changing the ethanol fraction from 0% to 5% with deionized water and filling ratio from 25% to 75%. The results confirmed that the highest condensation heat transfer coefficient (∼45 kW/m2·K) was obtained at a filling ratio of 38% and an ethanol volume fraction of 0.075%, which was approximately 4 times greater than the TPCT with the same filling ratio without ethanol. It was confirmed that the Marangoni effect could improve the thermal performance of the TPCT, and it is expected that this work can be utilized in various TPCT-based applications.

Effects of Sloshing Motions on Condensation Heat Transfer Characteristics of Integral-Fin Tubes Under Sea Conditions

Abstract Integral-fin tubes with high heat transfer capability are a promising solution for improving the compactness of condensers used in the exploitation of offshore natural gas at sea, and the sloshing motions including rolling and pitching would inevitably affect the performance of tubes. For applying integral-fin tubes offshore, the effects of rolling and pitching motions on condensation heat transfer characteristics of integral-fin tubes should be known. In this study, the condensation heat transfer characteristics of integral-fin tubes under rolling and pitching motions are experimentally investigated and the effects of motion angle and frequency are quantitatively analyzed. The results show that the sloshing motions have both positive and negative effects on the heat transfer of integral-fin tubes during a period, and the pitching motion has a greater influence than the rolling motion. As the sloshing angle increases from 0 deg to 12 deg, the maximum increase and reduction rates of the ratio of local wall subcooling temperature under pitching motion to that under static conditions are 10.9% and 12.5%, respectively, and the time-averaged condensation heat transfer coefficient (HTC) increases by 3.5% maximally. As the sloshing frequency increases from 0 to 0.25 Hz, the maximum increase and reduction rates of the ratio of local wall subcooling temperature under pitching motion to that under static conditions are 7.7% and 15.2%, respectively, and the increase rate of the time-averaged condensation HTC remains about 2%.

Measured dropwise condensation heat transfer coefficients from moist air under near-quiescent conditions

Condensation heat transfer from moist air is critical in dehumidification, fog collection, and cooling tower water reclamation; however, it is less studied than steam condensation. Although there are many visualization studies of dropwise condensation, few dropwise condensation heat transfer coefficients were reported in the literature for moist air. In this work, condensation occurred on a Teflon-coated, aluminum plate which was placed in an environmental chamber with controlled temperatures and relative humidities; air flowed from the plate’s bottom to top at velocities of 3–4 m/s. The plate was cooled on the backside by dry air flowing through five channels in an additively-manufactured, ABS plastic heat exchanger. The apparatus was validated using a heating case at temperatures above the dew point. Dropwise condensation was observed and heat transfer coefficients of approximately 40 W/m2K and 120 W/m2K were measured for the ambient conditions of 40 °C at 40% relative humidity (RH) and 40 °C at 60% RH, respectively. The thermal resistance from diffusion exceeds the thermal resistance of the droplets during condensation from moist air; enhancement mechanisms could focus on improving diffusion.

Flow condensation heat transfer of propane refrigerant inside a horizontal micro-fin tube

Due to the phase-out of CFCs and HCFC refrigerants, propane is a nature refrigerant occurring substance produced by natural gas production and oil refining. As a result, propane has a higher latent heat and lower density than conventional refrigerants while maintaining a comparable saturation pressure and thermal conductivity. So, propane refrigerant is already widely used in domestic fridges and freezers for many years. However, propane’s operating pressures and temperatures are well suited for air conditioning equipment, including chillers. This study investigates the contributions of different heat transfer mechanisms in two-phase flow condensation heat transfer coefficients for propane inside a 6.3-mm ID micro-fin copper tube. Data were collected through an experiment with a two-phase flow condensation. Measurements were taken at different refrigerant mass fluxes from 100 to 300 kg/m2s and heat fluxes from 3 to 9 kW/m2. In addition, the experiments investigated effect of vapor quality, mass flux, and heat flux on the heat transfer coefficients. Finally, a new heat transfer coefficient correlation was developed based on the experimental data with good agreement.

Hydrocarbon refrigerants condensation local heat transfer coefficients inside a brazed plate heat exchanger (BPHE)

This paper presents the local heat transfer coefficients of R290 (propane) and R1270 (propylene) condensation inside a Brazed Plate Heat Exchanger (BPHE). A new test section was designed for measuring the local heat transfer coefficient in refrigerant two-phase heat transfer in a BPHE. The test section includes two corrugated plates instrumented with 36 T-type thermocouples for measuring the local plate surface temperature, the local heat flux and the local heat transfer coefficient in 9 positions along the refrigerant channel. The experimental tests were carried out at a condensation temperature of 30°C, in the refrigerant mass flux range 5 − 17.5 kg m−2s−1 with an inlet vapour quality around 1.00 and an outlet vapour quality ranging from 0.13 to 0.17. A transition point between gravity-dominated and forced convection condensation was found for a refrigerant mass velocity around 10 kg m−2s−1. The experimental data was compared against theoretical models: Nusselt (1916) analysis for vertical surface shows a fair agreement with the data in gravity-dominated condensation, while Longo et al. (2015) model predicts the data in forced convection condensation with a Mean Absolute Percentage Error (MAPE) around 20%. The experimental data were further compared with some original measurements obtained with R404A and with data available for R410A. R290 and R1270 exhibit condensation heat transfer coefficients similar to those of traditional HFC refrigerants, such as R410A and R404A.

Development of correlations for steam condensation over a vertical tube in the presence of noncondensable gas using machine learning approach

Steam condensation is an important phenomenon encountered in nuclear reactor under severe accidents. Even though many correlations for predicting steam condensation heat transfer coefficient (HTC) in the presence of noncondensable gas (NCG) have been proposed over the past decade, a more reliable and accurate model is still required. Thus, in this study, multigene genetic programming (MGGP), a biologically inspired machine learning method, is applied to develop new correlations for condensation HTC of steam-NCG mixture over a vertical tube in turbulent free convection regime. To this end, a consolidated database with 1440 data points from 18 sources is compiled. Then, using the database, both a new empirical correlation and a MGGP model are developed for better comparison. The performance of the MGGP-based correlation selected using Pareto tournaments strategy is compared with the new developed empirical correlation and another 20 relevant correlations. The results reveal the superiority of the MGGP-based correlation. In addition, it is found that the tube length is excluded in the best-trained correlation, even though it is used as the input of MGGP, which agrees well with the results of previous theoretical and experimental studies. The present study demonstrates that MGGP is promising in developing explicit, accurate, and compact models for the complex heat transfer and multiphase flow phenomena such as steam condensation in the presence of NCG.

Steam entrainment and heat transfer characteristic of steam submerged jet condensation within steam-water mixture layer

Steam-water interface and mixture layer are the key window for understanding the heat and mass transfer mechanism of steam submerged jet condensation. In this paper, the steam-water two-phase mixture layer is captured and the interfacial vortex is observed with a quasi-two-dimensional submerged steam jet visualization experimental platform. Then, the volume heat transfer capacity of steam-water mixture layer and heat transfer coefficient with steam-water inner interface are obtained. Furthermore, a new turbulent eddy entrainment model is developed to calculate the local entrainment mass rate and local condensation heat transfer coefficient. Both the local entrainment mass rate and local condensation heat transfer coefficient increases along steam jet direction, and reaches the maximum value at the tail of the mixture layer. The calculated condensation heat transfer coefficient ranges from 0.88 to 2.94 MW·m−2·K−1, which is about the half of the value of hypothetical heat transfer coefficient with inner interfacial area.

A universal correlation for flow condensation heat transfer in horizontal tubes based on machine learning

Accurate and universal prediction of in-tube condensation heat transfer coefficients (HTCs) is vital for designing compact condensers. This study presents machine learning (ML) methods for predicting flow condensing HTCs inside horizontal tubes based on an assembled database. The database contains 6064 experimental data of 28 pure fluids and covers broad operating conditions. Furthermore, the database is serviced to train and evaluate five ML models based on K-nearest neighbors (KNN), artificial neural network (ANN), convolutional neural network (CNN), random forest (RF), and Extreme gradient boosting (XGBoost) algorithms. The designed ML models show excellent predictive performances for 1213 test data points with the best mean absolute relative deviation (MARD) of 5.82% achieved by CNN and the coefficient of determination (R2) of 0.98 or higher for both XGBoost models. Based on the parametric importance analysis conducted by the trained XGBoost models, a new universal correlation is developed by incorporating several key parameters to characterize condensation heat transfer. This correlation shows reliable predictions for all data points in the consolidated database with the mean relative deviation (MRD) of −1.77% and MARD of 19.21%. An additional excluded database is collected to validate the universality of the new correlation and these ML models. It illustrates that ML models are effective predictive tools for HTCs, and can also help develop the heat transfer correlation with high accuracy and universality.

FILM –WISE CONDENSATION OF R1234yf AND R134a REFRIGERANTS ON FINNED TUBE WITH 32 FINS PER INCH

Researchers have been motivating by the global warming challenge to develop alternatives substances to compounds that contribute to this problem. The refrigerant R134a (HFC134a) has been identified as one of the most environmentally damaging gases. As a result, the refrigerant R1234yf has been employed in air conditioning systems as a substitute to the refrigerant R134a. The condensation heat transfer coefficient (HTC) of the refrigerants R1234yf and R134a was measured on smooth and standard finned tubes in this study. The finned tube is characterized by 32 Fins per inch (FPI) and 1 mm fin height. The condensation process was investigated at 37°C and 40°C condensing temperatures and 16°C to 28°C water inlet temperatures. The Nusselt theory accurately predicted the condensation HTCs on the smooth tube within mean absolute percentage deviation (MAPD) of 5.3% for R134a and 4.7% for R1234yf. As the wall sub-cooling increases, the condensation HTC decreases. With a drop in LMTD, the overall heat transfer coefficient (HTC) rises. For finned tube, the refrigerant R134a showed a greater HTC than R1234yf. In comparison to smooth tube, the enhancement ratio in HTC was 78% at 37 and 82% at 40°C for R134a. The enhancement ratio with R1234yf was 65% and 81% at 37 and 40 ° C, respectively. The experimental data was compared with predictions of two previous analytical models for film condensation on finned tubes.

Condensation heat transfer of pure refrigerants R1234yf and R32 inside multiple circular minichannels

This study experimentally investigated condensation heat transfer coefficients inside horizontal multiple circular minichannels with inner diameters of 0.81 and 0.49 mm, using pure refrigerants R1234yf and R32. The effects of mass flux, vapor quality, channel size, heat flux, and refrigerant properties on condensation flow characteristics within a mass flux range of 50–400 kgm−2s−1 were clarified. Annular, churn, slug–annular, and plug (intermittent) flows were visualized inside multiple circular minichannels. It was determined that the heat transfer coefficients of R1234yf and R32 were affected by mass flux, vapor quality, and heat flux. At lower mass fluxes, the contribution of surface tension to heat transfer was dominant relative to that of forced convection. The heat transfer coefficient increased with decreasing channel size, and R32 exhibited higher values of the heat transfer coefficient compared to those exhibited by R1234yf. The proposed heat transfer correlation, accounting for the effects of forced convection and surface tension, predicted heat transfer coefficients for circular minichannels with a mean absolute deviation of 15.2%.

The mass transfer characteristics of R134a/R245fa during stratified flow condensation in rectangular channel

• The mass fraction of zeotropic mixture was measured with encapsulated probe sampling method. • A parametric study on the mass transfer resistance and heat transfer coefficient was analyzed. • A prediction method on mass transfer resistance in stratified flow condensation was proposed. The measurement experiment on the mass fraction of zeotropic mixtures R134a/R245fa during stratified flow condensation in rectangular channel was carried out with encapsulated probe sampling and gas chromatograph analysis. The mass fraction of lower boiling point component R134a, the mass transfer in the vapor phase and the heat transfer characteristics were studied and analyzed comprehensively. Both the vapor convective flow and the thickness of liquid film affected the mass transfer resistance. The liquid phase thermal resistance caused by the liquid film and the mass transfer resistance in the vapor phase affected the condensation heat transfer coefficient of zeotropic mixtures. Considering the mass fraction, temperature glide and working conditions, a prediction method of mass transfer resistance in the vapor phase of zeotropic mixtures during flow condensation was proposed.