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Industrial heat pumps have been developed to recycle surplus heat from various industrial processes for steam generation. A condenser in an industrial heat pump needs to meet the high condensation temperature. Alternative refrigerants are also needed for condensers. The objective of this study was to compare condensation heat transfer characteristics of R1234ze(E), an alternative refrigerant at high reduced pressure, and R134a, a conventional refrigerant. A test section of copper tube with a diameter of 1/2 inch and a length of 4 m was used. The test section was installed inside a PVC tube which was cooled with brine. Experimental conditions were: reduced pressure from 0.5 to 0.7 and mass flux of 500–600 kgm-2s-1. Condensation heat transfer coefficients of R1234ze(E) and R134a decreased with an increase in reduced pressure. Effects of mass flux on refrigerants decreased with an increase in reduced pressure. A Travis model showed the best performance for estimating condensation heat transfer coefficients of R1234ze(E) and R134a under high reduced pressure conditions.

The condensation heat transfer coefficient and the pressure drop were investigated experimentally and numerically in a microtube condenser using R134a. The microtube condenser comprises of trapezoi...

Aiming at studying the condensate flow phenomenon and air-steam–mixture condensation heat transfer underneath a containment vessel surface, a test bench was constructed. The plate dimension was 1.5...

In this work, the condensation heat transfer and pressure drop characteristics of plate heat exchangers were simulated, and the 3-D temperature, pressure, and velocity fields were obtained. From the flow field, we can see that the velocity of vapor is higher than that of condensate. From the pressure field, we can see that the pressure shows a downward trend along the flow direction, and there is, the more pressure drop in the first half of the plate. From the temperature field, we can see that the temperature gradient increases with the increase of velocity and pressure gradient. Meanwhile, the effect of vapor mass-flow, dryness and super-heat on condensation heat transfer coefficients and pressure drops were investigated. The results show that the pressure drop and heat transfer coefficient both increase with the increase of dryness, degree of superheat and mass-flow. In addition, the correlation equations developed to predict the condensation heat transfer and friction factor perfectly agree with the experimental results.

The present paper presents a review of condensation heat transfer across smooth and enhanced horizontal surfaces due to its significance in refrigeration, air conditioning and heat pump applications. The emphasizes is on the recent understanding of experimental as well as the semi-empirical correlations to investigate the heat transfer phenomena during condensation associated with enhanced geometries. An effort has been made to submit free-convection condensation effects outside of single tubes and the tube bundle with the influence of tube geometries, condensate retention and gravity on film condensation; however, comparison of forced convection is also presented. Alternative of conventional refrigerants in condensation process by low-global warming potential (GWP) refrigerants is addressed as well due to increase in atmospheric burden affected by hydro-fluoro-carbons (HFCs). Although many researchers have reviewed the condensation impact across enhanced surfaces, a few of them revised its behavior across pin-fin tubes. The effects of geometry, surface wettability, and operating conditions on the location, amount and form of condensate film are discussed. Various theoretical models prediction with the new experimental data across pin-fin tubes is also revealed. This review is distributed into two main sections: the first section focuses on condensation across enhanced tubes, sub dividing the study into integral-fin and pin-fin tubes based on theoretical and experimental investigations. It covers the geometrical effects concerning three dimensional (3D) surfaces, fin density, fin spacing and fin thickness. The later part of the paper concentrates on condensation behavior across the tube bundle incorporating the effects of fin density and refrigerant mixtures highlighting both theoretical and experimental knowledge. Recent research shows an agreement between theoretical and experimental models in the defined area; though, a considerable amount of work on semi-empirical correlation formulation is visible in the literature. The strength of this paper is the latest findings on condensation against different geometrical parameters of extended surfaces specifically across pin- fin tubes and the tube bundle. Finally, theoretical enhancement factors along with many heat transfer correlations are presented and recommendations are suggested for the future work.

Condensation heat transfer of R1234yf inside smooth and microfin tube with 2.5 mm outer diameter are studied experimentally. The experiments are carried out at a saturation temperature of 20°C and 30°C, mass velocity ranging from 50 to 200 kg m−2s−1 and vapor quality ranging from 0-1. The effects of mass velocity, vapor quality, and saturation temperature on condensation heat transfer coefficient are analyzed with R1234yf and R134a. Condensation heat transfer correlation for smooth tube is developed considering present experimental data and other researchers’ data. Correlation is developed using experimental data for 2.5 mm to 10 mm outer diameter tubes and refrigerants are R134a, R1234yf, R123 and R1234ze (E) by including other researchers’ data. Newly developed correlation is successfully predicted experimental data and other sources data within mean deviation of 15 %. Experimental data are also compared with previous correlations proposed for smooth and microfin tube.

In order to study the condensation heat transfer characteristics of non-azeotropic hydrocarbon mixtures in helically coiled tubes for large-scale spiral-wound heat exchangers, a simplified physical model of three-section helical tubes was proposed. Reasonable governing equations and boundary conditions were set up, and the grid independence was verified. Then, the condensation heat transfer characteristics of mixture refrigerants were analyzed. In addition, considering the effect of mass transfer resistance of non-azeotropic mixtures on heat transfer during condensation, a method combining numerical simulation with the Bell and Ghaly correction method was proposed to calculate the condensation heat transfer coefficient of mixtures. By comparing with the experimental results, the accuracy of the calculation model is verified, which provides theoretical support for the design of large-scale spiral-wound heat exchangers.

During condensation process, the formation of condensate film is main resistance to retard heat transfer. This liquid condensate on horizontal pin-fin tube is known as condensate retention that generally blocks the lower part of tube and act as an insulation resulting in the form of resistance to heat transfer. Various, tube geometries experimentally tested with different pin-fin longitudinal and circumferential thickness and spacing, pin-fin height, internal and external tube diameters under the effect of vapour velocity are selected for model development. As it is extremely important to estimate the extent of condensate retention on such pin-fin tubes in order to make more effective horizontal pin-fin tubes in terms of heat transfer. The development of semi empirical correlations for condensate retention on pin-fin tubes as a function of vapour velocity (forced convection condensation) is proposed in this paper. Various geometric parameters and fluids are considered for model development. Accurate data are used for the model development. The proposed model which is based upon the dimensional analysis successfully predicts available data to within 5%. Relative standard deviation was about 2.44, 2.30 and 1.73 for water, ethylene glycol and refrigerant respectively. The development of such a semi empirical model is the first important step required for the development of full-scale heat transfer model of condensation heat transfer on horizontal pin-fin tubes during forced convection.

This study aims to provide an experimental investigation and comparison of the condensation heat transfer characteristics in a plate–fin heat exchanger (PFHE). The heat flux, mass flux, and saturation pressure were adjusted as experimental parameters to verify the effects on the condensation heat transfer. In addition, condensation heat transfer correlation of two-stream PFHEs was provided based on the experimental data for utilization as a design reference for the heat exchanger. The turbulence is the most influential in heat transfer. One of the ways to foster turbulence is to increase shear stress. The higher flow velocity results in the higher shear stress. That was why increasing mass flux or the flow with higher vapor quality showed the higher heat transfer coefficient (HTC). Refrigerant properties such as viscosity and specific volume of vapor changed according to the saturation pressure. It is expected they affect the degree of turbulence too in similar manners. The mass flux was more influential than the heat flux and saturation pressure. Thus, the equivalent mass flux of the refrigerant is dominant in the derived correlation model. The average difference between experimental and calculated HTC from correlations was about 6.5%. Multi-stream PFHE comprises an additional heat transfer surface, which implies a more active droplet formation. The average pressure drop in the multi-stream is 15% larger than that of the two-stream.

An experimental investigation of shell-side flow condensation was performed on three-dimensional surface enhanced tubes, including a herringbone micro-fin tube and a newly developed 1-EHT tube. An equivalent plain tube was also tested for performance comparison. All the test tubes had similar geometry parameters, i.e., inner diameter 11.43 mm and outer diameter 12.7 mm. The outer shell diameter was 24.5 mm with a wall thickness of 0.6 mm. Tests were conducted using R410A as the working fluid at a dew point of 45 °C. The mass flux range of 10–55 kg/(m2 · s) with an inlet quality of 0.8 and an outlet quality of 0.1. Experimental results showed that the plain tube exhibited a better condensation heat transfer performance. Moreover, the mass flux had a significant influence on the heat transfer coefficient for shell-side condensation. A new prediction model based on the Cavallini’s equation was developed to predict the condensing coefficient where the mean absolute error is less than 4%.

The main objective of this work is to develop a numerical model to analyze heat transfer and condensation of a rising spherical bubble. The model included the bubble shrinkage during condensation, which can be utilized to analyze the bubble’s total energy loss, raising velocity, and condensation rate of a single bubble compared to multiple bubbles with the same total thermal energy. The equations of motion, heat, and mass transfer were developed. The model results were verified with the bubble condensation experiment data in the literature, in which they exhibited a good agreement. For the validation, the model results were compared with bubble condensation experiment data in the literature, which showed a good agreement with the experimental results. The dynamic term of the model is developed using the force balance on a gravity-driven bubble, including hydrodynamic drag force and gravity/buoyancy force, which acting with and against the bubble’s motion direction. For the thermal part of the model, a condensation correlation has been adapted to represent the Nusselt number as a function of Reynolds number (Re), Jakob number (Ja), and Prandtl number (Pr). A MATLAB code is developed in order to calculate the instantaneous velocity, the radius, and the mass loss of the vapor bubble in each time step. Moreover, the fundamental behavior for a single bubble and multiple bubbles was investigated in various initial conditions under the same total thermal energy. The effects of the initial bubble radius and the temperature difference between the liquid and vapor phases were analyzed for both scenarios in order to examine the condensation rate. It was found that the thermal behavior of the condensing bubble can be improved by forcing the bubble to collapse into sub bubbles, which will increase the total interfacial area and the rising velocity. Farther, due to generated sub bubbles, the resultant velocity increased the turbulency and the heat transfer rate accordingly. This study can lead to improve the heat transfer rate and allow for more intensive research to enhance the condensation rate.

Experiments on the two-phase flow condensation heat transfer of R410A, R22, R32, and R290 (propane) inside a multiport minichannel tube are investigated in this study. The experiments are conducted...

A new type of three-dimensional pin–fin plate with elliptical cross-section was proposed. Condensation heat transfer of FC-72 in a narrow rectangular channel with the proposed pin fins was experimentally studied in normal gravity and microgravity. The effects of pin geometry, thermal conductivity, mass flow rate and gravity on condensation heat transfer were investigated. The visualization experiment under microgravity was carried out and the condensate behaviour was observed by high CCD camera. The results showed that all the elliptical pin-fin plates exhibited substantially better performance than the flat plate. The influence of pin geometry and thermal conductivity on condensation heat transfer coefficient was great. The smaller pin size and higher thermal conductivity were favourable for condensation enhancement. The average condensation heat transfer coefficient increased with the increase of mass flow rate. In microgravity, obvious fluctuations and climbs occurred in gas-liquid interface. However, the condensate behaviour on the condensing surface was unconspicuous. For unsteady state, the vapor-side temperature difference increased evidently in microgravity. Microgravity had a certain effect on temperature evolution of the condensing base. Short-term microgravity degraded the condensation heat transfer coefficient in quasi-steady state or unsteady state, but had little effect on pulsating state.

Steam condensation on the containment vessel is a significant cooling strategy to cope with the design basis accidents in the third-generation reactors with passive safety features. Aiming to evaluate the heat removal capacity of steam condensation, a number of condensation experiments have been conducted on a horizontal plate with the same surface condition as CAP1400 containment vessel. The effects of surface sub-cooling, air concentration, bulk pressure and different steam injecting models on condensation heat transfer have been experimentally investigated. In the experiments, the condensation heat transfer coefficients (within the range of 77–1297 W/m2 K) on the downward-facing plate are successfully obtained under the conditions of bulk pressure ranging from 0.154 to 0.607 MPa, air molar fraction ranging from 1.1% to 82.9% and surface sub-cooling ranging from 12.6 to 49.3 °C. In addition, an empirical correlation for heat transfer prediction has been developed based on the experimental data in this work. Besides, the experimental data have also been compared with four existing empirical correlations proposed by Uchida, Tagami, Dehbi and Liu, respectively. The comparing results show that most of condensation heat transfer coefficient data on the test plate could be overestimated by these four correlations.

This study experimentally investigated the condensation heat transfer and pressure drop characteristics of R1234ze(E) inside horizontal small-diameter (4.0-mm) microfin tubes with three different t...

A numerical study of condensation heat transfer in curved square and triangle microchannels with various curvatures is conducted. The model is based on the volume of fluid approach and user-defined...

The flow condensation heat transfer performances of R1234ze(E) and R32 in a horizontal single circular minitube with the inner diameter of 2 mm are investigated experimentally. Tests are carried ou...

Simple and accurate prediction models are highly demanded for industrial design of heat exchangers using refrigerant mixtures. This paper presents some data taken during condensation of R32/R1234ze(E) and proposes a new method to predict condensation heat transfer coefficient of zeotropic mixtures inside horizontal tubes. The method is developed based on the heat transfer model by Cavallini et al. (2006) for pure fluids by including additional heat transfer resistances during zeotropic mixtures condensation. The heat transfer resistances are modified from the Bell and Ghaly (1973) method by considering the effect of interfacial roughness and non-equilibrium phenomena, following the approach by Del Col et al. (2005). This new model is easy to implement and requires low computational effort. The predicted results by the model show a satisfactory agreement with experimental data covering various mixtures and a wide range of working conditions.

Small channel heat transfer with condensation or boiling is utilized to handle the more and more intense heat dissipation load nowadays. To further enhance the annular condensation heat transfer inside these channels, diverging-shaped small channel is considered in this work analytically. It is testified that diverging channels do improve condensation heat transfer significantly compared to small channels with constant cross-sectional area. With refrigerant mass flux density increasing or channel size decreasing, diverging channels become more and more efficient in enhancing condensation heat transfer.

In this study, condensation heat transfer and multi-phase pressure drop of CO2 near the critical point are investigated occurring in a Printed Circuit Heat Exchanger (PCHE) for a supercritical CO2 power cycle application in mind. Homogeneous Equilibrium Model (HEM) approach is used to evaluate and develop appropriate heat transfer and pressure drop correlations. The experiment was performed with the CO2 test facility called SCO2PE (Supercritical CO2 Pressurizing Experiment) in KAIST. The heat transfer and pressure drop test was conducted with the PCHE in the facility. Existing correlations were compared to the test data and a new set of correlations was necessary to be developed. A new set of correlations is newly suggested in this paper which captures physical characteristics reasonably well.

Designing a novel scaled modular test facility as a part of an experiment for condensation heat transfer (CHT) in small modular reactors (SMRs) is the main focus of this study. This facility will provide data to evaluate models' scalability for predicting heat transfer in the passive containment cooling system (PCCS) of SMR. The nuclear industry recognizes SMRs as future candidates for clean, economic, and safe energy generation. However, licensing requires proper evaluation of the safety systems such as PCCS. The knowledge gap from the literature review showed a lack of high-resolution experimental data for scaling of PCCS and validation of computational fluid dynamics tools. In addition, the presently available test data are inconsistent due to unscaled geometric and varying physics conditions. These inconsistencies lead to inadequate test data benchmarking. To fill this research gap, this study developed three scaled (different diameters) condensing test sections with annular cooling for scale testing and analysis. This facility considered saturated steam as the working fluid with noncondensable gases like nitrogen and helium in different mass fractions. This facility also used a precooler unit for inlet steam conditioning and a postcooler unit for condensate cooling. The high fidelity sensors, instruments, and data acquisition systems are installed and calibrated. Finally, facility safety analysis and shakedown tests are performed.

Coalescence-induced droplet jumping has the potential to enhance the performance of a variety of applications including condensation heat transfer, surface self-cleaning, anti-icing, and defrosting to name a few. Here, we study droplet jumping on hierarchical microgrooved and nanostructured smooth superhydrophobic surfaces. We show that the confined microgroove structures play a key role in tailoring droplet coalescence hydrodynamics, which in turn affects the droplet jumping velocity and energy conversion efficiency. We observed self-jumping of individual deformed droplets within microgrooves having maximum surface-to-kinetic energy conversion efficiency of 8%. Furthermore, various coalescence-induced jumping modes were observed on the hierarchical microgrooved superhydrophobic surface. The microgroove structure enabled high droplet jumping velocity (≈0.74U) and energy conversion efficiency (≈46%) by enabling the coalescence of deformed droplets in microgrooves with undeformed droplets on adjacent plateaus. The jumping velocity and energy conversion efficiency enhancements are 1.93× and 6.67× higher than traditional coalescence-induced droplet jumping on smooth superhydrophobic surfaces. This work not only demonstrates high droplet jumping velocity and energy conversion efficiency but also demonstrates the key role played by macroscale structures on coalescence hydrodynamics and elucidates a method to further control droplet jumping physics for a plethora of applications.

This study was performed to investigate the heat transfer and pressure drop of R134A during condensation inside a stainless steel micro-scale enhanced surface tube (EHT tube) and smooth tube. The tests were conducted at a saturation temperature of 45°C, over the mass fluxes range of 100 to 200 kg/m2s, the heat fluxes of 14–25 kW/m2, an inlet vapor quality of 0.8 and outlet vapor quality of 0.2. The heat length and inner diameter of the tested tube were 2 m and 11.5 mm. The micro-scale enhanced surface tube has complex surface structures composed of dimples and petal arrays background patterns. It can be observed the condensation heat transfer coefficients of the EHT tube is about 1.6–1.7 times higher than that of a stainless steel smooth tube. Enhancement of the EHT tube was achieved due to disruption of the boundary layer, secondary fluid generation, increasing fluid turbulence and heat transfer area. In addition, considering the friction pressure drop, the EHT tube produces the larger friction pressure drop, which is 1.05–1.20 times as compared to the smooth tube. Finally, the performance factors were performed to evaluate the enhancement effect of the EHT tube based on heat transfer coefficient-pressure drop evaluation criteria value (η1) and heat transfer coefficient-area evaluation criteria value (η2).

In this paper, the condensation heat transfer characteristics of R134a inside enhanced tubes using two types of surface structures with different materials were investigated, which were then compared with plain tubes under the same test conditions. The enhanced tubes were: 1EHTa tube with dimpled and petal arrays structure and 1EHTb tube with protrusion and similar petal arrays structure. The experiment was conducted for a mass flux ranging from 100 to 200 kg m−2 s−1 with saturation temperature of 318.15 K. The inlet and outlet vapor qualities were fixed at 0.8 and 0.2, respectively. The test tubes had the same outer diameter of 12.7 mm. Results showed that the dimpled and protruded surface tubes enhanced the convection condensation heat transfer and the heat transfer coefficient was 1.4–1.6 times higher than that of the smooth tube. Heat transfer enhancement of the 1EHTa and 1EHTb tube was mainly due to the complex roughness surface structures that created swirling and increased the interface turbulence. The condensation heat transfer coefficient increased slightly with increasing mass flux. The pressure drop penalty was found to increase as mass flux increased. Compared with the smooth tube, the pressure drop of Cu-1EHTa tube, SS-1EHTa tube, and Cu-1EHTb tube were 1.15, 1.21, and 1.14 of smooth tube, respectively. Enhanced tubes exhibited higher performance factors (PFs) compared to the smooth tube. The average PF was 1.3–1.5. A new correlation of heat transfer coefficient has been developed within ±15% error band.

A numerical model of condensation heat transfer and frictional pressure drop in a circular tube was developed and validated. In order to facilitate the model validation, the physical model was built according to the experiment condition in the existing literature. In the numerical models proposed in this work, the following models were involved: volume of fluid (VOF) multiphase model, Lee’s phase change model and Reynolds Stress turbulence model. The importance of boundary-layer mesh size was analyzed, and the effects of entrainment, turbulent Prandtl number and gas-liquid interface turbulence damping on the simulation results of heat transfer coefficient (HTC) and frictional pressure drop (FPD) were evaluated and modified. The numerical model was validated with Neeraas’s experimental data and Steiner's correlation results at various mass fluxes, vapor qualities, pressures and fluids. The simulation results of void fraction showed good agreement with Steiner's correlation; the HTC and FPD showed good agreement with Neeraas’s experimental data, which indicated the model developed in this work has good universality and accuracy.

Filmwise condensation plays an important role in many industrial applications. With the presence of noncondensable gas, the condensation process can be complicated and an appropriate modeling of the phenomena is necessary. This study takes the approach of modeling condensation with Computational Fluid Dynamics (CFD) based on species diffusion, with only the gas mixture modeled as the entire computational domain. The condensation rate is modeled as a sink term for the conservation equations. In addition, we suggest the use of free surface boundary condition, that is, a shear free boundary, as opposed to traditional approaches where the condensation is modeled to occur on a dry, no-slip wall. The free surface assumption provides better representation of the physical condensing interface without having to include both liquid and gas phases in the computational domain, which can bring great increase in computational cost with limited benefit. The free surface assumption is validated via case studies considering reasonable range of interfacial conditions, showing that the error from the free surface assumption can be quantified and is reasonably low for the considered range of conditions. Then, the developed condensation model and the free surface assumption for the condensing interface are implemented into the CFD codes and validated against a set of experimental data. The performance of the condensation model and the free surface assumption are assessed based on the prediction of the condensation heat transfer coefficient. The results show that the predictions are improved with applying the free surface boundary condition for the condensing interface compared to the results with the traditional no-slip boundary conditions.

The thermal-hydraulic system code, MARS-KS1.3, tends to underestimate the condensation heat transfer under the presence of non-condensable gases. To improve its condensation heat transfer model, we adopted the Herranz's diffusion layer model and further developed it, mainly focusing on thermal-hydraulic conditions in a nuclear containment during a hypothetical accident. Two key modifications include (i) the correlations to calculate heat and mass transfer on a vertical external surface for various flow conditions are adopted and (ii) a turbulent diffusion coefficient is applied to consider the effect of turbulence on mass diffusion. The modified diffusion layer model was implemented into MARS-KS1.3 and it has been validated using 157 condensation experiments from six different facilities. By using the turbulent diffusion coefficient in the modified diffusion layer model, the effect of turbulence on mass diffusion and then condensation was captured very well. For most cases, the results of the modified model are in a better agreement with the experimental data, resulting in a root-mean-square error of 21.3%. It is also shown that the modified diffusion layer model can predict local condensation heat transfer change along the condensation surface well.

The NRF, TESP, and University of Pretoria/Stellenbosch University. SANERI/SANEDI, CSIR, EEDSM Hub and NAC.

An experimental study of condensation heat transfer characteristics of flow inside horizontal micro-fin tubes is carried out using R410A, R22, and R32 as the test fluids. This study especially focu...

In this study, heat transfer coefficients and pressure drops of R-134a inside round and flat tubes are investigated experimentally with mass flux of 450, 550, and 650 kg m−2 s−1 at saturati...

This study investigated the condensation heat transfer coefficient and pressure drop characteristics of smooth and microfin small-diameter tubes, with a 4 mm outside diameter, and R32, R152a and R410A refrigerants. The condensation heat transfer coefficients and pressure drops were measured in the range of mass velocities, from 100 to 400 kg m-2 s-1, at a saturation temperature of 35 °C. The frictional pressure drop of the microfin tube was approximately 1.6 times greater than that of the smooth tube for each refrigerant and mass velocity. The heat transfer coefficient of the microfin tube was approximately 2–7 times greater than that of the smooth tube for R32 at 200 kg m-2 s-1. The experimental values of the frictional pressure drop and condensation heat transfer coefficient, of smooth and microfin tubes, were compared to the predicted values obtained using the previous correlation. However, the previous correlation for the heat transfer coefficient of small-diameter microfin tubes was not estimated with high accuracy. Therefore, we conducted the experimental of heat transfer coefficient and frictional pressure drop for smooth and microfin small-diameter tubes with a 4 mm outside diameter, and also suggested the purpose of those general correlations.

This study presents experimental data of CO2 flow condensation heat transfer for mass fluxes ranging from 100 to 500 kg/m2-s inside a 4.73 mm inside diameter, smooth horizontal copper tube, at saturation temperatures between −10 and 0 °C under a wide range of vapour quality conditions. Experimental data were obtained from an open-loop test rig which discharged high-pressure CO2 liquid from bottles to the atmosphere. Experimental results showed that when the test mass flux was greater than or equal to 300 kg/m2-s, for vapour qualities greater than 0.4, the rate of heat transfer increased with increasing mass flux and vapour quality, and increased with decreasing saturation temperature. The flow regimes under these working conditions were predicted as annular from the values of the Soliman Froude number (Frso > 14). Three recently proposed CO2 flow condensation models from the open literature were evaluated against the data from the current experiment. Overall, the model of Li and Norris (2016) gave the most accurate predictions, but under-predicted the low Nusselt number heat transfer rates. This model was modified using the current data, and then re-evaluated against experimental data from the current and other experiments, and was found to have a mean absolute percentage deviation of 7%.

In this study, condensation heat transfer of R-600a (Iso-butane) has been analyzed experimentally over different finned tubes varying different parameters. These parameters like saturation pressure, wall sub-cooling temperature, fin geometry, refrigerant properties, and coolant flow rate are major factors affecting the performance of refrigeration and air-conditioning (RAC) systems. The parameters were varied within the range of operating conditions for most of refrigeration and air-conditioning systems. Based upon experimental data and exclusive analysis, best performing sets of different parameters have been concluded, and also a generalized correlation in non-dimensional form covering different parameters has been developed.

Considerable attention has recently been given to R245fa for applications such as high temperature heat pump. In this paper, the condensation heat transfer characteristics of R245fa in a smooth tube and an internally enhanced tube are experimentally studied. The ranges of condensation temperature, mass flux and cooling water flux are 30~45°C, 84~197kg/m2·s and 732~1228kg/m2 ·s, respectively. The two tubes with a 4.58 mm inner diameter, 5mm outer diameter and 2000 mm length are used. The heat transfer coefficient in each case was analyzed carefully. The case study results show that condensation heat transfer coefficients increase with the increase of mass flux, but decrease with the condensation temperature. And the influence of cooling water flux on heat transfer coefficient is small. Compared the heat transfer coefficient between the smooth tube and the internally enhanced tube, Enhanced rates is 1.8 to 2.5.

The effects of interficial shear between liquid film and flowing-steam cannot be neglected during the steam condensation process in vertical tubes, and the Nusselt condensation model should be modified. In this paper, the heat transfer characteristics of steam condensation in vertical tube were investigated by experiments. Both the Nusselt theoretical model and the modified model considering interficial shear effects were adopted and compared with the experimental measurements. The results show that interfacial shear stress have significant influence on the liquid film flow state and thin liquid film thickness, which further results in higher condensation heat transfer coefficient. As the modified model considers interficial shear correctly, and its calculation results agree well with the experimental results.

The condensates generated in the process of film condensation, such as condensing, falling, and acting condensates, are identified and defined to obtain precise inundation effect model of 3D finned tube bundle. Furthermore, the influence of three categories of condensates on the film condensation under different heat fluxes and condensing temperatures is experimentally investigated via the homologous method. A test bench with a test section contains two arrays of 8 horizontal tubes is initially constructed. Experimental results show that the inundation effect coefficient decreases from 1.00 to 0.78 as acting condensate Re increases from 75 to 1860. The influence of heat flux on three categories of condensates is more significant than that of condensing temperature. As tube row depth increases from 1 to 6, the proportion of condensing condensate Re to acting condensate Re decreases from 100% to 15.0%, whereas the proportion of falling condensate Re to acting condensate Re increases from 0 to 85.0%. Furthermore, the condensation heat transfer model of single 3D finned tube and inundation effect model are established, and the deviations of results between experiments and models are almost within ±3.0%. The deviations of inundation effect coefficients between experiment and model proposed in this study are 92.5% and 50.0% less than those between experiment and models using routine method and considering single condensate with homologous method, respectively. Moreover, the inundation effect model proposed in this study reveals that different proportions of condensing or falling condensates to acting condensate lead to different inundation effect coefficient at the same acting condensate Re. The research results will lay the foundation for further revealing the mechanism of film condensation on 3D finned tube bundle and guide the thermal design of 3D finned tubes applied in shell-and-tube condensers.

Mechanistic models for predicting condensation heat transfer in the annular and intermittent flow regimes are presented and compared with data for different working fluids (R134a and R245fa) over a range of mass fluxes, saturation temperatures (30 ≤ Tsat ≤ 50 °C), saturation-to-wall temperature differences (1.5

The cylinder dryer is the most energy-consuming part of the papermaking drying section. Whether the drying cylinder can effectively drain the drying cylinder affects the drying efficiency of the drying cylinder. The design of the multi-channel drying cylinder effectively improves the problem of the difficulty of the water accumulation discharge. In order to obtain a channel cross-sectional shape with better drainage and better heat transfer, two channels with different cross-sectional shapes are selected to study the flow and heat transfer of steam in this experiment. The changes of the channel heat transfer coefficient under different working conditions are studied and compared. The result show that the U-shaped channel heat transfer effect is better than that of other shape channels in the multi-channel dryer.

Double-roughness surfaces can be used to mimic lotus surfaces. The apparent contact angles (ACAs) of droplets on these surfaces were first calculated by Herminghaus. Then Patankar utilized the pillar model to improve the Herminghaus approach and put forward the formulas for ACAs calculation of the homogeneous double-roughness surfaces where the dual-scale structures and the bases were the same wettable materials. In this paper, we propose a numerical calculation method of ACAs on the heterogeneous double-roughness surfaces where the dual-scale structures and the bases are made of different wettable materials. This numerical calculation method has successfully enhanced the Herminghaus approach. It is promising to become a novel design approach of heterogeneous superhydrophobic surfaces, which are frequently applied in technical fields of self-cleaning, anti-icing, antifogging, and enhancing condensation heat transfer.

In this paper, the multi-objective optimization of R-245fa vapour condensation inside horizontal tube has been carried out using teaching–learning-based optimization algorithm. The teaching–learning-based optimization algorithm is teaching–learning procedure motivated and works on the impact of a teacher on the outcome of students in a class. Heat transfer coefficient and pressure drop with two parameters have been considered to evaluate the performance of the tube. The mass flux and vapour quality of refrigerant are taken as the parameters. The limit of mass flux and vapour quality are from 100 to 300 kg/m2 s and 0.1 to 0.8, respectively. The optimum values of heat transfer coefficient 2820.5 W/m2 K and pressure drop 1360.2 Pa are obtained with mass flux 137.65 kg/m2 s and vapour quality 0.77 using teaching–learning-based optimization algorithm.

Laminar film condensation inside large space occurs during accidents of nuclear power plants. To further improve the reliability of the passive emergency system, diversion panels are designed to enhance this condensation heat transfer. With simple structures facilitating manufacture and assembly, these diversion panels are also theoretically proved to be able to enhance the film condensation significantly. Effects of the three dependent parameters (length ratio between diversion panel and cylinder wall, diversion panel number and inclined angle of diversion panel) on the overall heat transfer performance are also analyzed elaborately and the optimum configuration of the diversion panel can be identified correspondingly.