Experimental investigation of two phase flow condensation of alternatives to HCFC-22 inside enhanced surface tubing

This paper presents an experimental study of two phase flow condensation of some alternative zeotropic refrigerant mixtures to R-22, inside air/refrigerant horizontal enhanced surface tubing. The alternatives considered in this study are; R-507, R-404A, R-407C, and R-408A as well as R-410A. It was evident from the condensation experimental data that R-408A has the highest heat transfer rate compared to the other blends under the investigated range of refrigerant mass flow rates and heat flux. However, when the thermophysical properties are factored in, the condensation data showed that R-410A has the highest heat transfer rate at Reynolds number higher than 2.35E+7 Furthermore, experimental data of two phase condensation pressure gradient data across the test section at different Reynolds numbers showed that R-410A has the highest convective pressure drop among the blends under investigation.     

Prediction of condensation characteristics of alternatives to R-502 inside air–refrigerant enhanced surface tubing

In this paper, an experimental study on the heat transfer characteristics of two-phase flow condensation of alternative azeotropic refrigerant mixtures to R-502, on air/refrigerant horizontal enhanced surface tubing, is presented. The condensation data indicated that the heat transfer coefficient on the blend R-408A has the highest heat transfer rate among the blends under investigation. The condensation data also showed that R-502 and R-407B have similar heat transfer rates when plotted against the refrigerant mass flow rate. It also can be observed that, as the mass flux increases, heat transfer coefficient increases. Correlations were proposed to predict the heat transfer characteristics such as average heat transfer coefficients, as well as pressure drops of alternatives to R-502; such as R507, R404A, R407B and R408A in two-phase flow condensation inside enhanced surface tubing. In addition, proposed correlations were found to fairly predict the two-phase flow heat transfer condensation data.     

An Experimental Study of Condensation Heat Transfer in Sub-Millimeter Rectangular Tubes

The characteristics of local heat transfer and pressure drops were experimentally investigated using condensing R134a two-phase flow, in single rectangular tubes, with hydraulic diameter of 0.494, 0.658, and 0.972 mm. New experimental techniques were used to measure the in-tube condensation heat transfer coefficient especially for the low heat and mass flows. Tests were performed for a mass flux of 100, 200, 400, and 600 kg/m2s, a heat flux of 5 to 20 kW/m2, and a saturation temperature of 40℃. In this study, effect of heat flux, mass flux, vapor qualities, and hydraulic diameter on flow condensation were investigated and the experimental local condensation heat transfer coefficients and frictional pressure drop are shown. The experimental data of condensation Nusselt number are compared with previous correlations, most of which are proposed for the condensation of pure refrigerant in a relatively large inner diameter round tubes.     

Prediction of two‐phase condensation characteristics of some alternatives to R‐22 inside air/refrigerant enhanced surface tubing

The results of an experimental study on the heat transfer characteristics of two‐phase flow condensation of some azeotropic refrigerant mixtures, proposed as alternatives to R‐22, on air/refrigerant horizontal enhanced surface tubing are presented. The condensation data indicated that the heat transfer coefficient of the blend R‐408A has the highest heat transfer rate among the blends under investigation. The condensation data also showed that R‐507 and R‐404A have similar heat transfer rates to that of R‐22 when plotted against the refrigerant mass flow rate. It can also be observed that, as the mass flux increases, the heat transfer coefficient increases. Correlations were proposed to predict the heat transfer characteristics such as average heat transfer coefficients as well as pressure drops of alternatives to R‐22 such as R‐507, R‐404A, R‐407C and R‐408A, as well as R‐410A in two‐phase flow condensation inside enhanced surface tubing. In addition, proposed correlations were found to fairly predict the two‐phase flow heat transfer condensation data. Copyright © 2000 John Wiley & Sons, Ltd.     

Experimental study on saturated flow boiling heat transfer of R290/R152a binary mixtures in a horizontal tube

An experimental study on the saturated flow boiling heat transfer for a binary mixture of R290/R152a at various compositions is conducted at pressures ranging from 0.2 to 0.4 MPa. The heat transfer coefficients are experimentally measured over mass fluxes ranging from 74.1 to 146.5 kg/(m²·s) and heat fluxes ranging from 13.1 to 65.5 kW/m². The influences of different parameters such as quality, saturation pressure, heat flux, and mass flux on the local heat transfer coefficient are discussed. Existing correlations are analyzed. The Gungor-Winterton correlation shows the best fit among experimental data for the two pure refrigerants. A modified correlation for the binary mixture is proposed based on the authors’ previous work on pool boiling heat transfer and the database obtained from this study. The result shows that the total mean deviation is 10.41% for R290/R152a mixtures, with 97.6% of the predictions falling within ±30%.     

Numerical Study of Condensation Heat Transfer in Curved Square and Triangle Microchannels

Abstract

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 routines. The predictive accuracy of the numerical results is assessed by comparing the heat transfer coefficient with available correlation. After the validation, the effects of the mass flux and heat flux on heat transfer coefficient are analyzed in detail. Increasing mass flux could strengthen heat transfer performance, while wall heat flux has little effect on condensation heat transfer coefficient. The curved microchannels show an advantage in heat transfer enhancement comparing with the straight ones, and the enhancement performs better in curved microchannels with larger curvatures. Besides, the heat transfer performance could be enhanced in triangle microchannels in comparison with square microchannels.     

Condensation of organic binary mixtures flowing horizontally in a horizontal tube bundle

Both heat and mass transfer in the gas phase and heat transfer in the liquid phase are examined experimentally for film condensation of organic binary mixtures such as ethanol-water and methanol-water. Experimental results on the average heat flux, vapor-liquid interface temperature and liquid-phase Nusselt number are compared with analytical solutions based on stagnant film theory and heat-transfer relationships for film condensation from a pure vapor. Experimental heat transfer results agree well with the analytical solutions, except that the experimental liquid-phase Nusselt numbers under conditions of low mass fraction of water are considerably higher than predicted by the analytical solutions. This high value of the liquid-phase Nusselt number is considered to be caused by dropwise condensation in the liquid phase. However, its effect on the tube bundle is not so remarkable compared with that in gravity-controlled condensation on a vertical surface. This is considered to be caused by the condensate inundation effect. © 1997 Scripta Technica, Inc. Heat Trans Jpn Res, 25(6): 342–361, 1996     

Experimental study on condensation heat transfer enhancement and pressure drop penalty factors in four microfin tubes

Heat transfer and pressure drop characteristics of four microfin tubes were experimentally investigated for condensation of refrigerants R134a, R22, and R410A in four different test sections. The microfin tubes examined during this study consisted of 8.92, 6.46, 5.1, and 4 mm maximum inside diameter. The effect of mass flux, vapor quality, and refrigerants on condensation was investigated in terms of the heat transfer enhancement factor and the pressure drop penalty factor. The pressure drop penalty factor and the heat transfer enhancement factor showed a similar tendency for each tube at given vapor quality and mass flux. Based on the experimental data and the heat-momentum analogy, correlations for the condensation heat transfer coefficients in an annular flow regime and the frictional pressure drops are proposed.     

Boiling Heat Transfer Characteristics for Methane,Ethane and Their Binary Mixtures

Abstract

Methane (R50) and ethane (R170) are the dominated components of natural gas and the important components in mixture refrigerants for the mixture Joule–Thomson refrigeration cycle. In this article, experimental investigations on nucleate pool boiling and flow boiling heat transfer characteristics of R50, R170, and their binary mixtures are presented. The effects of saturation pressure, heat flux, mass flux, concentration, and vapor quality on heat transfer coefficients are analyzed and discussed. Firstly, the pool boiling heat transfer data were compared with six well-known correlations. Labuntsov correlation shows the best agreement with a mean absolute relative deviation (MARD) of 11.3%. Secondly, a new flow boiling heat transfer correlation for pure fluids was proposed based on the asymptotic addition of forced convection and pool boiling. The modified enhancement factor and suppression factor were developed to account for their relative contribution. In addition, in order to consider the mass transfer resistance of mixtures, a new mixture factor was deduced. The new flow boiling heat transfer correlations can well predict the experimental data with the MARD of 9.5% for pure fluids and 8.3% for mixtures.     

Condensation heat transfer and pressure drop of refrigerant R-410A flow in a vertical plate heat exchanger

Heat transfer and associated frictional pressure drop in the condensing flow of the ozone friendly refrigerant R-410A in a vertical plate heat exchanger (PHE) are investigated experimentally in the present study. In the experiment two vertical counter flow channels are formed in the exchanger by three plates of commercial geometry with a corrugated sinusoidal shape of a chevron angle of 60°. Downflow of the condensing refrigerant R-410A in one channel releases heat to the upflow of cold water in the other channel. The effects of the refrigerant mass flux, imposed heat flux, system pressure (saturated temperature) and mean vapor quality of R-410A on the measured data are explored in detail. The results indicate that the R-410A condensation heat transfer coefficient and associated frictional pressure drop in the PHE increase almost linearly with the mean vapor quality, but the system pressure only exhibits rather slight effects. Furthermore, increases in the refrigerant mass flux and imposed heat flux result in better condensation heat transfer accompanying with a larger frictional pressure drop. Besides, the imposed heat flux exhibits stronger effects on the heat transfer coefficient and pressure drop than the refrigerant mass flux especially at low refrigerant vapor quality. The friction factor is found to be strongly influenced by the refrigerant mass flux and vapor quality, but is almost independent of the imposed heat flux and saturated pressure. Finally, an empirical correlation for the R-410A condensation heat transfer coefficient in the PHE is proposed. In addition, results for the friction factor are correlated against the Boiling number and equivalent Reynolds number of the two-phase condensing flow.     

Surprising effects of combined vapour and liquid mass transfer resistances when condensing a mixture outside tube banks

Detailed calculations are carried out for condensation of a binary zeotropic mixture outside a tube bank to investigate combined effects of mass transfer resistances in the liquid and vapour phases. The question is how a change in mass transfer resistance in the vapour phase can influence the heat flux. The surprising result is that a decrease in resistance in the vapour phase by reducing the tube pitch, and thus increasing the vapour velocity, reduces the heat flux between 20% and 50% for the conditions studied. This is due to a combination of mass transfer resistance, depletion of the heavy volatile component, and a reduction of the phase interface temperature.     

Effect of an interfacial shear stress on steam condensation in the presence of a noncondensable gas in a vertical tube

Experimental and analytical studies were performed to examine local condensation heat transfer coefficients in the presence of a noncondensable gas inside a vertical tube. The experimental data for pure steam and steam/nitrogen mixture bypass modes were compared to study the effects of noncondensable nitrogen gas on annular film condensation phenomena. The condenser tube had a relatively small inner diameter of 13 mm. The experimental results demonstrated that the local heat transfer coefficients increased as the inlet steam flow rate increased and the inlet nitrogen mass fraction decreased. The results obtained using steam/nitrogen mixtures with a low inlet nitrogen mass fraction were similar to those obtained using pure steam. Therefore, the effects of noncondensable gas on steam condensation were weak in the small-diameter condenser tube because of interfacial shear stress. A new correlation based on dimensionless shear stress and noncondensable gas mass fraction variables was developed to evaluate the condensation heat transfer coefficient inside a vertical tube with noncondensable gas, irrespective of the condenser tube diameter. A theoretical model using a heat and mass transfer analogy and simple models using four empirical correlations were developed and compared with the experimental data obtained under various experimental conditions. The predictions of the theoretical model and the simple model based on a new correlation were in good agreement with the experimental results.     

Two‐phase flow convective condensation of refrigerant mixtures under gas/liquid injection

The influence of gas/liquid injection on two‐phase flow condensation heat transfer characteristics of some refrigerant mixtures in horizontal enhanced surface tubing is presented. Correlations were proposed to predict the impact of the gas/liquid injection on the heat transfer characteristics such as average heat transfer coefficient of R‐507, R‐404A, R‐410A, and R‐407C in two‐phase flow condensation inside enhanced surface tubing. The data also revealed that gas, liquid and gas/liquid injection is beneficial at certain gas/liquid injection ratios to the heat transfer coefficient depending upon the Reynolds number and the condensation point of the refrigerant mixtures in question. It was also evident that the proposed condensation correlations and the experimental data were applicable to the entire heat and mass flux, investigated in the present study under gas/liquid injection conditions. The deviation between the experimental and predicted under gas/liquid injection were less than ± 10, for the majority of data. Copyright © 2005 John Wiley & Sons, Ltd.     

Condensation of n-Hexane and Isopropanol Mixed with a Noncondensable Gas in a New Plate Heat Exchanger Geometry

This article presents a study of heat transfer during condensation of n-hexane or isopropanol with a noncondensable gas (nitrogen) in a new plate heat exchanger geometry. Three test sections were installed on the test rig devoted to condensation of mixtures, either in reflux or co-current condensation configurations. For both configurations, heat transfer measurements were carried out. In single-phase flow tests, experimental data reduced by a log mean temperature difference were compared with new correlations on the gas side, adapted to the present specific plate geometry. Correlations of the Fanning friction factor were deduced from gas-side pressure drop measurements on the two geometries tested. In two-phase flow tests, the log mean temperature difference method was assumed to be correct to the first-order for the comparison of results in two test sections. The condensation curve method was applied to the present results, and co-current and reflux condensation configurations were then compared in terms of experimental overall heat transfer coefficients. It is shown that for a gas Reynolds number higher than 2,000, heat transfer coefficients in reflux condensation become higher than those for co-current condensation. Flooding phenomena were observed for specific experimental conditions in reflux condensation mode. The flooding experimental data are compared with five existing correlations (i.e., Wallis, modified Wallis, English et al., McQuillan & Whalley, and Zapke & Kröger) to observe fluid property effects for the same ranges of heat duty and mass flow rates in the condenser. The English et al. and Zapke & Kröger correlations show the best agreement with experimental flooding data in the present geometry.     

Nucleate Pool Boiling Heat Transfer of Pure Refrigerants and Binary Mixtures

Heat transfer coefficients in nucleate boiling on a smooth flat surface were measured for pure fluids of R-134a, propane, isobutane and their binary mixtures at different pressure from 0.1 to 0.6 MPa. Series of experiments with different heat flux and mixture concentrations were carried out. The influences of pressure and heat flux on the heat transfer coefficient for different pure fluids were studied. Isobutane and propane were used to make up binary mixtures. Compared to the pure components, binary mixtures show lower heat transfer coefficients. This reduction was more pronounced as the heat flux increasing. Several heat transfer correlations are obtained for different pure refrigerants and their binary mixtures.     

水平管外TFE/NMP部分膜状冷凝热、质耦合传递过程研究

通过对水平管外双组分(TFE／NMP为三氟乙醇／氮甲基吡咯烷酮)部分膜状冷凝过程特点的分析，建立起部分膜状冷凝过程中热质传递过程的物理模型。以双膜理论为基础，利用部分膜状冷凝的特点，通过对界面传质、液膜内质量平衡、界面相平衡、界面能量平衡和汽膜截面能量平衡的分析计算，得到汽相温度和界面温度分布、汽相及液相NMP质量分数分布，由此进一步计算出冷凝膜厚分布、液膜传热系数分布和热流密度的分布。计算的热流密度与相关实验作了比较，发现与实验能较好的吻合。     

The experimental and numerical investigation of a grooved vapor chamber

An effective thermal spreader can achieve more uniform heat flux distribution and thus enhance heat dissipation of heat sinks. Vapor chamber is one of highly effective thermal spreaders. In this paper, a novel grooved vapor chamber was designed. The grooved structure of the vapor chamber can improve its axial and radial heat transfer and also can form the capillary loop between condensation and evaporation surfaces. The effect of heat flux, filling amount and gravity to the performance of this vapor chamber is studied by experiment. From experiment, we also obtained the best filling amount of this grooved vapor chamber. By comparing the thermal resistance of a solid copper plate with that of the vapor chamber, it is suggested that the critical heat flux condition should be maintained to use vapor chamber as efficient thermal spreaders for electronics cooling. A two-dimensional heat and mass transfer model for the grooved vapor chamber is developed. The numerical simulation results show the thickness distribution of liquid film in the grooves is not uniform. The temperature and velocity field in vapor chamber are obtained. The thickness of the liquid film in groove is mainly influenced by pressure of vapor and liquid beside liquid–vapor interface. The thin liquid film in heat source region can enhance the performance of vapor chamber, but if the starting point of liquid film is backward beyond the heat source region, the vapor chamber will dry out easily. The optimal filling ratio should maintain steady thin liquid film in heat source region of vapor chamber. The vapor condenses on whole condensation surface, so that the condensation surface achieves great uniform temperature distribution. By comparing the experimental results with numerical simulation results, the reliability of the numerical model can be verified.     

Condensation in a vertical tube bundle passive condenser – Part 2: Complete condensation

An experimental study of the tube bundle effect on heat removal capabilities in complete condensation mode of a passive condenser was performed. A full scale test section, with four condenser tubes, was designed and constructed to simulate operating conditions of a passive containment cooling system. For complete condensation analysis, pure steam was supplied to the test section and heat transfer properties were measured for pressure from 100 to 280 kPa. The condensation heat transfer results were similar to the findings from single tubes, except for a slightly higher condensate mass flux. This was determined to be a result of turbulent mixing in the secondary boiling water caused by the tube bundle.     

High-pressure Condensing Refrigerant Flows Through Microchannels,Part II: Heat Transfer Models

ABSTRACT

Condensation of high-pressure refrigerants in small-diameter channels over a wide range of reduced pressures approaching the critical point is investigated in this two-part study. Part I presented pressure drop measurements and a two-phase pressure drop model. In this paper, Part II of the study, a condensation heat transfer model is presented. Heat transfer coefficients were measured during condensation of R404A in circular channels (inner diameter = 0.86, 1.55, 3.05 mm) over the entire quality range. The saturation temperature was varied from 30 to 60°C, and mass flux from 200 to 800 kg m^-2 s^-1, to evaluate their effects on condensation heat transfer coefficient. The heat transfer model is developed using a microchannel flow regime map and the void fraction model previously developed by the authors. The resulting model predicts 93.6% of the data within ±25%. The model exhibited good agreement with data from condensing ammonia and carbon dioxide, predicting 84.8% and 97% of their data within ±25%, respectively.     

Evaporation heat transfer and pressure drop characteristics of R-290 (propane), R-600 (butane), and a mixture of R-290/R-600 in the three-lines serpentine small-tube bank

This paper reports an experimental investigation of heat-transfer and pressure-drop behavior of R-290, R-600, and R-290/R-600 in the three-lines serpentine small-diameter (2.46 mm) tube bank. Heat transfer coefficients and pressure drop characteristics are measured for a range of heat flux (5–21 kW/m²), mass flux (250–500 kg/m² s), equilibrium mass quality (0–0.86), and the fixed mixture composition ((R-290/R-600 (55 wt.%/45 wt.%)). The results show that the flow boiling heat transfer coefficients for R-290, R-600, and R-290/R-600 are 1.66–1.96-fold, 1.28–1.38-fold and 1.57–1.88-fold greater as compared with those for R-134a under equal heat and mass fluxes. Also, the two-phase flow frictional pressure drop for R-600, R-290/R-600 and R-290 are 1.41–1.60-fold, 1.32–1.50-fold and 1.22–1.40-fold smaller as compared with that for R-134a. A new heat transfer correlation was presented by using a superposition model to predict the experimental data for both pure refrigerants and refrigerant mixtures. Experimental results were compared with several correlations which predict the evaporative heat transfer, which are in good agreement with experimental data.