Heat Transfer Coefficient Of R134a Research Articles

Experimental study on falling film evaporation heat transfer outside a horizontal tube in refrigeration system

Experimental study on falling film evaporation heat transfer outside a horizontal tube in refrigeration system

Condensation Heat Transfer Experiments of R410A and R32 in Horizontal Smooth and Enhanced Tubes

Abstract A horizontal smooth copper tube and two enhanced tubes (a dimpled tube and a diamond-shaped tube) with a length of 2 m and an outer diameter of 9.52 mm were studied in a two-phase condensation experiment using R410A and R32 as heat transfer working fluids. The condensation heat transfer performance of different heat transfer tubes at various mass fluxes ranging from 150 to 400 kg/(m2s) and different vapor qualities ranging from 0.8 to 0.2 was studied experimentally. For R410A, the heat transfer coefficients (HTCs) of the dimpled tube and the diamond-shaped tube were found to be 1.39–1.52 times and 1.30–1.35 times higher than those of the smooth tube, respectively. For R32, the HTCs were found to be 1.46–1.59 times higher for the dimpled tube and 1.26–1.35 times higher for the diamond-shaped tube than for the smooth tube. The diamond-shaped tube was found to be effective in directing the flow of the liquid phase and in thinning the liquid film thickness. The dimpled tube was found to promote droplet entrainment and disturbance. Both of those effects contributed to improving the HTCs in the two enhanced tubes investigated. The HTCs of R410A were found to be lower than those of R32 because of the smaller specific heat capacity, smaller latent heat of condensation, and relatively poorer thermal conductivity of R410A. Taking the combined effect of heat transfer and pressure drop into account, a performance enhancement factor (PEF) was computed and was found to range from 0.9 to 1.51. Based on the experimental data collected, a new empirical correlation equation has been proposed with a maximum error band of 10%. Flow pattern maps for the tested tubes have also been generated and are presented in the paper. Both of the two enhanced tubes were found to promote the development of annular flow. The HTCs were found to be highest when the flow pattern was of the annular flow type.

Experimental study of the heat transfer of supercritical R1234yf as a substitute for R134a in a horizontal micro-fin tube

R1234yf is regarded as an ideal substitute for R134a in supercritical organic Rankine cycles. This study experimentally analyzed the convective heat transfer coefficients of supercritical R1234yf in a micro-fin tube. The experiments show the influence of the system operating parameters including pressure, heat flux and mass flux on the heat transfer. Then, this paper compares the heat transfer rates for R1234yf and R134a at supercritical pressures and the ability of existing correlations to predict the heat transfer coefficients with R1234yf. The results show that as q/G increases, the buoyancy increases Nubottom, while the variations in Nutop are divided into two regions based on the bulk fluid enthalpy. The influence of pressure on the heat transfer is also related to the bulk fluid enthalpy. When the bulk fluid enthalpy is less than a critical value, Nubottom and Nutop both increase with decreasing pressure and then decrease above this critical enthalpy. The heat transfer coefficient is no longer enhanced at the top with large buoyancy forces. For low mass fluxes, the heat transfer coefficients of R134a and R1234yf are similar. For high mass fluxes, the heat transfer coefficients of R134a are higher than those of R1234yf. The Wang correlation, that was based on R134a data, more accurately predicts the heat transfer coefficients than other correlations for supercritical R1234yf in the horizontal micro-fin tube. Among all the 4050 experimental points, 90.17% of Nutop and 84.49% of Nubottom were predicted with errors of less than 30% by the Wang correlation.

Flow condensation heat transfer and pressure drop of R134a alternative refrigerants R513A and R450A in 0.95-mm diameter minichannels

Due to the Kigali amendment to the Montreal Protocol, refrigerants such as R134a are targeted for phasedown or phaseout due to their global warming potential (GWP) and lower GWP refrigerants are being considered to replace R134a. Since the condenser is typically responsible for 50% of the charge of a refrigeration system, it is vital to have a fundamental understanding of the flow condensation heat transfer performance of low GWP refrigerants such as R513A and R450A. Experimental flow condensation heat transfer coefficient data are reported for R134a, R513A, and R450A in seven parallel 0.95 mm diameter mini-channels for a range of mass fluxes (i.e., 200 – 500 kg/m2s) and qualities (i.e., 0.2 – 0.8) at a saturation temperature of 40 °C. The heat transfer coefficient uncertainties for all experiments were ± 6.3 – 21.2%, with an average of ± 9.8%. Condensation heat transfer coefficients for R134a, R513A, and R450A all increased with increasing mass flux and quality. R513A condensation heat transfer coefficients were 2.6 – 25.6% lower than R134a heat transfer coefficients and pressure drops were 4.5 – 14.0% lower than R134a pressure drops. R450A heat transfer coefficients were 2.4% higher than R134a at higher mass fluxes and qualities and up to 11.7% lower than R134a at lower mass fluxes than R134a heat transfer coefficients; R450A pressure drop were comparable to R134a pressure drop (i.e., 5.0% higher to 9.5% lower). The data were compared to three condensation correlations – Shah (2016), Kim and Mudawar (2013), and Cavallini et al. (2011); the data were predicted with mean average errors of 23.4%, 15.9%, and 23.4%, respectively.

R410A flow boiling coefficient in horizontal annular channels of enhanced tubes, Part II: Heat transfer

Flow boiling heat transfer coefficient of R410A in horizontal annular channels were evaluated with a 279 K saturation temperature over a mass flux range of 50–80 kg/(m2s) and a vapor quality range of 0.2–0.8. All the four tested annulus have a 19 mm outer diameter of the flow channel containing three types of enhanced tubes (a micro-porous tube, a ring-shaped finned tube, and an independent small-bosses surface tube) and a smooth tube. The micro-porous tube benefitted by its surface shows the highest heat transfer coefficient (the enhancement factor exceeds 2.52) in flow boiling. The smooth tube shows a higher heat transfer coefficient than the independent small bosses tube due to its special surface structure. For changing average vapor quality of outlet and inlet, the heat transfer coefficients of the micro-porous tube and smooth tube increase with the increase of the average vapor quality. Considering the heat transfer coefficient and the data of pressure drop in all of these annular channels reveals that the micro-porous tube can be a great choice for flow boiling on the annular side for the best performance. The results from correlation analysis of smooth tube predict experimental data with a ± 10% error band. The improved correlations for enhanced tubes were presented, and the experimental values are predicted within a ± 2% error band.

Experimental study of condensation heat transfer of R134a inside the micro-fin tubes at high mass flux

The flow condensation heat transfer coefficient of R134a inside two helical micro-fin tubes with outer diameter of 6.35 mm and helical angles of 18o and 28o respectively were experimentally studied at a high mass flux ranging from 500 to 1100 kg m−2 s−1. The condensation temperatures are 35°C, 40°C and 45°C, and the vapor qualities ranges from 0.95 to 1.00 at the inlet section and from 0.00 to 0.05 at the outlet section. Experimental results show that there are annular and intermittent flow regimes inside the tube under experimental conditions, the ratio of annular flow region to the total heat transfer region is about 70%. The liquid film flow changes from rotational flow to coexistence of rotational and horizontal flows when the vapor quality is 0.475±0.08, 0.486±0.06 and 0.521±0.05, respectively and the corresponding saturation temperature is 35°C, 40°C and 45°C. Based on the experimental data, the heat transfer coefficient increases with increasing mass flux and fin helical angle, and with decreasing saturation temperature and Reynolds number of cooling water. In addition, the heat transfer coefficient of annular flow is greater than that of intermittent flow, in other words, the heat transfer coefficient increases with increasing vapor quality. The heat transfer coefficient obtained at high mass flux was compared with the calculated data of some published correlations used at low mass flux. It was found that most correlations underestimate the experimental heat transfer coefficient inside the micro-fin tube, and these prediction deviation increases with increasing mass flux and fin helical angle. By introducing some dimensionless numbers as well as considering the flow mechanism of liquid film inside the tube, two heat transfer coefficient correlations were proposed based on the experimental data. The ratio of liquid film thickness to fin height was used to characterize whether the liquid film flow is rotational flow or coexistence of rotational and horizontal flows in the proposed correlation, which shows a better prediction accuracy with a mean deviation of less than 7.3%.

Comparison of the mixed flow and heat transfer characteristics in the evaporator of a vapor compression heat pump in normal gravity and microgravity

As a thermal control system for space applications, the vapor compression heat pump is crucial for the future development of aerospace technology. The evaporator in the heat pump is significantly affected by the space environment. Lubricant is present in the system during the operation, and the gas-liquid separation is difficult to achieve in a microgravity environment. The oil-containing refrigerant may form an oil film on the evaporator wall, and deposition may occur. A mixed flow and heat transfer model of the refrigerant and lubricating oil in the evaporator of the vapor compression heat pump was established to investigate the gas-liquid separation and lubricating oil deposition of the vapor compression heat pump in microgravity. The heat flux effects on the flow and heat transfer characteristics were simulated in normal gravity and microgravity using FLUENT. The simulation and experimental results of the evaporator outlet temperature in normal gravity were compared, and the simulation results of the heat transfer coefficient of the refrigerant R134a were compared with experimental data obtained from the literature. The results demonstrate that the velocity field exhibits a large gradient and an asymmetric distribution in normal gravity and an asymmetric distribution with lower values in the lower and upper right positions in microgravity. The heat transfer performance of the evaporator is lower in microgravity than in normal gravity for the same heat flux. For the same heat flux (100000 W/m2), the vapor phase volume ratio of the evaporator outlet is 0.95-1 in normal gravity and 0.6-0.7 in microgravity. After the phase change of the refrigerant and lubricant mixture in the evaporator, the lubricant deposition is not affected by the heat flux in normal gravity and microgravity, and normal oil return occurs. A maximum deviation of 14.9% is observed between the simulated and experimental values of the evaporator outlet temperature in normal gravity. The heat transfer coefficient of the R134a obtained from the simulation is within the range of the experimental values in the literature. This work expands our understanding of microgravity two-phase flow heat transfer and provides theoretical guidance for the development of the evaporator in vapor compression heat pumps for aerospace applications.

An Experimental Investigation on R134a Evaporation inside an Internally Discrete Inclined Grooved Tube

In this experimental study, heat transfer and pressure drop characteristics of R134a evaporating flow are investigated inside a horizontal internally grooved tube with discrete inclined grooves. The test evaporators are made of smooth and grooved copper tubes of 20 mm inner diameter. The length, width, and depth of grooves are 6, 2, and 0.5 mm, respectively, and the angle of the grooves with the tube centerline is 30°. The test conditions include mass flux in the range of 16.5 to 105 kg/m2s, vapor quality of 0.06 to 0.98, and heat flux of 3.5 to 25 kW/m2. The experiment results show that the boiling heat transfer coefficient of R134a in the grooved tube is 1.25 to 1.65 times higher than that of the smooth one. The frictional pressure drop of R134a inside the grooved tube is 10% to 60% higher than the smooth tube. Moreover, by increasing mass flux, the heat transfer coefficient, and frictional pressure drop of R134a refrigerant inside horizontal smooth and grooved tubes increase as well. In conclusion, the energy performance of R134a evaporating flow inside the grooved tube is more efficient than that in the smooth tube regarding energy saving in most experiments.

Effect of subsurface tunnel on the nucleate pool boiling heat transfer of R1234ze(E), R1233zd(E) and R134a

Nucleate pool boiling heat transfer of R1234ze(E), R1233zd(E) and R134a were investigated outside two reentrant cavity tubes. The two tubes have different fin density while the size of subsurface tunnel width and fin height are almost the same. In the experiment, the pool boiling heat transfer is tested at the saturation temperature of 6 °C and heat flux of 10–80 kW/m 2 . A brief summary of pool boiling experimental data of Hydrofluoroolefins(HFO) refrigerants on different enhanced tubes from recent work is also provided. It is found that the combinations of tube and refrigerant: R134a and R13234ze(E) outside Tube-B1 shows almost equivalent boiling heat transfer performance. The two combinations also yield the highest averaged overall heat transfer coefficient. At the lower heat flux less than 60 kW/m 2 , for the tube with larger fin density and thinner fin thickness, the number of nucleation cavities is found to be more than that with larger fin thickness. At the heat flux more than 40 kW/m 2 , the boiling heat transfer coefficient of R134a and R1234ze(E) for the two enhanced tubes nearly merges into a single curve. At the higher heat flux, boiling heat transfer shows weak dependence on the surface structures. The boiling heat transfer coefficient of R1233zd(E) is more than 40 percentages lower than R134a for the two tubes at the nearly identical conditions. The research is helpful for the designer to summarize the boiling heat transfer performance of some typical HFO refrigerants.

Experimental study on flow boiling heat transfer characteristics of R134a, R245fa and R134a/R245fa mixture at high saturation temperatures

The flow boiling heat transfer characteristics of R245fa, R134a and non-azeotropic mixture R134a/R245fa (0.33/0.67 by mass) at high saturation temperatures were investigated in a horizontal tube with 10 mm I.D. Effects of high saturation temperatures on heat transfer coefficients of R134a, R245fa and the mixture were investigated from 55 °C to 95 °C. Heat flux was controlled from 6 to 24 kW/m2 and mass flux ranged from 100 to 300 kg/m2.s. The results show the heat transfer coefficient of the mixture (R134a/R245fa with 33%/67% by mass) is much lower than that of pure R134a and is close to that of pure R245fa. At high saturation temperatures, mass flow rate has less influence on heat transfer coefficient of R245fa and the mixture at a large heat flux. The heat transfer coefficients of three working fluids increase slightly when the saturated temperatures change within 10 °C. The pressure drops of pure R245fa and the binary mixture were studied and the pressure drop of the mixture (R134a/R245fa with 33%/67% by mass) is a little higher than that of R245fa.A modified heat transfer correlation considering the mixing effect of binary mixture is proposed for the mixture of R245fa/R134a, and the mean absolute deviation is within 20%. A modified two phase frictional factor for the mixture is proposed and the deviation of the mixture using modified two phase frictional factor is between −6% and +22%.

Pool boiling heat transfer on a plain tube in saturated R-134a and R-410A

The present paper presents the results of an experimental investigation on nucleate pool boiling heat transfer of pure fluid R-134a and environmentally harmless azeotropic refrigerant mixtures R32/R125 (R-410A) on a plain horizontal copper tube. The experiment has been carried out at saturation temperatures of 5, 10, 15 and 20 °C for heat fluxes ranging from 10 to 70 kW/m2 with an interval of 10 kW/m2 in the increasing order of heat flux. The diameter of the test tube was 25.4 mm and an effective length of 130 mm. From experimental results, it is found that the boiling heat transfer coefficient increases with increasing the heat flux and also found that the heat transfer coefficient of refrigerant R-134a was 20–39% lower than that of refrigerant R-410A. Experimental data were compared with empirical correlations available in the literature. The Jung and Gorenflo correlations were well balanced with the present data of both refrigerants at given saturation temperatures. The Jung correlation over-estimates the experimental data of R-134a by 19% and 23% for R-410A where as Gorenflo correlation overpredics the present data of refrigerants R-134a and R-410A about 20% and 50% respectively. The thermal performance of a plain tube was correlated in terms of non-dimensional form having different dimensionless numbers to evaluate the pool boiling heat transfer coefficients of R-134a and R-410A. This correlation showed a good agreement with measured data within an error of ±12 percent.

Film-wise condensation of R-134a, R-1234ze(E) and R-1233zd(E) outside the finned tubes with different fin thickness

Film-wise condensation of R-134a, R-1234ze(E) and R-1233zd(E) outside two enhanced tubes was experimentally investigated. The two tubes have the same fin density and similar fin height while the fin thickness is different. In the experiment, the saturation temperature was 36 °C. Heat flux was in the range of 20–90 kW·m−2. It was found that R-134a was more efficient than other refrigerants and gave the highest heat transfer performance outside the two tubes. R-1233zd(E) was the lowest. Condensing heat transfer coefficient of R-134a was approximately 2 times higher than R-1233zd(E). As heat flux was higher than 20 kW·m−2, condensing heat transfer coefficient of R-134a and R-1234ze(E) all decreased as the increasing of heat flux. While for R-1233zd(E), up to the heat flux of 90 kW/m2, the condensing heat transfer coefficient is ever-increasing as the increasing of heat flux. The condensing heat transfer of R-134a was 10–20% higher than R-1234ze(E). The trend of variations for the heat transfer performance of R-134a and R-1234ze(E) was similar. The present work examined the heat transfer characteristics of finned tubes with different fin thickness. It is helpful for the designers to summarize the heat transfer performance of some new HFOs refrigerants having the potential to be used in the water cooled chillers or heat pumps.

Experimental heat transfer coefficient during condensation of R-410A in horizontal micro-fin tubes

Condensation heat transfer coefficient has been calculated experimentally in microfin tubes of outer diameter 9.52mm with helix angles 15° and 18°. Condensation of refrigerant R-410A include mass fluxes from 200 to 600 kg/m2s, vapour qualities between 0.1 to 0.9 and saturation temperature at 35 °C and 40°C. The experimental results indicate that the average heat transfer coefficients of R-410A in micro-fin (MF) tubes were increased 1.15-1.47 times larger than those of smooth tube (ST). The experimental results are compared with the existing correlations of heat transfer coefficient proposed by other authors. The comparison indicated good agreement with these existing correlations within ±30%. A correlation has also been developed for predicting condensation heat transfer coefficient in micro-fin tubes.

Condensing heat transfer coefficients of R134a in smooth and grooved multiport flat tubes of automotive heat exchanger: An experimental investigation

Condensation heat transfer coefficient of R134a was obtained in multi-port micro channel smooth and grooved flat tubes of automotive heat exchanger. The test consisted of two smooth and one grooved tube. The test range covered mass flux 490–1600 kg/m2 s, heat flux 5.5–19 kW/m2 and saturation temperature 51–68 °C. Results revealed that condensation heat transfer coefficient increased with an increment of mass flux, vapor quality and decreased with the increase of saturation temperature. The effect of heat flux on heat transfer coefficient was negligible. The grooved tube showed larger heat transfer coefficient than that of smooth tubes. A comparison of the present data of flat tube with existing correlations revealed that the heat transfer coefficient was not reasonably predicted, therefore new correlation was developed for heat transfer coefficient that predicted 86% data within ±30% with a mean error of 16%.

Comparative analysis for the prediction of boiling heat transfer coefficient of R134a in micro/mini channels using artificial intelligence (AI)-based techniques

ABSTRACTRefrigerant R134a has been extensively used in the past because of its zero ozone depletion potential (ODP). In the present research, artificial intelligence (AI)-based gene expression programming (GEP), artificial neural networks (ANN) and support vector regression (SVR) models have been developed for the prediction of heat transfer coefficient for the boiling of R134a in micro/mini channels. The performances of developed models were compared and evaluated against the experimental results in terms of statistical parameters such as coefficient of determination (R2) and average absolute relative error (AARE). The obtained results and findings from this research reveal that SVR is an effective technique for predicting the heat transfer coefficient of R134a, with lowest AARE value of 3.62% and a high R2 value of 0.9749 in comparison with other AI-based models. Furthermore, performance of the ε-SVR with four different kernels: linear, polynomial, sigmoid and radial basis functions (RBF) have also been assessed in this paper.Abbreviations: AARE: Average absolute relative error; AI: Artificial intelligence; ANN: Artificial neural networks; GEP: Gene expression programming; MRE: Mean relative error; RMSE: Root mean square error; SD: Standard deviation; SVM: Support vector machines; SVR: Support vector regression

Wilson Plot 방법을 적용한 막 응축용 전열촉진관들의 열전달 및 압력강하 특성비교

In this study, experimental investigations were carried out to compare the heat transfer and pressure drop characteristics of enhanced tubes using film condensation. Five enhanced tubes were selected for the performance comparison experiment. The velocity of the coolant ranged from 1.4 m/s to 2.6 m/s. The saturated condensation temperature, fixed at 38℃. R134a and R1234ze(E), were used as refrigerants. The resulting outside and inside heat transfer coefficients were between 11.04 kW/m²·K and 21.30 kW/m²·K and between 10.38 kW/m²·K and 24.69kW/m²·K. The film condensation heat transfer coefficients of R134a showed an average of about 10% higher than that of R1234ze(E). The heat transfer rate of enhanced tube number 4 obtained from the experiment was about 36% higher than that of enhanced tube number 1. This study proposed a performance comparison of enhanced tubes and development of experimental heat transfer correlations for coolant. In the present study, an experimental correlation of the Nusselt number for the coolant was proposed, and this correlation has a ±20% margin of error.

An experimental investigation of flow boiling heat transfer coefficient and pressure drop of R410A in various minichannel multiport tubes

The present work demonstrates the two-phase flow boiling heat transfer coefficient and pressure drop of R410A inside various minichannel multiport tubes. The experimental investigation was performed in four tube types with the hydraulic diameters of 1.16, 1.14, 1.07 and 0.96 mm and the number of parallel channels are 7, 11, 16 and 9, respectively. The data were conducted with the heat fluxes of 3 and 6 kW m−2, the mass flux ranging from 50 to 500 kg m−2 s−1, the saturation temperature of 6 °C and the vapor quality up to 1.0. The heat transfer coefficient of R410A was found to be affected by the heat flux, mass flux, vapor quality and the geometry of channel. The frictional pressure drop gradient was also affected by the mass flux and vapor quality but independent with the variation of heat flux. In addition, the present data were compared with various heat transfer coefficient correlations and pressure drop models in literature. Finally, new correlation of heat transfer coefficient was proposed based on the present experimental data.

Condensation heat transfer of R134a, R1234ze(E) and R290 on horizontal plain and enhanced titanium tubes

An experimental investigation on the condensation of R134a, R1234ze(E) and R290 outside plain and enhanced titanium tubes was conducted. The saturation temperature in the experiments was 35 °C to 40 °C, and heat flux was in the range of 8–80 kW/m2. Effects of heat flux, refrigerant and saturation temperature on heat transfer were investigated. The heat transfer enhancement ratio of overall heat transfer coefficient decreased with increasing heat flux. It was found that the condensing heat transfer coefficient of R134a, compared with R1234ze(E) and R290, was the largest for plain and enhanced tubes. Saturation temperature had minor effect on condensing heat transfer coefficient for R134a, R1234ze(E) and R290 for plain tube. The effect of saturate temperature on the condensing heat transfer of R134a and R1234ze(E) was even negligible for enhanced tube. While, the condensing heat transfer coefficient of R290 for enhanced tube was increasing with increment of saturation temperature. Experimental condensing heat transfer coefficient were also compared with five predicting models for low-fin tube. It showed that the model of Briggs–Rose gave a better prediction result for R134a and R1234ze(E), while the model underestimated the experimental result for R290.

Evaporation Heat Transfer Coefficients of R-446A

ABSTRACTThe present study investigated the evaporation heat transfer coefficients of R-446A, as a low global warming potential alternative refrigerant to R-410A. The evaporation heat transfer coefficients were obtained by measuring the wall temperature of a straight stainless tube and refrigerant pressure. The heat transfer coefficients were measured for the quality range from 0.05 to 0.95, the mass flux from 100 to 400 kg/m2s, heat flux from 10 to 30 kW/m2, and saturation temperature from 5 to 10°C. The evaporation heat transfer coefficient of R-410A was verified by comparing the measured evaporation heat transfer coefficient with the value predicted by the existing correlation. The evaporation heat transfer coefficient of R-446A was measured using a proven experimental apparatus. When the heat flux was 10 kW/m2, the evaporation heat transfer coefficient of R-446A was always higher than that of R-410A. But, when the heat flux was 30 kW/m2, the evaporation heat transfer coefficient of R-446A was measured to be lower than that of R-410A near the dry-out point. The effect of the tube diameter on the R-446A evaporation heat transfer coefficient was negligible. The effect of saturation pressure on the evaporation heat transfer coefficient was prominent in the low quality region where the nucleate boiling was dominant.

Experimental investigation and development of new correlation for flow boiling heat transfer in mini-channel

The flow boiling heat transfer of refrigerant R134a in horizontal multiport mini-channel was experimentally investigated in this paper. Two kinds of mini-channels made of aluminum alloy with the hydraulic diameter of 0.63 mm for 23 rectangular channels and 0.72 mm for 14 rectangular channels were studied. Electric heating film was adopted to provide direct uniform heat flux. The experimental results were obtained with the vapor quality between 0 and 1, the heat flux ranging from 10 to 60 kW/m2, the mass flux ranging from 128 to 560 kg/(m2.s) and the saturation pressure from 0.22 to 0.58 MPa. It was found that nucleate boiling dominates in the low vapor quality region and the heat transfer coefficients of mini-channel are higher than those in conventional channel. The heat transfer coefficients increase with the increasing of both heat flux and saturation pressure but have little dependence with the mass flux. In the high vapor quality region, connective boiling is the main contributor. Heat flux and saturation pressure have little influence on the heat transfer coefficients, but the influence of mass flux is obvious. There is a small increase in heat transfer coefficient with an increase of mass flux. Accordingly, a new correlation for flow boiling heat transfer in mini-channel of R134a was proposed based on Gungor and Winterton correlation. The mean relation deviation is −1.76% and the mean absolute relation deviation is 19.0% respectively. This new correlation is proved to have an obvious accuracy improvement in predicting the flow boiling heat transfer coefficient of R134a in mini-channel. The present work can provide a guidance to the design of mini-channel heat exchanger.