Condensation Heat Transfer Of R410A Research Articles

Condensation heat transfer in annuli outside horizontal stainless steel enhanced tubes

The condensation heat transfer of R410A outside several enhanced heat transfer (EHT) tubes [dimple/herringbone (DIM/HB), herringbone (HB), and dimple (DIM)] and smooth tube were evaluated. All tubes are made of stainless steel; the test length is 2 m; the outer diameter is 12.7 mm; the inner diameter is 11.5 mm. Experimental conditions were set at a saturated temperature of 45 °C; condensed vapor mass decreased from 0.8 to 0.2; mass flux ranged between 75 and 225 kg m−2 s−1. As a result, the HB tube effectively improved flow condensation performance outside tubes; while the dimple-only structure is not effective since it produces a lower heat transfer coefficient (HTC) than a smooth tube (at some low flow rate conditions). Substantial enhancement is produced by the DIM/HB composite surface produced from dimple and herringbone microfin patterns, which is due to the combination of the liquid drainage effects by herringbone structure to remove condensate and causing strong turbulence of dimple structure. With the increase of mass flux and average vapor quality, the condensation heat transfer coefficient and pressure drop of each test tube increase as well. Additionally, an improved Nusselt equation for external condensation on a smooth tube was developed to predict the heat transfer coefficient for the experimental conditions considered here. Finally, correlations of enhanced heat transfer (EHT) tubes (microfin – HB, dimple - DIM, and composite surface – DIM/HB) to predict condensation heat transfer coefficient were developed and evaluated.

Condensation heat transfer characteristics and pressure drops of R410A, R22, R32, and R290 in a multiport rectangular channel

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 with heat fluxes in the range of 3 to 15 kW/m2, working fluids mass fluxes in the range of 50 to 500 kg/m2s, and vapor quality up to 1.0, at a fixed saturation temperature of 48 °C. The test section is an aluminum multiport minichannel tube with a hydraulic diameter equal to 0.83 mm and 18 rectangular channels. The effects of mass flux, heat flux, and thermal properties of refrigerants on the heat transfer performance and pressure drop are illustrated and analyzed. The experimental heat transfer coefficients are compared with well-known correlations. Finally, from the experimental data, a new condensation heat transfer coefficient correlation for all refrigerants is proposed.

Condensation heat transfer of R410A on outside of horizontal smooth and three-dimensional enhanced tubes

Experimental investigations of flow condensation on the outside surface of one smooth tube and two enhanced surface tubes with the same outer diameter of 12.7 mm were conducted. The refrigerant flowed in an annular space between the test tube and the outer tube. The newly developed 2EHT three-dimensional surfaces have multiple enhancement patterns made up of staggered petal arrays and parallel wavy channels. Tests were performed using refrigerant R410A over a mass flux range of 75–250 kg m−2 s−1, at average saturation temperatures ranging from 35 to 45 °C. For the smooth tube, the external heat transfer coefficient decreases first and then flattens out gradually at low mass fluxes. Relative significance of inertia force might be the major reason. New prediction correlations for smooth tubes based on the Nusselt's theory were presented, having all data points within ± 4% error band. The effects of saturation temperature, mass flux and vapor quality on heat transfer coefficients for all the tested tubes were analyzed. In addition, the condensation heat transfer coefficient ratio of the 2EHT-2 tube to a smooth tube is only 0.86–0.94 for mass fluxes ranging from 100 to 250 kg m−2 s−1. This phenomenon can be explained by the retention of condensate and surface tension effects. New correlations for film condensation in the annular channel outside the 2EHT tubes were also developed, showing a good agreement with experimental data.

An experimental study of R410A condensation heat transfer and pressure drops characteristics in microfin and smooth tubes with 5 mm OD

Heat transfer and pressure drop characteristics of R410A condensing flow in horizontal small microfin and smooth tubes with outer diameter of 5.0 mm were studied experimentally at relatively high mass fluxes ranging from 390 to 1583 kg/m2 s with different saturation temperatures of 309.15 K, 316.15 K, and 323.15 K. The results indicate that heat transfer coefficients and pressure gradients increase with increasing mass flux and with decreasing saturation temperature for both microfin and smooth tubes. The lower vapor density, higher liquid thermal conductivity, and higher surface tension effect all contribute to the higher heat transfer coefficients at a lower saturation temperature. The experimental heat transfer coefficients and frictional pressure gradients fit well with the empirical correlations. The heat transfer coefficient ratios between microfin and smooth tube range from 1.65 to 1.28 which means that microfin tubes can enhance heat transfer coefficients efficiently. Both heat transfer enhancement ratio and pressure drop penalty ration decrease with increasing mass flux and saturation temperature. Compared with other refrigerant properties, the liquid-vapor density contributes more to the heat transfer enhancement ratio at high mass flux.

R32 and R410A condensation heat transfer coefficient and pressure drop within minichannel multiport tube. Experimental technique and measurements

The present paper reports the construction of an experimental installation to measure local condensing two-phase flow heat transfer coefficient and frictional pressure drop within mini-channel tubes, the validation measurements developed with R134a and the experimental measurements of heat transfer coefficient and frictional pressure drop made with R32 and R410A.This experimental work is carried out in a test apparatus which allows determining the local heat flux extracted from the condensing fluid. For this purpose, the wall temperature is measured along the test section in several points.The saturation temperature is determined from the saturation pressure, which is measured at the inlet and the outlet of the test channel.Experimental data of R32 and R410A are also compared with some predicting models widely accepted in the literature.

Condensation heat transfer and pressure drop of R-410A in a 7.0 mm O.D. microfin tube at low mass fluxes

R-410A condensation heat transfer and pressure drop data are provided for a 7.0 mm O.D. microfin tube at low mass fluxes (50–250 kg/m2 s). The heat transfer coefficient of the microfin tube shows a minimum behavior with the mass flux. At a low mass flux, where flow pattern is stratified, condensation induced by surface tension by microfins overwhelms condensation induced by shear, and the heat transfer coefficient decreases as mass flux increases. At a high mass flux, where flow pattern is annular, condensation induced by shear governs the heat transfer, and the heat transfer coefficient increases as mass flux increases. The pressure drop of the microfin tube is larger than that of the smooth tube at the annular flow regime. On the contrary, the pressure drop of the smooth tube is larger than that of the microfin tube at the stratified flow regime.

Theoretical analysis for condensation heat transfer of binary refrigerant mixtures with annular flow in horizontal mini-tubes

A theoretical model is developed for condensation heat transfer of binary refrigerant mixtures in mini-tubes with diameter about 1.0 mm. Condensation heat transfer of R410A and R32/R134a mixtures at different mass fluxes and saturated temperatures are analyzed, assuming that the phase flow pattern is annular flow. The results indicate that there exists a maximum interface temperature at the beginning of condensation process for azeotropic and zeotropic mixtures and the corresponding vapor quality to the maximum value increases with mass flux. The effects of mass flux, heat flux, surface tension and tube diameter are analyzed. As expected, the condensation heat transfer coefficients increase with mass flux and vapor quality, and increase faster in high vapor quality region. It is found that the effects of heat flux and surface tension are not so obvious as that of tube diameter. The characteristics of condensation heat transfer of zeotropic mixtures are consistent to those of azeotropic refrigerant mixtures. The condensation heat transfer coefficients increase with the concentration of the less volatile component in binary mixtures.

Experimental study on condensation heat transfer characteristics of R410A in short vertical tubes

An experimental study on condensation heat transfer of R410A in short vertical tubes (8.02 mm ID and 10.7mm ID) was presented. Experiments were performed in eight short copper tubes length varied from 300mm to 600mm at mass fluxes range of 58–246 kg m−2s−1 and saturation temperature of 38°C. Effects of mass flux, tube length on condensation heat transfer coefficient were investigated. The distribution of temperature, thickness of condensate film and local condensation heat transfer coefficient along the tube were also analyzed. It is indicated that the entrance effect played an important role in condensation heat transfer of vertical tube, and the influence of entrance effect on average condensation heat transfer coefficients will weaken with the length of tube in the experimental condensation. The experimental results were compared with four well known correlations available in literatures, and the Chen correlation shows good agreement with the experimental data but with ±40% deviation. A new modified condensation heat transfer correlation with 12.7% mean deviation was developed to predict the condensation heat transfer coefficients in short vertical tube based on the experimental data.

CONDENSATION HEAT TRANSFER AND PRESSURE DROP OF R-410A IN A 5.0 MM O.D. SMOOTH AND MICROFIN TUBE

R-410A condensation heat transfer and pressure drop data are provided for a 5.0 mm O.D. microfin tube having 40 fins with 18 degree helix angle and 40 degree fin apex angle. Tests were conducted for a range of quality (0.2 ~ 0.8), mass flux (346 ~ 692 kg/m2s) and saturation temperature (45 ~ 55°C). Data are compared with smooth tube counterpart. It was found that both heat transfer coefficient and pressure drop increased as mass flux increased. The range of pressure drop penalty factor (1.83 ~ 2.62) was slightly larger than that of heat transfer enhancement factor (1.24 ~ 1.66). Data are compared with available heat transfer and pressure drop correlations.

Influence of oil on flow condensation heat transfer of R410A inside 4.18 mm and 1.6 mm inner diameter horizontal smooth tubes

The influence of oil on condensation heat transfer of R410A inside 4.18 mm and 1.6 mm inner diameter horizontal smooth tubes is investigated experimentally. The experimental condensing temperature is 40 °C, and nominal oil concentration range is from 0% to 5%. The test results indicate that the presence of oil deteriorates the heat transfer, and the deterioration effect becomes obvious with the increase of oil concentration. At oil concentration of 5%, the heat transfer coefficient decreases by maximum 24.9% and 28.5% for 4.18 mm and 1.6 mm tubes, respectively. A new correlation for heat transfer coefficients of R410A–oil mixture flow condensation inside smooth tubes is proposed, which agrees with all the experimental data within a deviation of −30% ∼ +20%.

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.

Condensation heat transfer of R410A inside internally grooved horizontal tubes

Heat transfer coefficients were measured for the condensation of R410A and R22 inside internally grooved horizontal tubes. The experiment was performed for five different kinds of internally grooved tubes of about 8.00 mm o.d. the shapes of which were conventional helical grooved and herring-bone grooved ones. To measure the local heat transfer coefficients, the test section was subdivided into 10 small sections having 1 m working length. The ranges tested are as follows: the refrigerant mass velocity was from 130 to 400 kg/(m2/s) for R410A and R22, and the vapour pressure was 2.4l MPa for R410A and 1.53 MPa for R22. The obtained heat transfer data of R410A and R22 indicate that the values of the local heat transfer coefficients of the herring-bone grooved tube are about twice as large as those of helical one. All measured local heat transfer coefficients of condensation were compared with the predicted values from previous correlations proposed by other researchers, and were well correlated with the empirical equation using the frictional coefficients for each tube proposed by the author.

D141 R410A の凝縮伝熱特性に及ぼす管内面形状の影響

D141 R410A の凝縮伝熱特性に及ぼす管内面形状の影響