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/m(2) 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. (C) 2018 Elsevier Ltd. All rights reserved.