Development of the general correlation for condensation heat transfer and pressure drop inside horizontal 4 mm small-diameter smooth and microfin tubes

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.