Condensation and evaporation of pure refrigerant flowing in small diameter micro-fin tubes.

The heat transfer coefficients were measured for condensation and evaporation of R134a and R1234yf inside smooth and micro-fin tubes. The experiments were performed for a smooth tube of 2.14 mm inner diameter and three micro-fin tubes of 2.17 mm, 2.68 mm and 3.18 mm equivalent diameter respectively. To measure the local heat transfer coefficient, the test section is sub-divided into three sections and having a total of 852 mm working length. The ranges of refrigerant mass flux were from 50 -100 kg m-2 s-1, and the saturation temperature was 20 °C for condensation and 13 °C for evaporation. Effects of mass flux, vapour quality, tube diameter and refrigerant properties on heat transfer coefficient were considered. During the evaporation test, the heat transfer coefficient of R1234yf was found to be lower than that of R134a. Microfin tubes are more efficient than smooth tube. Typical correlations were used to predict the measurement.