Experimental study of falling film evaporation of refrigerants, R32, R1234yf, R410A, R452B and R454B on horizontal tubes

This study investigates the heat transfer performance of the falling film evaporation and pool boiling of low-GWP refrigerants, R452B and R454B, for the replacement of R410A. Fluids including pure refrigerants R32, R1234yf, and near-azeotropic mixtures R410A, R452B, and R454B were tested on smooth tubes and 60FPI fin tubes at various conditions of saturation temperature (5, 15 °C), volume flow rate (150∼300 ml/min), and heat flux (10∼50 kW/m²). For the falling film evaporation on smooth tubes, the R32 yielded the highest heat transfer coefficient among all test fluids. R410A has higher heat transfer among the three mixtures with the help of the component of R32, with lower Marangoni number and consequent lower critical heat flux. In addition, the heat transfer coefficients of film evaporation of R452B and R454B is about 18.2% and 14.5% lower than that of pool boiling, respectively, at Re_f=833–865. The heat transfer coefficient of fin tubes is 2.84–3.87 folds that of the smooth tubes for R452B. Based on 339 sets of falling film test data of near-azeotropic fluids, an empirical correlation was established. It predicts experimental data with mean absolute error (MAD%) of 8.28%.