Prediction method for evaporation heat transfer of non-azeotropic refrigerant mixtures flowing inside internally grooved tubes

Local heat transfer coefficients were experimentally measured for evaporation of R417A (R125/R134a/R600) flowing inside horizontal smooth and two internally grooved tubes with different geometrical parameters. The experimental results of R417A inside different test tubes were analyzed and compared with existing correlations; several microfin correlations failed to predict heat transfer coefficients of refrigerant mixtures and could not express the local variation of heat transfer coefficients during the evaporation. Based on the experimental data of R417A, an empirical correlation for microfin tubes was developed by introducing the enhancement factors into the modified Kattan model. The comparison of the calculations and the experimental results reveals that the microfin correlation suggested at the present study generally predicts experimental data with a deviation of ±30% for vapor qualities below 80% and also expresses the local variation of heat transfer coefficients for refrigerant mixtures evaporating inside microfin tubes.