Experimental study and general correlation of condensation heat transfer for zeotropic mixture refrigerants in smooth and microfin tubes.

This study investigated the condensation heat transfer of R32/R1234yf mixtures in smooth and microfin tubes with outer diameters of 5.0 and 3.5 mm, respectively. The experiments were conducted at mass velocities of 50, 100, and 200 kg m-2 s -1 and saturation temperatures of 20◦C. The effect of mass velocity, vapor quality, and mass fraction on heat transfer was evaluated. For the smooth tube, R32/R1234yf mixture with mass ratio of 21.5/78.5 has lower heat transfer than pure R1234yf in all mass velocities due to the heat transfer degradation phenomenon. For the microfin tube, R32/R1234yf with mass ratio of 68.9/31.1 has higher heat transfer compared to R1234yf, but cannot exceed the heat transfer of R32. Meanwhile, the mixture R32/R1234yf with mass ratio of 21.5/78.5 has less heat transfer than pure R1234yf for mass velocities of 50 and 100 kg m-2 s -1. However, at a low vapor quality and a mass velocity of 200 kg m-2 s -1, the heat transfer is almost the same as that of R1234yf due to less heat transfer degradation. The new correlations were developed by adding the heat transfer degradation effect to the Nusselt number for forced and natural convection. The correlation developed to predict condensation of mixture refrigerants for smooth tubes can be applied to tubes with inner diameters between 4 and 8.4 mm. It can predict both the present experimental data and other researchers’ data with mean deviation of 16.4%. Meanwhile, the correlation developed to predict the condensation of mixture refrigerants for microfin tubes can be applied to tubes with inner diameters ranging from 2.5 to 8.9 mm, and it can predict current experimental data and data from other researchers with an average deviation of 19.8%.