Heat transfer coefficient and pressure gradient of R32 and R1234yf mixtures flow boiling in a microchannel tube

This paper presents the flow boiling heat transfer coefficient and pressure gradient measurements of R32 and R1234yf mixtures in a microchannel tube at three concentrations: 15/85, 50/50, and 85/15 by mass. R32/ R1234yf mixture has a temperature glide curve that the 15/85 R32/R1234yf mixture has low-temperature glide (0.5 K) while the opposite concentration (85/15) has the highest glide (7 K). The experiment was conducted on a 24-port microchannel tube with an average hydraulic diameter of 0.643 mm. The experiment covers mass flux from 100 to 200 kg-m-2 s-1, heat flux from 0 to 6 kW-m-2, and vapor quality from 0 to 1. Mass flux has a strong effect on both HTC and dP/dz. Heat flux affects HTC but not dP/dz. In addition, the results are compared to pure fluid to discuss the effect of temperature glide. When the glide is higher, the HTC is lower and flatter. At fixed quality, as R1234yf concentration increases, HTC of the mixture decreases slightly first and then increases dramatically. Furthermore, two experiment methods are compared: evaporation in one pass and in one test section. The non-equilibrium in two-phase flow affects concentration gradient in the two phases and further affects the HTC of mixtures with high-temperature glide.

Automated summary

This paper presents the measurements of flow boiling heat transfer coefficient and pressure gradient for R32 and R1234yf mixtures in a microchannel tube. The results show that mass flux has a significant effect on both heat transfer coefficient and pressure gradient, while heat flux only affects the heat transfer coefficient. Furthermore, the temperature glide curve has an impact on the heat transfer coefficient.