Flow Boiling Heat Transfer of Binary Mixtures HFO1234yf/R32 in a Smooth Horizontal Tube

HFO1234yf is a promising alternative for automobile air conditioners because of its low GWP of 4 and thermophysical properties similar to those of R134a. However, its performance is inferior to R410A. This makes it difficult to be applied to residential air-conditioners. A mixture of HFO1234yf and R32 is expected to balance both the GWP and COP requirement when applied to residential air-conditioning systems. In this study, flow boiling heat transfer coefficients of HFO1234yf and R32 (80:20 and 50:50 by wt%) were measured in a smooth horizontal tube at a saturation temperature of 15°C. The inner diameter (ID) of the test section is 4 mm. The mass flux ranges from 100 to 300 kg/m 2 ·s, and the heat flux changes from 6 to 24 kW/m 2 . Heat transfer coefficients of the mixtures and pure HFO1234yf were summarized at three Bo numbers. The influence of Bo on mass discussion was observed and discussed. It is found that there is notable influence of mass diffusion on heat transfer when Bo is large. When Bo is small, the convective heat transfer at high vapor qualities seems to be suppressed due to the effects of mass diffusion. Results show that the heat transfer coefficient of the 50:50 wt% mixture of HFO1234yf and R32 is higher than that of the 80:20 wt% mixture and is also the same or even higher than that of pure HFO1234yf. A theoretical model was proposed to predict the heat transfer coefficients of the mixtures HFO1234yf and R32 under two concentrations. The prediction model can catch 80% of the data within deviation of ±20%.