Experimental study of R134a and its alternative mixture R450A flow boiling in a microchannel tube

Abstract

R450A has a low Global Warming Potential, which is considered a replacement for R134a. This study measures the pressure gradient and heat transfer coefficient of both R134a and R450A during boiling in a multiport microchannel tube. The mass fluxes change from 100 to 200 kg-m⁻² s⁻¹, heat fluxes from 2 to 4 kW-m⁻², and inlet saturation temperatures from 10 to 30 °C. Both refrigerants exhibit increased HTC with rising vapor quality, peaking at moderate vapor qualities (0.4 to 0.6). R450A shows higher increase in heat transfer coefficient at higher heat fluxes compared to R134a. Heat transfer coefficient enhances about 75 % when mass flux doubled for both refrigerants. The pressure gradient increases with vapor quality for both refrigerants, with R450A showing higher dP/dz. due to its lower vapor density and saturation pressure at the same saturation temperature. Higher mass flux results in higher and steeper pressure gradient. Lower saturation temperatures increase the pressure gradient due to lower vapor density. Kim and Mudawar model and Mishima and Hibiki model are both recommend for predicting pressure gradient. Liu and Winterton has low MAE and ME when comparing the predictions to measurements in this study, showing it is a relatively accurate model for predicting HTC for both R134a and R450A.