Effect of refrigerant thermophysical properties on flow reversal in microchannel evaporators

The amount and frequency of reverse flow in microchannel evaporators largely depends on the thermophysical properties of the working fluid. In this study, four refrigerants (R134a, R1234yf, R245fa and R32) are examined in the same air conditioning system operated under flash gas bypass mode with venting of reversed vapor (to provide better control of the flow). The flow rate and frequency of reversed vapor are measured for each refrigerant. It has been found that fluids with lower heat of vaporization and higher specific volume difference between vapor and liquid phase) tend to generate more reversed vapor flow. Experimental results validate qualitatively and in most cases quantitatively the mechanistic model presented in Li and Hrnjak (2017a). The validated model is used to demonstrate the effects of thermophysical properties on flow reversal for nine widely used refrigerants.