Evaporation and condensation heat transfer performance of flammable refrigerants in brazed plate heat exchanger

Average Nusselt numbers were measured for R22, R290, R290/600a, and R32/152a undergoing evaporation and condensation in a brazed plate heat exchanger. The refrigerants experienced wavy, stratified flow at low heat and mass fluxes, 1.3 kW/m2 to 8.3 kW/m2 and 1.6 kg/m2 s to 19 kg/m 2 s, respectively. Heat transfer correlations from the literature for in-tube and channel flow of refrigerants with similar heat and mass fluxes were compared to the measured Nusselt numbers. The agreement was found to be unsatisfactory. Evaporation and condensation heat transfer correlations were developed from the data for this study for the combined data of R22, R290, and R290/600a and the data for R32/152a. Separate correlations were needed because the lubricant used for R32/152a was different than the lubricant used for the other refrigerants.