Experimental study of the effect of low GWP refrigerant R449A on the heat transfer performance of a multi-branch direct expansion (DX) evaporator

Abstract

The performance comparison experiment of R449A replacing R507A and R22 refrigerant was carried out for the multi-branch direct expansion (DX) evaporator, and a new rectifier nozzle type distributor was proposed to be applied in the experimental research to study the effects of different refrigerants on the heat transfer performance of the evaporator and the distribution performance of the distributor. The parameters such as cooling capacity, pressure drop, heat transfer coefficient of the evaporator as well as superheat inhomogeneity and pressure drop of the new rectifier nozzle type distributor were analyzed using heat balance method. The results show that the application of R449A as alternative refrigerant can effectively reduce the pressure difference between the evaporator inlet and outlet and the superheat inhomogeneity of the distributor, and the evaporator refrigeration capacity and heat transfer coefficient were decreased. We further analyzed the gas-liquid state of the refrigerant and found that the R449A refrigerant had the smallest percentage of liquid volume before distribution. There is a strong correlation between the refrigerant liquid volume percentage situation and the uniformity of distributor distribution, the smaller the liquid volume percentage, the more uniform the refrigerant distribution. At the -18 °C test temperature, the superheat inhomogeneity of the distributor with R449A was reduced by 49.89 % and 40.48 %, and the cooling capacity was reduced by 3.01 % and 8.61 % compared to the use of R507A and R22, respectively. At low temperatures, R449A refrigerant can be considered as one of the alternatives to R507A and R22 refrigerants.