Performance of Flat-Tube Louvered-Fin Automotive Evaporator With R1234yf

Abstract

Following the Kyoto Protocol and the more recent Kigali agreement, Hydrofluoroolefins (HFOs) are considered as the low global warming drop-in or substitute refrigerants for hydrofluorocarbons (HFCs) which have high global warming potential. The HFO R1234yf gained significant importance as a replacement for R134a in automobile air conditioning. In this context, the performance of a two-slab automotive evaporator with R1234yf numerical simulation is reported in this paper. The simulation is conducted by considering the heat transfer from air to the outside wetted surface consisting of louvered fins and tube wall, from there to the inside tube wall, and from there to the bulk of the boiling refrigerant inside the tube. The combined effect of heat and mass transfer from air to the wetted surface is described by the enthalpy potential method. For the two-phase and superheating regions suitable heat transfer correlations are employed. The results show that the refrigerant side heat transfer coefficient increases with increase in vapour quality up to around 80% and then decreases with further increase in the vapour quality. The major contribution to the cooling capacity is the latent heat abstraction during the flow boiling process occurring inside the tube. The temperatures of the condensate water film surface and the inner and outer tube wall surfaces are nearer to the bulk temperature of the refrigerant because of the high heat transfer coefficient on the refrigerant side. Results are also presented for the refrigerant side pressure drop and the evaporator exit air temperature and humidity ratio.