Condensation and evaporation heat transfer performance by using HFO-1234yf refrigerant in flat-tube: ∼The effect of projection on flat-tube inner wall and lubrication oil on heat transfer∼

Currently, R134a is used for car air-conditioner. This refrigerant has 1430 GWP. But the refrigerants which have more than 150 GWP like R134a can't be used for car air-conditioner by MAC (Mobile Air-Conditioner) regulation. In substitution, R1234yf which has 4 GWP was developed, and its thermo-physical properties are similar to that of the R134a. This refrigerant might be expected as taking the place of R134a in early future. Therefore we have been investigating condensation and evaporation heat transfers in flat multiple-hole aluminum tube. This research was especially focused on influence of inner wall projection and lubrication oil on condensation and evaporation heat transfer performance. The experimental apparatus was a general refrigerating cycle which consists of compressor, condenser, expansion valve, and evaporator. For condensation experiment, test section of condenser was double tube of counter-flow type, and the refrigerant flowing in the inner tube was condensed by heat exchange with cooling water flowing in the annular section. For evaporation experiment, in the test section of evaporator, heating the tube surface with electric heater, the refrigerant flowing in the tube was evaporated. Pressure and temperature of refrigerant were measured before and after test section, and temperature of tube surface was measured. Using these experimental data, heat transfer coefficient and pressure drop were calculated. Finally comparison of heat transfer coefficient and pressure drop was made under various experimental conditions taking into account the effect of inner wall projection and lubrication oil concentration level.