Abstract
After the phase out of R12, R134a has been used successfully for car air-conditioners. However the refrigerant having more than 150 GWP like R134a is prohibited to use by the MAC regulation. As the alternative R134a, the low GWP (GWP=4) refrigerant HFO-1234yf was developed, and its thermo-physical properties are similar to that of R134a. This refrigerant might be expected as taking the place of R134a. Therefore we have been investigating the condensation heat transfer in a flat multiple-hole aluminum tube. This research was especially focused on the influence of inner wall projection and lubrication oil on condensation heat transfer performance. The experimental apparatus was general refrigerating cycle which consisted of compressor, condenser, expansion valve, and evaporator. Test section of the 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. Finally, comparison of heat transfer and pressure drop was made under various experimental conditions taking into account the effect of inner wall projection and lubrication oil concentration level.
