Cooling heat transfer characteristics of R744 - Experimental research on the cooling heat transfer and pressure drop in supercritical condition

This paper describes the cooling heat transfer and hydraulic characteristics of R744 refrigeration cycle. In this experiment, using R744 as the working refrigerant and the comparison is made between the experimental data and the proposed correlating equations to confirm the cycle simulation method. The main test section is a double tube heat exchanger of a stainless tube with ID of 3.0 mm and 300 mm in length, and the outside tube is used an acrylic tube. Throughout the experiments, it is recognized that heat transfer coefficient reaches its peak value at around the supercritical temperature, and pressure drop increases with rising refrigerant temperature and it increases dramatically at the supercritical condition. Moreover, when the mass flux becomes high, the heat transfer coefficient and the pressure drop increase while the influence of the heat flux is negligible. Finally, it is clear that both of heat and hydraulic characteristics are very sensitive about the effect of the lubricating oil.