The Cooling Heat Transfer Characteristics of the Supercritical CO2 in Micro-fin tube

Abstract

This study intended to verify the cooling heat transfer characteristics of supercritical gas for refrigerating and air-conditioning devices that use CO2, a natural refrigerant, as the operating fluid. The heat transfer coefficient according to the mass flow rate peaked at the low cooling pressure of 8.0 MPa in the gas cooler, and reached its minimum at the high pressure of 10.0 MPa. Also, when the mass flow rate of the refrigerant increased, the coefficient increased faster with the lower cooling pressure in the gas cooler. The heat transfer coefficient according to the shape of the heat transfer tube showed that the maximum values of the CO2 cooling heat transfer coefficients of the smooth tube and the micro-fin tube were found at 34.5°C and 44.7°C, respectively, which were the critical temperatures for the entrance pressures. It was found that the cooling heat transfer coefficient of the micro-fin tube increased by 12-39% more than that of the smooth tube. The experiment results for the CO2 heat transfer coefficients of the smooth tube and the micro-fin tube were compared with the values that were estimated from previous correlation equations. It was found that the experiment values generally significantly differed from and the experiment values greater than the estimated values. The differences were especially greater in the vicinity of the critical temperature points.ding to the mass flow rate peaked at the low cooling pressure of 8.0 MPa in the gas cooler, and reached its minimum at the high pressure of 10.0 MPa. Also, when the mass flow rate of the refrigerant increased, the coefficient increased faster with the lower cooling pressure in the gas cooler. The heat transfer coefficient according to the shape of the heat transfer tube showed that the maximum values of the CO2 cooling heat transfer coefficients of the smooth tube and the micro-fin tube were found at 34.5°C and 44.7°C, respectively, which were the cr