The Effect of Lubricant Oil Concentration on the Performance of a Gas Cooler Using Carbon Dioxide

Abstract

The effect of PAG oil concentration on the heat transfer performance and pressure drop of a fin-tube heat exchanger using carbon dioxide(CO₂) heat pump during the gas cooling process of CO₂ was investigated by experiment. The experimental apparatus consisted of a gas cooler, a pre-heater, a sub-cooler, a mass flow meter, pumps and a measurement system. Experiments were conducted for various conditions of inlet temperature(110°C), mass flow rate of refrigerant(50, 55, 60, 65, 70 g/s) and PAG oil concentration(0 to 2.6 wt%). The heat transfer rate decreased with the increase of the oil concentration and the decrease of the inlet pressure. And the pressure drop increased with increases of the oil concentration and the mass flow rate of the refrigerant. The COP reduction by the deterioration of gas cooler performance with oil concentration was analyzed. When the inlet pressure of the gas cooler was 100 bar, the COP reduction was estimated to be 6% under 1 wt% of oil concentration.