In the CO₂ transcritical cycle of air-conditioning and heat pump systems, the heat exchanger operating at supercritical pressures is called a gas cooler. Refrigerant-side heat transfer and pressure drop in gas coolers are different from single-phase in-tube heat transfer and pressure drop at subcritical pressures. This paper offers a comprehensive survey of single-phase in-tube heat transfer correlations of constant thermo-physical property fluids, CO₂ supercritical heat transfer and friction factor correlations, the calculation of pressure drop in supercritical conditions, and the heat transfer and friction factor correlations on gas cooler air sides. Based on comparisons among in-tube heat transfer and friction factor correlations, some suggestions are made.

Units: SI