An experimental study was conducted to investigate the heat transfer characteristics of supercritical CO₂ gas cooling down in a microchannel gas cooler over a range of operating conditions encountered in typical residential heat pumps. The microchannels used in the present study had a hydraulic diam¬eter of approximately 1 mm. The experiments were conducted to evaluate the heat transfer performance of the microchannel gas cooler at different test conditions by varying airflow rates, air temperatures, refrigerant inlet temperatures, and mass flow rates. All experimental results are tabulated in the present paper. It was found that the refrigerant mass flow rate is the dominant factor for the capacity of a CO₂ gas cooler, and a significant portion of the heat transfer in a CO₂ gas cooler was carried out in the heat exchanger module on the refrigerant inlet side. The temperature and pressure of CO₂ significantly affect the heat transfer and fluid flow characteristics due to the fact that some important thermal physical properties of CO₂ (such as specific heat, density, viscosity) are strongly dependent on its temperature and pressure. All experiments were successfully conducted with an energy balance of +/-3%.

Units: SI