Study of New Mini-Channel Trans-Critical CO₂ Heat Pump Gas Cooler

A gas cooler is one of the important parts of a carbon dioxide (CO₂) heat pump water heater, and it must meet the needs of not only pressurization but also heat transfer. It is important to study gas coolers. In this paper, a heat exchanger with a spiral channel is studied. ANSYS CFX software was used to analyze the flow and heat transfer characteristics of the heat exchanger (single-plate model). The influences of the cooling pressure of CO₂, the mass flux of CO₂, the mass flux of water and the channel radius of CO₂ are discussed. In this paper, the results show that the cooling pressure of CO₂, the mass flux of CO₂ and the channel radius of CO₂ all have a large influence on the local heat transfer coefficient: with an increase in the cooling pressure of CO₂, the peak value of the heat transfer coefficient of CO₂ decreases and the average heat transfer coefficient decreases; with an increase in the mass flux of CO₂, the peak value of the heat transfer coefficient of CO₂ increases and the average heat transfer coefficient increases; and with a decrease in the channel radius of CO₂, the peak value of the heat transfer coefficient of CO₂ increases. The water mass flux has only a slight effect on heat transfer, and the lower cooling pressure of CO₂ corresponds to a higher peak heat transfer coefficient, which can reach 27.5 kW∙m^-2∙K^-1 at 9 MPa.