Heat transfer characteristics of supercritical CO₂ flow in small-channeled structures

Carbon dioxide (CO2) has been proposed as a "natural refrigerant" for various kinds of refrigeration systems and has attracted increased attention from researchers and engineers all over the world. The heat transfer and flow characteristics of supercritical CO2 in a multi-port extruded aluminum test section, which had ten circular channels with inner diameter of 1.31 mm, were investigated experimentally. The CO2 was cooled with chilled copper blocks attached at the both sides of the test section. Local heat fluxes and temperatures at the outer surface of the test section were measured using 12 heat flux sensors and 24 K-type thermocouples, respectively. The mean temperatures of CO2 at the inlet and outlet of the test section were also measured. The higher heat transfer rates were achieved in the near-critical region, and the system pressure, mass velocity, and temperature of CO2 all were observed having significant effects on the heat transfer. An empirical correlation was then developed for forced convective heat transfer of supercritical CO2 in horizontal micro/mini channels.