Numerical simulation of heat transfer phenomena in a microchannel evaporator for a transcritical CO2 air conditioning system

This study presented a numerical simulation of heat transfer characteristics in a microchannel evaporator for a transcritical CO2 air conditioning system, and the simulated results have been validated by the experimental data. The evaporator consists of 6 passes with 29 flat tubes. Each flat tube has 10 microchannels having a 1.2 x 0.6 mm cross-section. The two-phase flow was simulated in the range of evaporation temperatures from 5 to 15 degrees C; the mass flow rates of 24.16, 30, and 34.96 g/s; and inlet vapor qualities of 0.5, 0.61, and 0.75, respectively. The results show that the two-phase flow with the evaporative temperature at the inlet of 5, 10, and 15 degrees C became superheated at the 3rd, the 4th, and the 5th pass, respectively. At the evaporation temperature of 15 degrees C, the heat transfer coefficient decreases from 8.1 to 3.6 kW/m(2) K as the vapor quality increases from 0.75 to 1. With the mass flow rate of 30 g/s, in the tube length range from 0 to 1.1 m, the heat flux achieved around 1.55 kW/m(2). The numerical cooling capacity gets the maximum value of 2.85 kW at the evaporative temperature of 10 degrees C. The numerical results are in good agreement with those obtained from the experimental results and the other published results, with a deviation of less than 10%.