Numerical Investigation on Flow Boiling Heat Transfer in Elliptic Microchannel Heat Exchanger with Micro Fins

The results of numerical research on boiling heat transfer of R410A refrigerant in an elliptic tube with four microchannels and micro fins are presented in this paper. The boiling performance of elliptic microchannel tubes with different inlet vapor qualities is studied, keeping saturation temperature constant at 278.15 K corresponding to the saturation pressure at 93,623 Pa with 3 kW/m² heat flux and 150 kg/(m²s) mass flux. The Martinelli parameter, heat transfer coefficient, pressure drop, and so on are investigated in the present paper. The CFD results are compared with and verified by the previous two-phase heat transfer correlations. The discrepancies in flow rate, heat transfer performance, and two-phase flow pattern between the middle and the two sides of the elliptic tube are compared. The velocity field and flow trajectory of gas-liquid two-phase flow in the elliptic tube microchannels are discussed and analysed. The results show that when the inlet vapor quality is high, there will be a distinct heat transfer deterioration area in the microchannels during the boiling process. The large area of gas film can weaken the heat transfer performance of the microchannel heat exchanger up to 35.42 % in the region without micro fin. The local highest heat transfer coefficient can reach 2,886.8 W/(m²K) in the physical model. The micro fins can not only increase the heat transfer area and enhance the nucleate boiling but also divide the gas film to form a local annular flow pattern and inhibit the deterioration of boiling heat transfer. The present paper is of great significance for scientific utilization and optimization of the heat exchanger, the reduction of energy consumption, and the enhancement of the exergy efficiency of the system.