Simulation model of boiling heat transfer and flow maldistribution in parallel mini-channels heated unequally

Heat exchangers using parallel refrigerant mini-channels have been developed recently to improve the performance of air conditioning systems. Due to the unequal heat loads among channels, the boiling flow is unevenly distributed across parallel mini-channels in evaporators. Because this phenomenon sometimes causes deterioration of the heat exchange performance and difficulty in performance prediction, thus, it is essential to understand the characteristics of boiling heat transfer under unequally heated conditions. In this study, a novel simulation model was developed to predict the heat transfer characteristics and flow maldistribution of refrigerants flowing in parallel mini-channels with different heat fluxes or wall temperatures among channels. The model predicted well the flow maldistribution and the local quality, heat transfer coefficient, and dryout region of the two parallel mini-channels heated unequally. The mean heat transfer rate of the channels decreased remarkably with the increasing difference in wall temperature between the channels. The validity of the model was confirmed by comparing the predicted heat transfer rate with the experimental results. Furthermore, for ten parallel mini-channels, the decrease in the channel-mean heat transfer rate was indicated by the model, and the rate of decline varied significantly depending on the wall temperature distribution across the channels.