Predicting evaporation heat transfer coefficient distribution in multi-path alternating-laminated-microchannel-tube (ALMT) heat exchanger based on infrared thermography

The alternating-laminated-microchannel-tube (ALMT) heat exchanger has emerged in the refrigeration and air conditioning industry. However, existing studies on evaporation heat transfer coefficient are limited to a single microchannel tube, while research on multi-path ALMT heat exchanger is lacking. The evaporation heat transfer in actual multi-path heat exchangers is influenced by secondary fluid non-uniform heating and refrigerant flow maldistribution, making direct measurement more difficult. Therefore, the infrared thermography-based method is proposed to predict evaporation heat transfer coefficient distribution in actual multi-path heat exchangers. Firstly, the secondary fluid-side temperature distribution based on infrared thermography derives non-uniform heat flux distribution by finite volume partition, equal to that on the refrigerant side. Then, the refrigerant-side evaporation heat transfer coefficient distribution along length is obtained. Further, the refrigerant flow distribution is quantified according to the pressure drop balance and evaporation coefficient distribution with vapor quality is also obtained. The prediction method is experimentally validated within a 10% deviation. Results show that the evaporation heat transfer coefficient distribution curve exhibits diverse peak values as influenced by non-uniform heat flux and refrigerant flow maldistribution. These peaks are at a vapor quality of around the 0.44–0.79 range. Moreover, the heat exchanger is optimized based on the predicted results, with micro-finned tubes placed in the appropriate region to bring a maximum increase of 8.9% in heat transfer capacity.