Thermal performance of a two-pass microchannel evaporator

Microchannel evaporator is one of the key components in many thermal systems such as heat exchanger of HAVC and refrigeration system. The evaporation heat transfer performance of microchannel evaporator, which usually has many flow paths, is highly affected by the distribution of liquid flow that will seriously deteriorate the flow boiling performance due to the lack of liquid supply, local dryout, etc. In this study, a novel two-pass microchannel evaporator (L × W × H = 103 × 64 × 20 mm) is designed and fabricated. The width, height and length of each individual channel are 0.6, 1 and 65 mm, respectively. To significantly improve liquid redistribution after the first-pass, evenly distributed spacers with different diameter holes were placed in the connecting flow path. Additionally, the channel number ratio between the first and second pass plays an important role. Therefore, three different channel ratios of 1:1, 1:2, and 3:5 were selected in this study. The heat transfer and flow characteristics of the two-pass microchannel evaporator using working fluid HFE-7100 were experimentally studied for flow rate varying from 30 ml/min to 110 ml/min. The inlet subcooling keeps about 30 K. Also, visualization studies were conducted for the explanations. The experimental results indicate that the thermal performance is superior in microchannel evaporator with channel ratio of 1:2. By considering Reynolds number of each channel in the first pass, microchannel evaporator with channel ratio of 1:1 outperforms other two evaporators. Furthermore, the wall temperature uniformity of this evaporator is better than others. The achieved heat flux of 20 W/cm2 is much higher than the reported studies. The overall two-phase HTC of this microchannel evaporator is about 4.5 kW/m2K. •A novel two-pass microchannel evaporator is designed with spacers to improve liquid distribution.•The effect of channel number ratio between the first and second pass of the evaporator in the performance was investigated.•Thermal performance is superior in microchannel evaporator with channel number ratio of 1:2.•A high heat flux of 20 W/cm2 is achieved using HFE7100.