Investigation of thermal enhancement factor in micro pulsating heat exchanger using LIF visualization technique

This study investigates the thermal flow in an asymmetric micro pulsating heat exchanger (MPHE). In the design and fabrication of the MPHE, the MEMS processes were used to fabricate symmetric and asymmetric MPHEs on which 14 and 16 parallel rectangular channels were formed, respectively. Ethanol mixing with fluorescence dye (rhodamine B) was used as a working fluid in order to visualize the thermal flow by a laser induced fluorescence technique. The fluid columns inside the micro channel were changed rapidly by deforming the interface of liquid slug and gas in the asymmetric MPHE. Thermal resistance was evaluated under various operating conditions. The asymmetric MPHE filled with 60% working fluid has the highest heat transfer efficiency under vertical orientation. From the thermal flow visualization inside the asymmetric MPHE filled with ethanol, the annular flow by dispersing and generating was identified as the key mechanism of circulating motion. The circulating motion of asymmetric channels supports the heat transfer more actively than the oscillating motion of symmetric channels.