Channel design to effectively increase oscillation amplitude in micro-pulsating heat pipes

Abstract

A channel design of micro-pulsating heat pipes (MPHPs) to increase the oscillation amplitude in the horizontal orientation is proposed. For this, the topology optimization is performed in the direction of maximizing the ratio of pressure drop in the backward direction to that in the forward direction, defined as diodiciy (Di). It is numerically confirmed that the topology-optimized Tesla-valve (TV) has a high Di value of 1.9. MPHPs with conventional and topology-optimized channel design are fabricated to investigate the effects of the TV on flow characteristics and thermal performance of MPHPs. The width, length, and thickness of MPHPs are 53.5 mm, 80 mm, and 2 mm, respectively. A closed-loop square channel with ten-turn and an average hydraulic diameter of 0.9 mm is engraved on 1 mm thick silicon. Then, 1 mm thick glass is anodically-bonded on the top of the etched silicon for flow visualization. Inside the channel, HFE-7000 is filled by 54% as a working fluid. Experiments are conducted at various input powers in a horizontal orientation. The movements of menisci are tracked through a high-speed photography. It is experimentally confirmed that the TV effectively increases oscillation amplitude at input powers of more than 24 W. Consequently, the thermal resistance of the MPHP with the TV is 35% lower on average than that of the conventional MPHP. In this study, a channel design of MPHPs capable of increasing oscillation amplitude in the horizontal orientation is proposed for the first time, which allows MPHPs to overcome the limitation of performance attributed to the inclination angle.