Enhancement on heat transfer of a passive heat sink with closed thermosiphon loop

Abstract

Passive heat sinks contain features like simple configuration, easy installation and power-free fanless operation which make them quite attractive as effective heat dissipation equipment. This paper experimentally investigates the thermal performance of the passive single-fin heat sink embedded with the proposed novel closed thermosiphon loop (CTL) in comparison with a conventional aluminum fin. The novel CTL features an uneven tube diameter at both condenser and evaporator to incorporate effective circulation of the working fluid upon phase change with much less amount of liquid filling. The effects of filling ratio (FR) and power input distribution on the thermal performance are also examined. Result shows that the maximum temperature difference can be averagely reduced by 16.5%, 18.6% and 7.5%, and the temperature distribution can be improved by 47.6%, 40.2% and 35.3%, respectively, when the total power inputs of 30 W, 60 W and 90 W are applied. Meanwhile, for the case with non-uniform power input distributions, the improvement mechanisms are clarified by analyzing the temperature distribution on fin surface and the flow visualization of the two-phase flow. It is indicated that the liquid level is suggested to cover the place where most of power input is supplied. On the other hand, the saturated temperature of refrigerant should also be considered, thereby the higher filling ratio is not always better. As the result, the refrigerant filling ratios with 30% and 70% are recommended when dominant power input is applied at lower part and upper part, respectively. Additionally, three samples with different evaporation spaces are tested. The height at the evaporation space ranges from 130 to 170 mm. Noticed that the case with smaller evaporation region suggests better thermal performance, which can provide a narrow evaporation channel at a higher liquid level with a fixed FR.