Study on the thermal performance of micro pulsating heat spreader

Abstract

In this thesis, flow characteristics and heat transfer characteristics of the pulsating heat pipe with single turn were experimentally and theoretically investigated. The flow patterns and flow characteristics of the glass pulsating heat pipe with single turn using high speed video camera were observed. The pulsating heat pipe has inner diameter of 1.7 mm and total length of 140 mm and ethanol was used as a working fluid. The pulsating heat pipe transports heat by periodic expansion and contraction of vapor bubbles. At low input power below 40 W, oscillating flow was observed. As the input power increases beyond 50 W, circulatory flow was observed which causes increasing thermal performance of pulsating heat pipe. Based on the flow visualization results, theoretical model which is founded on modified Thome model for flow boiling in a microchannel was suggested to investigate heat transfer mechanism of the pulsating heat pipe. The model well predicts the experimental results within 20 %. From the theoretical study, the film evaporation through the thin film accounts for a significant portion, about 70 % of total heat transfer of pulsating heat pipe. Micro pulsating heat spreader operating in microchannel was developed and its thermal performance was experimentally evaluated. A total of 10 parallel interconnected rectangular channels forming a meandering closed loop were engraved on a silicon wafer with thickness of 1 mm. The hydraulic diameter of the rectangular channel was about 0.57 mm. The MPHS has a length of 50 mm, width of 15.5 mm, and total thickness of 1.5 mm. Ethanol was used as a working fluid. The MPHS achieved the maximum effective thermal conductivity of 600 W/m.K which is 3.5 times higher than that of silicon (k = 163 W/mK) and 1.5 times higher than that of copper (k = 400 W/mK). The MPHS designed in the present study show higher thermal performance than an existing wicked flat micro heat pipe of similar size (keff = 504 W/mK). The MPHS is compet...