An Experimental Investigation of Micro Pulsating Heat Pipes

Two Si-based micro pulsating heat pipes (mu PHPs) charged using HFE-7100 were either horizontally or vertically oriented and were tested using several heating powers. The width of each channel was 0.8 mm in one mu PHP containing uniform channels, and the channel width was 1.0 mm or 0.6 mm in the other mu PHP, which did not contain uniform channels. The depth of each channel was 0.25 mm. The overall size of each mu PHP was 60 x 10 x 1.25 mm. Visual observation and temperature measurement of the mu PHPs under various conditions were performed and the results were analyzed. The results indicated that when the mu PHPs were operated horizontally at a heating power ranging from 1 to 7 W, the pulsating two-phase flow in the channels of the mu PHPs could not begin, except when the mu PHP containing nonuniform channels was tested at a heating power of 7 W. With a heating power less than 5 W, the frequency of the sine-like oscillating displacement of the vapor slug increased and the displacement of the vapor slug reduced in either vertically oriented mu PHP, as the heating power increased With a heating power higher than 5 W, periodic start-stop behaviors were observed in the vertical mu PHP containing nonuniform channels.