An experimental investigation of micro pulsating heat pipes

Si-based micro pulsating heat pipes (μPHP) charged with HFE-7100 were tested at several heating powers with two orientations, θ = 0° and 90°. The width of the channel is 0.8 mm in a μPHP having uniform channels, and 1.0 mm or 0.6 mm in the other μPHP. The depth of each channel is 0.25 mm. The overall size of each μPHP is 60 mm × 10 mm × 1.25 mm. Both visual observation and temperature response of the present μPHPs at various conditions were performed. The performance was compared between two μPHPs having either uniform channels or non-uniform channels at difference heating powers. Results showed that both μPHPs could not start the pulsating two-phase flow in the channel of μPHPs as the μPHPs were operated horizontally at heating power ranging from 1 W to 7 W, except when the μPHP having non-uniform channels was tested at heating power of 7 W. Unlike the failure start-up for horizontal arrangement of μPHPs, μPHPs with a vertical arrangement shows a significant start-up phenomenon for both μPHPs with uniform and non-uniform channels due to the assistance in the start-up of both μPHPs arising from gravity force.