Effect of Inclination Angle on Pulsating Heat Pipe Performance

Micro-electronic devices are creating ever-increasing demands on their thermal management systems due to their decreasing size and increasing power. Pulsating heat pipes (PHPs) are one possible solution for electronics cooling applications. A PHP is a passive, two-phase heat transfer system which has been shown to have the advantages of the ability to accommodate very high heat fluxes and of relatively low cost, due to its wickless construction. In this investigation, a 20-turn PHP was constructed out of 1.6-mm inner diameter copper tubing. The PHP was operated in vertical and horizontal positions with a filling ratio of 77%. PHP pressure variations, indicating PHP operation, were first observed when the power was increased to 16 W for the vertical orientation (90°). For angles orientations, in general more power was required to induce pulsation. For the 60°, 45°, and 30° orientations, the required startup power was similar to that for the vertical case. In the PHP in the horizontal orientation (0°), pulsation did not begin until a heater input of 30 W was applied, and the thermal resistance only decreased slightly upon startup. Under steady-state operation at the highest heat fluxes, the thermal resistance was lowest for the vertical orientation.