Miniaturization and Thermal Performance Enhancement Using Evaporator Surface Structures for Closed Loop Pulsating Heat Pipe

Abstract

The present paper focuses on miniaturizing the micro loop pulsating heat pipe (MLPHP) for small-scale electronic devices to augment the transfer of generated heat from the high-power density semiconductor chips and enhance the thermal performance. The two mini-MLPHPs, smooth surface and discrete structures (dimple cavity), are fabricated on a pure copper substrate on the floor of the evaporator surface. The thermo-fluidic features like bubbles nucleation, growth, detachment, slug-plug motion, and dry-out condition during the loop operation after generating efficient pressure difference inside the channels with the application of variable heat loads (0 - 25 W), filling ratio (FR) of methanol at 40% is used as a working fluid are observed. The thermal performance is tested for the dimple cavity as a discrete structure on the floor of the evaporator in the mini-MLPHP against smooth surface mini-MLPHP to determine the quantitative consequence for heat transfer enhancement and compare the same with the standard MLPHP with smooth surface evaporator. Based on the results data, mini-MLPHP with dimple cavities on the floor of the evaporator surface gives the lowest thermal resistance compared to smooth surface mini-MLPHP. The maximum reduction in the thermal resistance for dimple cavities mini-MLPHP is 16% compared to smooth surface mini-MLPHP at 25W. Also, mini-MLPHP with discrete structures have high evaporator contact surface heat flux (83 W/cm2 at 25 W heat supply) as compared to MLPHP, i.e., 6.67 W/cm2.