Numerical investigation of oscillating heat pipes with smooth surface, full and partial capillary wicks

Abstract

Thermal management is becoming a challenge for many high-power electronic devices and energy systems. Oscillating heat pipes (OHPs) are highly efficient passive thermal management devices with simple structure, lightweight, and high effective thermal conductivity. Despite extensive studies on the OHPs with smooth channels, theoretical and numerical investigations of OHPs with capillary wicks remain limited. In this work, a one-dimensional numerical model is extended to investigate the OHPs with smooth channels, fully covered capillary wicks, and partially covered capillary wicks. The friction factor governing liquid slug movement is evaluated using the Colebrook-White equation to account for wick-induced surface roughness. Numerical results show that fully covered capillary wicks significantly reduce liquid slug oscillation amplitude and velocity due to increased flow resistance. In contrast, partially covered capillary wicks effectively balance the flow resistance and phase-change driving force. Compared with the OHPs with smooth channels, the liquid slug oscillation amplitude increases by 1 %∼8 % for partially covered wicks and decreases by 34 %∼49 % for fully covered wicks, while the slug velocity increases by 2 %∼6 % and decreases by 21 %∼31 %, respectively. Consequently, partially covered capillary wick OHPs exhibit superior heat transfer performance, with numerical predictions showing a 102 %∼108 % increase in heat transfer power under the same temperature difference. Experimental results further confirm this enhancement, demonstrating a 6 %∼24 % improvement in heat transfer power.