Advances and Unsolved Issues in Pulsating Heat Pipes

TLDR

Pulsating heat pipes are two‑phase devices that use oscillatory liquid–vapor flow in a coiled tube without a wick, and have attracted extensive experimental and theoretical study over the past decade. This review surveys advances in flow visualization, heat‑transfer performance, and theoretical modeling of pulsating heat pipes, and highlights remaining open questions. The authors compile key experimental and theoretical findings, including critical parameters, into a comprehensive tabular summary. The review identifies unresolved issues concerning the operating mechanism, modeling, and practical applications of pulsating heat pipes.

Abstract

Pulsating (or oscillating) heat pipes (PHP or OHP) are new two-phase heat transfer devices that rely on the oscillatory flow of liquid slug and vapor plug in a long miniature tube bent into many turns. The unique feature of PHPs, compared with conventional heat pipes, is that there is no wick structure to return the condensate to the heating section; thus, there is no countercurrent flow between the liquid and vapor. Significant experimental and theoretical efforts have been made related to PHPs in the last decade. While experimental studies have focused on either visualizing the flow pattern in PHPs or characterizing the heat transfer capability of PHPs, theoretical examinations attempt to analytically and numerically model the fluid dynamics and/or heat transfer associated with the oscillating two-phase flow. The existing experimental and theoretical research, including important features and parameters, is summarized in tabular form. Progresses in flow visualization, heat transfer characteristics, and theoretical modeling are thoroughly reviewed. Finally, unresolved issues on the mechanism of PHP operation, modeling, and application are discussed.