Performance enhancement of oscillating heat pipes by structural modification: A comprehensive review

Abstract

Oscillating Heat Pipes (OHPs) are attractive thermal devices with significant effective thermal conductivity in small temperature differences. Among the influential items in their thermal characteristics, geometrical features, due to their impact on the fluid motion and circulations, are among the important factors that must be taken into account for performance enhancement. A variety of ideas have been introduced by the scholars to enhance the performance of OHPs with particular focus on the structural and geometrical modifications. Effectiveness of these techniques can be impacted by some other factors like operating conditions and working fluid. The aim of the present article is to review the research works on the structural and geometrical modifications of OHPs. For this purpose, studies on the applications of structural modifications in OHPs are gathered and their important findings are represented and summarized in the current article. From the results of reviewed studies, it can be concluded that there are some approaches to facilitate fluid motion such as employment of tubes with different diameters and interconnecting the channels that lead to reduction in the thermal resistance which means increment in the transferred at constant temperature difference. According to the findings of the reviewed works and other relevant works, some recommendations are proposed for upcoming efforts on the performance improvement of OHPs. As an example, it is recommended to utilize structural modification in conjunction with other enhancement techniques, e.g. use of nanofluids, to achieve higher effective thermal conductivity.