Review on Key Factors in Closed-loop Pulsating Heat Pipes within Atmospheric Temperature

A closed-loop pulsating heat pipe within atmospheric temperature relies on the pulsation and phase change of the internal working fluid. It has been widely used for the heat dissipation of electronic components owing to its high heat transfer efficiency, simple structure, and low cost. In this study, the factors affecting the startup and heat transfer performance of pulsating heat pipes are divided into three categories, namely, structural parameters, operating conditions, and working fluid properties. First, the structural parameters, including factors such as diameter, cross-sectional shape, number of U-bends, and length ratio of each section, are summarized. Second, the influence of operating conditions, including the heating power, inclination angle, and liquid filling rate, is analyzed. Finally, the physical parameters of the working fluid are divided into flow and heat transfer properties. To improve the start-up and heat transfer performance of pulsating heat pipes, future research should focus on conducting in-depth investigations into the critical number of U-bends. The anti-gravity performance of heat pipes must be improved for adapting to small inclination angles and negative angle conditions. A comprehensive evaluation criterion describing the influence of physical parameters on performance should also be established.