A two-phase theoretical model incorporating liquid film dynamics for pulsating heat pipes

Abstract

Pulsating Heat Pipes (PHPs) hold significant potential for efficient thermal management of electronic devices due to their superior heat transfer capabilities, flexible design, and cost-effective manufacturing. However, in view of the fact that there may be different heat transfer distances between heat sources and heat sinks, the widespread application of PHPs has been limited by the lack of accurate models and experimental data to predict and understand their flow and heat transfer performance at varying heat transfer distances. To address these limitations, a two-phase heat and mass transfer model incorporating liquid film dynamics was developed and partial visualization experiments were conducted to validate the reliability of the theoretical model. Based on these, the flow and heat transfer performance of R1336mzz(Z)-PHPs under various heat transfer distances were numerically simulated and experimentally investigated. The flow and heat transfer characteristics of R1336mzz(Z)-PHPs were compared with those of water-PHPs and ethanol-PHPs to investigate the influence of working fluids on the operating performance of PHPs through numerical simulation. The results revealed that the two-phase heat and mass transfer model could capture the local dry-out phenomenon and accurately simulate the heat and mass transfer process in PHPs through the comparison of experimental results with simulation results. According to simulation results, increasing heat input enhanced both flow and heat transfer performance for R1336mzz(Z)-PHPs, especially at shorter heat transfer distances. There was an optimal heat transfer distance at which the flow and heat transfer performance of the PHP were best. Compared to water and ethanol, R1336mzz(Z) generated a greater driving force while experiencing lower flow resistance, resulting in a higher average flow velocity of the working fluid. This enabled the transition from oscillatory flow to one-way circulation flow at various heat transfer distances and avoided the occurrence of local dry-out, leading to superior flow performance. Besides, the performance of the R1336mzz(Z)-PHP was relatively less affected by heat transfer distance. Even at a large heat transfer distance, R1336mzz(Z) maintained superior flow and heat transfer performance.