Investigation on the Mechanism of Maximum Efficiency Point for Helium-Based Oscillating Heat Pipe

Abstract

Liquid helium cryogenic system is crucial for achieving low-temperature superconductivity in particle accelerator and controllable nuclear fusion devices. However, the heat conductivity of copper in the 4K region is 400–800 W m⁻¹ K⁻¹, which limits the performance of superconductivity system. The application of helium-based oscillating heat pipe (OHP) promotes this deficiency mitigation, with a maximum effective thermal conductivity (ETC) ranging from 4000 to 16,000 W m⁻¹ K⁻¹. Although numerous scholars have experimentally observed the maximum efficiency point of OHP, but its underlying mechanism remains unclear. In this study, a test rig for measuring the heat transfer performance and dynamic parameters of helium-based OHP in the 4K region was constructed. A numerical simulation method for the gas–liquid two-phase unsteady flow process in the OHP was established. The amplitude and period distribution of dynamic pressure fluctuations in OHP were analyzed. The correlation between its pressure fluctuations and heat transfer process was explored. Finally, the mechanism of the maximum efficiency point was revealed with the oscillating characteristics for helium-based OHP in the 4K region.