Fluid charging effects on thermal performance of sodium heat pipes and new approach for optimal filling

Abstract

This study investigates the influence of fluid charging on the thermal performance of sodium heat pipes and introduces a novel method for determining the optimal filling ratio. Sodium heat pipes are known as highly efficient heat transfer devices, utilizing phase change to maintain minimal temperature differences over long distances. However, their performance is highly dependent on the amount of working fluid charged. Underfilled heat pipes are susceptible to evaporator dry-out and temperature drops at the condenser caused by fluid depletion, resulting in significant temperature gradients. Conversely, overfilled heat pipes experience liquid pooling in the condenser due to excess liquid, which obstructs vapor flow and leads to temperature drops. These challenges are particularly evident in horizontal configurations and liquid metal heat pipes, where uncertainties in filling conditions persist due to the lack of effective methodologies. These temperature gradients substantially reduce the effective thermal conductivity of heat pipes. To address these issues, this study presents a series of experiments on sodium heat pipes under varying filling conditions. The findings offer practical methods for achieving optimal charging conditions and highlight the critical role of precise fluid charging in enhancing thermal performance and ensuring operational reliability.