Analysis of Key Material Parameters of Evaporator Wicks and Working Fluids for a Loop Heat Pipe Operating in the Temperature Range of 500–700 K

TL;DR

This paper evaluates wick materials and working fluids for heat pipes operating at high temperatures, identifying optimal combinations for performance and reliability.

Contribution

The study introduces a systematic evaluation of wick-fluid pairings for high-temperature loop heat pipes, focusing on capillary pressure and flow resistance.

Findings

Nine porous wicks and seven working fluids were analyzed for capillary pressure and flow resistance.

Optimal wick-fluid pairings were identified based on thermal performance and structural integrity.

The results provide a foundation for developing high-temperature loop heat pipe prototypes.

Abstract

This study presents a preliminary evaluation of candidate wick material and working fluid for a flat-loop heat pipe (F-LHP) designed to operate within the temperature range of 500–700 K. The selection process considered key thermal and physical parameters, including thermal conductivity, chemical compatibility between wick and fluid, capillary pressure generation, pressure drop across the wick structure, and structural integrity at elevated temperatures. A range of metallic and ceramic wick materials, along with suitable high-temperature working fluids, were reviewed and compared based on performance metrics and practical availability. Special attention was given to oxidation and corrosion resistance, capillary performance, and thermal stability under elevated-temperature conditions. Nine different porous wicks with distinct materials and microstructures—differing in pore size, porosity, and permeability—were analyzed in combination with seven different working fluids. The analysis focused on determining which combinations generated the highest capillary pressure and which exhibited the lowest flow resistance due to external flow, thereby enhancing the LHP’s performance. Based on these results, the study identifies the most effective wick–fluid pairings for F-LHP applications, offering an optimal balance of thermal performance and long-term reliability. These findings provide a foundation for further experimental validation and the development of prototypes.

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