Improvement of Model for High-temperature Heat Pipe Wick Considering Effect of Gaps

High-temperature heat pipes rely on the capillary force provided by the wick to enable the reflux of condensed working fluid, where the mass transfer capacity of the wick directly affects the heat transfer performance of the heat pipe. However, in the current design and manufacturing of high-temperature heat pipes, due to the generally high hardness of metal wire meshes, interlayer gaps exist between mesh layers after being rolled into wicks, and current design calculations do not consider the influence of these interlayer gaps on wick performance. Therefore, wire mesh wicks are often selected and manufactured based on previous production experience, making it impossible to exclude wire mesh selection as a factor when the heat pipe performance is poor. This paper focused on wire mesh wicks for high-temperature heat pipes, conducting experimental research on permeability performance and modifying existing mathematical models by considering interlayer gaps, resulting in a mathematical model that better fits experimental results. The research results show that the porosity of different types of wire mesh wicks under the same process conditions ranges from 0.433 to 0.879, the porosity of single-mesh-number wicks should decrease monotonically with increasing mesh number, but due to the poor liquid absorption capacity caused by the large pores of 50-mesh wicks, their porosity is anomalously small. The 600-mesh wick has the highest permeability at 2.070×10⁻⁹ m², and there is a positive correlation between porosity and the effective capillary radius of the wick. The effective capillary radius first decreases and then increases with increasing mesh number, while permeability shows a trend of decreasing-increasing-decreasing with increasing mesh number. Existing mathematical models cannot correctly characterize the microscopic parameters of wire mesh wicks, with the permeability results for 800-mesh wicks differing by two orders of magnitude, and even the smallest error for 50-mesh wire mesh reaching 278.1%. Moreover, the larger the mesh number, the greater the error between experimental and theoretical values. Under electron microscope observation, a wire mesh wick model considering gap effects was proposed and compared with experimental results. The theoretical permeability calculations for wire mesh wicks with gaps better match the experimental values, with relative errors of 33.63% and 24.68% for 50-mesh and 400-mesh wire meshes, respectively, while the trend of permeability changes with mesh number also aligns well with experimental results. Overall, the error is reduced by 1-2 orders of magnitude compared to the original mathematical model. The findings of this study hold significant implications for wick parameter selection and design optimization of high-temperature heat pipes.