Capillary performance characterization of porous sintered stainless steel powder wicks for stainless steel heat pipes

Stainless steel heat pipes have attracted increasing attentions for applications in extreme environments. The stainless steel wick structure as the key component is of high importance for the thermal performance of stainless steel heat pipe. Here, sintered porous wicks using stainless steel powders are developed to evaluate the capillary performance that directly governs the liquid circulation in heat pipes. Systematical experiments of permeability tests and capillary rise tests are conducted for porous wicks with spherical and irregular morphologies in different powder sizes. Water droplets spread entirely on both kinds of porous samples in tens of milliseconds, implying the sintered powder wicks present excellent wetting property. The irregular powder samples show a permeability improvement with a factor of 1.5-4.8 compared to the spherical powder ones with the same powder size, whereas they provide smaller capillary pressures. This is attributed to the more complicated morphologies of the irregular powders that are easier to form larger interconnected inner pores. The wicks with medium powder size of 90-120 um, maintaining a good balance between permeability and capillary pressure, exhibit the optimal capillary performance, which is indicated by the highest capillary factor that can comprehensively reflects the combined effects.