Cross-plane and in-plane porous properties measurements of thin metal felts: applications in heat pipes

Abstract Measurements of the porous media character of sintered micro-fibrous metallic felts are reported for both the in-plane (longitudinal) and cross-plane (transverse) orientation liquid permeability and effective pore size. The family of samples tested included felts fabricated from 316L stainless steel or Haynes 188 fibers, between 6 and 50 μm in diameter, with bulk porosities from 0.55 to 0.91, and aspect ratios ranging from 80:1 to 5000:1. Both random lay and parallel lay materials are included in this sample set. The samples tested resided in four distinct classifications depending on the fiber size and resulting fiber lay orientation (parallel or random). A large range in effective pore size (6.1–281 μm radius) and liquid permeability (1.2–925 μm2) was found in addition to a noticeable anisotropic feature (in-plane versus cross-plane) to these felts. Finally, the application of these materials for use as heat pipe wicking materials is evaluated by comparing the existing property data for competing porous media materials, such as sintered powders and stacked screens. This evaluation is based upon comparing the effective pore size versus liquid permeability for each of the four sample classes tested. It is found that these felt materials perform as good or better than traditional wicking materials (screens and powders) while offering the additional benefits of a flat and conformal geometry.