Structured, sintered, and rastered strategies for fluid wicking in additively manufactured heat pipes

Abstract

This work compares three different strategies for creating wicking structures with Laser Powder Bed Fusion (LPBF) for use in additively manufactured monolithic heat pipes: (i) structured wicks, fabricated with intentionally designed lattice geometries, (ii) sintered wicks, created by partially melting and fusing the metal powder used in the LPBF manufacturing processes, and (iii) rastered wicks, created by modifying the laser raster infill grid parameters to generate fluid flow paths. The study was performed in three phases. Phase I examined wick fluid absorption, porosity, volumetric energy density, and wick manufacturability for a broad range of production parameters. A subset of promising wick production approaches was identified for fluid rate-of-rise characterization in Phase II. One high performing wick production approach was selected for each strategy for detailed characterization in Phase III. In this last phase, the wick candidates were studied through X-ray microtomography, scanning electron microscope (SEM) imaging, porosity analysis, and computational simulations of directional sample permeability and thermal conductivity (using geometry data from X-ray imaging). Advantages and disadvantages of each wick design approach were explored in the context of both manufacturability using LPBF, and wick performance. Of the three strategies, the rastered approach was found to have the most potential for applications in future additively manufactured heat pipe designs due to its wide LPBF manufacturability process window and its relatively high permeability with low directional dependence.