Hot-spot thermal management by phase change materials enhanced by spatially graded metal meshes

•Phase change materials (PCMs) are an effective approach to thermal management, but heat dissipation rates for PCMs that melt near room temperature are limited by their low thermal conductivity.•We show that the time averaged heat dissipation rate can be vastly improved by using spatially-dependent enhancements to thermal conductivity, that can be achieved using graded mesh structures.•Meshes with optimized spatial distributions are predicted to enhance heat transfer rates by 900% (300%) in spherical (cylindrical) geometries, relative to those achieved by uniform meshes of equivalent average volume fractions. Graded mesh inserts that spatially enhance the thermal conductivity of phase change materials (PCM) are optimized to minimize the time averaged thermal resistance between the heat source and the melt-front, to improve heat dissipation rates for electronics. Conventionally, the low thermal conductivities of PCM are enhanced by incorporating spatially-homogeneous porous fillers with high thermal conductivities. We investigate the relative advantages of porous fillers that spatially distribute enhancements to thermal conductivity. An arbitrary polynomial form of the spatial variation is optimized based on a numerical solution to the heat diffusion equation, to enhance heat dissipation rates in one-dimensional spherical and cylindrical coordinates. The most desirable spatial distributions are non-linear, have higher thermal conductivity near to the hot-spot, and a positive second derivative with respect to the radial coordinate (i.e. concave-up). We demonstrate enhancements of heat dissipation rates for constant temperature hot-spots, or reductions in temperature for constant power hot-spots, by factors of 900% and 300% in spherical and cylindrical coordinates, relative to those achieved by uniform fillers of equivalent average volume fractions. Recent advances in additive manufacturing make metal meshes with spatially graded volume fraction realizable.