A composite phase change material thermal buffer based on porous metal foam and low-melting-temperature metal alloy

Composite phase change materials consisting of a high-latent-heat phase change material (PCM) embedded in a high-thermal-conductivity matrix are desirable for thermally buffering pulsed heat loads via rapid absorption and release of thermal energy at a constant temperature. This paper reports a composite PCM thermal buffer consisting of a Field's metal PCM having high volumetric latent heat (315 MJ/m³) embedded in a copper (Cu) matrix having high intrinsic thermal conductivity [384 W/(m·K)]. We demonstrate thermal buffer samples fabricated with Cu volume fractions from 0.05 to 0.2 and sample thicknesses ranging between 1 mm and 4 mm. Experiments coupled with finite element method simulations were used to determine the figures of merit (FOMs), cooling capacity η_eff, energy density E_eff, effective thermal conductivity k_eff, and the buffering time constant τ. The cooling capacity was measured to be as high as η_eff = 72 ± 4 kJ/(m²·K^1/2·s^1/2) for the 1.45 mm thick thermal buffer sample having a Cu volume fraction of 0.13, significantly higher than theoretical values for aluminum-paraffin composites [45 kJ/(m²·K^1/2·s^1/2)] or pure paraffin wax [8 kJ/(m²·K^1/2·s^1/2)]. Our work develops design guidelines for high-FOM thermal buffer devices for pulsed heat load thermal management.