Liquid Metal Thermal Buffer (APL)

T. Yang, J. G. Kang, P. B. Weisensee, B. Kwon, P. V. Braun, N. Miljkovic, W. P. King, “A composite phase change material thermal buffer based on porous metal foam and low-melting-temperature metal alloy“, Appl. Phys. Lett. 116 (2020) 071901

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.