Phase change doped sand storage for isothermal thermoelectric heat delivery

Abstract

Household-scale sand-based thermal energy storage (TES) integrated with thermoelectric generators (TEGs) is constrained by insufficient radial thermal transport, interfacial heat transfer losses, and uncertain cyclic durability. This study addresses all three issues through a finite-element parametric investigation of thirty composite configurations spanning five dopant candidates, three volume fractions, and two spatial architectures. The 30 vol% functionally graded Solar Salt formulation produced a well-defined isothermal plateau near 493 K at the TEG interface, stabilizing the hot-side temperature to within 10 K through a spatially coherent phase-change front. No purely conductive dopant reproduced this temporal stability despite achieving higher peak temperatures. Interfacial analysis revealed that a 0.1 mm thermal interface material layer imposed a 40 K temperature discontinuity comparable to the TEG operating differential. Thermomechanical screening across nine insulation-shell material combinations demonstrated that compatibility among the coefficients of thermal expansion governed long-term reliability, with zirconia paired with Inconel 718 achieving a fatigue safety factor exceeding 2.0 over the 20-year service horizon projected by the power-law ratcheting extrapolation. Furthermore, coupled parametric mapping of interface conductivity and contact pressure identified an optimized design point capable of delivering 82% of the thermal energy to the TEG surface. This interfacial optimization secured a projected thermal interface material (TIM) fatigue life of 6,200 cycles (approximately 17 years) and ultimately yielded an end-to-end electrical efficiency of approximately 5%. These findings establish quantitative design criteria for transitioning sand-based thermal storage to compact household-scale modules.

Keywords

Thermal energy storage / phase change material / thermoelectric generator / interfacial thermal resistance / thermomechanical fatigue / sand battery

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