Cyclic Properties of Thermal Storage/Discharge for Al-Si Alloy in Vacuum for Solar Thermochemical Fuel Production

Abstract

Abstract Thermal energy storage using phase-change materials (PCM) can be utilizedfor load shaving or peak load shifting when coupled to a solar thermochemical reactor, reformer, or gasifier for the production of solar fuel. The PCM is embedded in packages or used in bulkin these storage systems, and therefore the compatibility of the encapsulation materials and the selection of the PCM arekey factorsfor ensuring the long operational life of the system. Variouskinds of molten fluoride, chloride and carbonate salts,andmixed moltensalt, which functionat high temperatures of over 500 °C, are known to cause corrosion or thermaldegradation. It is therefore worth studying newhigh-temperature PCM thermal storage alternatives to these molten salts foruse in solar thermochemical processes.In this study, the focus was on aluminum-silicon alloy (Al-Si alloy)as a high-temperature PCM thermal storage medium,and thecompatibility of this alloy with graphite-carbon encapsulation material wasexperimentally examined. The cyclic properties of thermal storage/discharge for Al-Si alloy as a latent-heat energy storage material was studied with respect to various thermal cycles. Athermal stability test was performed for the Al-20wt%Si, Al-25wt%Si, Al-30wt%Si, and Al-35wt%Si alloysplacedin the graphite container in vacuum. The temperatureincreasing and cooling performances of the Al-Si alloy weremeasured duringthe thermal storage (heat-charge) mode and during the cooling (heat-discharge) mode. Theoxidation levelof the Al-Si alloy after the cyclic reaction (20 cycles) was evaluated using an electron probe microanalyzer (EPMA).