Calcium chloride hexahydrate based supercooling phase change material for a long-term recovery of low-grade thermal energy

The low-grade waste thermal energy massively exists in industrial processes and is difficult to be recovered in a long-term manner due to severe heat loss. This study presents a group of calcium chloride hexahydrate (CCH)-based phase change materials (PCMs) with a large degree of supercooling and high latent heat. The large degree of supercooling of the proposed PCMs could harness the low-grade thermal energy, store the latent heat in a long-term manner and release the heat by a trigger when required. A group of composite phase change material (CPCM) is proposed based on CCH as the core salt hydrate, calcium chloride as the solute, and polyethylene glycol (PEG 200) as the additive. This CPCM has a large supercooling capacity and high thermal storage density. The optimal ratio of CPCM components is found to be 88.9 wt% CCH with 2.22 wt% PEG 200, and 8.88 wt% CaCl2 with a phase transition temperature of 29.8 °C and a latent heat value of 193.74 kJ/kg. This represents a 35.6 % increase in latent heat compared to the pure CCH with a latent heat of 142.85 kJ/kg. Additionally, the reason for the addition of PEG 200 to improve CCH supercooling has been explored. This article creatively proposed the use of solubilizer PEG 200 to significantly increase the latent heat value and supercooling degree of hydrated salt PCMs, providing a promising direction for the preparation of large-scale supercooled high latent heat CPCMs to recover ultra-low-grade waste heat energy.