Experimental and numerical study on cold storage properties of organic/ inorganic composites in thermal energy storage

Additive-containing aqueous solutions can serve as phase change materials (PCMs) in energy storage technology. Molecular dynamics simulation used to study PCMs, is rarely applied in the cold storage field below 0 degrees C to explain the properties of cold storage materials. In this work, experiments and molecular dynamics simulations were used to study the effect of additive concentration and type on the cold storage performance of organic/ inorganic PCMs. Results show that additives reduce the proportion of hydrogen bonds between water molecules, requiring a lower temperature for PCMs to form regular ice crystal structures, thus lowering the phase change temperature, despite the buffering effect of van der Waals forces. Additionally, additives increase intermolecular interactions, weakening the diffusion of water molecules and reducing surface tension, which decreases heat and mass transfer capabilities and contact angle, thereby extending cold storage time and reducing supercooling. Moreover, the proportion of hydrogen bonds and self-diffusion coefficients decrease with the increase in the number of hydroxyl and chlorine atoms, leading to ethylene glycol/CaCl2 having the lowest phase change temperature, the longest cold storage time, and the lowest supercooling.