17. Evaluation of Thermal Properties of Refrigerant Clathrates with Additives

A modeling study is conducted to evaluate the heat transfer capabilities of novel refrigerant clathrate-based phase change materials with salts and nanoparticles as additives. The formation of refrigerant clathrates is studied for both active and passive cooling applications. In this regard, the refrigerants, e.g., R134a, R141b, and R32 clathrates are studied at different refrigerant mass fractions since the solubility of refrigerants, in water, change with change in temperature. The sodium chloride and magnesium nitrate hexahydrate are used as salt additives. The nanoparticles of pure aluminum, copper, and graphene are also studied to investigate the improvement in their thermal properties. Some empirical correlations are used to predict the thermal conductivities of refrigerant clathrates and the improvement with the addition of additives. The results show that an increase in refrigerant mass fraction lowers the thermal conductivity of the refrigerant clathrate but not extensively. The addition of salts results in a minor improvement in thermal conductivity. The inclusion of nanoparticles significantly improved the thermal conductivity of the phase change material. It is also obtained that adding the nanoparticles improves the thermal conductivity more than the salts. The specific heat capacity, however, was not generally improved by the nanoparticles as it depended on the additive used.