Evaluation of thermophysical properties of refrigerant clathrates with additives

A modeling study is conducted to evaluate the heat transfer properties of novel refrigerant clathrate-based phase change materials (PCMs). Novel PCMs with large specific energy densities are formed by using different additives in the refrigerant clathrates. Refrigerant clathrates of R134a, R1234yf and R32 are investigated at different refrigerant mass percentages with water. Glycols, sodium chloride, magnesium nitrate hexahydrate, nanoparticles of pure aluminum, copper and graphene are used as additives. Empirical correlations are used to predict the liquid-phase thermal conductivities of refrigerant clathrates and the improvement obtained with the addition of different additives. The results show that an increase in refrigerant mass percentage lowers the thermal conductivity of the refrigerant clathrate but not extensively. The addition of salt results in a minor improvement in thermal conductivity while addition of glycols as liquid additives greatly improves the liquid-phase thermal conductivity. The inclusion of nanoparticles significantly improved the thermal conductivity of the phase change material. The liquid-phase specific heat capacity, however, is not generally improved by the nano-particles as it depended on the additive used.