Experimental investigation on copper foam/hydrated salt composite phase change material for thermal energy storage

Abstract

Latent thermal energy storage based on hydrated salt as phase change material (PCM) has the potential to store large amounts of energy in relatively small volume. However, the problems of phase separation, high supercooling degree and low thermal conductivity are the common drawbacks for hydrated salts and thus critically limit their energy storage applications. In this study, the hydrated salt of sodium acetate trihydrate (SAT) is firstly modified by using additives with the aim of solving the phase separation and supercooling degree problems, and then the copper foam/hydrated salt composite PCM is prepared by using the modified SAT as PCM and copper foam as supporting matrix to overcome the low thermal conductivity. The thermophysical properties and thermal performance of modified SAT and copper foam/SAT composite PCM are tested and analyzed by using Differential Scanning Calorimeter (DSC), HotDisk Thermal Constant Analyzer and a lab-scale experimental setup. The DSC analysis showed that the modified SAT with the additives of 0.5wt% carboxyl methyl cellulose (CMC) as the thickener and 2.0wt% disodium hydrogen phosphate dodecahydrate (DHPD) as the nucleator has the best performance to avoid phase separation. The cycled test revealed that modified SAT has good thermal stability and its supercooling degree is lower than 3°C. The experimental results showed that the effective thermal conductivity of copper foam/SAT composite PCM is about 11 times higher than that of pure SAT, and it’s volume heat storage energy density is as high as 467MJ/m3, and this value is 2.2–2.5 times of that of conventional water tank. The results indicated that the copper foam/SAT composite PCM is a promising phase change material for thermal energy storage due to its good thermal stability, low supercooling degree and high thermal conductivity.