CaCl2-containing composites as thermochemical heat storage materials

The purpose of this paper is to enhance the heat storage and mass transfer performances of mesoporous materials by adding a hygroscopic salt. Silica-gel, alumina, and bentonite were chosen as supports of 15 wt% of calcium chloride. Comparison between the three series of composites was done by analyzing the impact of the salt addition on the physico-chemical and sorption properties of the three host matrixes. Moreover, the water sorption/desorption kinetics on the different composites under operating conditions, close to those of heat pump application, has been studied. The thermal behavior of the composite materials was examined by TG/DSC analysis. The addition of calcium chloride increased the quantity of sorbed water and released heat. The composite silica gel/CaCl2 showed the highest sorption capacity (0.27 g(H2O) gsample(-1)) accompanied with the highest heat storage (746 J &ample 1). The activation energy determined for the desorption process was following the silicagel/CaCl2 < bentonite/CaCl2 < alumina/CaCl2 order, opposite to the pore size of the various composites, that was the larger for silica-gel based materials. Finally, the experimental results of rehydration were fitted with kinetics model in order to describe the kinetics of water vapor adsorption of the three mesoporous composites. Moreover, using the experimental data of rehydration a kinetic model was applied to describe water vapor diffusion in the three mesoporous composites.