Experimental Investigation of the Concentration Dependent Maximum Storage Capacity of two Inorganic Phase Change Materials

In large latent heat storages with the phase change material (PCM) being a salt hydrate, it is difficult to assure the stoichiometrically correct hydrate concentration of the salt hydrate. In this study, the influence of the composition of CaBr2 + H2O around the congruent melting CaBr2·6H2O and CaCl2 + H2O around the semi-congruent melting CaCl2·6H2O on the maximum storage capacity is investigated via differential scanning calorimetry (DSC). For a CaBr2 concentration around 0.8 wt% lower than the concentration of CaBr2·6H2O, a decrease of over 17% is found for the maximum storage capacity. For a CaCl2 concentration around 0.7 wt% lower than the concentration of CaCl2·6H2O, a decrease of over 11% is found for the maximum storage capacity. While reproducible results for the maximum storage capacity for samples of the same concentration of CaBr2 + H2O are obtained via DSC, this is not the case for the CaCl2 + H2O samples. Thus, the difficulty to measure representative enthalpy curves of non-congruent melting salt hydrates via DSC is shown.