Fabrication and characteristics of eutectic hydrated salts/fumed silica composite as form-stable phase change materials for thermal energy storage

In this research, a novel form-stable composite phase change material (PCM) for building envelopes was prepared and evaluated. Calcium chloride hexahydrate (CCH) and magnesium nitrate hexahydrate (MNH) were dissolved and mixed uniformly to obtain the binary eutectic hydrated salt (BEHS) with adjustable phase change temperature. With the increase of MNH content, the phase change temperature and latent heat of BEHS gradually decreased. The BEHS with the onset temperature and peak temperature of 21.26 °C and 27.51 °C and corresponding latent heat of 142.4 J/g was selected as the PCM and combined with the support material SiO2 to obtain BEHS/SiO2 composite PCMs，where the minimum SiO2 content to prevent BEHS from leaking was 25 wt%. The characterization results of SEM, XRD and FT-IR indicated that BEHS was successfully filled into the pore structure of SiO2, and there was good compatibility between them. By adding 2.5 wt% strontium chloride hexahydrate as a nucleating agent, the supercooling degree of BEHS/SiO2 composite PCMs was eliminated. The onset temperature and peak temperature of BEHS/SiO2 composite PCMs were measured to be 17.85 °C and 27.28 °C, respectively, and the corresponding latent heat was 97.3 J/g. A 300 melting and solidification cycles test proved that it possessed good thermal reliability. Moreover, the numerical simulation was performed to evaluate the effect of BEHS/SiO2 composite PCMs on the thermal performance and energy performance of the building. The obtained results showed that composite PCMs could effectively reduce room temperature fluctuations and energy consumption.