MgCl2·6H2O-Mg(NO3)2·6H2O eutectic/SiO2 composite phase change material with improved thermal reliability and enhanced thermal conductivity

MgCl 2 ·6H 2 O-Mg(NO 3 ) 2 ·6H 2 O eutectic has a proper melting point and high latent heat for solar water heating systems with latent heat storage . In this paper, the exact composition of the eutectic and the corresponding phase change temperature are determined by measuring the phase change characteristics of mixtures of MgCl 2 ·6H 2 O and Mg(NO 3 ) 2 ·6H 2 O in various ratios. MgCl 2 ·6H 2 O-Mg(NO 3 ) 2 ·6H 2 O eutectics, the melting temperature of which is around 58   °C, can be obtained with the mass fraction of MgCl 2 ·6H 2 O ranging from 35% to 50%. The eutectics are composited with porous fumed silica to improve its thermo-physical properties. The eutectic/SiO 2 composite retains a similar melting point of the pure eutectic, is of no liquid leakage even after melting while the SiO 2 weighs more than 15   wt%, and the specific enthalpy reaches 88.13   kJ   kg −1 . The eutectic/SiO 2 composite has a thermal conductivity 5% higher than pure eutectics and better thermal stability and cycle stability. The thermogravimetric analysis shows its weight loss is 8.03% less than pure eutectic at 300   °C. And the eutectics suffers a decrease in phase change enthalpy after 100 thermal cycles by 9.2%, much lower compared with the 37.23% for pure eutectics due to the phase separation during the thermal cycles. Thermo-physical properties and stability of MgCl 2 ·6H 2 O-Mg(NO 3 ) 2 ·6H 2 O eutectic have been enhanced by fumed silica.