Thermal characteristics of magnesium nitrate hexahydrate and magnesium chloride hexahydrate mixture as a phase change material for effective utilization of urban waste heat

The objective of this study is effective utilization of urban waste heat from emerging co-generation systems, typically available at temperatures of 60–100 °C. The authors investigated latent heat storage by materials with phase change temperatures in the above range, and focused on a mixture of magnesium nitrate hexahydrate as a base material and magnesium chloride hexahydrate as an additive to modulate the melting point. Addition of 5–10 wt% of the latter resulted in a modulated melting point of around 80 °C and a heat of fusion of about 150 kJ/kg. Increasing the mix ratio had little effect on heat of fusion, but allowed the melting point to be reduced to about 60 °C. Repeated melting and solidification tests showed that the heat of fusion and melting point retained their original values after 1000 cycles.