Experimental study on composite silica gel supported CaCl2 sorbent for low grade heat storage

A composite sorbent was prepared by utilising a mesoporous silica gel impregnated with the hygroscopic salt CaCl2 to improve the specific thermal energy storage (TES) capacity in low grade heat storage. The properties of water sorption on the composite sorbent were measured in an open environment. A much larger sorption amount of up to 0.73 g water per gram composite sorbent was obtained at the temperature of 30 °C and the relative vapor pressure of 0.8, which conformed a high increase in the specific capacity compared 0.15 g g−1 for the silica gel. The TES performance of the composite sorbent was investigated in an open-type TES setup equipped with 40 kg composite sorbent pellets. The experimental results show that the heat discharging temperature of the composite sorbent varied from 30 °C and 45 °C and the TES system was charged efficiently below 90 °C. At the preset heat supply temperature of 30 °C and the charging temperature below 90 °C, the specific TES capacity of approximately 1 kJ g−1 and the storage efficiency of 0.78 for the composite sorbent were obtained. The sorption stability of the composite sorbent was also studied through over 500 repeated sorption/desorption cycles. The composite sorbent showed an approximately stable 0.95 kJ g−1 in the specific TES capacity. A comparison of the composite sorbent and the other TES materials was made and it was found that the composite sorbent provides great potential to obtain the TES system of small size and high storage density for low grade heat storage.