Theoretical and experimental investigation of a closed sorption thermal storage prototype using LiCl/water

A 1 kWh lab-scale sorption prototype using LiCl-water was theoretically and experimentally investigated for sorption thermal energy storage. A type of consolidated composite matrix is developed for the system by using AC (activated carbon), LiCl, expanded natural graphite treated with sulphuric acid (ENG-TSA) to increase heat transfer and SS (silica solution) to enhance mechanical strength. Thermal conductivity and permeability were measured first. A two-dimensional model considering the combined heat and mass transfer was developed to predict the sorption kinetics of the reactor. Under the operation condition of a charging temperature of 85 °C and a discharging temperature of 40 °C, the experimentally recovered heat is 2517 kJ, resulting a heat storage efficiency of 93%. The heat storage density is 874 kJ/kg consolidated sorbent or 2622 kJ/kg LiCl. The experimental results of the prototype were compared with the simulated results. The established two-dimensional model proves to be effective since the general evolution trends of experimental and simulated outlet fluid temperatures are in good agreement. An average gap of about 0.4 °C between the experimental and simulated outlet temperature may be caused by the heat loss and the constant pressure assumption.