Durability of thermochemical heat storage demonstrated through long-term repetitive CaCl₂/H₂O reversible reactions

Thermochemical heat storage is a promising technology for improving thermal energy efficiency. In this study, CaCl₂ and H₂O were selected as the reactant and working medium, respectively, assuming the utilization of low-grade waste heat. To investigate the durability of the CaCl₂/H₂O reaction, 1000 repetitive operations were conducted at the same 110 °C charging and discharging temperatures. During the long-term repetitions, a decrease in the average volumetric power density was observed. The peak value in repetitions 901-1000 was 11% lower than the peak value in the initial 50 repetitions. This trend was mainly caused by a decrease in the heat transfer rate; it was observed after the repetitive experiments that reactant particles had moved out of the heat exchanger. Although a decreasing trend in the power density was observed, a peak value of Q = 320 kW/m³ and a conversion ratio of approximately 0.7 were observed in repetitions 901-1000. In addition, approximately 90% of the stored heat was released in all 1000 repetitions. Thus, using long-term repetitions (1000), this study confirmed the durability of the CaCl₂/H₂O reaction for thermochemical heat storage.