Numerical investigation of a thermal energy storage system based on the serpentine tube reactor

Thermochemical heat storage (TCHS) technology is widely concerned for its high energy storage density (ESD) and long-term storage of energy in the form of chemical energy for long-term thermal storage applications. TCHS with hydrated salt as the thermochemical material (TCM) has low regeneration temperature, clean reaction products, and appropriate heat release temperature, which is suitable for the application of medium and low temperature applications. A 3D numerical model is developed to simulate and understand the hydration (heat discharging) process of the serpentine tube reactor filled with hydrate of K₂CO₃. The coupled multiphysics includes fluid flow, heat and mass transfer, and chemical reaction process. Variations of hydration characteristics, such as temperature and conversion, are discussed in detail. The heat discharging processes at different vapor pressure (1200 Pa–1600 Pa) and different inlet flow rates (0.5–5 m/s) of heat transfer fluid (HTF) are investigated. It is found that higher vapor pressure can significantly increase output temperature, and a higher HTF inlet flow rate can improve overall heat exchange performance. By increasing the vapor pressure from 1200 Pa to 1600 Pa, the maximum outlet temperature lift could be significantly increased by 7.9 %. However, pipe shape has little effect on enhancing the performance of the reactor.