Study on the cycle characteristics of chemical heat storage with different reactor module types for calcium chloride hydration

To be able to use a chemical heat pump (CHP) practically, it is necessary for the reactor and heat exchanger to perform well. Herein, we examine the heat input/output and coefficient of performance (COP) for reactor modules of a CHP under a calcium chloride (CaCl₂) hydration reaction. Various reactor modules were investigated, including plate-tube heat exchangers that comprise of reactors with packed beds of different widths, along with expanded graphite and porous nickel (Ni) metal plates. We found that the heat input/output characteristics could be improved by reducing the heat and mass transfer resistances in the packed-bed reactor. During the heat release, when the reactor and evaporator pressures were the same, the heat transfer rate had a higher impact on the heat output than the water transfer rate. On the contrary, the water transfer rate had a higher impact on the heat input than the heat transfer rate, when the reactor and condenser pressures were the same during heat storage. Furthermore, a COP of 0.43 was achieved for chemical heat storage, at the required temperature, using a plate exchanger with a porous Ni metal plate. Conclusively, a preferred reactor module is one that demonstrates high heat input/output and COP, so that the heat and mass transfer rates can be improved to enable the hydration of large quantities of CaCl₂.