Studies on Reaction Rates of CaSO₄/CaSO₄·1/2H₂O Reversible Reaction for Chemical Heat Pump

Abstract

We previously proposed chemical heat storage and chemical heat pump using a reversible calcium sulphate/water reaction system. Calcium sulphate has possibility of storing thermal energy at the temperature level of around 373 K and releasing hot heat at the same level and cold heat at the 273 K level. Although we proposed reaction equilibrium and reaction rate equations for an open system, more reaction rate studies are necessary for this reaction system, especially for reaction rate in semi-closed and closed systems. In this study, we considered three conditions to decide the reaction rate equations: (1) the difference of diffusion rate in the material core, (2) the difference of material temperature based on convection heat transfer solved by the unsteady heat transfer equations, and (3) the adsorption rate of saturated water vapor at high pressure range. As a result, it was found that calculated data by the proposed reaction rate equations could reproduce the experimental data. Furthermore, the possible operating temperature range and the reaction rates were shown by the simulation.