Thermodynamic and kinetic study of CaCl2-CH3OH adducts for solid sorption refrigeration by TGA/DSC

Addition compounds of CaCl2 and CH3OH are promising thermochemical materials for thermal energy storage and conversion. Achievable evaporation temperatures lie within the operating range of standard building and industrial refrigeration applications. In heterogeneous gas-solid reactions the cooling power of the respective reaction pair is mainly dependent on the uptake rate of the gaseous reactant. In this paper, a comprehensive study on the influence of various procedural parameters and thermal cycling on the cooling efficiency performance of CaCl2 methanolates was carried out at material scale to provide insights on application design principles. SCPs and cooling COPs were calculated from experimental data obtained by simultaneous TGA/DSC. SCPs, averaged over a methanolation time of 60 min, varied between 157 W/kg and 366 W/kg, whereas maximum SCPs reached values between 232 W/kg and 1029 W/kg depending on methanol partial pressure. The results indicate possible applications with evaporator temperatures around 10 °C, as for the cooling of buildings. COPs were within the range of 0.59 and 0.76. Results showed that thermodynamic conditions and thermophysical properties of the material had a great impact on the methanolation/demethanolation reaction kinetics. Under periodic conditions a slight attenuation of the maximum cooling power was observed, whilst the more practically relevant average SCP was stable over a number of 18 cycles. With respect to application design, different regeneration (demethanolation) temperatures as well as the impact of the thermal history of the material were investigated. The reaction pair can also be used with regeneration temperatures of ≤100 °C.