Thermal Conductivity Measurements of Calcium Oxalate Monohydrate as Thermochemical Heat Storage Material

Abstract

Thermochemical energy storage (TCES), based on reversible solid-gas reactions, offers the possibility to store heat without heat loss as long as both reactants are separated from each other. Furthermore, higher energy densities compared to sensible or latent heat storage systems are possible. Thermal transport properties of mainly powdery thermochemical materials (TCM) have an important implication on the performance of a TCES. This study has chosen calcium oxalate monohydrate (CaC2O4·H2O) which dehydrates to calcium oxalate (CaC2O4) after thermal treatment, to showcase the characterization of the thermal transport properties of a TCM. Preliminary thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) or simultaneous thermal analysis (STA) tests were carried out to identify reaction free temperature intervals and specific heat capacity cp(T). Light flash technique (LFA) was used to measure the effective thermal diffusivity aeff(T). Effective thermal conductivity was calculated with eff(T) = aeff(T)·cp(T)·B(T) on the compacted CaC2O4·H2O samples with B = 1638 kg·m-3. In addition, direct eff(T) measurements in the packed bed with B = 386 kg·m-3 were conducted by using the Transient Hot Bridge (THB) method.