Thermo-elastic model for the prediction of thermodynamic properties of high temperature phase change materials under confinement: Isobaric and isochoric regimes

Thermal energy storage through encapsulation of phase change materials is critical for the efficient usage of renewable energy. In this paper, a model is proposed to include thermal and pressure induced density changes in a confined phase change material. To the best of the authors’ knowledge, the local energy balance at the interface and the total mass balance that couple thermal and pressure induced density changes during melting of confined phase change materials are proposed for the first time. The proposed model is solved for a KNO3 salt and several values of the elastic constant in order to probe the phase transition in the whole pressure domain. The behavior of the thermodynamic variables is investigated for other kinds of salts used in high temperature thermal energy storage applications and in the high pressure regime. In all the examples shown, and when the phase change process takes place close to the isochoric regime, the effects of temperature dependent densities are found to be enhanced by pressure induced density changes. However, close to the isobaric regime, the effects of temperature dependent densities are almost negligible. Finally, the thermal energy stored during the melting process is obtained. Close to the isochoric regime, and depending on the types of boundary conditions, the sensible heat stored is found to be enhanced by thermal expansion, while the latent heat absorbed is significantly reduced.