Modeling of heat capacity peaks and enthalpy jumps of phase-change materials used for thermal energy storage

We consider three phase-change materials (PCMs) in which a change between two phases may be used to store/release thermal energy. Their enthalpy and heat capacity were measured in a quasistatic regime by adiabatic scanning calorimetry and show, within a certain temperature range, a single distinct jump and peak, respectively. We present a microscopic development from which the jumps and peaks can be accurately fitted and that could be analogously applied even to other PCMs. In addition, we determine the baseline and excess part of the heat capacity and thus the latent heat associated with the phase change. The development is based on the observation that PCMs often have polycrystalline structure, being composed of many single-crystalline grains. The enthalpy and heat capacity measured in experiments are therefore interpreted as superpositions of many contributions that come from the individual grains.