Theoretical Predictions for Latent Heats and Phase-Change Temperatures of Polycrystalline PCMs

摘要

We had previously developed a microscopic approach from which it is possible to fit enthalpy jumps and heat capacity peaks of polycrystalline phase-change materials that consists of a large number of grains. It is also possible to determine the corresponding latent heat and phase-change temperature. These results are given in a form of sums over grain diameters that can be evaluated numerically. Therefore, their behavior and dependence on physical parameters are not susceptible to straightforward interpretations. Here we use the results to derive simple formulas for the maximum position (T_(max)), height (H), and an asymmetry factor (α) of those heat capacity peaks that are very asymmetric. In addition, we express the phase-change temperature as a simple combination of T_(max), H, α, and the peak's area. We apply our formulas to Rhubitherm 27 as an example PCM for which the heat capacity peak is so asymmetric that it has about 80 % of its total area below its maximum position.