An equivalent self-adjusted heat capacity method for modelling heat diffusion problems with solid-liquid phase-change

This work evaluates the thermal behaviour of a small aluminium-container-based thermal energy storage (TES) unit filled with a microencapsulated phase change material (PCM) – Micronal® DS 5001 X. ANSYS CFX® software is used for the 3D numerical simulations, which are based on the Effective Heat Capacity (EHC) method considering a purely diffusive transient model. In the formulation, a new artificial self-adjusted triangular profile was considered to account for the variation of the effective specific heat with temperature. Due to the artificial nature of this procedure, the correct prediction of the phase-change kinetics was analysed. For that purpose, some previously obtained experimental data were used for validating the numerical results. The amount of stored and released energy during charging and discharging was also evaluated. The main results of this numerical study show a very good agreement with both the kinetics of the phase-change processes (average and maximum errors of 2.9 % and 11.6 %, respectively, during charging; average and maximum errors of 1.7 % and 5.0 %, respectively, during discharging) and the total amount of stored/released energy during a complete experimental charging/discharging cycle of the PCM. Moreover, it was concluded that the EHC method with a self-adjusted triangular profile to account for the variation of the effective specific heat with temperature is a good method for modelling heat diffusion problems with solid-liquid phase-change