Comparison of Different Numerical Models for Solidification of Paraffin-Based PCMs and Evaluation of the Effect of Variable Mushy Zone Constant

The impact of the mushy zone parameter (Amushy) and the numerical model during the solidification of a commercial paraffin-type PCM in a vertical cylinder under T-history conditions was examined numerically. The cooling process was simulated using three methods implemented in the CFD code ANSYS Fluent 2020 R2: the enthalpy–porosity method, the AHC method, and a new model proposed by the authors, in which heat capacity is directly introduced into ANSYS Fluent. To determine the precise boundary conditions, radiative heat transfer between surfaces is considered. Moreover, the effect of the mushy zone parameter on simulation accuracy and solidification rate has been investigated, with a variable Amushyintroduced as a function of the liquid fraction. The results indicate that the proposed model demonstrates excellent agreement with experimental data for cooling temperature, providing a more accurate prediction than the other models. Additionally, it shows that temperature varies with time but not with position, suggesting that this model more effectively meets the lumped system condition—a key characteristic of the T-history experiment—compared to the other models. The effect of Amushyy indicates that simulations with a high mushy zone parameter are more accurate and predict a shorter solidification time. Additionally, using a variable mushy zone parameter based on liquid fraction yields similar results, leading to an increased solidification rate.