Numerical analysis of solidification of paraffin-type PCMs by using customary fixed-grid methods

A numerical study is conducted to predict temperature measurements during the solidification of a commercial paraffin-type PCM in a vertical cylinder under T-history conditions. Two fixed-grid techniques are implemented: the enthalpy-porosity formulation and the Apparent Heat Capacity (AHC) method. As it is known, the first, originally devised for metals and alloys, raises questions about its applicability to other materials. Additionally, there may be uncertainties surrounding the assignment of internal parameters when representing the transitional “mushy” region. On the other side, there are limited publications that utilize the AHC method, and even fewer have addressed and compared both methods. Phase-change properties of the paraffin material are determined through the use of differential scanning calorimetry (DSC): phase change temperature range, latent heat, and specific heat capacity vs. temperature curve ($c_p-T$). Results show that there is significant disagreement between measurements and simulation results for both methods. The enthalpy-porosity technique may not be entirely suitable for accurately modeling phase changes in paraffin-type PCM. Furthermore, while the AHC method can effectively predict the initial and final stages of solidification, it tends to struggle with accurately simulating the mushy zone. An interesting observation is that in the AHC method, the cooling rate is a critical factor influencing the accuracy of solidification simulations and results depend very much on the DSC $C_p-T$ curve introduced, determined under a constant cooling rate, which is indeed variable during the experiment