The role of the phase-change material properties, porosity constant, and their combination for melting problems using the enthalpy-porosity scheme

Abstract

This study investigates the effects of consistently altering the PCM thermophysical properties, the porosity constant, and their combination on the accuracy of melting models. To the best of the authors’ knowledge, this is the first systematic evaluation of this coupled effect, which challenges a common literature practice: to validate the model and use it with another PCM or in a completely different scenario. To this end, a mathematical model is formulated and numerically solved with Ansys® Fluent, being validated with two experimental datasets, comprising distinct geometries and PCM properties. Initially, the discussion centers on the alteration of the porosity constant, revealing its sensitivity in both isothermal and non-isothermal PCMs, with a more pronounced influence in materials exhibiting a mushy region. Subsequently, the effect of altering the parameters included in the Boussinesq approximation was assessed, being shown that a proper selection of the coefficient of thermal expansion is more critical than that of density, altering the liquid fraction in 7.5% and 0.5%, respectively. The phase-change temperature also influenced the results, with a 6.9% higher deviation when switching from the liquidus to the average solidus–liquidus temperature. Furthermore, it was evidenced that, by holding the porosity constant of validation in another geometry, deviations as high as 38.0% could be achieved, whereas this error could be reduced to 5.7% with a proper adjustment. This discrepancy may be even greater if the PCM is altered, leading to unclear results. Lastly, the study provides valuable insight suggesting that, as natural convection intensifies, reducing the porosity constant can mitigate errors. These findings hold practical significance for models developed using the enthalpy-porosity scheme, emphasizing the importance of careful consideration when extending the model applicability beyond the validation conditions.