SIMULATING PHASE CHANGE HEAT TRANSFER USING COMSOL AND FLUENT: EFFECT OF THE MUSHY-ZONE CONSTANT

This paper presents a numerical study aimed at understanding the impact of the mushy-zone constant, A(mush), on simulated phase change heat transfer. This parameter is found in the Carman-Kozeny equation which is used in the enthalpy-porosity formulation for modeling natural convection driven phase change. The melting of dodecanoic acid inside a rectangular thermal storage unit was simulated in COMSOL 4.4 and FLUENT 15.0; with A(mush) and the melting temperature range, Delta T, being varied per study. The simulated melt front positions were directly compared to experimental results. Results showed that A(mush) is an important parameter for accurately modeling phase change heat transfer; in particular, high A(mush) values corresponded to slower melting rates and the smallest A(mush) values resulted in unphysical predictions of the melt front development. Additionally, it was concluded that A(mush) and Delta T are not independent of one another in their roles of accurately modeling the melting rate; different values of Delta T would require different values of A(mush) to achieve the same melt front development. However, certain combinations of A(mush) and Delta T do lead to an overall melt fraction progression for the overall process and are in line with the experimental results, although the numerically predicted movement of the melting interface in such cases is not always correlated to the experiment. Further efforts are required to identify ideal values for these parameters, as well as to determine the extent to which these parameters hold for different materials and physical setups. It is anticipated that this paper will lead to further discussion on the significance of the mushy zone as a numerical technique for accurately modeling phase change heat transfer.