An enthalpy-porosity technique is used in Ansys Fluent for modeling the solidification/melting process. In this technique, the melt interface is not tracked explicitly. Instead, a quantity called the liquid fraction, which indicates the fraction of the cell volume that is in liquid form, is associated with each cell in the domain. The liquid fraction is computed at each iteration, based on an enthalpy balance.Computational cells that are undergoing a phase change are modelled as pseudo porous media with porosity, being a function of H and ranging between 1 (fully liquid) and 0 (fully solid).

For more details on enthalpy porosity technique please refer research paper: Enthalpy-Porosity Technique for modeling convection-diffusion phase change:Application to the melting of a pure metal by A.D.Brent, V.R.Vollar, K.J.Reid

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