A physical model is proposed for the solid/liquid interfacial drag in both globular and dendritic equiaxed solidification. By accounting for the presence of multiple particles and the nonsphericity and porosity of the individual equiaxed crystals, a drag correlation is developed, which is valid over the full range of solid volume fractions. It is shown that neither the solid liquid interfacial area concentration nor the grain size alone is adequate to characterize the interfacial drag for equiaxed dendritic crystals in both the free particle and packed bed regimes; thus, the present model is based on a multiple length scale approach. The model predictions are compared to previous analytical and numerical results as well as to experimental data available in the literature, and favorable agreement is achieved.
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