Modeling flowability of mushy zone with a hybrid model utilizing coherency solid fraction

This paper reports on the progress made in the development of a hybrid model of the mushy region in phase change problems. The mushy region is modeled as a non-Newtonian semi-solid medium below the coherency point and a porous medium thereafter. The validity of the model is tested on the solidification of a generic binary alloy in a 2D rectangular cavity. The predictions include temporal evolution of the flow and thermal fields and spatial distribution of the viscosity, velocity components and temperature. The predicted results are comparable with those of the conventional porous medium model. The predicted maximum viscosity isopleths appear as ‘islands’ suggesting that the hybrid model has potential to represent interdendritic flow. The choice of the coherency point has a profound effect on the velocity, thermal gradient and size of the mushy region, especially at the bottom of the cavity.