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J.W. Garvin

Ph.D. Candidate, Department of Mechanical Engineering, University of Iowa

Modeling particle-solidification front interactions

J.W. Garvin and H.S. Udaykumar

The interaction between a micron-sized particle and a solidification front is important in many natural and industrial processes, ranging from metal-matrix composite (MMC) manufacture, to frost heaving in soils, and cryopreservation. The development of the solidified microstructure in such systems depends on complex interactions between non-planar solidification fronts and multiple particles. The particle-front interaction is a multiscale process as the dynamics at the micro-scale hinges on the interactions (intermolecular in nature) between the phase boundary and the particle which occurs across a nano- scale gap. Numerical simulations are performed to study such an interaction. For such systems, the full solution of the Navier-Stokes equations including the nano-scale gap between their interacting surfaces would be impossible due to resolution demands placed on the mesh. Therefore an embedded model for the interaction dynamics is needed.  The dynamics of the interaction obtained from an embedded interaction model is coupled to the full phase change calculation. A sharp-interface method is used to track both the phase boundary and the particle.  The results obtained differ from the results of previous models where the solidification process is calculated from a simplified analytical expression.  In addition, the force models adapted are carefully scrutinized and shown to inadequately describe the nature of the interaction.  Results are also obtained for cases where a premelting layer is assumed to exist in between the particle and the solidification front.  It is shown that by assuming a premelting layer the pushing/engulfment transition of the particle is determined solely from the dynamics of the system and hence no arbitrary d- cutoff is needed to determine engulfment.