Sedimentation speed of a free dendrite growing in an undercooled melt

Free equiaxed dendrites in solidifying alloy melts are subjected to hydrodynamic effects as a result of gravity. The sedimentation of dendrites is one such effect and believed to be a cause of macro segregation in partitioning alloys. A novel computational model is proposed to estimate the settling speed of free dendrites at moderate Reynolds numbers. Growth of the dendrite, momentum changes, internal solid fraction evolution within a spherical dendrite envelope of changing diameter, and surface morphology of the dendrite while settling are taken into account in the development of the model. Comparison with results from a series of equiaxed dendrite settling experiments, on solidifying transparent alloy analogues to metals, shows good agreement between predicted and experimental settling speeds. The correlation between surface morphology of the dendrite which affects drag force and the physical parameters of the settling dendrite is studied. The feasibility of applying the proposed model to metallic systems is also explored and the outlook is positive.