Simultaneous observation of melt flow and motion of equiaxed crystals during solidification using a dual phase particle image velocimetry technique

Abstract

A dual phase Particle Image Velocimetry (PIV) technique is applied to study the flow and coupled equiaxed-columnar solidification in an ingot of NH 4Cl-H2O solution. This technique is able to monitor simultaneously both velocities of the liquid flow and motion of equiaxed crystals. Before solidification started, a stable thermal buoyancy driven flow, laminar and 2D, was initialized in the ingot. As soon as solidification began, solutal buoyancy together with falling crystals destabilized the initial laminar flow into multiple chaotic cells, and a 3D turbulent regime was achieved. The kinetic energy for the flow was calculated. The interaction between the equiaxed grains and the melt flow was analyzed according to relative velocities. The settling velocity of an isolated equiaxed crystal was found to be 41 times smaller than the calculated one of a spherical crystal of equivalent size. The coupling between the fluid flow and the equiaxed crystal was found to be important in area of high crystal density. Chaotic and turbulent behaviors were found to be damped in regions of high equiaxed crystal density. © Published under licence by IOP Publishing Ltd.