Simulation and experimental verification of solutal convection in the initial stages of crystal growth from an aqueous solution

Abstract

Three-dimensional, unsteady numerical simulation of transport phenomena during the initial stages of growth of the KDP crystal from its aqueous solution and comparison with experiments have been presented. The convective field in the solution is set-up due to density differences between the supersaturated solution in the bulk and the saturated solution in the vicinity of the crystal. The flow field in the solution has been visualized using a shadowgraph technique. Numerical as well as experimental results of the growth under free convection show that convection is initially set-up in the vicinity of the crystal, while the solution in the rest of the growth chamber is relatively stagnant. The initial flow patterns show symmetry to a great extent. The influence of the crystal rotation on the concentration field has been additionally studied through numerical simulations. When the crystal is rotated, the gradients in concentration between the region near to the crystal and far away from it are high. This is a desirable requirement for a higher crystal growth rate. With the passage of time, the length scales of convection span the growth chamber, and a purely unsteady flow field is established. The numerical simulation could not be continued for such long durations owing to excessive requirement of computational resources. However, a good agreement between simulation and experiments for short times indicates that the imaging of the flow field provides a useful strategy for continuous monitoring of crystal growth.