Numerical simulation of the hydrodynamics and mass transfer in 3D spiral motion system for KDP crystal growth

A numerical study of the unsteady turbulent flow and mass transfer involved in the potassium dihydrogen phosphate crystal growth from an aqueous solution with a three-dimensional spiral motion configuration was performed using the standard k-ε model with an enhanced wall treatment. The three-dimensional spiral motion is composed of a uniform circular motion on the horizontal plane and a reciprocating motion in the vertical direction. The simulation indicates that the crystal spiral motion will drive the mainstream solution rotating around the axis of the growth vessel and form an oscillatory flow near the crystal, which results in a periodical reversal of the supersaturation distribution on the crystal faces and effectively suppresses the morphological instability of the crystal surfaces. With the increase of the orbital radius R or the characteristic rotation rate ω, the line speed V0 of crystal in the horizontal plane will increase, leading to a decline of the thickness of the diffusional boundary layer and an increase of the time-averaged supersaturation on the crystal faces. At the same time, the homogeneity of the surface supersaturation will be improved too, which would benefit the morphological stability of the crystal surfaces. However, when the crystal size increases, the time-averaged supersaturation on the crystal faces will decrease and its homogeneity will deteriorate. Therefore, with crystal growth, increasing the orbital radius, R, and reducing the period, T1, of the crystal circular motion are necessary.