Numerical Simulation Research On The Crystal Growth Of KDP With Different Rotation Radii And Inlet Conditions

Firstly, numerical simulations of crystal growth of Potassium dihydrogen phosphate(KDP) by using falling temperature method with different rotation radii have been carried out to solve the problem in the crystal growth with traditional concentric rotation method in this paper. The influences of rotation radii on the value and distribution of surface supersaturation are analyzed and the mechanisms of action of rotation radii are studied. Moreover, the laying modes of crystal are changed for finding methods to further increase the surface supersaturation and improve the uniformity of the crystal surface supersaturatSion. Secondly, the solution circulating method is common used to grow large scale KDP crystal in the industrial production. In order to help the actual industrial production process of crystal growth of KDP in theory, numerical simulations of the crystal growth of KDP using solution circulating method with different inlet conditions have been carried out in this paper. This section research is based on the study of influences of rotation radii on the crystal growth of KDP before. The influence rules of different inlet conditions on the value and distribution of surface supersaturation are studied. The main research contents and conclusions are as follows:(1) Numerical simulations of the KDP crystal growth by using falling temperature method with different rotation radii have been carried out for covering the shortage of traditional concentric rotation method. The results show that the supersaturation of all the crystal surfaces increases with the increase of rotation radius from 0cm to 3cm. At the same time, the average standard deviation of prismatic face decreases with the increase of rotation radius, and the average standard deviation of pyramidal face firstly increases and then decreases with the increase of rotation radius. The force convection is enhanced and the limitation of mass transfer decrease with the increase of rotation radius. The results prove that the growth rate of KDP crystal and the homogeneity of crystal surface supersaturation can be improved by increasing the rotation radius. Besides, the supersaturation distribution of crystal surfaces varied with time are discussed when the rotation radius is 3cm.(2) Numerical simulations of the KDP crystal growth with three different laying modes of KDP which are named “prismatic face incident flow” and “edge incident flow” and “pyramidal face incident” have been carried out. The results show that the surface supersaturation is the highest when the crystal laying mode is “prismatic face incident flow”. The value of surface supersaturation of crystal under “edge incident flow” takes the second place, while the surface supersaturation of crystal under “pyramidal face incident flow” is minimum. The average standard deviation of surface supersaturation is the largest when the crystal laying mode is “pyramidal face incident flow”. The average standard deviation under “prismatic face incident flow” takes the second place, while the average standard deviation under “edge incident flow” is the smallest. Although the surface supersaturation of crystal which uses the laying mode named “edge incident flow” is a little lower than the condition of “prismatic face incident flow”, the average standard deviation is minimum, which is useful to reduce the generation of inclusions.(3) In order to be closer to the practical production of KDP crystal in industry, numerical simulations of hydrodynamics and mass transfer in the growth of KDP crystal with solution circulating method have been performed in this paper. The solution circulating method is combined with rotating-crystal method with rotation radius. The temporal and spatial evolution of the surface supersaturation is studied with the change of inlet velocity, position of inlet pipe and incident angles. The results show that: Firstly, the time-averaged supersaturation of prismatic faces of crystal firstly decreases and then increases with the increase of inlet velocity, and the time-averaged supersaturation of pyramidal faces firstly decreases slightly and then increases with the increase of inlet velocity. The averaged standard deviation of both prismatic faces and pyramidal faces firstly increases and then decreases on the whole with the increase of inlet velocity. Secondly, the values of time-averaged surface supersaturation and standard deviation are different under different positions of inlet pipe. The surface supersaturation is higher and the standard deviation of surface supersaturation is lower when the center of inlet pipe and the center point of crystal are at the same heights. Finally, the time-averaged supersaturation of prismatic faces firstly increases and then decreases with the increase of incident angles, while the averaged standard deviation of prismatic faces firstly decreases and then increases with the increase of incident angles. The time-averaged supersaturation of pyramidal faces firstly increases and then decreases and then increases with the increase of incident angles, while the trend of the averaged standard deviation of pyramidal faces is opposite with the increase of incident angles. The time-averaged surface supersaturation is the highest and the averaged standard deviation is the lowest when the axis of inlet pipe is tangent to the movement track of tip of R-Py pyramid.