Numerical Simulation Of Flow And Mass Transfer In The KDP Growth System With Jet Rotating Crystal Method

The high-energy lasers used for inertial confinement fusion research need large plates of nonlinear crystals for electro-optic switching and frequency converting.KDP?KH₂PO₄?is the only nonlinear crystal currently used for these applications due to its exclusive physical properties.With the improvement of laser power,the rapid growth of high-quality and large-scale KDP crystal has become the focus of research in recent years.According to the existing research,it is known that the distribution of the supersaturation of the crystal surface was related to the stability of the crystal surface morphology and the formation of the inclusions,which directly determined the final quality of the crystal.Therefore,the focus of the study was to find a way to obtain a relatively uniform and high supersaturation field on the crystal surface.For the growth of KDP crystals in solution,the solution usually convected in such a way that the crystal is rotated.on the one hand,it could play a role in the mechanical stirring of the solution,on the other hand,solute boundary layer would be more thick and the capacity of mass transfer would be increased by the control of the shear force of the crystal surface was controlled by the speed regulation.Although rotating KDP crystals could achieve the purpose of increasing the crystal growth rate,there would be a problem in the rotation process.Since the relative velocity of the crystal surface near the rotating axis was smaller than that of the surrounding solution,the surface shearing force was small and the surface shearing force is inversely proportional to the thickness of the solute boundary layer.As a result,the natural convection became the main solute transport in the vicinity of the crystal tip mechanism.Because the convective ability of natural convection was less than forced convection,it will eventually lead to unevenness of crystal conical supersaturation,and the consequence of unevenness of crystal surface supersaturation will greatly increase the probability of occurrence of inclusions.It can be seen that convection is particularly important in controlling crystal growth.It is important to understand the flow pattern in the crystal growth process and to make reasonable design and parameter selection crystal growth process.It is very difficult to understand the flow field and the supersaturation distribution of crystal surface with the complex geometric structure and high-speed crystal movement,especially,only relying on the traditional experimental means.Therefore,numerical calculation has gradually become an important means to study and optimize the crystal growth process with the highly developed of computer technology.Based on the above background,this article started from the basic theoretical knowledge of computational fluid dynamics and focused on some problems in the numerical simulation of solution crystal growth.Based on the existing problems in the preparation of KDP crystal by conventional crystal method,the new system of KDP crystal growth with jet was proposed,and the flow and mass transport characteristics of the new system were analyzed by numerical means.The specific research contents were as follows:?1?Based on the theory of crystal growth from aqueous solution,the CFD model of simulated crystal growth was established and analyzed by a simple crystal growth model.For the effect of the crystal growth source term,we solved the problem by loading a volume source with a suitable thickness perpendicular to the crystal face;For the two commonly used turbulence models in CFD,it was considered that the "standard k-? model" plus the method of "enhance wall treat" was more reasonable by comparing the experimental data;The influence of natural convection on the supersaturation of the crystal surface was analyzed.Increasing the relative velocity of the crystal surface and the surrounding solution could change the flow state of the solution.The mass transfer capacity of the turbulence was obviously better than the laminar flow's.?2?Based on the shortcomings of the growth of KDP crystal by traditional method,a new KDP crystal growth system with jet was proposed and the flow field and mass transport of the new system was simulated.The temporal and spatial characteristics of the turbulent flow field of the two methods were discussed.The surface supersaturation distribution was studied emphatically.The characteristics of the new growth system were quantitatively investigated by changing the crystal size,jet velocity and rotational speed.The results showed that the magnitude and the uniformity of supersaturation of pyramidal of the new method were significantly better than those of the traditional crystal method.The increase of the jet velocity could improve the crystal surface supersaturation,but the mean square error would decrease at first and then increase;With the increasement of the rotational speed,the shear force of the crystal edge increased gradually,so the supersaturation also increased,and the mean square error becomed smaller;With the increase of the crystal size,the variance of the supersaturation of the pyramidal increased,and the average supersaturation of the pyramidal increased first and then decreased...