The Effect Of Fluid Shear Force On Crystal Growth

Crystal nucleation and growth are two important processes in the control of industrial crystalline products.The crystal growth is directly related to the surface environment conditions and forces.In the process of crystal growth,shear force or other forces such as collision affect the formation,accumulation and shedding of crystal surface lattice,determine the shape and size of crystal,and ultimately affect the quality of product crystal.On the basis of clarifying the mechanism of fluid shear force on crystal growth,the quality of crystal products can be precisely controlled by adjusting the influence parameters.In this paper,the crystallization process of inorganic potassium dihydrogen phosphate and organic glycine solution was studied.The effect of fluid shear force on crystal growth was experimentally measured,and the model description was carried out to reveal the mechanism of fluid shear force on crystal growth.The main research contents and conclusions were as follows:Firstly,The flow rates of potassium dihydrogen phosphate(KDP)and glycine in saturated aqueous solution were 5.04×10-3 m/s～6.05×10-2 m/s;the viscosity of solutions was 1.15×10-3 Pa·s～1.29×10-3 Pa·s for KDP,and 1.16×10-3 Pa·s～1.23×10-3 Pa·s for glycine;the supersaturation was 0.17%～1.69%(solute proportion per unit mass solution).In the range of the above conditions,the growth rates of the two kinds of crystals in the corresponding aqueous solution increased with the increase of supersaturation and shear force;when the solution viscosity increases,the crystal growth rate increases first and then decreases;the growth rate of KDP crystal is faster than that of glycine in corresponding aqueous solution.Furthermore,based on the analysis of the influence of viscosity,supersaturation and shear force of saturated solution on the crystallization growth of two kinds of crystals in corresponding supersaturated aqueous solution,the diffusion and mass transfer model suitable for inorganic salt and organic crystal growth is established on the strength of crystal growth diffusion theory and Newton’s law of viscosity.(?)Ignoring crystal surface lattice formation process,crystal growth can be described as a process in which drag force Fd(the integral sum of fluid shear forces)on the crystal surface affects the thickness of surface boundary layer,and accelerates or slows down the migration and growth processes of supersaturated solute(ΔC)from the main solution to the surface of crystal.By studying crystal growth behavior and model in supersaturated solution,the precise description of crystal growth by hydrodynamics is derived,which provides a basis for the growth control process of crystal in supersaturated solution.