Micromixing Characteristics And Dimensionless Correlation For The Segregation Index In A Stirred Tank

Influences of micromixing on particle size, particle size distribution, and morphology of crystalls were investigated. Segregation index was characterization by conditions of operating, which particle size, and particle size distribution of crystals were provided for the basis. In this paper, efficiency of micromixing was researched by changing feeding time, feeding position, stirring speed, reactant concentration, viscosity, volume ratio, mass transfer coefficient and diffusion coefficient, where the segregation index was correlationed by dimension analysis. The main work was summarited as follows:Influences of micromixing on the reaction of crystallization were researched. Parallel competing reation system of Ba(OH)₂+ NaHSO₄+ CLCH₂COOC₂H₅ is selected as the research system with stirred tank as crystallizer. The efficiency of micromixing is valued by the yield of ethanol. To investigatting the influence of reaction conditions on the efficiency of micromixing, which affecten the micro-mixing were known by single factor experimental and theoretical analysis. The main parameters of the model were stirring speed, reactant concentration, feeding position, viscosity, mass transfer coefficient, and diffusion coefficient. Using dimensional analysis (Rayleigh Law or Buckingham Law), dimensionless number were deduced from conditions of operating and segregation index as follows: (?)Parameter of model of Xs was obtained by using multiple linear regression, and correlation coefficient (R2) was 0.9937. The related average error of experimental value and calculated value was less than 18%. The results indicated that experimental value and calculated value was consistented. From the equation, we can get the crystal size and crystal size distribution of products and determine the range of dimensionless.Based on the above work, and particle size and its distribution of BaSO₄ was characterized by particle size analyzers and transmission electron microscopy (TEM). The results indicated that size distribution were effected by Re, Sc, and Sh. Re≥3800, proportion of mian size BaSO₄ (223 nm) was more than 77%, ultrafine particles of narrow size distribution was obtained. Segregation index was increased follows Sc increase. 2800≤Sc≤3500, main size of BaSO₄ (223 nm) distribution was ranged from 86% to 65%. Small crystal size and narrow crystal size distribution of ultrafine can been prepared when viscosity was ranged from4.0 mp.s to6.0 mp.s. Segregation index was increased as Sh. 800≤Sh≤1200, main size of BaSO₄ distribution was more than 80%.