Effect of Circulating Flow on Particle Dispersion in a Stirred Vessel with Dual Paddle Impellers

Particle dispersion in a stirred vessel with dual paddle impellers was numerically investigated by a commercial CFD code. The working fluid was assumed a weak shear-thinning non-Newtonian fluid or Newtonian fluid having low viscosity (ca. 4.0 Pa · s). Particles were initially set in the lower half region in the vessel. Numerical simulations were conducted by varying rheological property, location of the impellers and discharge flow rate of impellers. Numerical results showed that the viscosity was lower near the impeller in the non-Newtonian fluid than in the Newtonian fluid due to strong shear near the forefront of impeller. Consequently, the velocity of discharge flow from impeller was larger in the non-Newtonian. Larger velocity of the discharge flow took more particles to the tank wall as compared with Newtonian fluid. The present work adopted the mean value and the standard deviation of particle concentration as particle dispersion indexes. It has been found that the standard deviation depends on particle dispersion process.