Experimental Study of Turbulent Mixing of Viscoelastic Fluids

摘要

The viscoelastic behavior of fluids was related to the hydrodynamics, energy dissipation, and homogenization for turbulent pipeline flow and stirred tank reactors. For both mixing systems a significant influence of viscoelasticity on the hydrodynamics is found in locations with a high shear rate, such as occur in the boundary layer of pipeline flow and in the trailing vortices of the blade of a Rushton turbine. This results in a dramatic drop of the overall energy dissipation for very low values of elasticity number. In tube flow there is a threshold for the drag reduction phenomenon. The friction factor appears to be also a function of the elasticity number. The homogenization process of polymer solutions is also slower due to the lower energy dissipation, causing less dispersion. The energy dissipation and homogenization can be related to a characteristic fluid time and the elasticity number. The effect of inserted mixing elements on turbulent pipe flow was studied. The pressure drop of the mixers is almost independent of the concentration of polyacrylamide, but mixing will be less when the characteristic time of the solutions increases.