Evaluation of Performance of Mixing Apparatus for High Viscosity Fluids

Abstract

There exists no universally accepted technique for evaluating the functional status of equipment for high-viscosity mixing based upon generalized basic information such as flow patterns and shearing deformation characteristics. This paper deals with the measurement of flow patterns. After obtaining the overall flow patterns in a mixing vessel, circulation capacity and fluid deformations which cover information about energy dissipation were correlated with the homogenizing time. The physical meanings of C^nT^and C2=TM "]/Pvgcj[i, are interpreted by using a concept of striation thickness. A measure of an averaged dimensionless shear rate number l/Pvgcl/u ln ' s plotted against the dimensionless nearest distance between moving part and fixed wall in the mixing vessel. This diagram could give an useful comparison as to averaged shear rate characteristics for any device for high-viscosity mixing regardless of geometrical configuration. A novel technique is also proposed for quick evaluation of tha shear distribution in a given apparatus.

Numerical solution for the flow of highly viscous fluid in agitated vessel with anchor impeller

“…A variation in streamline pattern with a change of Reynolds number was ob tained. These patterns agreed qualitatively with the experimental results of Peters andSmith (1967,1969) and Murakami et al (1972), and it was found that the mean rotational velocity of the fluid relative to the impeller was affected slightly by Reynolds number and decreased with increasing Reynolds number.…”

“…These patterns show tendencies similar to those of the experimental results reported by Peters andSmith (1967, 1969) and Murakami et al (1972). Namely, with increasing Reynolds number, the symmetry evidence of the flow respect to the blade is gradually lost, and at Re = 50, a region where the fluid moves with the blade is seen behind the blade as shown in Figure 8.…”

“…Analysis of the flow around the vertical blades of an anchor impeller provides significant information on agitation with closeclearance impellers regarding power consumption and mixing and heat transfer performance. Although some experimental studies on flows in the region of anchor impeller blades have been reported (Peters andSmith, 1967,1969; Murakami et al, 1972), it seems to have been difficult for these experimental studies to give detailed information on flow characteristics such as shear rate distribution, which is usually obtained by differentiating experimental data.…”

Heat transfer and power consumption for ribbon impellers. Mixing efficiency

“…Its value is closely related to the way, in which liquid circulates in the tank. As follows from the literature, the main geometrical parameters affecting the circulation in the tank are the diameter and the pitch of the ribbon (Bourne and Butler, 1969;Murakami et al, 1972;Soliman, 1985). With a decrease of clearance c between the rotating ribbon and the tank wall the peripheral and axial velocities in the tank increase, so the rate at which the external part of wall layer is "scratched off" from the wall grows.…”

Modeling of the 3D hydrodynamics of 2‐blade impellers in stirred tanks filled with a highly viscous fluid

“…Two-blade impellers are generally used for smooth mixing with the tip speed varying from 1.2 to 2.3 m/s. These impellers have been experimentally and theoretically studied previously, Several types of experimental equipment have been used in order to study the flow structure generated by blade impellers (Murakami et al, 1972; Kuriyama et al, 1982; Bertrand and Couderc, 1982;Youcefi, 1993 of these studies show that for a low impeller speed, the flow is essentially tangential. Hiraoka et al (1978) and Bertrand and Couderc (1981) studied the 2D flow of viscous Newtonian and non-Newtonian fluids generated by two-blade impellers and paddle agitators, using Computational Fluid Dynamics.…”