The mixing of fluids in agitated vessels is one of the most important unit operations for the chemical, bio­chemical, pharmaceutical, petrochemical, food and process industries. Determining the level of mixing, small or large scale, the influence of mixing on reactions, and the overall behavior and performance of the mixing tank is important and can be understood using Fluent CFD, which includes Mixsim , Polyflow , PolyStat and Hypertrace.

Using MixSim, mixing tank analysis is made easier. MixSim accepts the input of the tank dimensions, baffle number and dimensions, a number of the internals, including coils, draft tubes, and a choice of impeller from an extensive library of equipment vendor mixers and data from the BHR Groups FMP data.

These brief examples of stirred tank configurations were setup in MixSim. The impeller geometries are courtesy of Chemineer Inc. and Lightnin Inc.

Tanks with single impellers, such as this 45° Pitched Blade Turbine (PBT) can be modeled accurately. The axial velocity contours are displayed below the impeller. Red indicates upward flow while blue indicates downward flow. Pathlines released from the impeller-swept surface immediately below the impeller are shown, colored by velocity magnitude. CFD illustrates the regions of poor mixing

This contour plot shows the integral length scale computed from k^3/2/e. This data can be interpreted to identify the importance of the different scales of mixing: macromixing, mesomixing and micromixing, in this process vessel.

As shown in the graphics, contour and vector plots, and particle animation can be used to visualize the gross mixing patterns in the stirred tanks. Quantitative analysis of the power draw, thrust, pumping rate, mixing time, circulation and residence time distributions, and more can be obtained from the CFD solution.

Three Lightnin A340 Impellers in a Conical Bottomed Vessel

Up to 20 impellers can be assembled by MixSim in a mixing tank/column. Three Lightnin A340 impellers were modeled here. Contours of axial velocity are shown illustrating the up-pumping mode of operation.

Profiled contours of axial velocity

Analysis of additional physics such as solids suspension, chemical reactions, and liquid-liquid mixing can be introduced in additional to hydrodynamical modeling of the reactor. Refer to other applications described on this web site.