Behavioral model mixer

Fig. 4.6. Behavioral model of mixer with ideal level control.

Mg. 11.2. Environmental and behavioral model for mixer with self-adjusting level. 

The dispersed plug flow model has been successfully applied to describe the flow characteristics in the Kenics mixer. The complex flow behavior in the mixer is characterized by the one-parameter. The Peclet number, Np, is defined by ... 

Dolan, K. D. and Steffe, J. F. 1990. Modeling rheological behavior of gelatinizing starch solutions using mixer viscometry data. J. Texture Stud. 21 265-294. 

In order to realize the Polyamide-6 scenario problem presented in Subsect. 5.3.2, a process description is defined using ModKit+. The elementary models for the reaction section, the separator, and the extruder, already imported into ROME, are added as submodels of the overall process. Further, a mixer is defined in order to combine feed and recycle streams corresponding mass balances are added to the elementary mixer model. After this modeling activity the model repository ROME contains all necessary models for the overall Polyamide-6 process. The model behavior is partly described by equations (for the mixer) and partly described by model implementations in the form of input files for the modeling tools Aspen Plus, gPROMS, and MOREX. 

Quantitative shear stress—shear rate data can be obtained with agitators having complex geometries assuming that the shear rate is directly proportional to the rotational speed of the agitator and if the flow behavior of the fluid can be described by the power law model. The mixer viscometric technique is based on the assumption that for complex geometries one can assume an effective shear rate that is dependent on the RPM and on the design characteristic of the impeller (22, Z , 21, 28., 22, 20.) The procedure has been described in detail by Rao (27 ) and will be considered only in brief here. 

In the model of the mixer, the mixing of the streams at the column inlet is taken into account. The residence-time behavior of the piping can be described as a plug-flow reactor. Backmixing effects outside the column can be described by an ideal stirrer tank (Fig. 9.9). 

A mixer is a simple example that demonstrates the principle of interacting balances. Behavior is determined by two differential equations one total mass balance and one component balance. If the level is constant by means of an ideal level controller, the number of balances reduces to one. This wdl be demonstrated in a subsequent chapter. This chapter limits itself to the environmental model. 

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