Agitated vessels flow patterns

This chapter reviews the various types of impellers, die flow patterns generated by diese agitators, correlation of die dimensionless parameters (i.e., Reynolds number, Froude number, and Power number), scale-up of mixers, heat transfer coefficients of jacketed agitated vessels, and die time required for heating or cooling diese vessels. 

In fluid agitation, the direetion as well as the magnitude of the veloeity is eritieal. The direetions of the veloeity veetors throughout an agitated vessel are refeiTed to as the flow pattern. Sinee the veloeity distribution is eonstant in the viseous and turbulent ranges, the flow pattern in an agitated vessel is fixed. 

Finally, the reactor vessel has been assumed to be perfectly mixed. Imperfect mixing and a flow pattern created by different types of agitators, baffles, feed locations and other reactor vessel configurations will cause the performance to be below that indicated by perfect mixing. 

Small blade high speed agitators are used to mix low to medium viscosity liquids. Two of the most common types are the six-blade flat blade turbine and the marine type propeller shown in Figures 5.1 and 5.2 respectively. Flat blade turbines used to mix liquids in baffled tanks produce radial flow patterns primarily perpendicular to the vessel wall as shown in Figure 5.3. In contrast marine type propellers used to mix liquids in baffled tanks produce axial flow patterns primarily parallel to the vessel wall as shown in Figure 5.4. Marine type propellers and flat blade turbines are suitable to mix liquids with dynamic viscosities up to 10 and 50 Pa s, respectively. 

Norwood, K.W. and Metzner, A.B., Flow patterns and mixing rates in agitated vessels, AIChE Journal, 6, pp. 432-7 (1960). 

The energy consumption in agitation depends on the basic principles of fluid mechanics however, the flow patterns in a mixing vessel are much too complex for their rigorous application. Therefore, empirical relationships based on dimensionless groups are used. Here, because most fluid foods are non-Newtonian in nature, the... 

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