Agitated tank flow patterns

The propeller agitator with three blades rotates at relatively high speeds of 60-300 ips high efficient mixing is obtained. The generated flow pattern is axial flow since the fluid moves axially down to the centre and up the side of the tank. 

The flow patterns for single phase, Newtonian and non-Newtonian liquids in tanks agitated by various types of impeller have been repotted in the literature.1 3 27 38 39) The experimental techniques which have been employed include the introduction of tracer liquids, neutrally buoyant particles or hydrogen bubbles, and measurement of local velocities by means of Pitot tubes, laser-doppler anemometers, and so on. The salient features of the flow patterns encountered with propellers and disc turbines are shown in Figures 7.9 and 7.10. 

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. 

According to the flow pattern reactors can be stirred-tank and tubular type. A stirred-tank reactor is a tank whose contents or reaction mixture is agitated... 

Agitated Tank Reactors Flow Patterns of Gas and Liquid... 

For a tank with reagent added at the top of the tank and removed near the bottom at the opposite side k =. 9, and k = 1.8 for a tank with the reverse flow pattern. V, is the tank volume in cubic meters and Fagit is the agitator pumping rate in cubic meters per hour. It is observed that it is difficult to reduce td below about 9 seconds without causing excessive splashing and air entrainment. 

The characteristic solid body rotation is the primary flow pattern in un-bafiled tanks. To avoid these phenomena, baffles are installed in the tank. On wall baffles are sketched in Fig 7.1. Generally, baffles are placed in the tank to modify the flow and surface destroy vortices. Baffles mounted at the tank wall are most common, but also bottom baffles, floating surface baffles and disk baffles at the impeller shaft are possible. Often tank wall baffles are mounted a certain distance from the wall, as illustrated in Fig 7.3. This creates a different flow pattern in the tank. The purpose of installing baffles away from the wall is to avoid dead zones where liquid is seldom exchanged and where impurities accumulate. Experiments have confirmed that the flow patterns in baffled agitated tanks are different from the flow patterns in unbaffled agitated tanks. In baffled tanks the discharge flow dissipates partly in the bulk... 

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