Impeller bottom-entering

Impellers usually enter the vessel from the top however, very large or novel vessels find it useful for the impeller to enter from the bottom or side (Hamby et al.. 

Axial-tlow impellers rnav also be mounted near the bottom of the cylindrical wall of a cssel as shown in Fig, 18-10, Such side-entering agitators are used to blend low- iscositv fluids [<(), Pa-s (100 cP)] or to keep slowly settling sediment suspended in tanks as large as some 4000 rn (1(P gal). Mixing of paper pulp i.s often carried out by sideentering propellers. 

Standard Geometry describes a vessel and mixer design based on a fluid depth equal to vessel diameter and a top-entering impeller having a diameter equal to 1/3 of vessel diameter and located with a clearance of 1/3 of vessel diameter above the bottom of the vessel. 

Steady Bearing a bearing located at the bottom of the shaft of a top entering impeller to minimize shaft deflection and vibration. It is immersed in the fluid being mixed. 

In this case foam can be re-entered into the mixture by this action, and solids or liquids added will enter the impeller rather rapidly. The deeper the liquid above the baffle the greater the rotating action. Bottom srvirling action allows the segregation of heavy solid particles [21]. 

Stirred tanks are often used for gas-liquid reactions. The usual geometry is for the liquid to enter at the top of the reactor and to leave at the bottom. The gas enters through a sparge ring underneath the impeller and leaves through the vapor space at the top of the reactor. A simple but effective way of modeling this and many similar situations is to assume perfect mixing within each phase. 

Agitated slurry reactor (ASR) This is a mechanically agitated gas-liquid-solid reactor (Figure 3.13). The liquid is agitated by a mechanical apparatus (impeller). The fine solid particles are suspended in the liquid phase by means of agitation. Gas is sparged into the liquid phase, entering at the bottom of the tank, normally just under the impeller. This reactor can also be of continuous type or of semibatch type. This type is used only in catalysis. 

Step 4. The chlorine enters the absorber Ihrough a pipe in the bottom that ends in a sparger (something like a showerhead nozzle) located close to the impeller. The chlorine comes out of the sparger in thousands of liny bubbles, which are then dispersed by the... 

The axial impeller discharges fluid mainly axially, parallel to the impeller shaft. The fluid is pumped through the impeller, normally towards the bottom of the tank. Since the flow make a turn at the bottom, the velocity vectors fan out radially at approximately D/2 beneath the impeller. Then, the flow moves along the bottom and rises near the tank wall. Analyzing the flow pattern, one can see that a back-flow eddy region is formed directly under the impeller. Upon examining the flow around the axial impeller one can also observe that a large contribution to the inlet flow enters radially at the tip of the impeller blade. This pattern is shown in Fig 7.1. 

Three types of impellers are commonly used in the low viscosity region, propellers, Fig. 1 turbines. Fig. 2 and axial flow turbines. Fig. 3. Impellers used on small portable mixers shown in Fig. 4, are oflen inclined at an angle as well as being off-center to give a good top-to-bottom flow pattern in the system. Fig. 5. Large top-entering drives usually use either the axial flow turbine or the radial flow flat blade turbine. For aerobic fermentation, the radial flow disc turbine is most common and is illustrated in Fig. 6. 

As the broth in a fermenter or bioreactor becomes more viscous and is subjected to agitation from sparging (the introduction of tiny sterilized air bubbles at the bottom of the liquid) and from mixing by the impeller, it has a tendency to foam. This can be a serious problem as the level may rise to the point where it enters the exhaust gas lines clogging the ultrafilters and possibly jeopardizing the sterile environment within the reactor. Various antifoam strategies can be employed to correct this situation, however, detection of the condition is first required. 

The emulsion enters the colunm at the lowest section, flows upward through the colunm driven by its buoyancy, and coalesces in the top of the colunm (in a stage that does not have an impeller). The feed solution containing the selenium and sulfate enters the colunm at the top section, flows down through the coliunn, and is removed at the bottom. The interface between the emulsion and the feed solution is controlled by a gravity leg. The flowrates of feed solution and emulsion are checked before and after the extraction runs. 

---