In a mixing tank

The pumping number is a function of impeller type, the impeller/tank diameter ratio (D/T), and mixing Reynolds number Re = pND /p.. Figure 3 shows the relationship (2) for a 45° pitched blade turbine (PBT). The total flow in a mixing tank is the sum of the impeller flow and flow entrained by the hquid jet. The entrainment depends on the mixer geometry and impeller diameter. For large-size impellers, enhancement of total flow by entrainment is lower (Fig. 4) compared with small impellers. 

The velocity head JT in a pipe flow is related to Hquid velocity hy H = I Qc The Hquid velocity in a mixing tank is proportional to impeller tip speed 7zND. Therefore, JTin a mixing tank is proportional to The power consumed by a mixer can be obtained by multiplying and H and is given... 

Fig. 11. Computer-simulated recirculating patterns in a mixing tank with full baffles (a) elevation view shows circulation patterns generated by turbine blades (b) plane view shows the effect of the baffle on the radial velocity vectors above the turbine blades.

When the flow pattern in a mixed tank is primarily tangential, the fluid discharge from the impeller to the surroundings and its entrainment into the impeller are small. Also, fluid transfer in the vertical direction is at a minimum. The mixing effect is lowest when the rotational velocity of the liquid approaches that of the mixer. 

Figure 12. Variation of velocity distribution in a mixing tank on insertion of full side wall baffles.

Corn steep liquor contains 2.5% invert sugars and 50% water. The rest of the feed is considered as residual solids. Beet molasses containing 50% sucrose, 1% invert sugar, 18% water and remainder solids are mixed with corn steep liquor in a mixing tank. Water is added to produce a diluted mixture with 2% invert sugar, 125 kg com steep hquor and 45 kg molasses, which is fed into an enzymatic hydrolysis tank. 

The mean shear rate produced by an agitator in a mixing tank ym is proportional to the rotational speed of the agitator N [Metzner and Otto (1957)]. 

Since the mean shear rate in a mixing tank ym is given by equation 5.1... 

In studying residence time distribution in a tank-flow electrolyzer, a tracer injected into it is recovered in a mixing tank placed downstream. If both tanks are perfectly stirred, then with a tracer pulse, the mole balance for the tracer can be written as... 

Figure 5 Liquid formulation unit. Technical grade pesticide products are blended with solvents and emulsifiers or other agents in a mix tank. Formulated products are filtered before packaging (from Ref. 8).

All reagent fluids are first mixed at predetermined pressure and temperature in a mixing tank before they are sent through an inlet gas control valve into an auxiliary preheater and the reactor. The latter is a refractory-1ined, rectangular sheet-metal vessel and after a coal block has been closely fitted into the reactor, one or more 3A" " 2" diameter horizontal holes, which serve as initial reaction channels, and appropriately placed vertical injection and production holes are drilled into it. 

All mixing of powdered admixture must be done in a mixing tank which is separate from the admixture storage tank from which the admixture is fed into the dispenser. The density of the admixture mixed in this manner should... 

Electrophoresis can also be conducted on-line, as an element of industrial process monitoring and/or control. In this case a slip-stream sample is usually withdrawn from a process vessel, diluted in a mixing tank to reduce the sample turbidity, and then pumped through an electrophoresis cell that is fitted with stop-flow solenoid valves. The flow is stopped for long enough to make an electrophoresis measurement and then resumed. The sampling can be either intermittent or continuous. An example is described in reference [265]). 

Blending the heated oil-soluble additives mixture into the warm oil in a mixing tank. Slowly adding the warmed water-soluble additives mixture into the blend to produce a water-in-oil emulsion. 

Oyama and Aiba (O10) observed the mean flow patterns in a mixing tank by use of a small rotating pointer, similar to a weather vane, suspended at the end of a pipe at different locations in the vessel. Their studies on two-blade flat paddles in an unbaffled cylindrical vessel confirm the expected presence of a vortex, deepening with speed of rotation, and of swirling flow about the tank axis with a slight amount of flow up the tank walls and down in the center. 

The pasteurized batch is transferred to a holding tank for use in the emulsion preparation. The process of mixing and pasteurization of a batch takes less than 2h (84). The water-milk phase can alternatively be prepared in a mixing tank and pasteurized using a modern type of multisection plate pasteurizer. The prepared... 

The experiments were conducted in a mixing tank (diameter (D) = 0.2 m, height (H) = 0.3 m), that could work either with or without baffles. The mixer was equipped with a stirrer made of 6 paddles (D = 0.1 m, height of a single paddle = 0.2 m). Mixing velocities varied from 1.26 s to 9.33 s . ... 

In other words, this apparatus-related boundary condition is not included in any dimensionless number, the drag characteristic of the sphere is unequivocally described in the space Cd,Re, where Ca is the drag coefficient. Such a situation is echoed in stirring technology, where the flow conditions in a mixing tank also essentially depend upon whether baffles are present or not, and this fact is only included as a boundary condition and is not reflected in any dimensionless number ... 

Figure 6.29 compares the flow streamlines in a mixing tank of a Newtonian fluid and a viscoelastic fluid. The flow streamlines of polymer solution are different from those of water. The blind area at the bottom of the tank is much larger for polymer solution. There is a difference in speed between the blade tip and the surrounding polymer solution, but approximately the same for water. These problems increase the energy requirement to rotate the blade and the time to dissolve polymer powder. After the blade was redesigned, the energy... 

FIGURE 6.29 Comparison of flow streamlines in a mixing tank with (a) a Newtonian fluid and (b) a viscoelastic fluid. Source Wang (2001). 

Figure 22. Photograph of flow patterns in a mixing tank in the turbulent region, made by passing a thin plane of light through the center of the tank.

Table 2 describes four different macroscale shear rates of importance in a mixing tank. The parameter for the microscale shear rate at a point is the root mean square velocity fluctuation at that point, RMS. 

Figure 15.52 shows the application of ratio control to the effluent pH for a wastewater neutralization process applied in a mixing tank. This controller can effectively handle wastewater feed flow rate changes when the chemical makeup of the wastewater remains relatively constant. Small changes in the chemical makeup of the wastewater can usually be handled by the feedback controller, which adjusts the reagent-to-wastewater ratio to maintain the specified effluent pH. 

For laboratory usage, normally a 0.5% stock solution is prepared and should be discarded after one week due to the reduction in polymer activities. Further dilution to 0.05% is necessary before adding to the slurry. The shelf-hfe for the 0.05% solution is about 1 to 2 days, so fresh samples need to be prepared daily. For plant applications, a polymer solution of 0.5% should be prepared in the storage tank and added to the slurry in a mixing tank or by in-line injection with sufficient mixing. 

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