Mixing impellers Turbines

Entrainment is an important element in the mixing operation and involves incorporation of low velocity fluid into the mass of the fluid stream or jet issuing from a source such as a mixing impeller. The axial flow from a propeller under proper physical conditions serves as a circular cross-section jet to produce mixing by turbulence and entrainment. The flat-blade turbine issues a jet for entrainment at the top and bottom, areas of the ring [2]. It is significant to estimate the relative amount of liquid involved due to entrainment, as this helps to describe the effectiveness of the operation. 

External jackets, 326-328 Helical coils, 312, 326, 327 Vertical coils, 326, 327 Mixing impellers, 290-297 Anchor, 290-329 Blending, 324, 326 Characteristic curves, 306 Chart to examine turbine applications, 296 Efficiency of propellers, 299 Flow of propellers. 298, 299 Flow patterns, 309-312 Gas-Liquid contacting, 324, 326 General list impellers, 291 Helical, 290, 329 Liquid-liquid dispersion, 326 Multiple, 297... 

The impeller is the part of the agitator that impacts force to the material being mixed. Propellers, turbines, gates, anchors, and paddles are all types of impellers. Typically, the impeller is a single propeller or turbine blade connected to a shaft that is driven by an electric motor at a fixed speed. There are two classes of impeller agitators axial-flow and radial-flow, and the mixing characteristics are shown in Figure 3.14. 

Liquid mixing impellers basic, propeller,turbine, r Li JL n-Lo UJ Motor (5) u-... 

Liquid mixing impellers propeller,turbine, anchor... 

Liquid-Liquid Mixer Design Many different types of impellers are used for liquid-liquid extraction, including flat-blade and pitched-blade turbines, marine-type propellers, and special pump-mix impellers. With pump-mix designs, the impeller serves not only to mix the fluids, but also to move the fluids through the extraction stages of a mixer-settler cascade. The agitated vessel should be baffled if the vessel is operated with a gas-liquid surface, to avoid forming a vortex. As noted earlier in reference to Eq. (15-172), baffles are not needed if the vessel is operated with the liquid full [Weinstein and Treybal, AIChEJ., 19(2), pp. 304-312 (1973)]. 

Mixing impellers (a) three-blade marine propeller (b) open straight-blade turbine (c) bladed disk turbine (d) vertical curved-blade turbine (c) pitched-blade turbine. 

Vertical and horizontal capacitive apparatus appointed by mechanical mixers of impeller, turbine, ribbon, disk, extrusion type including stirring rod for high viscosity mediums mixing are referred to stirring reactors or cascade of flow reactors [3-5, 10]. However, application of apparatus with mechanical mixing for polymers synthesis is limited by maximum limit of viscosity 10-10 Pa-sec. Nevertheless, about 90% of plastics and synthetic rubbers, and 70% of fibers are produced in stirred tank reactors [10]. 

Newton no. inertial force 10 mixing impellers ro-todynamic machinery. Power number = Newton no. if Pr no. not important that is no vortex. For Re > lO", for turbines Po usually = 1-6 for marine propellers, Po usually = 0.2-1... 

Simulated distributions of gas hold-up, mass transfer coefficient, and dissolved oxygen concentrations in a mixed impeller system (J Rushton turbine, 2 pitched blade impellers) are shown in Fig. 16. At a stirrer speed of 100 min" and a gassing rate of 0.224 m s , the simulated voliune averaged values of gas hold-up and volumetric mass transfer coefficient are Eg = 0.17 and kiU = 532 h , respectively. The value of the volumetric mass transfer coefficient shows a reasonable agreement with /Cifl = 610 h" estimated from the empirical equation suggested by van t Riet [62]. As illustrated in Fig. 16, the gas hold-up is maximal close to the ring sparger. 

In emulsion polymerization, a high shear rate may cause coagulation. However, a certain amount of turbulence is required for emulsification and to avoid phase segregation. Moreover, high fluid circulation is needed in order to guarantee the macroscopic uniformity and to enhance mass and heat transfer. In this way, mixed-flow turbines with features of both radial and axial flow can be useful. The most common of these impellers is the 45° angled blade turbine. Multiple impellers on the same shaft can also be employed. 

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. 

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