Impeller rotating, power input

These calculations are checked by consulting manfacturers literature concerning pumps (Refs. P7 and P8). Graphs presented in the literature enable a final sizing of the pump, including factors such as rotational speed, impeller diameter, power input and minimum net positive suction head. 

Considering a stirred vessel in which a Newtonian liquid of viscosity p, and density p is agitated by an impeller of diameter D rotating at a speed N the tank diameter is DT, and the other dimensions are as shown in Figure 7.5, then, the functional dependence of the power input to the liquid P on the independent variables (fx, p, N, D, DT, g, other geometric dimensions) may be expressed as ... 

Plo power input without gas flow, kW nb,imp number of impeller blades himp rate of rotation of impeller, Hz dimp diameter of impeller, m... 

Repeat Example 24-2 for the xylene (B) oxidation reaction carried out in an agitated tank reactor (instead of a bubble-column reactor). Use the data given in Example 24-2 as required, but assume the diameter D is unknown. Additional data are the power input without any gas flow is 8.5 kW the impeller rotates at 2.5 Hz the height and diameter of the tank are the same (h = D) the impeller diameter is DI3, and the impeller contains 6 blades assume ubr = 1.25usg. In addition to the vessel dimensions for the conversion specified (/B = 0.16), determine the power input to the agitator (P,). 

An impeller in a tank functions as a pump that delivers a certain volumetric rate at each rotational speed and corresponding power input. The power input is influenced also by the geometry of the equipment and the properties of the fluid. The flow pattern and the degree of turbulence are key aspects of the quality of mixing. Basic impeller actions are either axial or radial, but, as Figure 10.4 shows, radial action results in some axial movement by reason of deflection from the vessel walls and baffles. Baffles contribute to turbulence by preventing swirl of the contents as a whole and elimination of vortexes offset location of the impeller has similar effects but on a reduced scale. 

Here, P0 is the impeller power, s0 is the impeller speed, d, is the impeller diameter, Pl and v l are the density and kinematic viscosity of the liquids, respectively. The term tf Myr adjusts the actual impeller speed to the speed at which a fan-disk turbine would rotate for the same power input per unit mass. Although no gas was used in this study, the correlation should be useful as a first estimate for Ks in various types of stirred three-phase slurry reactors. 

Many other definitions of the Weber number have been used in other situations. Equations (9.48) and (9.49) predict that the average drop size varies with jj-i.2jrj-o.8, Qj. approximately with the reciprocal of the impeller tip speed, and that better dispersion is obtained at the same power input by using a smaller impeller rotating at high speed. 

Concave blade disc turbines are of interest in gas-liquid dispersion because they are able to handle more gas than Rushton-type turbines before flooding (Smith et al., 1977 Vasconcelos et al., 2000). The mass transfer capacity for the concave blade disc turbine is very similar to the Rushton-type turbine, but Chen and Chen (1999) found that the blade curvature could be optimized for a certain power input to produce higher gas-liquid mass transfer coefficients. Unlike the Rushton-type turbine, the concave blade disc turbine requires the cup orientation to be in the direction of impeller rotation (Tatterson, 1994). 

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