Impeller blade thickness

Impeller size relative to the size of the tank is critical as well. If the ratio of impeller diameter D to tank diameter T is too large (Z)/r is > 0.7), mixing efficiency will decrease as the space between the impeller and the tank wall will be too small to allow a strong axial flow due to obstruction of the recirculation path (21). More intense mixing at this point would require an increase in impeller speed, but this may be compromised by limitations imposed by impeller blade thickness and angle. If P/Pis too small, the impeller will not be able to generate an adequate flow rate in the tank. 

One must design the mechanical components, such as shaft diameter, impeller blade thickness, baffles and supports, bearings, seals, etc. (see Chapter 21). 

To design an effective stirred tank, an efficient impeller should be chosen for the process duty. More than one impeller may be needed for tanks with high aspect ratio (Z/T > 1.5). Sizing of the impeller is done in conjunction with mixer speed to achieve the desired process result. The appropriate size and type of wall baffles must be selected to create an effective flow pattern. The mixer power is then estimated from available data on impeller characteristics, and the drive size is determined. The mixer design is finalized with mechanical design of the shaft, impeller blade thickness, baffle thickness and supports, inlet/outlet nozzles, bearings, seals, gearbox, and support structures. 

When macro-scale variables are involved, every geometric design variable can affect the role of shear stresses. They can include such items as power, impeller speed, impeller diameter, impeller blade shape, impeller blade width or height, thickness of the material used to make the impeller, number of blades, impeller location, baffle location, and number of impellers. 

For now, the characteristic length scale Lc is assumed to scale with the impeller diameter, not the tank diameter. If geometric similarity is observed and all impeller dimensions are scaled with the impeller diameter (including details such as blade thickness), the characteristic length scale (CpD) will scale any of the impeller dimensions equally well only Cl will change. The constants and Cl are a function of the impeller and tank geometry selected. For now, however, we retain them as constants. 

The commonly known or calculable force acting on the impeller blade is the force related to torque, which is horsepower, P [hp] W, divided by rotational speed, N [rpm] rps, divided by the number of blades, nb, or the first term inside the parentheses in eq. (21-26). Because the pressure force acts normal to the blade and the torsional force must be horizontal for a vertical rotating shaft, a factor of the reciprocal of the sine of the blade angle enters the expression for blade thickness. The equivalent pressure force must act at some moment arm from the center of rotation, which would be the impeller radius, D/2 [in.] m, if the force acted at the blade tip. However, because pressure forces are lost around the tip of the blade, causing a vortex flow pattern, the effective force must act at a... 

Calculations for the stub blades or welded attachment points of impeller blades can be done like calculations for the extension blade thickness. The details of welding, casting, or other methods of attachment become critical in the design. Conventional calculations for structural strength may be adequate, but for com-phcated geometry, finite element models can provide better design information. 

At calculations, according to the analytical model 12.1, in an entrance part gas-liquid a stream free boundary lines of a stream are replaced with shaped channels of blades of an impeller. In a blow point 0,a relative wind, it is atomized and flows round curvilinear surface AB, thus speed attains the maximum value ft and remains a constant on length of all section. In cross-sectionC, a stream, it is possible to observe as homogeneous, moving with a speed ft, and impeller shovels have a final thickness, the breakaway of a stream from impeller blades does not occur. Airflow, the stream flow is carried out without pressure loss to critical cross-section C-C after which static pressure in a stream initiates to drop. 

Propeller A fan with an impeller with a small number of broad blades of uniform material and thickness designed to operate in an orifice. 

Hot flocking. Powder coating is one of the best ways to coat a large impeller or a mixing blade with a layer of thick fluoropolymer. Usually, the process starts with a cold electrostatic powder coating step... 

For the batch mixing of thick pastes and doughs using ribbon impellers and Z- or sigma blade mixers, the tanks may be mormted horizontally. In such imits, the working volume of pastes and doughs is often relatively small, and the mixing blades are massive in construction. 

P=cp p, D, T, g, N, impeller geometric parameters such as blade width, blade angle, thickness, and other geometric details relating impeller and vessel dimensions). The usual dimensionless group approach leads to the following functional relationship ... 

Slight geometry changes. Small differences in impeller or vessel geometry can affect the power number of the impeller and hence the breakup and coalescence of drops. It may also be postulated that details such as blade sharpness or baffle thickness affect drop size in some cases. 

Impeller Geometry. The impeller geometry must be exactly scaled down from full scale dimensions. Thickness of blades, hub size, hub thickness, and placement of blades can all have significant effects on power draw, velocity profiles, and turbulence characteristics. 

Solid surfaces, particularly those easily wetted by the dispersed phase, can be major collectors of drops. In the case of a rotating impeller, drops collect and coalesce on blade surfaces to form a condensed film. As this film grows in thickness, it flows under centrifugal forces to the impeller tips and disperses into tiny drops. This process is similar to the breaknp of a cylindrical Uqnid jet. A film of dispersed phase can also collect on free snrfaces, baffles, tank walls, and the impeller shaft, where the surface vortex meets the shaft. In the case of emulsion and suspension polymerization, coalescence also leads to fonUng of heat transfer surfaces. 

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