Breakage impeller

N = impeller speed Breakage occurs when N > Nc,-Maximum enhancement before breakage was factor of 2.0. 

For instaUations in which suspended sohds must be handled with a minimum of solids breakage or degradation, such as pumps feeding filter presses, special attention is required either a low-shear positive-displacement pump or a recessed-impeller centrifugal pump may be called for. 

Values of kj a for viscoelastic liquids in aerated stirred tanks are substantially smaller than those in inelastic liquids. Moreover, less breakage of gas bubbles in the vicinity ofthe impeller occurs in viscoelastic liquids. The following dimensionless equation [8] (a modified form of Equation 7.37) can be used to correlate kj a in sparged stirred tanks for non-Newtonian (including viscoelastic) liquids ... 

Mass-Transfer Models Because the mass-transfer coefficient and interfacial area for mass transfer of solute are complex functions of fluid properties and the operational and geometric variables of a stirred-tank extractor or mixer, the approach to design normally involves scale-up of miniplant data. The mass-transfer coefficient and interfacial area are influenced by numerous factors that are difficult to precisely quantify. These include drop coalescence and breakage rates as well as complex flow patterns that exist within the vessel (a function of impeller type, vessel geometry, and power input). Nevertheless, it is instructive to review available mass-transfer coefficient and interfacial area models for the insights they can offer. 

The workhorse impeller is the pitched-blade mrbine because of its ability to create good circulation at relatively low shear. These attributes help reduce secondary nucleation and crystal breakage while achieving good suspension and circulation. The flat-blade turbine is less versatile because of high shear and less overall circulation. The Ekato Intermig has proven to have superior performance in some crystaUization operations because of its combination of excellent circulation and low shear. 

Turbulent action forces the gas to break away from the cavity and exit the impeller zone. This breakage is the source of gas dispersion in STRs. The large cavity deserves special attention because it induces gas breaking away less violently than the other cavity types. Large cavities also have an advantage in that they hold more gas and have more surface area from which gas can break away. 

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