Pumps dimensionless groups

Not only is the type of flow related to the impeller Reynolds number, but also such process performance characteristics as mixing time, impeller pumping rate, impeller power consumption, and heat- and mass-transfer coefficients can be correlated with this dimensionless group. 

This is probably the most important dimensionless group used to represent the actual flow during mixing in a vessel. Flow Number, Nq (or pumping number) ... 

The rotating disc and rotating cylinder have been successfully applied in the laboratory to study the effect of flow on corrosion rates and are much easier to use than actual pipelines and other real geometries. The results of these tests can now be correlated to geometries likely to be found in pipes, pumps, bends, etc. in plant by use of dimensionless group analysis. There-... 

The flow rate, head, and impeller speed at the maximum or best efficiency point (BEP) of the pump characteristic can be used to define a dimensionless group called the specific speed ... 

Another dimensionless group, analogous to the specific speed, that relates directly to the cavitation characteristics of the pump is the suction specific speed, Nss ... 

Geometrically similar pumps are those that have all the dimensionless groups numerically the same. In such cases, two different sets of operations are related as follows ... 

The flow can be forced, e.g., by a pump or an impeller, it can be driven by gravity or even by surface tension gradients. In most cases, the flow is too complex to be analysed theoretically, and empirical correlations are used for predicting values of the mass transfer coefficient for given conditions. These correlations are usually presented as functions of dimensionless groups, in order to generalize the applicability. 

Here AP is the pressure drop per chamber, caused by the pressure in front of the die, and is the Newtonian viscosity. These two dimensionless groups for throughput and pressure are very powerful. When these groups are used, the characteristics for the completely filled pumping zone of twin-screw extraders are straight Unes that are independent of viscosity and speed of rotation of the screws. Figure 6.9 presents an example of these Unes and their dependence on the size of the... 

The dimensionless quantity toQ 2/(ghf/A is a characteristic for a particular type of centrifugal pump, and, noting that the angular velocity is proportional to the speed N. this group may be rewritten as ... 

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