Screw pumps power input

The equations given in Fig. 6.5a and/or 6.5b can also be applied to an extruder section. In general, however, we do not know the power input to the shafts for an extruder section or, therefore, the specific energy input for this section. The pumping efficiency can be of use here it is determined in advance for the screw geometry in question (measurements taken with a model fluid are adequate, see Section 6.7) or determined by 3-dimensional calculations (as shown in Fig. 6.7). 

Highly viscous polymeric reactions (e.g., the hydrolytic polyamide reaction) are often carried out in a gear-pump reactor (Tadmore and Klein, 1970). This type of reactor is often difficult to operate because the clearance of the gear teeth is increased by wear caused by flow and the reaction process. For smaller viscosity of the melt, a screw reactor or a twin-screw extruder is often used. Sterbecek et al. (1987) used a twin-screw extruder (i.e., Wemer-Pfleiderer extruder ZSK 83) for studying fast ion-catalyzed polymerization (6-caprolactam) in a melt. They indicated that power input and quality of product in such a reactor depends on the slot width between reactor wall and impeller in a twin screw extruder. They provided an optimum design of a twin-screw reactor for a fast ion-catalyzed polymerization in a melt. 

This power should be used to calculate the temperature increase in the polymer melt. Since the pumping efficiency is usually less than 10%, the amount of power dissipated In the screw channel will generally be more than 90% of the total power Input. 

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