Power Consumption in Melt Conveying

The power consumption in the melt conveying zone is an important parameter to consider in screw design and in the analysis of actual extrusion operations. The power consumed for pumping in the channel is  

The shear stresses can be evaluated from Eqs. 7.223 and 7.224 and the equations for down-channel velocity profile, Eq. 7.197 or 7.216, and the-cross channel velocity profile, Eq. 7.211. The power consumption in the screw channel can be written as  

Equation 7.236 is valid if the clearance is negligible. The ratio of pressure flow to drag flow is often referred to as the throttle ratio (Drossel quotient in German). It enables a compact expression for the combined drag and pressure flow  

The specific energy consumption in the channel can be determined by dividing the power consumption by the throughput  

The pumping efficiency is the ratio of the theoretical energy requirement to develop pressure AP (= VAP) divided by the actual energy requirement (= dZ,ii). Thus, the pumping efficiency in the channel can be written as  

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