Cross Channel Flow in a Single Screw Extruder

2 Cross Channel Flow in a Single Screw Extruder 

The cross channel flow is derived in a similar fashion as the down channel flow. This flow is driven by the x-component of the velocity, which creates a shear flow in that direction. However, since the shear flow pumps the material against the trailing flight of the screw channel, it results in a pressure increase that creates a counteracting pressure flow which leads to a net flow of zero1. The flow rate per unit depth at any arbitrary position along the 2-axis can be defined by 

1 This assumption is not completely true, since some of the material flows over the screw flight into the regions of lower pressure in the up-channel direction. 

Once the pressure is known, we can compute the velocity profile across the thickness of the channel using 

This velocity profile is schematically depicted in Fig. 6.4. As shown in the figure, the cross flow generates a recirculating flow, which performs a stirring and mixing action important in extruders for blending as well as melting. 

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