Average Shear Rates in the Screw Elements of a Corotating Twin-Screw Extruder

The rapid estimation of the average shear rate encountered by the material as it flows along the screw elements of a corotating twin-screw extruder is a key point for many applications. In this paper, two methods of evaluation are presented that allow the calculation of the average shear rate as a function of the screw geometry, feed rate, and screw speed. A comparison is made between the approximate and exact methods. It is shown that it is crucial to take into account the shear component due to the pressure flow, especially in the left-handed screw elements.

Disruption of granules by hydrodynamic force in internal circulation anaerobic reactor

A process of granule disruption by hydrodynamic force is discussed in this paper. Shear force and attrition among granules originated from hydrodynamic force are the main causes of the disruption. Since it is positively correlated to the attrition force, the shear force is utilized to describe the effect of hydrodynamic force on granule disruption. In the experiment, when increase rate of average shear rate (IRγ) of the 1st stage is about 0.2 s−1·d−1, the granules are disrupted; while re-granulation could develop when IRγ is about 0.07 s−1·d−1; even when the shear rate is as high as about 30 s−1, the granulation rate keeps stably at a relatively high level, which shows that granules could bear the high hydrodynamic force only if it increases by low increase rate. The experimental results would be valuable for the operation and controlling of the upflow reactors.