Scaling-Up of Thermoplastic Starch Extrusion

Scaling-up of thermoplastic starch extrusion suffers from the same general problems that are encountered in many other processes in the process industry  

Thermoplastic Starch. Edited by Leon P.B.M. Janssen and Leszek Moscicki 2009 WILEY-VCH Verlag GmbH Co. KGaA, Weinheim ISBN 978-3-527-32528-3 

The degree to which a process is adiabatic can be estimated from the Brinkmann number (Br), which can be rewritten for extruders as  

A particular dependency is the quadratic occurrence of the diameter. This implies that the Brinkmann number is generally large for production machines. It is generally not possible to keep the Brinkmann number constant for large-scale and small-scale machines. To obtain reliable predictions on a small-scale machine the Brinkmann number for this machine should at least be much larger than unity, which set its limitations to the minimum screw diameter of the small scale machine. If this number is smaller than unity for laboratory machines, reliable scaling-up is not possible. 

In order to obtain complete thermal similarity, the screw rotation rate has to be decreased drastically, relative to the adiabatic case, with increasing screw diameter. As a result, the scale factor for the throughput is only 1.5 for Newtonian fluids (and decreases even fruilier for fluids with pseudo-plastic behavior). This scaling-up factor q) for the throughput is defined from  

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