Applicability of a shear induced rate constant model to conversion of corn meal in a twin-screw extruder
1995
Gogoi, B.K. | Wang, S.S. | Yam, K.L.
Data obtained from extruding corn meal in a corotating twin-screw extruder was used to test an Arrhenius type shear induced rate constant model, ks = ks,o exp (-ES/tau nu) where ks was shear induced rate constant, Es was shear activation energy, tau was shear stress, and nu was molar volume. A rheological zone was created by placing a reverse screw 300 mm from the die where the temperature was at 60C, sufficiently low that thermal effect on conversion of the material into gel or melt could be neglected. Throughput was used as an independent variable to generate various levels of shear input, while screw speed and feed moisture content were kept constant. Conversion of the material in the rheological zone was determined using differential scanning calorimetry, and the rate constant ks was calculated assuming zero order kinetics. A plot of ks vs. 1/tau nu followed a straight line, confirming the applicability of the model to twin-screw extrusion under the experimental conditions. The shear activation energy Es was 40 cal/mole, comparable to the literature values obtained from single screw extrusion and capillary rheometry.
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