Average Shear Rate in a Twin‐screw Extruder as a Function of Degree of Fill, Flow Behavior Index, Screw Speed and Screw Configuration

Abstract

Mixer viscometry assumptions were used to model average shear rate in a co-rotating twin-screw extruder. Screw speed was varied at 50, 100, 200, 300 and 400 rpm in an MPF-19APV twin-screw extruder for Newtonian and non-Newtonian fluids with different flow behavior indices (n). A composite screw configuration was used. Degree of fill was varied from 0.4 to 1.0. Also, for three separate all-one-type screw configurations, screw speed was varied from 50 to 400 rpm to estimate the average shear rate for 30°forwarding paddles, single-lead, and twin-lead screws individually for 1.0°fill. A modified matching viscosity technique was used to estimate average shear rate for all conditions.Average shear rate was modeled as a function of extruder constant (k′), screw speed and an empirical parameter a. The k′ increased as a power-law and a decreased linearly with degree of fill. The k′ ranged from 5.7 to 45.1 s a-1 rev -a and was independent of screw speed and flow behavior index. Alpha increased with n. Average shear rates for the composite screw configuration ranged from 10.5 to 404 s -1 for fluids with flow behavior indexes of 0.24, 0.60 and 0.67, respectively. For the separate screw configurations at fill = 1.0, average shear rate at a constant screw speed was highest for 30 forwarding paddles, followed by single-lead and twin-lead screws. Corresponding PRACTICAL APPLICATIONSPractical applications include providing a convenient method to estimate average shear rate for composite screw configurations under partial-fill conditions. Also, the study provides the basis for follow-up studies where the influence of shear on food product quality and nutritional value can be examined. 962 M. SUPARNO ET AL. AVERAGE SHEAR RATE IN EXTRUDER 963 1 6 10 15 11 100 1 . , e T n 970 M. SUPARNO ET AL.

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