Residence time distribution and flow patterns in twin screw extrusion of starch

MPhil Student: Felycia Edi Soetaredjo
Supervisors: Dr. Rulande Rutgers, Dr. Bhesh Bhandari and Dr. Peter Torley

This study is part of bigger project on the kinetics of degradation and losses of microencapsulated volatiles during high temperature short time extrusion. The result of this study will supply a methodology for the investigation of flow patterns during twin-screw extrusion of starch-based dough, and to assess the suitability and limitations of current constitutive equations for the description of extrusion flow behaviour of food pastes.

The flow history in a twin-screw extruder will be assessed by residence time distribution and flow pattern studies. Based on literature study, Allura red and Gadolinium were chosen as tracers to measure the residence time distribution and to determine the flow patterns. Preliminary experiments have been carried out to identify a set of extrusion conditions which results in steady non-expanding extrudate NMR spectrometry and UV-Vis spectrophotometry were chosen for the tracer concentration analysis. The flow patterns will be modelled using Polyflow, which is a commercial finite element method based solver that specially developed for extrusion problems of non-Newtonian flows. A mesh superposition technique will be used to simulate the complex geometry of the twin-screw extruder for Polyflow simulation. Due to computational complexity, only a short section of the barrel will be simulated initially.

Schematic representation of structure of research