Mathematical modeling of flow behavior and cell structure formation during extrusion of starchy melts

Abstract

The primary purpose of this research was to develop a mathematical model for flow behavior of starchy melts inside an extruder barrel and bubble growth dynamics after exiting the extruder using mass, heat and momentum transfer equations and obtain the physical characteristics of the product, such as expansion ratio and bubble radius, using input parameters such as feed rate, screw speed, water input in the extruder and pre-conditioner, etc. The model was written in Visual Basic and experimentally validated using pilot-scale twin screw extrusion for processing of cereal-based cellular products. Process and product data were measured at different in-barrel moisture contents (19–28% dry basis) and experimental screw speeds (250–330 rpm). Experimental process parameters such as die temperature (Tdie) (120.7–170.6 °C) and pressure (Pdie) (3160–7683 kPa) and product expansion ratio (ER) (3.3–16.9) and cell size (R) (435–655 μ) compared well with simulated results viz., Tdie(116.8–176.1 °C), Pdie(3478–6404 kPa), ER(4.6–19.4) and R(426–728 μ).