Abstract
This paper aims to investigate a method to perform non-isothermal flow simulations in a complex geometry for generalised Newtonian fluids. For this purpose, 3D numerical simulations of starch based products are performed. The geometry of a co-rotating twin-screw extruder is considered. Process conditions concern high rotational speed (up to 1800 rpm), different flow rates (30, 40 and 60 kg/h) and water contents (22% and 36%), for a total of 54 simulations. To cope with the geometry complexity a Mesh Superposition Technique (MST) was adopted. The pseudoplastic behaviour of the fluid is taken into account by considering viscosity as function of shear rate (Ostwaldde Waele relationship) and temperature (Arrhenius law). Simulated temperature variations are compared with measurements at same process conditions for validation. Qualitative behaviour of temperature T and shear stress along the screw are analysed and comparisons of different process conditions are presented. By these simulations a database is formed to develop a process control strategy for novel extruder operating points in food technology.
Highlights
Since their massive development in the first half of 20th century, extruders have been experiencing a non-stop growth in all industrial fields, in plastic industry and in food processing
The influence of the specific mechanical energy (SME) on cornmeal viscosity was illustrated by Chang et al [3] while product degradation and expansion mechanisms were widely studied in many other works [4] [5] [6] [7]
Due to the complexity of the extrusion process and high number of design variables, most research has been historically carried out on an experimental basis and only recently, with the growth in computer science, the empirical approach has been supported by numerical contributions
Summary
Since their massive development in the first half of 20th century, extruders have been experiencing a non-stop growth in all industrial fields, in plastic industry and in food processing. (2014) 3D Thermo-Fluid Dynamic Simulations of HighSpeed-Extruded Starch Based Products. Engineering aspects of extruder performances from an energy point of view have been investigated [9] [10] and assessment of twin-screw extrusion in producing snack food [11] as well as effects on product characteristics [12] have been experimentally studied. Ishikawa et al [15] modelled six discrete angular positions of the screw geometry and performed a non-isothermal quasi-steady-state simulation of a polypropylene material. The MST as well as the Mesh Partitioning Technique [17] allows simulating the extrusion process without regenerating the finite element mesh as the screws rotate. Use of MST to perform isothermal fluid dynamic simulations of extruded starch based matrix can be found in [18]
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