Two different techniques to analyze non-Newtonian viscous flow in complex geometries with internal moving parts and narrow gaps are compared. The first technique is a non-conforming mesh refinement approach based on the fictitious domain method (FDM), and the second one is the extended finite element method (XFEM). The refinement technique uses one fixed reference mesh, and to impose continuity across nonconforming regions, constraints using Lagrangian multipliers are used. The size of elements locally in the high shear rate regions is reduced to increase accuracy. FDM is shown to have limitations; therefore, XFEM is applied to decouple the fluid from the internal moving rigid bodies. In XFEM, the discontinuous field variables are captured by using virtual degrees of freedom that serve as enrichment and by applying special integration over the intersected elements. The accuracy of the two methods is demonstrated by direct comparison with results of a boundary-fitted mesh applied to a two-dimensional cross section of a twin-screw extruder. Compared with non-conforming FDM, XFEM shows a considerable improvement in accuracy around the rigid body, especially in the narrow gap regions. A. S. FARD ET AL. of the deformed mesh is preserved, and the accuracy of the ALE method is higher than any fixed mesh method. ALE methods have some limitations if the internal moving part has a rigid complex geometry because the fluid mesh highly deforms and becomes distorted. Sometimes remeshing helps to overcome this problem, but in case of three-dimensional problems, it is really complicated or impossible to deform the finite element mesh with flow advection (e.g., the three-dimensional geometry of a TSE). On the other hand, remeshing of a deformed mesh is, from a computational time view, expensive.Fixed mesh methods were introduced to circumvent deforming mesh problems and were based on a reference mesh and immersing boundaries of moving parts through the fixed mesh. The original immersed boundary (IB) method was introduced by Peskin [3] and used a fixed mesh for the computational domain that is intersected by the fluid/solid interface. Using a level set function, the additional interface nodes are added to the computational domain with additional degrees of freedom (DOF). A special treatment is then applied to the solid region and the interface DOF [4]. Recently, Ilinca and Hétu [5] applied the IB method to simulate the flow inside single-screw extruders and TSEs. Avalosse [6] presented a mesh superposition technique (MST) applied to a TSE. With MST, the whole computational domain is covered with one fixed mesh without considering the internal moving rigid bodies and one separate dynamic mesh for the moving parts. At each time, the position of the moving part mesh is updated. With superposition of these two meshes, the kinematics of the dynamic mesh are imposed on the static mesh using penalty constraints. This method is easy to implement, but to avoid diffusion errors, precise mesh refinement at the interface of fluid-rigid bod...
Liquid-phase adsorption has hardly been established in micro-flow, although this constitutes an industrially vital method for product separation. A micro-flow UV-photo isomerization process converts cis-cyclooctene partly into trans-cyclooctene, leaving an isomeric mixture. Trans-cyclooctene adsorption and thus separation was achieved in a fixed-bed micro-flow reactor, packed with AgNO 3 /SiO 2 powder, while the cis-isomer stays in the flow. The closed-loop recycling-flow has been presented as systemic approach to enrich the trans-cyclooctene from its cis-isomer. Inflow adsorption in recycling-mode has hardly been reported so that a full theoretical study has been conducted. This insight is used to evaluate three process design options to reach an optimum yield of trans-cyclooctene. These differ firstly in the variation of the individual residence times in the reactor and separator, the additional process option of refreshing the adsorption column under use, and the periodicity of the recycle flow.
Co-rotating twin-screw extruders are widely used compounding machines. They are mainly configured based on extensive experience and iterative approaches to optimise output and composite quality. The visualisation technology developed in the EU-project PEPTFlow allows visualisation of composite flow in twin-screw extruders under realistic processing conditions by tracking radioactive tracer particles in the polymer melt, using a specially developed camera system. This new approach allows polymer flow to be studied in different screw elements and screw configurations under realistic compounding conditions at normal temperatures and melt pressures. The paper presents the latest developments in the camera systems as well as the different ways to use and interpret the results. Detailed analysis of residence times and residence time distributions for standard compound screw elements, like kneading discs, conveying elements and reverse elements are presented. In addition for a better understanding of the flow field inside twin-screw extruders, numerical particle tracking is done. The Stokes equation, using XFEM method, are solved and the numerical RTD's (residence time distribution) are compared for various screw designs.
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