119 research outputs found
Boundary-Conforming Finite Element Methods for Twin-Screw Extruders: Unsteady - Temperature-Dependent - Non-Newtonian Simulations
We present a boundary-conforming space-time finite element method to compute
the flow inside co-rotating, self-wiping twin-screw extruders. The mesh update
is carried out using the newly developed Snapping Reference Mesh Update Method
(SRMUM). It allows to compute time-dependent flow solutions inside twin-screw
extruders equipped with conveying screw elements without any need for
re-meshing and projections of solutions - making it a very efficient method. We
provide cases for Newtonian and non-Newtonian fluids in 2D and 3D, that show
mesh convergence of the solution as well as agreement to experimental results.
Furthermore, a complex, unsteady and temperature-dependent 3D test case with
multiple screw elements illustrates the potential of the method also for
industrial applications
Boundary-Conforming Finite Element Methods for Twin-Screw Extruders using Spline-Based Parameterization Techniques
This paper presents a novel spline-based meshing technique that allows for
usage of boundary-conforming meshes for unsteady flow and temperature
simulations in co-rotating twin-screw extruders. Spline-based descriptions of
arbitrary screw geometries are generated using Elliptic Grid Generation. They
are evaluated in a number of discrete points to yield a coarse classical mesh.
The use of a special control mapping allows to fine-tune properties of the
coarse mesh like orthogonality at the boundaries. The coarse mesh is used as a
'scaffolding' to generate a boundary-conforming mesh out of a fine background
mesh at run-time. Storing only a coarse mesh makes the method cheap in terms of
memory storage. Additionally, the adaptation at run-time is extremely cheap
compared to computing the flow solution. Furthermore, this method circumvents
the need for expensive re-meshing and projections of solutions making it
efficient and accurate. It is incorporated into a space-time finite element
framework. We present time-dependent test cases of non-Newtonian fluids in 2D
and 3D for complex screw designs. They demonstrate the potential of the method
also for arbitrarily complex industrial applications
Combining Boundary-Conforming Finite Element Meshes on Moving Domains Using a Sliding Mesh Approach
For most finite element simulations, boundary-conforming meshes have
significant advantages in terms of accuracy or efficiency. This is particularly
true for complex domains. However, with increased complexity of the domain,
generating a boundary-conforming mesh becomes more difficult and time
consuming. One might therefore decide to resort to an approach where individual
boundary-conforming meshes are pieced together in a modular fashion to form a
larger domain. This paper presents a stabilized finite element formulation for
fluid and temperature equations on sliding meshes. It couples the solution
fields of multiple subdomains whose boundaries slide along each other on common
interfaces. Thus, the method allows to use highly tuned boundary-conforming
meshes for each subdomain that are only coupled at the overlapping boundary
interfaces. In contrast to standard overlapping or fictitious domain methods
the coupling is broken down to few interfaces with reduced geometric dimension.
The formulation consists of the following key ingredients: the coupling of the
solution fields on the overlapping surfaces is imposed weakly using a
stabilized version of Nitsche's method. It ensures mass and energy conservation
at the common interfaces. Additionally, we allow to impose weak Dirichlet
boundary conditions at the non-overlapping parts of the interfaces. We present
a detailed numerical study for the resulting stabilized formulation. It shows
optimal convergence behavior for both Newtonian and generalized Newtonian
material models. Simulations of flow of plastic melt inside single-screw as
well as twin-screw extruders demonstrate the applicability of the method to
complex and relevant industrial applications
Dynamic modeling of the reactive twin-screw co-rotating extrusion process: experimental validation by using inlet glass fibers injection response and application to polymers degassing
International audienceIn this paper is described an original dynamic model of a reactive co-rotating twinscrew extrusion (TSE) process operated by the Rhodia company for the Nylon-66 degassing finishing step. In order to validate the model, dynamic experiments have been performed on a small-scale pilot plant. These experiments consist in a temporary injection of glass fibers at the inlet of the extruder after it has reached a given operating point. The outlet glass fibers mass fraction time variation is then measured. This experiment does not lead to the RTD measurement. As a matter of fact, due to the high quantity of glass fibers that is introduced, the behavior of the flow through the extruder is perturbed so that the glass fibers cannot be considered as an inert tracer. The dynamic model that we have published elsewhere (Choulak et al., Ind. Eng. Chem. Res., 2004, 43(23), 7373-7382) is adapted to take into account this nonlinear behavior of the extruder with respect to the glass fibers injection and is favorably compared to experimental results. The description of the degassing operation is also included in the model. The model allows simulations of the complete dynamic behavior of the process. When the steady state is reached, the good position of the degassing vent with respect to the partially and fully filled zones positions can also be checked, thus illustrating the way the model can be used for design purposes
Design of rotor for internal batch mixer and mixing elements for twin screw extruder for polyolefin processing
Mixing is the key component of polymer processing to achieve homogeneity of final product. Previous researchers have reported poor mixing performance of internal batch mixer (IBM) and twin screw extruder (TSE) due to improper distributive and dispersive mixings. This leads to poor product properties. Hence to overcome the problem, this research aims to design a rotor and mixing element to improve mixing performance of IBM and TSE. The basic rotor design for IBM was developed on the concept of Banbury and roller rotors and this design was then optimized to attain secondary flow. Distributive mixing performance of the optimized rotor was compared with commercial rotors using ANSYS Polyflow, with results showing the new rotor was found to be better than commercial rotors. Based on these results, a prototype of optimized design rotor was developed using Computer Numerical Control machine. Using this prototype rotor, nano calcium carbonate was dispersed in high density polyethylene and its morphology was analysed via scanning electron microscopy (SEM). SEM results showed improved dispersive mixing performance of prototype rotor compared to that of commercial rotor. This prototype rotor design was later modified into two mixing elements namely, Bean-UTM for intermeshing co-rotating TSE and Blade-UTM for intermeshing counter-rotating TSE. The Bean-UTM and Blade-UTM were examined for dispersive mixing (mixing index) and distributive mixing (logarithm of length of stretch, instantaneous efficiency and time average efficiency) and then were compared with commercial TSE mixing elements. The results showed Bean-UTM has better mixing performance than kneader mixing element of Dr. Collin TSE and the Blade-UTM has better mixing performance than screw mixing element of Coperian TSE. The findings of this research will hopefully solve the issue of poor mixing in IBM and TSE
Optimization of polymer processing: a review (Part I - Extrusion)
Given the global economic and societal importance of the polymer industry, the continuous search for improvements in the various processing techniques is of practical primordial importance. This review evaluates the application of optimization methodologies to the main polymer processing operations. The most important characteristics related to the usage of optimization techniques, such as the nature of the objective function, the type of optimization algorithm, the modelling approach used to evaluate the solutions, and the parameters to optimize, are discussed. The aim is to identify the most important features of an optimization system for polymer processing problems and define the best procedure for each particular practical situation. For this purpose, the state of the art of the optimization methodologies usually employed is first presented, followed by an extensive review of the literature dealing with the major processing techniques, the discussion being completed by considering both the characteristics identified and the available optimization methodologies. This first part of the review focuses on extrusion, namely single and twin-screw extruders, extrusion dies, and calibrators. It is concluded that there is a set of methodologies that can be confidently applied in polymer processing with a very good performance and without the need of demanding computation requirements.This research was funded by NAWA-Narodowa Agencja Wymiany Akademickiej, under
grant PPN/ULM/2020/1/00125 and European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie Grant Agreement No 734205–H2020-MSCA-RISE-2016.
The authors also acknowledge the funding by FEDER funds through the COMPETE 2020 Programme
and National Funds through FCT (Portuguese Foundation for Science and Technology) under the
projects UID-B/05256/2020, UID-P/05256/2020
Polymer Processing: Modeling and Correlations Finalized to Tailoring the Plastic Part Morphology and Properties
The analysis of polymer processing operations is a wide and complex subject; during polymer processing, viscoelastic fluids are forced to deform into desired geometries using non-homogeneous velocity and temperature fields down to solidification. The objective of analysis is the identification of processing conditions, which are finalized in the optimization of product final properties, which, in turn, are determined by the final part morphology. Depending on the operating conditions, the properties of the final part can change more than one order of magnitude. Properties of interest include the mechanical, optical, barrier, permeability, and biodegradability, and any other property of practical relevance including the characteristics of the surfaces as its finishing and wettability, which are connected to one another. The scope of this Special Issue is to select progress in or reviews of the understanding/description of the phenomena involved along the chain of processing–morphology–properties. Along this virtual chain, modeling may be a useful approach, and within the objective of understanding fundamental aspects, it may also be relevant to compare selected characteristics of the process and the material with the characteristics of the resulting morphology and then with the properties of the final part. This approach suggests the title: “Polymer Processing: Modeling and Correlations Finalized to Tailoring the Plastic Part Morphology and Properties”
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