CFD Analysis of the Frame Invariance of the Melt Temperature Rise in a Single-screw Extruder

Habla, Florian; Obermeier, S.; Dietsche, Laura; Kintzel, O.; Hinrichsen, Olaf

doi:10.3139/217.2753

Cited by 8 publications

(5 citation statements)

References 6 publications

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“…Prescribing this rotational movement at the topknown as barrel rotation or inverse kinematics -might appear intuitively questionable as the resulting flow field does not seem to resemble physical conditions. However, we follow the argumentation of Habla et al [36] who prove frame invariance of the melt temperature and in general discuss the negligibility of centrifugal and Coriolis forces. At the inflow, we thus prescribe a linear velocity profile u = (0, v, 0), with v = 0.027646 z 0.0075 m s −1 .…”

Section: Test Case Generationmentioning

confidence: 91%

Numerical Design of Distributive Mixing Elements

Hube,

Behr,

Elgeti

et al. 2021

Preprint

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This paper presents a novel shape-optimization technique for the design of mixing elements in single-screw extruders. Extruders enable the continuous production of constant-cross-section profiles. Equipped with one or several screwshaped rotors, the extruder transports solid polymer particles towards the outlet. Due to shear heating, melting is induced and a melt stream is created, which can be further processed. While many variants of multi-screw extruders exist, a significant share of all extrusion machines is made up of single-screw extruders due to their comparatively low operating costs and complexity. While the reduced complexity yields economic benefits, single-screw extruders' mixing capabilities, i.e., their ability to produce a melt with a homogeneous material and temperature distribution, suffer compared to multi-screw extruders. To compensate for this shortcoming, so-called mixing elements are added to the screw to enhance dynamic mixing by recurring flow reorientations. In view of the largely unintuitive flow characteristics of polymer melts, we present an optimization framework that allows designing these mixing elements numerically based on finite-element simulations of the melt flow. To reduce the computational demand required by shape optimization of a complete mixing section, we only focus on the shape optimization of a single mixing element. This paper presents advances in three aspects of numerical design: (1) A combination of free-form deformation and surface splines is presented, allowing to parameterize the mixing element's shape by very few variables. (2) The combination of this concept with a linear-elasticity-based mesh update method to deform the computational domain without the need for remeshing is demonstrated. (3) A simple yet robust and sensitive new objective formulation to assess distributive mixing in laminar flows based on a measure for the interfacial area is proposed for the optimization.

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Section: Test Case Generationmentioning

confidence: 91%

Numerical Design of Distributive Mixing Elements

Hube,

Behr,

Elgeti

et al. 2021

Preprint

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“…This has been shown using complete finite element analysis. [26][27][28][29] Further research, demonstrated both experimentally and with screw and barrel rotation-based models, showed that barrel rotation models over-predict the temperature rise in screw channels while screw rotation models give the proper trends for dissipation and polymer flow channel temperature rise. [30] The reasons for the limitation of the conventional barrel analysis when compared to the general predictions of the screwrotation analysis were recently discussed in detail.…”

Section: Screw Rotation Melting Analysismentioning

confidence: 99%

“…[ 32 ] This screw rotation model predicted that the solid bed melted due to dissipation and heat transfer in all four melt films surrounding the melting solid bed, as illustrated in Figure 9. [ 17 ] Previous analysis of barrel rotation dissipation in extrusion [ 28 ] over‐predicted the polymer melt temperature when barrel rotation dissipation was used in the to analyze the pumping section of the screw. The screw rotation velocities were used in this analysis because the process is dissipation dominated, and dissipation is not frame indifferent (http://extrusionwiki.com).…”

Section: Modeling Melting Dynamicsmentioning

confidence: 99%

A proposed mechanism for solid bed encapsulation: Based on comparing three dimensional andone‐dimensionalscrew melting models

Campbell

Wetzel²,

Spalding

2022

Polymer Engineering & Sci

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This paper describes how the initial melt generation physics with differing pressure generation dynamics lead to either conventional melting or one dimensional (1D) melting. An historic review of the development of single screw melting models is presented. First, a review of the classic model is briefly presented. Second, after an analysis of literature melting data developed using the Maddock solidification procedure, a screw rotation concept melting model is presented that correlates very well with the melting analysis. Third, a new 1D film melting model is developed to analyze melting when the melt film does not encapsulate the solid bed. This physical model provides for the first time a quantitative model for the initiation and ultimate solid bed melting of the 1D melting process. Finally, a new concept and resulting model demonstrate that Reynold's barring concept for pressure generation in the initial melt film at the barrel interface may provide the mechanism that relates to whether the solid bed is or is not encapsulated.

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“…Investigation of the accuracy given by this kinematics assumption is addressed in different works [ 81 , 82 , 83 , 84 ].…”

Section: Models For the Materials Extrusionmentioning

confidence: 99%

“…Temperature field is also the same in the two kinematic conditions, and this has been demonstrated by means of the FVM method [ 84 ].…”

Section: Models For the Materials Extrusionmentioning

confidence: 99%

Analytical and Numerical Models of Thermoplastics: A Review Aimed to Pellet Extrusion-Based Additive Manufacturing

2021

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Recent developments in additive manufacturing have moved towards a new trend in material extrusion processes (ISO/ASTM 52910:2018), dealing with the direct extrusion of thermoplastic and composite material from pellets. This growing interest is driven by the reduction of costs, environmental impact, energy consumption, and the possibility to increase the range of printable materials. Pellet additive manufacturing (PAM) can cover the same applications as fused filament fabrication (FFF), and in addition, can lead to scale towards larger workspaces that cannot be covered by FFF, due to the limited diameters of standard filaments. In the first case, the process is known as micro- or mini-extrusion (MiE) in the literature, in the second case the expression big area additive manufacturing (BAAM) is very common. Several models are available in literature regarding filament extrusion, while there is a lack of modeling of the extrusion dynamics in PAM. Physical and chemical phenomena involved in PAM have high overlap with those characterizing injection molding (IM). Therefore, a systematic study of IM literature can lead to a selection of the most promising models for PAM, both for lower (MiE) and larger (BAAM) extruder dimensions. The models concerning the IM process have been reviewed with this aim: the extraction of information useful for the development of codes able to predict thermo-fluid dynamics performances of PAM extruders.

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CFD Analysis of the Frame Invariance of the Melt Temperature Rise in a Single-screw Extruder

Cited by 8 publications

References 6 publications

Numerical Design of Distributive Mixing Elements

Numerical Design of Distributive Mixing Elements

A proposed mechanism for solid bed encapsulation: Based on comparing three dimensional andone‐dimensionalscrew melting models

Analytical and Numerical Models of Thermoplastics: A Review Aimed to Pellet Extrusion-Based Additive Manufacturing

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