Analyzing pellet agglomeration in underwater polymer extrusion pelletizers : a numerical simulation study / Bebhash S. Raj in INTERNATIONAL POLYMER PROCESSING, Vol. 39, N° 1 (2024)  

[article]  inINTERNATIONAL POLYMER PROCESSING > Vol. 39, N° 1 (2024) . - p. 80-98 Titre : Analyzing pellet agglomeration in underwater polymer extrusion pelletizers : a numerical simulation study Type de document : texte imprimé Auteurs : Bebhash S. Raj, Auteur ; Abhilash J. Chandy, Auteur Année de publication : 2024 Article en page(s) : p. 80-98 Note générale : Bibliogr. Langues : Anglais (eng) Catégories : Etat fondu (matériaux) Granulateurs Matières plastiques -- Extrusion:Polymères -- Extrusion Mécanique des fluides numériques La mécanique des fluides numérique (MFN), plus souvent désignée par le terme anglais computational fluid dynamics (CFD), consiste à étudier les mouvements d'un fluide, ou leurs effets, par la résolution numérique des équations régissant le fluide. En fonction des approximations choisies, qui sont en général le résultat d'un compromis en termes de besoins de représentation physique par rapport aux ressources de calcul ou de modélisation disponibles, les équations résolues peuvent être les équations d'Euler, les équations de Navier-Stokes, etc. La CFD a grandi d'une curiosité mathématique pour devenir un outil essentiel dans pratiquement toutes les branches de la dynamique des fluides, de la propulsion aérospatiale aux prédictions météorologiques en passant par le dessin des coques de bateaux. Dans le domaine de la recherche, cette approche est l'objet d'un effort important, car elle permet l'accès à toutes les informations instantanées (vitesse, pression, concentration) pour chaque point du domaine de calcul, pour un coût global généralement modique par rapport aux expériences correspondantes. Domaines d'application : La CFD est particulièrement employée dans les domaines des transports, pour étudier notamment le comportement aérodynamique des véhicules (automobile, aéronautique, etc) conçus. La CFD est également utilisée dans le domaine des installations critiques telles que les salles de serveurs. Elle permet de réaliser une représentation 3D de la salle, comprenant toutes les informations relatives aux équipements informatiques, électriques et mécaniques. On obtient une carte graduée des différentes zones de chaleur présentes, ce qui permet de détecter les zones critiques et les points chauds (ou "hot spots"). Modèles mathématiques Index. décimale : 668.4 Plastiques, vinyles Résumé : The production of thermoplastic pellets using underwater die-face pelletizers is a widespread process in the thermoplastics compounding industry. One major challenge in this process is pellet agglomeration, which occurs when the polymer is pliable or easily deformed under heat. To tackle this issue, the non-Newtonian flow of a polymer, along with the turbulent flow of heating oil and heat transfer through the die, are modeled using three-dimensional (3D) computational fluid dynamics (CFD) calculations in ANSYS Fluent. The computational model is validated by comparing its predictions of temperature and pressure using two models with and without a slip method, to experimental measurements from an industrial-scale pelletizer, resulting in a maximum error of <3 % for temperature and <16 % for pressure. The efficiency of the underwater die pelletizer is typically evaluated based on the rate at which it produces pellets. Minor variations in operational parameters, such as the inlet mass flow rate and temperature of the polymer, the temperature of the heating oil, and the water temperature, can greatly affect the quality of the final product. Firstly, contours of pressure, velocity and temperature are presented to understand their impact on pellet agglomeration. However, to more specifically link pellet quality, i.e. pellet agglomeration rate, to the input conditions, the study develops a non-dimensional parameter called the pellet agglomeration number (PAN), as a non-linear function of three other non-dimensional numbers: Reynolds number, Euler number, and a non-dimensional temperature. The values of PAN at the exit and inlet are shown to correlate well with the experimentally measured pellet agglomerations, thereby demonstrating the usefulness of PAN in not only differentiating between good and bad pellet quality but also determining apriori the appropriate operating conditions leading to fewer pellet agglomerations in commercial pelletizers. Note de contenu : - Mathematical formulation : Fluid equations - Solid equations - Problem description : Experimental measurements - Mathematical model : Non-Newtonian viscosity of polymer - Results : Grid-independence study - Validation with experiments - Contours - Pellet agglomeration number DOI : https://doi.org/10.1515/ipp-2023-4404 En ligne : https://drive.google.com/file/d/1stf9B6k4t4nnM0uhIDXyBoPnb7P_aeNe/view?usp=drive [...] Format de la ressource électronique : Pdf Permalink : https://e-campus.itech.fr/pmb/opac_css/index.php?lvl=notice_display&id=40853 [article]

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Fill factor effects in highly-viscous non-isothermal rubber mixing simulations / I. Ahmed in INTERNATIONAL POLYMER PROCESSING, Vol. XXXIV, N° 2 (05/2019)  

[article]  inINTERNATIONAL POLYMER PROCESSING > Vol. XXXIV, N° 2 (05/2019) . - p. 182-194 Titre : Fill factor effects in highly-viscous non-isothermal rubber mixing simulations Type de document : texte imprimé Auteurs : I. Ahmed, Auteur ; H. Poudyal, Auteur ; Abhilash J. Chandy, Auteur Année de publication : 2019 Article en page(s) : p. 182-194 Note générale : Bibliogr. Langues : Anglais (eng) Catégories : Alliages polymères Caoutchouc Caoutchouc -- Propriétés physiques Caoutchouc -- Propriétés thermiques Fluides non newtoniens Modèles numériques Simulation par ordinateur Index. décimale : 668.4 Plastiques, vinyles Résumé : A finite volume technique in a commercial computational fluid dynamics (CFD) code is employed in this study to simulate transient, incompressible, non-Newtonian and non-isothermal rubber mixing. The simulation processes are conducted in a two-dimensional(2D) domain, where a mixing chamber partially-filled with rubber is equipped with a pair of two-wing non-intermeshing counter-rotating rotors. The main objective is to assess the effect of different fill factors of rubber on dispersive and distributive mixing characteristics by simulating 15 revolutions of the rotors rotating at 20 min−1. 50%, 60%, 70%, 75%, 80% and 90% are the six different fill factors chosen for the study. An Eulerian multiphase method has been applied to solve for the two different phases, rubber and air. The non-Newtonian property of rubber is handled using the shear rate dependent Carreau-Yasuda model, along with an Arrhenius function to include the temperature dependency. In addition to the governing equations related to the conservation of mass, momentum and energy, the volume of fluid (VOF) method is chosen to track the interface between air and rubber. With regard to the results, flow patterns, thermal distributions, viscosity behavior and volume fraction are analyzed for the different fill factors. In addition, dispersive and distributive mixing behavior is also assessed in detail using Lagrangian statistics, such as mixing index, cumulative distribution of maximum shear stress, cluster distribution index (CDI), scale of segregation (SOS) and length of stretch (LOS), calculated from massless particles. Both the Eulerian and Lagrangian results showed that fill factors between 70% and 80% presented the most reasonable and efficient mixing scenario, and also exhibited the best dispersive and distributive mixing characteristics combined. Note de contenu : - Geometry and materials - Governing equations - Computational model - Results and discussion : Thermal distribution - Flow pattern - Rubber volume fraction - Dispersive mixing - Distributive mixing DOI : 10.3139/217.3694 En ligne : https://www.degruyter.com/document/doi/10.3139/217.3694/pdf Format de la ressource électronique : Pdf Permalink : https://e-campus.itech.fr/pmb/opac_css/index.php?lvl=notice_display&id=32394 [article]

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Three-dimensional, non-isothermal simulations of the effect of speed ratio in partially-filled rubber mixing / H. Poudyal in INTERNATIONAL POLYMER PROCESSING, Vol. XXXIV, N° 2 (05/2019)  

[article]  inINTERNATIONAL POLYMER PROCESSING > Vol. XXXIV, N° 2 (05/2019) . - p. 219-230 Titre : Three-dimensional, non-isothermal simulations of the effect of speed ratio in partially-filled rubber mixing Type de document : texte imprimé Auteurs : H. Poudyal, Auteur ; I. Ahmed, Auteur ; Abhilash J. Chandy, Auteur Année de publication : 2019 Article en page(s) : p. 219-230 Note générale : Bibliogr. Langues : Anglais (eng) Catégories : Calcul Caoutchouc Ecoulement tridimensionnel Mélanges (chimie) Rhéologie Simulation par ordinateur Index. décimale : 668.4 Plastiques, vinyles Résumé : Three-dimensional, transient, non-isothermal calculations have been carried out using a commercial computational fluid dynamics (CFD) software in a two-wing rotor-equipped chamber partially-filled (75% fill factor) with rubber, to analyze the mixing efficiency for three different rotor speed ratios of 1, 1.125 and 1.5. The moving mesh technique has been used to incorporate the motion of the rotors. The Eulerian based volume of fluid (VOF) method has been used to track the interface between the two fluids, which are rubber and air. To assign the highly viscous and non-Newtonian properties of rubber, the Carreau-Yasuda model along with an exact Arrhenius formulation that accounts for the shear and temperature dependent viscosity, has been used here. Governing equations including the continuity, momentum and energy equations have been solved to characterize the flow field and various mixing parameters. Eulerian-based fields such as velocity magnitude, viscous heat generation, and average temperature and viscosity are compared between cases with different speed ratios. Dispersive and distributive mixing behaviour are assessed through a Lagrangian approach that tracks the paths of a set of massless particles. Statistical quantities such as cumulative distribution of maximum shear stress, cluster distribution index, and axial and inter-chamber particle transfer rates are calculated and presented as well. Results showed that the speed ratio of 1.5 displayed the best dispersive and distributive mixing characteristics in comparison to the other cases. Note de contenu : - Governing equations - Material properties and boundary conditions - Results : Eulerian results : flow and heat transfer - Lagrangian results : dispersive and distributive mixing measures DOI : 10.3139/217.3680 En ligne : https://drive.google.com/file/d/1u9g_UtA4YlEcu6gAGc8FUszdVBTZqS69/view?usp=drive [...] Format de la ressource électronique : Pdf Permalink : https://e-campus.itech.fr/pmb/opac_css/index.php?lvl=notice_display&id=32402 [article]

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