Article
Mechanics
H. Benkreira, A. P. Preece
Summary: This research demonstrates the control of extrudate swell and flow instabilities in thermoplastic extrusion by using a rotating roller die. The practical benefits include stable operation at higher flow rates and the ability to investigate various instabilities that arise in polymer melt die extrusion.
JOURNAL OF NON-NEWTONIAN FLUID MECHANICS
(2022)
Article
Mechanics
Samaneh Dehghani, Mahdi Salami Hosseini, Ehsan Behzadfar
Summary: The addition of esterified polyethylene glycol (PEG) can increase the slip velocities of high-molecular-weight high-density polyethylene, with a distinct slip zone at small shear stresses at 190 degrees C, while showing a weak slip regime at 210 degrees C.
Article
Polymer Science
Christos K. Georgantopoulos, Masood K. Esfahani, Ingo F. C. Naue, Manfred Wilhelm, Roland Kadar
Summary: The extrusion flow instabilities of two commercial polyethylenes (PE), both with similar weight average molecular weight, were characterized using capillary rheology, optical analysis, and modeling. The characteristic time periodicity τ* and spatial characteristic wavelength λ were obtained and compared using three different methods. It was found that both the characteristic time periodicity τ* and the spatial characteristic wavelength λ exhibit Arrhenius temperature-dependent behavior.
JOURNAL OF APPLIED POLYMER SCIENCE
(2023)
Article
Materials Science, Multidisciplinary
Christos K. Georgantopoulos, Masood K. Esfahani, Michael A. Pollard, Ingo F. C. Naue, Andrea Causa, Roland Kadar, Manfred Wilhelm
Summary: The study investigates the extrusion flow instabilities of commercial polybutadiene (PBD) by using different extrusion die geometries. Qualitative models are used to fit the experimental data and predict the spatial characteristic wavelength (lambda) for extrudates obtained by complex cross-section profile slit die geometries. The correlation between the ratio of extensional and shear stress at the die exit area and the characteristic dimension of the dies is presented. A geometry-dependent model is also used to predict the spatial characteristic wavelength of the extrusion flow instabilities.
MACROMOLECULAR MATERIALS AND ENGINEERING
(2022)
Article
Mechanics
Sourabh Dhawan, Malay Kumar Das, Pradipta Kumar Panigrahi
Summary: The research investigates the effectiveness of geometric modification in stabilizing viscoelastic fluid flow through a planar channel. The square cylinder positioned in front of the contraction plane pre-deforms the fluid, causing significant changes in flow characteristics. The study demonstrates that pre-deformation of the fluid stabilizes flow in a specific range and reduces the size of corner vortex in another range. Furthermore, an increase in a certain parameter initiates elastic turbulence in the flow.
Article
Polymer Science
Celio Fernandes, Ahmad Fakhari, Zeljko Tukovic
Summary: A new method based on the Arbitrary Lagrangian-Eulerian formulation has been developed to study the viscous flow of polymer melts. This method is validated by comparing the extrudate swell ratio under different flow conditions. Additionally, the study investigates the rheological behavior of the material and essential flow characteristics such as yield stress, inertia, and non-isothermal effects.
Article
Mechanics
Lorenzo Lombardi, Daniele Tammaro
Summary: The study explored the effect of die swell on extrusion foam of thermoplastic polymers, revealing a close link between die swell and foaming during the extrusion process. The anisotropic expansion of foam was found to be strongly affected by die swell, which significantly impacts the shape and density of the final product.
Article
Engineering, Chemical
Kui Liu, Minjie Wang, Hongxia Li, Danyang Zhao, Yifei Jin
Summary: The study explores the impact of characteristic scale on the swelling behavior of viscoelastic melt in micro-extrusion. Results indicate that an increase in characteristic scale reduces swell ratio and delays reaching equilibrium, while a decrease leads to larger changes in velocity field and faster stress field relaxation. The location of maximum velocity layer shifts towards the mandrel wall with increasing characteristic scale, and higher flow rates result in greater swell ratio. Elastic effects are more influential than viscous effects in determining viscoelastic swell behavior.
POLYMER ENGINEERING AND SCIENCE
(2021)
Article
Engineering, Environmental
Sujit Sharma, Mohit Goswami, Arghya Deb, Bhojraj Padhan, Santanu Chattopadhyay
Summary: The study explores the use of co-extrusion for manufacturing long polymeric profiles with two different textural rubber compounds, identifying the thermal and rheological parameters of EPDM rubber-based compounds and achieving accurate predictions through simulation. The numerical results were further cross-verified with experimental data, demonstrating a high level of efficiency and agreement.
CHEMICAL ENGINEERING JOURNAL
(2021)
Review
Materials Science, Multidisciplinary
Arit Das, Eric L. Gilmer, Saeid Biria, Michael J. Bortner
Summary: Material extrusion (MatEx) is an additive manufacturing technique for fabricating three-dimensional objects based on CAD files, and understanding the rheological properties of polymeric feedstocks is crucial. The rheological characteristics of polymers during MatEx process govern interlayer welding and mechanical performance of printed parts.
ACS APPLIED POLYMER MATERIALS
(2021)
Article
Physics, Applied
N. Sheoran, B. Boland, S. Thornton, J. R. Bochinski, L. I. Clarke
Summary: Chemically compatible additives were used to increase the ionic conductivity of polyethylene melts, resulting in a significant decrease in fiber diameter during unconfined electrospinning. This approach was confirmed for viscous melts with different conductivities and viscosities, suggesting its generality. The relationship between jet radius and conductivity followed a power law exponent of -1/4, similar to the exponent obtained from needle-based electrospinning. The article also discusses the connection between larger length scales and fluid properties.
APPLIED PHYSICS LETTERS
(2023)
Article
Chemistry, Medicinal
Wenxiu Tian, Xue Li, Wenjie Li, Aile Xue, Minyue Zheng, Xiao Lin, Yanlong Hong
Summary: This study explored the correlation between the surface roughness of extrudates and the molding quality of pellets. It was found that the addition of water influenced the properties of the extrudates, with traditional Chinese medicine formulations resulting in rougher surfaces. However, at optimal water addition levels, the quality of the pellets prepared from these formulations was ideal.
Article
Polymer Science
Ahmad Fakhari, Zeljko Tukovic, Olga Sousa Carneiro, Celio Fernandes
Summary: Extrudate swell, a phenomenon that occurs in polymer processing, can be effectively modeled numerically to support design tasks. An improved interface tracking algorithm and the PISO algorithm for grid movement have been developed, showing accuracy and robustness in simulating extrudate swell flows. Inertia's role in extrudate swell has been studied, with the solver's results demonstrating good agreement with reference data in the scientific literature.
Article
Mechanics
Toshan Lal Sahu, Ujjwal Chetan, Jagannath Mahato, Prabir Kumar Kar, Prasanta Kumar Das, Rajaram Lakkaraju
Summary: In this study, the breakup morphology of a swirling liquid jet is analyzed through numerical simulations. It is found that viscous forces dominate the flow and suppress the Kelvin-Helmholtz instability at the interface, while centrifugal instability destabilizes the helical rim and leads to the formation of droplets.
Article
Materials Science, Ceramics
Maria Chromcikova, Branislav Hruska, Roman Svoboda, Marek Liska, Aleksandra Nowicka, Els Bruneel, Klaartje De Buysser
Summary: Nine compositional series of glass-forming melts were studied, with ZnO and K2O identified as the components mostly influencing surface tension.
JOURNAL OF NON-CRYSTALLINE SOLIDS
(2021)
Article
Physics, Fluids & Plasmas
Vlasis Mitsoulas, Stylianos Varchanis, Yannis Dimakopoulos, John Tsamopoulos
Summary: The response of the endothelial glycocalyx (EG) to variations of the hemodynamic environment is crucial for maintaining blood vessel permeability and blood component balance. This study investigates the influence of geometric features and mechanical properties of individual fibers on the apparent permeability of EG, using modeling and experimental predictions.
PHYSICAL REVIEW FLUIDS
(2022)
Article
Physics, Fluids & Plasmas
D. Pettas, G. Karapetsas, Y. Dimakopoulos, J. Tsamopoulos
Summary: We investigated the flow of a Newtonian liquid film over an inclined hydrophobic wall textured with periodical microgrooves. Through numerical simulations and theoretical analysis, we explored the stability of the liquid flow under the influence of inertia, viscous, and capillary forces, as well as substrate wettability and geometric characteristics.
PHYSICAL REVIEW FLUIDS
(2022)
Article
Computer Science, Interdisciplinary Applications
Chris Dritselis, George Karapetsas
Summary: Two new control volume solvers, multiFluidInterFoam and rheoMultiFluidInterFoam, are presented for the simulation of Newtonian and non-Newtonian n-phase flows, fully accounting for interfacial tension and contact-angle effects for each phase. The solvers improve the efficiency and accuracy of surface tension driven flows, and the rheoMultiFluidInterFoam solver is capable of fully considering complex non-Newtonian effects.
COMPUTERS & FLUIDS
(2022)
Article
Mechanics
Konstantina Psaraki, Vlasios Mitsoulas, Stavros Pavlou, Yannis Dimakopoulos
Summary: We investigated the effects of variations in critical shearing parameters on the response of an endothelial cell monolayer. Specifically, we developed a rheometric emulation method that accounts for the interaction between blood plasma and deformable endothelial cells. Our findings provide quantitative predictions for the stresses on different cell compartments and their structural changes. In addition, we highlight the significance of the variation of Wall Shear Stress (WSS) along the cell membrane and its dependence on cell shape.
Article
Computer Science, Interdisciplinary Applications
Alexandros Syrakos, Oliver Oxtoby, Eugene de Villiers, Stylianos Varchanis, Yannis Dimakopoulos, John Tsamopoulos
Summary: This paper proposes a series of gradient reconstruction schemes based on orthogonal or oblique projections to solve over-determined systems. The schemes include weighted least-squares gradients and variations of consistent Green-Gauss gradients. Through testing and comparison on various grids, it is found that there may be numerical instability on high aspect ratio grids, and guidelines are provided for safely using weights within the least squares methods.
MATHEMATICS AND COMPUTERS IN SIMULATION
(2023)
Article
Energy & Fuels
Vasileios Georgitzikis, Dionisis Pettas, Konstantinos Loukas, Georgios Mavropoulos
Summary: This paper introduces a new engine kinematic mechanism as a potential replacement for the traditional crankshaft mechanism. The initial experimental results show that the new engine has promising prospects, particularly in hybrid automotive applications.
Article
Mechanics
G. Esposito, Y. Dimakopoulos, J. Tsamopoulos
Summary: This study investigates the motion of a viscous drop rising in a viscoelastic liquid with elastic and shear thinning effects. The numerical predictions are validated by comparing them with experimental data, showing agreement in terminal velocities and drop shapes. The interplay of viscous, elastic, and capillary forces is explored through a parametric study. Key findings include the transformation of a spherical drop into one with a cusp and an extended tail due to increasing material elasticity, and the confirmation that viscoelastic materials can encapsulate liquid drops generated by liquid filaments.
JOURNAL OF NON-NEWTONIAN FLUID MECHANICS
(2023)
Article
Chemistry, Multidisciplinary
Eleni Kouni, Pantelis Moschopoulos, Yannis Dimakopoulos, John Tsamopoulos
Summary: When a charged particle moves through a solution, the surrounding electric double layer deforms in response to fluid motion, creating an electric force opposite to the particle's direction of motion, which reduces its settling velocity. This phenomenon combines fluid mechanics and electrodynamics, and differs from the classical problem of an uncharged sedimenting particle. Its applications range from mechanical to biomedical fields.
Article
Physics, Fluids & Plasmas
A. Kordalis, D. Pema, S. Androulakis, Y. Dimakopoulos, J. Tsamopoulos
Summary: This study investigates the buoyancy-driven rise and interaction between two coaxial bubbles in an elastoviscoplastic material. The development of a shear stress bridge between the bubbles decreases drag force on the trailing bubble, initiating their approach. The material's solidlike behavior makes it softer for the trailing bubble. Normal stresses primarily extend the bubbles, but the leading bubble eventually adopts a less favorable shape that slows it down. Geometric characteristics and material properties also affect the approach time.
PHYSICAL REVIEW FLUIDS
(2023)
Article
Chemistry, Physical
P. Moschopoulos, E. Kouni, K. Psaraki, Y. Dimakopoulos, J. Tsamopoulos
Summary: This study investigates the stretching dynamics of a yield stress material with both elastic and viscoplastic behavior. The material forms a cylindrical liquid bridge initially and then a neck when subjected to stretching between coaxial disks. Theoretical analysis shows that an elongated thin neck is formed due to elasticity, connecting the upper and lower parts of the bridge. The findings suggest that the consideration of elasticity affects the pinching times and filament length in filament stretching procedures of yield stress materials.
Article
Mechanics
Mateus C. Guimaraes, Fernando T. Pinho, Carlos B. da Silva
Summary: A new theory is proposed to describe the conformation state of polymer chains in free turbulent shear flows of viscoelastic fluids. The theory shows the existence of minimum and maximum solvent dissipation reduction asymptotes and four different polymer deformation regimes, based on self-similarity arguments and new scaling relations for the turbulent flux of conformation tensor. In addition, analytical solutions for the self-similar transverse profiles of the conformation tensor components are obtained. The theory is validated through excellent agreement with direct numerical simulations employing the FENE-P rheological model.
JOURNAL OF NON-NEWTONIAN FLUID MECHANICS
(2024)
