J.G. Oldroyd's early ideas leading to the modern understanding of wall slip

Ghahramani, Nikoo; Georgiou, Georgios C.; Mitsoulis, Evan; Hatzikiriakos, Savvas G.

doi:10.1016/j.jnnfm.2021.104566

Cited by 14 publications

(6 citation statements)

References 47 publications

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“…The conventional no-slip boundary condition at the wall is known to not always apply to non-Newtonian fluids. − The occurrence of slip results in various phenomena including a drop in wall shear stress (or pressure drop in a capillary), , a dependency of the wall shear stress on the gap or diameter at a constant apparent shear rate, , and a discontinuous flow curve for pressure-driven capillary data. ,, Despite a great deal of effort to understand the slip behavior of polymer melts, its relation to the structure of polymers is not yet fully understood. ,,, A thorough understanding of the slip behavior of polymers is crucial to correct the rheometric data for the effect of slip , and for the correct design of industrial processes like extrusion. , …”

Section: Introductionmentioning

confidence: 99%

“…1,3,7 Despite a great deal of effort to understand the slip behavior of polymer melts, its relation to the structure of polymers is not yet fully understood. 1,3,8,9 A thorough understanding of the slip behavior of polymers is crucial to correct the rheometric data for the effect of slip 1,4 and for the correct design of industrial processes like extrusion. 1,2 Entanglements between polymer chains play a crucial role in the occurrence and characteristics of slip.…”

Section: ■ Introductionmentioning

confidence: 99%

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Wall Slip of Bimodal Polyethylene

2022

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Cohesive slip occurs in the flow of linear polyethylene melts over high-surface-energy walls, changing both the velocity profile and the stress. The slip behavior of bimodal molecular weight distribution (MWD) polymers is different from that of unimodal MWD polymers and is not yet fully understood. Here, we study a set of four polyethylenes with a systematic change in MWD, making it possible to examine the effect of bimodal molecular weight distribution on the slip behavior. The results show that slip in simple shear occurs over a broad range of stress. Higher short-chain content increases slip velocity at all stresses within the transition region before strong slip is fully engaged. At stresses where strong slip is fully engaged, the slip behavior is independent of molecular weight distribution. The stress at which the slip velocity is independent of MWD lowers as the short-chain content increases. Disentanglement between the adsorbed and mobile chains is evaluated via the change in friction coefficient with stress. This analysis reveals that the degree of entanglement at the cohesive failure interface drops sharply in the transition region. This region is only accessible in simple shear and not in capillary flows. Finally, melt rupture was observed to occur after the onset of slip for certain conditions.

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Section: Introductionmentioning

confidence: 99%

Section: ■ Introductionmentioning

confidence: 99%

Wall Slip of Bimodal Polyethylene

2022

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“…The no-slip boundary condition at the (rigid) solid–fluid interface remains the prevailing and unquestioned orthopraxy in many fluid dynamics problems. However, during the past quarter century, a violation of the no-slip boundary assumption for the flow of Newtonian and non-Newtonian materials/fluids near the solid walls has been demonstrated through a large number of experiments. ,− The phenomenon of slip refers to any situation at which the flow tangential velocity is different from that of the wall immediately at the contact zone . Understanding the slip phenomenon is of raising interest due to its practical applications in microfluidics, , porous media, − biological processes, , electro-osmotic flows, , extrusion through dies, lubrication, , and sedimentation .…”

Section: Slip Phenomenonmentioning

confidence: 99%

Modeling of Shear Flows over Superhydrophobic Surfaces: From Newtonian to Non-Newtonian Fluids

Rahmani,

Larachi,

Taghavi

2024

ACS Eng. Au

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The design and use of superhydrophobic surfaces have gained special attentions due to their superior performances and advantages in many flow systems, e.g., in achieving specific goals including drag reduction and flow/droplet handling and manipulation. In this work, we conduct a brief review of shear flows over superhydrophobic surfaces, covering the classic and recent studies/ trends for both Newtonian and non-Newtonian fluids. The aim is to mainly review the relevant mathematical and numerical modeling approaches developed during the past 20 years. Considering the wide ranges of applications of superhydrophobic surfaces in Newtonian fluid flows, we attempt to show how the developed studies for the Newtonian shear flows over superhydrophobic surfaces have been evolved, through highlighting the major breakthroughs. Despite the fact that, in many practical applications, flows over superhydrophobic surfaces may show complex non-Newtonian rheology, interactions between the non-Newtonian rheology and superhydrophobicity have not yet been well understood. Therefore, in this Review, we also highlight emerging recent studies addressing the shear flows of shear-thinning and yield stress fluids in superhydrophobic channels. We focus on reviewing the models developed to handle the intricate interaction between the formed liquid/air interface on superhydrophobic surfaces and the overlying flow. Such an intricate interaction will be more complex when the overlying flow shows nonlinear non-Newtonian rheology. We conclude that, although our understanding on the Newtonian shear flows over superhydrophobic surfaces has been well expanded via analyzing various aspects of such flows, the non-Newtonian counterpart is in its early stages. This could be associated with either the early applications mainly concerning Newtonian fluids or new complexities added to an already complex problem by the nonlinear non-Newtonian rheology. Finally, we discuss the possible directions for development of models that can address complex non-Newtonian shear flows over superhydrophobic surfaces.

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“…To detect wall slip effects, the apparent viscosity of the non‐Newtonian medium is plotted against the reciprocal of the wall shear stress for various rheometers with different geometries. [ 39,40 ] By applying the Oldroyd approach, a correction of the rheological data is possible, which is shown by Ghahramani et al [ 40 ] for a thermoplastic vulcanizate.…”

Section: Wall Slip Modelsmentioning

confidence: 99%

Improvement of a method for the correction of wall slip effects within the rheological measurements of filled rubber compounds

Kleinschmidt

Schöppner

2023

SPE Polymers

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Rubber compounds have an increased tendency to flow anomalies depending on the compound ingredients and the processing parameters. Due to wall slip effects, rheological material measurements and the material parameters derived from them are affected by errors, since the fundamental analytical and numerical calculation approaches assume wall adhesion. In the literature, various approaches for the description of wall slip effects exist, which partially lead to negative slip velocities as well as slip volume flows that exceed the total volume flow in the capillary. The purpose of this article is the improvement of an analytical model for the determination of slip velocities for both laboratory and near-process rheological investigations. A comparison shows the limitations of the established wall slip correction methods and the possibilities of the improved correction method.

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J.G. Oldroyd's early ideas leading to the modern understanding of wall slip

Cited by 14 publications

References 47 publications

Wall Slip of Bimodal Polyethylene

Wall Slip of Bimodal Polyethylene

Modeling of Shear Flows over Superhydrophobic Surfaces: From Newtonian to Non-Newtonian Fluids

Improvement of a method for the correction of wall slip effects within the rheological measurements of filled rubber compounds

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