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Wall Slip (wall + slip)

Distribution by Scientific Domains
Engineering50%
Chemistry21%

Selected Abstracts

Multi-linearity algorithm for wall slip in two-dimensional gap flow

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 12 2007
G. J. Ma
Abstract Wall slip has been observed in a micro/nanometer gap during the past few years. It is difficult to make a mathematical analysis for the hydrodynamics of the fluid flowing in a gap with wall slip because the fluid velocity at the liquid,solid interface is not known a priori. This difficulty is met especially in a two-dimensional slip flow due to the non-linearity of the slip control equation. In the present paper we developed a multi-linearity method to approach the non-linear control equation of the two-dimensional slip gap flow. We used an amended polygon to approximate the circle yield (slip) boundary of surface shear stress. The numerical solution does not need an iterative process and can simultaneously give rise to fluid pressure distribution, wall slip velocity and surface shear stress. We analysed the squeeze film flow between two parallel discs and the hydrodynamics of a finite slider gap with wall slip. Our numerical solutions show that wall slip is first developed in the large pressure gradient zone, where a high surface shear stress is easily generated, and then the slip zone is enlarged with the increase in the shear rate. Wall slip dramatically affects generation of the hydrodynamic pressure. Copyright © 2006 John Wiley & Sons, Ltd. [source]

Quadratic programming algorithm for wall slip and free boundary pressure condition

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 2 2006
C. W. Wu
Abstract Wall slip is often observed in a highly sheared fluid film in a solid gap. This makes a difficulty in mathematical analysis for the hydrodynamic effect because fluid velocity at the liquid,solid interfaces is not known a priori. If the gap has a convergent,divergent wedge, a free boundary pressure condition, i.e. Reynolds pressure boundary condition, is usually used in the outlet zone in numerical solution. This paper, based on finite element method and parametric quadratic programming technique, gives a numerical solution technique for a coupled boundary non-linearity of wall slip and free boundary pressure condition. It is found that the numerical error decreases with the number of elements in a negative power law having an index larger than 2. Our method does not need an iterative process and can simultaneously gives rise to fluid film pressure distribution, wall slip velocity and surface shear stress. Wall slip always decreases the hydrodynamic pressure. Large wall slip even causes a null hydrodynamic pressure in a pure sliding solid gap. Copyright © 2005 John Wiley & Sons, Ltd. [source]

Multi-linearity algorithm for wall slip in two-dimensional gap flow

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 12 2007
G. J. Ma
Abstract Wall slip has been observed in a micro/nanometer gap during the past few years. It is difficult to make a mathematical analysis for the hydrodynamics of the fluid flowing in a gap with wall slip because the fluid velocity at the liquid,solid interface is not known a priori. This difficulty is met especially in a two-dimensional slip flow due to the non-linearity of the slip control equation. In the present paper we developed a multi-linearity method to approach the non-linear control equation of the two-dimensional slip gap flow. We used an amended polygon to approximate the circle yield (slip) boundary of surface shear stress. The numerical solution does not need an iterative process and can simultaneously give rise to fluid pressure distribution, wall slip velocity and surface shear stress. We analysed the squeeze film flow between two parallel discs and the hydrodynamics of a finite slider gap with wall slip. Our numerical solutions show that wall slip is first developed in the large pressure gradient zone, where a high surface shear stress is easily generated, and then the slip zone is enlarged with the increase in the shear rate. Wall slip dramatically affects generation of the hydrodynamic pressure. Copyright © 2006 John Wiley & Sons, Ltd. [source]

Quadratic programming algorithm for wall slip and free boundary pressure condition

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 2 2006
C. W. Wu
Abstract Wall slip is often observed in a highly sheared fluid film in a solid gap. This makes a difficulty in mathematical analysis for the hydrodynamic effect because fluid velocity at the liquid,solid interfaces is not known a priori. If the gap has a convergent,divergent wedge, a free boundary pressure condition, i.e. Reynolds pressure boundary condition, is usually used in the outlet zone in numerical solution. This paper, based on finite element method and parametric quadratic programming technique, gives a numerical solution technique for a coupled boundary non-linearity of wall slip and free boundary pressure condition. It is found that the numerical error decreases with the number of elements in a negative power law having an index larger than 2. Our method does not need an iterative process and can simultaneously gives rise to fluid film pressure distribution, wall slip velocity and surface shear stress. Wall slip always decreases the hydrodynamic pressure. Large wall slip even causes a null hydrodynamic pressure in a pure sliding solid gap. Copyright © 2005 John Wiley & Sons, Ltd. [source]

Viscosity corrections for concentrated suspension in capillary flow with wall slip

AICHE JOURNAL, Issue 6 2010
Z. Y. Wang
Abstract Corrections for viscosity measurements of concentrated suspension with capillary rheometer experiments were investigated. These corrections include end effects, Rabinowitsch effect, and wall slip. The effects of temperature, particle concentration, and contraction ratio on the end effects were studied and their effects were accounted for using an entrance and exit losses model. The non-Newtonian effect and the nonlinearity of slip velocity against wall shear stress were described using a slip model. The true viscosity of a concentrated suspension with glass powder suspended in a non-Newtonian binder system was calculated as a function of shear rate and effective particle concentration, taking into consideration particle migration, which is calculated by a diffusive numerical model. Particle size was found to affect significantly the viscosity of the suspension with viscosity decreasing with increasing particle size, which can be reflected by a decrease in the value of the power-law index in the Krieger model. © 2009 American Institute of Chemical Engineers AIChE J, 2010 [source]

OSCILLATING VANE GEOMETRY FOR SOFT SOLID GELS AND FOAMS

JOURNAL OF TEXTURE STUDIES, Issue 6 2002
C. SERVAIS
ABSTRACT Several relationships between the torque and the stress exist for the vane geometry, but only a few equations have been proposed for the relationship between angular displacement and strain. In this study, an expression based on the infinite gap approximation for concentric cylinders is used and well-defined reference data are compared to oscillating vane data to validate the assumptions used. Gelatin gels are used for their property to stick to the wall and carrageenan gels are used to show that wall slip does not occur with oscillating vanes in serrated cup geometries. Shaving foams are used as a model low density, time and shear stable foam, which resists irreversible damage when loaded between serrated parallel plates. Results show that the assumptions used for the determination of stress and strain with the vane provide material viscoelastic properties that are not significantly different from reference values as obtained with concentric cylinders and parallel plates. [source]

An analytical model for steady coextrusion of viscoplastic fluids in thin slit dies with wall slip

POLYMER ENGINEERING & SCIENCE, Issue 4 2010
Dilhan M. Kalyon
Coextrusion is widely used to fabricate multilayered products with each layer providing a separate functionality, including barrier resistance to gases, strength, and printability. Here an analytical model of the coextrusion die flow of two incompressible, viscoplastic fluids in a slit die, subject to nonlinear wall slip and under fully developed and isothermal conditions, is developed to allow the prediction of the steady-state velocity and shear stress distributions and the flow rate versus pressure gradient relationship. The resulting model is applied to the coextrusion of two layers of viscoplastic fluids in a thin rectangular slit die (slit gap, h , slit width, W). The analytical solution recognizes a number of distinct flow conditions (eleven cases) that need to be treated separately. The solutions for all eleven cases are provided along with an apriori identification methodology for the determination of the applicable case, given the shear viscosity and wall slip parameters of the two viscoplastic fluids, the slit geometry and the flow conditions. Simplifications of the model would provide the solutions for the fully developed and isothermal coextrusion flows of any combination of Hershel-Bulkley, Bingham, power-law and Newtonian fluids with or without wall slip at one or both walls of the slit die. POLYM. ENG. SCI., 2010. © 2009 Society of Plastics Engineers [source]

Thickness uniformity of HDPE blown film: Relation to rheological properties and density

POLYMER ENGINEERING & SCIENCE, Issue 5 2004
Hiroyuki Higuchi
Previous work has elucidated that the wall slip velocity and viscosity of polymer melts influence the thickness uniformity of blown film. The present study investigates the effects of the stress dependence of wall slip, the shear thinning and the density on the uniformity. We have prepared high-density polyethylenes with a variety of molecular weight distributions, which have different rheological properties. Examination of the thickness uniformity of their blown film has shown that the uniformity is correlated with wall slip velocity, the stress dependence of the velocity, melt viscosity, shear thinning and density; the coefficient of the correlation is determined to be 0.990. The reason why the stress dependence of wall slip and the shear thinning affect the uniformity is explained in terms of polymer melt flow behavior in a die, while the effect of density is interpreted considering bubble fluctuation in the blow-up process. Polym. Eng. Sci. 44:965,972, 2004. © 2004 Society of Plastics Engineers. [source]