A mathematical model is developed for electro-osmotic peristaltic pumping of a non-Newtonian liquid in a deformable micro-channel. Stokes' couple stress fluid model is employed to represent realistic working liquids. The Poisson-Boltzmann equation for electric potential distribution is implemented owing to the presence of an electrical double layer (EDL) in the micro-channel. Using long wavelength, lubrication theory and Debye-Huckel approximations, the linearized transformed dimensionless boundary value problem is solved analytically. The influence of electro-osmotic parameter (inversely proportional to Debye length), maximum electro-osmotic velocity (a function of external applied electrical field) and couple stress parameter on axial velocity, volumetric flow rate, pressure gradient, local wall shear stress and stream function distributions is evaluated in detail with the aid of graphs. The Newtonian fluid case is retrieved as a special case with vanishing couple stress effects. With increasing the couple stress parameter there is a significant increase in the axial pressure gradient whereas the core axial velocity is reduced. An increase in the electro-osmotic parameter both induces flow acceleration in the core region (around the channel centreline) and it also enhances the axial pressure gradient substantially. The study is relevant in the simulation of novel smart bio-inspired space pumps, chromatography and medical micro-scale devices.

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Electro-osmotic flow of couple stress fluids in a micro-channel propagated by peristalsis

This article presents an analysis of a long journal bearing with a double-layer porous lubricant film using couple stress and Newtonian fluids. The porous layer with infinite permeability analyzed in this study simulates the surface layer. The Brinkman model was utilized to model the flow in the porous region. The effects of couple stresses were analyzed based on Stokes microcontinuum theory. A double-layer porous lubricant film configuration, with a low-permeability porous layer on top of a high-permeability bearing adherent porous layer, improved the journal bearing performance characteristics. A surface porous layered lubricant film configuration increased the load-carrying capacity and reduced the coefficient of friction in a journal bearing.

Analysis of Journal Bearing with Double-Layer Porous Lubricant Film: Influence of Surface Porous Layer Configuration

Mechanical and tribological properties of poly(hydroxyethyl methacrylate) hydrogels as articular cartilage substitutes

We make an effort to analyze the behavior of squeeze film characteristics of different finite plates with couple stress fluid in the presence of a transverse magnetic field. On the basis of the Stokes couple stress fluid model and hydromagnetic flow model, a modified Reynold's equation is derived, which is solved by using appropriate boundary conditions to obtain squeeze film pressure, load-carrying capacity, and squeeze film time. The graphical representation of the results suggests that the different bearing systems register an enhanced performance with couple stresses compared to that of a bearing system working with a conventional lubricant in the presence of a transverse magnetic field. It is observed that the effect of applied magnetic field on the squeeze film lubrication between different finite plates with conducting couple stress fluids is to increase the load-carrying capacity significantly and to delay the time of approach compared to the corresponding nonconducting Newtonian case. It is seen ...

Modified Reynolds Equation for Different Types of Finite Plates with the Combined Effect of MHD and Couple Stresses

A coupled contact model of cartilage lubrication in the mixed-mode regime under static compression

Non-Newtonian couple stress poroelastic squeeze film

On the basis of the Stokes microcontinuum theory, a numerical study of the combined effects of non-Newtonian couple stress and viscous shear forces on porous squeeze film behavior for parallel circular plates is presented in this article. A modified Reynolds equation governing the film pressure is derived using the Stokes constitutive equations to account for lubricant couple stress effects due to the presence of additives or suspended particles. The Darcy-Brinkman equations describing the fluid flow within the porous plate are used to account for viscous shearing forces. Numerical solutions for the squeeze film characteristics including film pressure, radial velocity, squeeze velocity, and response time are calculated for various values of the couple stress and viscous shear parameters. The simulation results indicate that the combined effects of couple stresses and viscous shearing forces are considerable.

Combined Non-Newtonian and Viscous Shear Effects on Porous Squeeze Film Behavior

Considering the rotation of ferromagnetic particles, the present study investigates hydrodynamic lubrication by ferrofluids of finite journal bearings using the Shliomis model. A magnetic field created by displaced finite wire is used. A numerical solution for the modified Reynolds equation using the finite difference method is obtained. Static characteristics of finite journal bearings are analysed using three control parameters: rotational viscosity, magnetization and volume concentration of the ferromagnetic particles. It is shown that the pressure, load capacity, attitude angle and side leakage increase and the friction coefficient decreases when increasing the value of each control parameter. Similar trends are also obtained when increasing values of eccentricity for a fixed value of each control parameter except for the decrease of the attitude angle. Copyright © 2016 John Wiley & Sons, Ltd.

Static characteristics of ferrofluid finite journal bearing considering rotational viscosity effect

The present paper deals with a numerical investigation of the hydrodynamic lubrication of a porous squeeze film between two circular discs. To this purpose, the thin film (reduced) Navier Stokes equations and a generalised porous medium model are solved. The numerical results show that the effect of the porous disc is to reduce the lubricating properties of the fluid film. This effect is increased during the squeezing action. In addition, it is shown that the film pressure, the load-carrying capacity and the velocity field based only on the Darcy model are predicted higher than those obtained from the generalised porous medium model. Copyright © 2009 John Wiley & Sons, Ltd.

Mohamed El Khlifi

Papers

Non-Newtonian couple stress poroelastic squeeze film

Combined Non-Newtonian and Viscous Shear Effects on Porous Squeeze Film Behavior

Static characteristics of ferrofluid finite journal bearing considering rotational viscosity effect

A general model for porous medium flow in squeezing film situations

Non-Newtonian effects on porous elastic journal bearings