Influence Of Wall Slip Research Articles

Influence of wall-slip on material removal in abrasive flow machining

Abrasive flow machining (AFM) process, as a widely known technique for finishing internal surfaces of complex parts, can significantly improve the performance and reliability of components in numerous industries. Prediction of material removal rate (MRR) is a vital task in AFM process because it significantly affects the efficiency and cost-effectiveness of the process. In-depth studies about the influence of input parameters on material removal in AFM process, however, are limited. In this paper, the mechanism of material removal was investigated, and a MRR modelling was then established in which viscoelastic extrusion modelling with wall slip conditions was employed in AFM process. A novel fixture with gradient shear flow channel was designed. MRR obtained by simulations and experiment showed a reasonable agreement. Finally, parameters, including abrasive media pressure, velocity and shape geometry of flow channel, were identified as key factors affecting MRR in AFM process. Established computational fluid dynamics (CFD) analysis and MRR modelling can be a powerful tool to determine MRR in future AFM process.

Influence of wall slip in the radial displacement of a yield strength material in a Hele–Shaw cell

The growth of viscous fingers in the radial displacement of a yield strength material confined between the plates of a Hele–Shaw cell is investigated. The apparatus is filled with an aqueous solution of Carbopol® before air is injected to start the displacement process. In addition to striking fingering patterns, we identify unyielded residuals of the Carbopol solution arrested on the plates' surfaces with the assistance of digital mobile microscopes placed above the top plate. These unyielded residuals are subjected to slip conditions on the surface walls and appear in different forms. The experimental observations are correlated with the wall slip behavior detected in rheometric measurements, i.e., observed in the flow curve for shear rates below a critical value. This correlation provides an estimate of a critical propagating radius beyond which shear rates drop to values lower than the critical one, and the influence of wall slip becomes significant. We observe that these residuals are uniformly distributed and appear as thin films where the radii are smaller than the critical value and the wall slip is minimum. However, in locations where the radii are larger than the critical one, the residuals turn into isolated blobs of different sizes, which may propagate in a stick-slip motion radially downstream inside the air fingers. In addition, we observe that the morphology of residuals depends on the gap width between the plates, the injection rate of the invading air, the yield strength of the Carpobol solution, and the wettability conditions of the surface walls.

Temperature-dependent wall slip of Newtonian lubricants

We discuss (i) the measurement, (ii) interpretation and (iii) technical impact of temperature-dependent wall slip and its activation energy for polar and non-polar hydrocarbon Newtonian fluids moving relative to machined metal surfaces. A newly developed apparatus, the slip length tribometer (SLT), overcomes the drawbacks of existing measurement devices in terms of characterising relevant rough surfaces by measuring the slip length at different temperatures over a sufficiently large wetted area. The experimental data show that the bulk viscosity and slip length at the fluid–metal interface is independent of the shear rate up to $10^5\,\mathrm {s}^{-1}$ , being consistent with recent results from molecular dynamics simulations by Mehrnia & Pelz (J. Mol. Liq., vol. 336, 2021, 116589). Furthermore, the activation energies for wall slip and bulk shear determined by means of the SLT differ by a factor of two, i.e. $E_{\lambda }\approx 0.5 E_\mu$ for non-polar hydrocarbon molecules sliding relative to metal walls. This difference is explained by a generalised Eyring model applied to wall slip. The paper closes with the impact of wall slip on Sommerfeld's similarity theory of tribology and the resulting Stribeck curve (Sommerfeld, Z. Math. Phys., vol. 50, 1904, pp. 97–155; Z. Tech. Phys., vol. 2. Jahrg., 1921; Mechanik der deformierbaren Medien, 1944, Akademische Verlagsgesellschaft Becker & Erler). For this purpose, Reynolds’ equation generalised for wall slip is solved in combination with the experimentally determined constitutive relations for bulk shear and wall slip to predict typical characteristics of journal bearings. The results show that, for a typical journal bearing, where the ratio of slip length to average bearing clearance is of the order of $10^{-2}$ , the influence of wall slip on both load-carrying capacity and dissipation is not negligible. This work combines nanofluidics and tribology in order to provide methods and knowledge for e.g. tailor-made fluids and interfaces.

Analysis of third‐grade liquid under the influence of wall slip and variable fluid properties in an inclined peristaltic channel

AbstractThe current model investigates the effect of wall slip on third‐grade liquid flow through an inclined peristaltic channel. The variation in viscosity and thermal conductivity are taken into account, along with wall properties. The governing equations are simplified using long wavelength and small Reynolds number approximations. The transformed equations are solved by using the perturbation technique. Physiological quantities such as velocity, streamlines, temperature, and concentration are obtained for different parameters of interest. The findings show that increasing the variable viscosity and slip term value improves the velocity profile. Furthermore, elasticity factors help flow, but damping causes fluid particles to slow down. Similarly, when the slip, variable viscosity, and inclination parameter values rise, the size of the trapped bolus grows, resulting in more bolus forms. Furthermore, the inclusion of variable properties helps understand the complex rheological properties of blood flowing through narrow or micro arteries.

Influence of wall slip, thixotropy and lubrication regime on the instrumental sensory evaluation of topical formulations.

Drawing parallels from rheotribology can be used to develop a robust instrumental protocol for non-subjective characterization, product development and design of topical dosage forms with desired sensory attributes. However, instrumental characterization of cosmetic products can be influenced by the measurement protocol, thixotropy, flow anomalies like shear banding or wall slip and nature of the film formed on the skin surface. In this study, we evaluated the influence of above parameters on the instrumental sensory evaluation of 12 topical formulations of different galenic forms. Oscillatory strain sweep measurements (SAOS and LAOS) were performed to investigate the influence of frequency and wall slip on the material parameters. The textural attributes at different consumer touchpoints were evaluated by accounting time-dependent simulation of viscoelastic flow. Further, the influence of film thickness and sample drying on the tactile properties of the topical formulations were studied on a non-biological skin model using a sliding probe tribometer. The study shows that the flow properties of the semi-solid formulations depend on the timescale of the problem. A few formulations exhibited wall slip to varying degrees in the linear viscoelastic regime where the behaviour was found not to be characteristic of a particular topical dosage form. The material functions obtained from the Lissajous plots suggest that the non-linear flow behaviour of different galenic forms is least influenced by the boundary conditions imposed by the measurement geometry. The results were statistically analysed using principal component analysis where the attributes used for discriminating skin creams during pick up and rub out are found to be closely associated with non-linear rheology. The friction coefficient exhibited speed dependence where it formed different parametric group with rheological data depending on the lubrication regime. The study highlights that correlations are possible amongst rheological, tribological and instrumental textural analysis data, which can act an impetus for the development of models to predict attributes that drive perception at different consumer touchpoints. However, the choice of instrumental settings, anomalies associated with rheological measurements and friction dependence on a number of parameters can influence the model prediction.

The effect of wall slip on the dewetting of ultrathin films on solid substrates: Linear instability and second-order lubrication theory

The influence of wall slip on the instability of a non-wetting liquid film placed on a solid substrate is analyzed in the limit of negligible inertia. In particular, we focus on the stability properties of the film, comparing the performance of the three lubrication models available in the literature, namely, the weak, intermediate, and strong slip models, with the Stokes equations. Since none of the aforementioned leading-order lubrication models is shown to be able to predict the growth rate of perturbations for the whole range of slipping lengths, we develop a parabolic model able to accurately predict the linear dynamics of the film for arbitrary slip lengths.

Influence of wall slip and jump in wall temperature on transport of heat energy in hybrid nanofluid

It is the first time that partial slip and jump in wall temperature during transfer of thermal energy in hybrid nanofluid are considered simultaneously. Modeling of a considered phenomenon is done, and numerical treatment is done by FEM in order to analyze the impact of partial slip and jump in wall temperature on the transport of energy. It is observed that wall momentum diffuses into nanofluid faster than its diffusion in hybrid nanofluid in the presence of partial slip. Thermal performance of hybrid mononanofluid is greater than that of nanofluid. It is also noted that hybrid nanofluid exerts less shear stress than the shear stress that of mononanofluid. Hence, the use of hybrid nanofluid is beneficial in two ways (1) its thermal performance is higher than the base fluid or nanofluid and (2) the hybrid nanofluid exerts less shear stress on the wall. Therefore, the use of hybrid particles is recommended to optimize the thermal performance of the working fluid.

Creating material data for thermoset injection molding simulation process

Thermoset material data for reactive injection molding simulation process is found in limited sources and seldom available from data bank of simulation tools because of complication not only in rheological and thermal properties measurement but also in writing optimization algorithm to model rheological and thermal mathematical equations. In this paper, rheological and thermal properties of thermoset injection molding compounds were successfully measured. In addition, a numerical method was developed to create material data of thermoset injection molding compounds, which was directly imported into a simulation tool, namely, Moldex3D to investigate its application in thermoset injection molding simulation process. Furthermore, a strong slip phenomenon on the interface between thermoset melt and wall surface which was investigated and detected during injection molding experiments was taken into account in the filling simulation process. The computation was found to be in good agreement with the experimental results, indicating that the new generated material data is reasonable and the influence of wall slip on the mold filling characterization of thermoset injection compounds during simulation process is not ignorable.

Numerical Simulation of Extrusion Molding of Single - Hole Propellant

In order to improve the simulation accuracy of single hole nitroguanidine propellant extrusion molding process, the influence of wall slip on the extrusion process was studied. The finite element method was used to simulate the extrusion forming of single pore nitroguanidine. The power law constitutive equation considering the effect of wall slip was constructed to calculate the slip factor and non-Newtonian index , the influence of the slip coefficient on the pressure field, velocity field and shear velocity field in the flow channel were analyzed. compared with the actual results, the error of the middle aperture is 1.37%, the arc thickness error is 0.96% and the outer diameter error is 1.12%.Those errors are less then 1.5%. So, the simulation results basically meet the production needs.

Evaluation of wall slip effects on the flow characteristics of petroleum coke–water slurry flow along pipelines

AbstractFlow characteristics of petroleum coke–water slurry (PCWS) were investigated in a slurry transportation facility. True rheological properties, drag reduction, and flow resistances of PCWS under the influence of wall slip were studied using the Tikhonov regularization method. Results show that the shear viscosity is insensitive to changes in the shear rate when the solid loading of PCWS is 59.8 wt%. However, the PCWS of 61.1 wt% exhibits typical dilatant fluid properties. As the shear rate increases, the PCWS of 63.4 wt% initially exhibits shear thinning, and then, the viscosity increases sharply when the shear rate exceeds 250 s−1. In addition, the slurry also displays shear thinning at the shear rates exceeding 600 s−1. Modified friction factor‐generalized Reynolds number correlation is established to describe the resistance properties of a laminar flow of PCWS. When increasing the velocity, the drag reduction produced by the wall slip behavior reduces for the 59.8 wt% PCWS but increases for the 61.1 wt% PCWS. The drag reduction decreases at the outset followed by an increase for the 63.4 wt% PCWS. A decrease in the inner diameter of pipeline could enhance the effect of drag reduction of PCWS flowing in a pipeline. © 2017 Curtin University and John Wiley & Sons, Ltd.

Evaluation of Influence of Wall Slip on Measurement of Rheological Parameters by Means of a Hydrodynamic Measuring System

The technique for processing the output signals of hydrodynamic measuring system of rheological parameters of non-Newtonian fluids is presented in the paper. Hydrodynamic measuring system is built on four serially connected bridge hydrodynamic converters. The paper shows that the error of determination of rheological parameters directly from the experimental flow characteristic in consistent variables is considerable if the non-Newtonian fluid has the effect of wall slip on measuring surfaces of sensors of bridge transducers. The technique for processing the output signals of the measuring system enables to detect the wall slip and to correct the values of fluid flow-rate in each bridge hydrodynamic converter using the values of the wall slip coefficient. Corrected flow characteristic is the basis for the determination of rheological parameters of controlled fluid. The influence of wall slip on the evaluation of rheological model of non-Newtonian fluid and results of measurement of its parameters are analyzed in the paper. It is shown that taking into account the effect of wall slip significantly improves measuring accuracy of rheological parameters. Розглянуто методику опрацювання вихідних сигналів гідродинамічної вимірювальної системи реологічних параметрів неньютонівських рідин. Гідродинамічна вимірювальна система побудована на базі чотирьох послідовно з’єднаних мостових гідродинамічних перетворювачів. У статті показано, що якщо неньютонівська рідина виявляє ефект пристінного ковзання на вимірювальних поверхнях чутливих елементів мостових перетворювачів, то похибки визначення реологічних параметрів безпосередньо за експериментальною витратною характеристикою у консистентних змінних будуть досить значними. Методика опрацювання вихідних сигналів вимірювальної системи дає змогу виявити наявність пристінного ковзання та скорегувати значення витрати рідини у кожному мостовому гідродинамічному перетворювачі, за допомогою знайдених значень коефіцієнта пристінного ковзання. Скорегована витратна характеристика є основою для визначення реологічних параметрів контрольованої рідини. Проаналізований вплив ефекту пристінного ковзання на встановлення реологічної моделі неньютонівської рідини та результати вимірювання її параметрів. Показано, що врахування ефекту пристінного ковзання істотно підвищує точність вимірювання реологічних параметрів.

Influence of wall slip in dilute suspensions

Navier's (1823) slip condition, where the tangential velocity is proportional to the shear stress, may apply at micro-scales for a viscous liquid on walls with modified surfaces, e.g. hydrophobic ones in water. Experiments by Lumma et al (2003) show the difficulties involved in measuring such a slip.At small scales, particle-wall hydrodynamic interactions are important. They are modeled here for a dilute suspension of spherical solid particles near a slip wall. Consider a translating and rotating sphere (on which the no-slip condition applies) in an ambient parabolic flow. Analytical solutions of Stokes equations for the various elementary flow fields were obtained (Feuillebois et al 2009, 2011) as series in bispherical coordinates. The coefficients in the series are solutions of an infinite linear system, which is solved by an extension of Thomas' algorithm, allowing to calculate a large number of terms. Accurate results are available for the force, torque and stresslet on a sphere, velocity of a freely moving sphere and diffusion tensor.The Aris-Taylor dispersion of Brownian particles in a shear flow near a slip wall gives a large bias in the measurement of slip (Vinogradova et al, 2009). It is calculated here from the advection-diffusion equation, using the expressions for the particle velocity and diffusion tensor near a slip wall.

Development Length in Planar Channel Flows of Newtonian Fluids Under the Influence of Wall Slip

This technical brief presents a numerical study regarding the required development length (L=Lfd/H) to reach fully developed flow conditions at the entrance of a planar channel for Newtonian fluids under the influence of slip boundary conditions. The linear Navier slip law is used with the dimensionless slip coefficient k¯l=kl(μ/H), varying in the range 0<k¯l≤1. The simulations were carried out for low Reynolds number flows in the range 0<Re≤100, making use of a rigorous mesh refinement with an accuracy error below 1%. The development length is found to be a nonmonotonic function of the slip velocity coefficient, increasing up to k¯l≈0.1-0.4 (depending on Re) and decreasing for higher k¯l. We present a new nonlinear relationship between L, Re, and k¯l that can accurately predict the development length for Newtonian fluid flows with slip velocity at the wall for Re of up to 100 and k¯l up to 1.

Influence of wall slip on the hydrodynamic behavior of a two-dimensional slider bearing

In the present paper, a multi-linearity method is used to address the nonlinear slip control equation for the hydrodynamic analysis of a two-dimensional (2-D) slip gap flow. Numerical analysis of a finite length slider bearing with wall slip shows that the surface limiting shear stress exerts complicated influences on the hydrodynamic behavior of the gap flow. If the slip occurs at either the stationary surface or the moving surface (especially at the stationary surface), there is a transition point in the initial limiting shear stress for the proportional coefficient to affect the hydrodynamic load support in two opposite ways: it increases the hydrodynamic load support at higher initial limiting shear stresses, but decreases the hydrodynamic load support at lower initial limiting shear stresses. If the slip occurs at the moving surface only, no fluid pressure is generated in the case of null initial limiting shear stress. If the slip occurs at both the surfaces with the same slip property, the hydrodynamic load support goes off after a critical sliding speed is reached. A small initial limiting shear stress and a small proportionality coefficient always give rise to a low friction drag.

The influence of wall slip on yield stress and viscoelastic measurements of cement paste

The influence of wall slip on the shear yield stress and modulus of cement paste was investigated using a rotational rheometer with smooth-walled concentric cylinders and a vane. The results show that the concentric cylinders suffer from slip during yield stress measurements due to the formation of a water-rich layer at the walls of the cylinders. The use of a vane eliminates slip since shearing occurs within the material. Oscillatory tests were conducted to measure the viscoelastic properties of cement paste. The data for the vane and concentric cylinders are in excellent agreement at stresses below the yield point. It is difficult to determine the influence of slip for stress sweep measurements. Frequency sweep data for various materials show the general applicability of the vane method over several decades of modulus.

The influence of wall slip in the measurement of solder paste viscosity

The wall slip phenomena is known to have a significant effect on the measurement of the viscosity of dense suspensions. In the measurement of the viscosity of solder pastes the effect of wall slip is such that the measured viscosity (also called the apparent viscosity) is much lower than the true viscosity of the paste. Therefore, correction needs to be applied to the measured viscosity in order to obtain the true viscosity of the solder paste. In this paper, we present work on the modeling of the influence of wall slip on viscosity measurement, and a model for predicting the true viscosity based on measurements using parallel plate viscometer. The apparent viscosity values measured at two different plate gaps, but at the same applied shear rate (also called the apparent shear rate), is used for predicting the true viscosity, the wall slip velocity and the thickness of the boundary slip layer. The model was validated using results from solder paste samples measured at three different plate gaps (H=0.5 mm, 1.0 mm and 1.5 mm). Our results show that the predicted values of the true viscosity using the data measured at any two gaps are in reasonably good agreement. The results also show that the influence of the wall slip is significant and that the ratio of the predicted viscosity to the apparent viscosity decreases with increasing apparent shear rate.

The flow properties of foam

The rheological behaviour of foam, prepared from an aqueous solution with lauryl sulphate as surfactant, has been measured with a viscometer as a function of the blow ratio, bubble diameter distribution and concentration of the thickener used. The influence of wall slip and of hysteresis effects on the rheological behaviour have been determined. Calculations and measurements pertaining to the pressure drop in pipes have been performed, in which the foam was considered as a compressible pseudoplastic whose rheology depended on blow ratio. The distribution of the foam passing through a closed distribution unit has been studied. This distribution unit consisted of a pipe and a cross‐head distribution slit. Complementary measurements of the flow of foam through narrow slits have been made. The design of a closed foam distribution unit is discussed. The consequences of the choice of several design parameters are examined.

Influence of wall slip on extrudate swell: a boundary element investigation

This paper reports a numerical study of the extrudate swell by a transient Boundary Element Method (BEM). Furthermore the fluid, which is modeled by a differential constitutive equation, is allowed to slip at the wall, where the slip velocity is a prescribed function of the wall shear stress. This function is a curve fit of the extensive data of Ramamurthy on linear low density polyethylene which incorporates two parameters: a critical wall shear stress above which slip occurs, and another parameter which governs the shape of the slip velocity versus shear stress curve. The results show that wall slip reduces both the amount of extrudate swell and the critical Weissenberg number above which our numerical scheme no longer converges.

Reacting Shock Layers with Slip and Catalytic Boundary Conditions

The influence of wall slip and catalytic atom-recombination on the flowfield and wall heat flux are calculated for high-altitude flight and arcjet-flow conditions. Boundary equations, which include velocity slip, temperature jump, and wall catalytic atom-recombination, are coupled to the viscous reacting multicomponent NavierStokes equation. These equations are solved using a time-dependent finite difference technique applied to spheres in an arcjet flow (Reynolds number of 550) and a high-altitude flight case representative of the space shuttle orbiter (Reynolds number of 450). The results indicate that catalysis strongly influences the temperature jump, but not the velocity slip. Slip increases the atom fraction and temperature at both the wall and in the flowfield. Likewise, the shock stand-off distance, the wall heat flux, and friction coefficient are increased over the nonslip cases. The reacting gas calculations confirm the chemically frozen nature of the shock layer in arcjet flows. design the reusable space shuttle orbiter for highaltitude, low Reynolds number, atmospheric entry necessitates a more comprehensive treatment and understanding of the interaction between a high enthalpy gas flow and a relatively cold surface. At low densities the continuum model of the gas breaks down in regions of large gradients such as those near a cold body. Corrections to the equations for the boundary conditions are then required for the flow. These influences are reflected in the calculations of surface heat-transfer rate and chemical composition of the flow near the wall. The aim of this paper is to quantify how these low density phenomena interact, how they influence interpretation of test data obtained on thermal protection systems, and how they alter the predictions of heating rates and performance of the space shuttle orbiter thermal protection system (TPS) during its long high-altitude entry. The approach taken here is to obtain finite difference solutions to the reacting Navier-Stokes equations for the flow around spheres in both space shuttle flight and arcjet environments. The wall boundary conditions for these solutions are obtained from slip and jump relations for a nonequilibrium multicomponent gas mixture. They include the effects of catalytic atom recombination. From the solutions one can assess the effects. of the boundary conditions on the flow properties, the heat flux, etc. At low densities, the continuum-flow equations are no longer adequate close to the wall because the mean free path becomes long compared to characteristi c lengths associated with significant changes in macroscopic-flow parameters. The flow in a region next to the wall having a thickness on the order of a mean free path (the Knudsen layer) cannot be described by the Navier-Stokes description (Kogan1). To determine the flow properties within the Knudsen layer requires the direct solution of the Boltzmann equation matched to the solutions for the outer flow (Navier-Stokes equation) and the wall boundary condition. This is most conveniently done through the use of a slip model in which slip and jump properties are used for the boundary conditions for the Navier-Stokes equations.