Wall Slip Effects Research Articles

Exploring unsteady radiative nanofluid dynamics: Thomson–Troian wall slip effects on a stretching rotating disk

AbstractFluid flow over rotating disk possesses many potential application in many engineering, biological, electrical, and chemical. Along with nanoparticles flow become more enriched in terms of chemical and physical properties. This study investigates the laminar, unsteady, incompressible flow of a water‐based nanofluid above a rotating, stretchable disk. The nanofluid consists of three distinct nanoparticles (magnetite), (copper), and (silver), under the influence of radiation. The behavior of the nanofluid is modeled using the Tiwari and Das model with generalized slip on the disk surface. The new facet of study is to examines the effects of different parameters including stretching, slip, radiation, skin friction, and Nusselt numbers on the flow dynamics. The fluid motion is driven by the rotation and stretching of the disk. Through appropriate similarity transformations, the governing partial differential equations for the flow and thermal transport processes are transformed into a set of coupled ordinary differential equations. These equations are then numerically solved using bvp4c method in MATLAB. The results indicate that velocities in both the radial and axial directions increase with rising stretching parameters, due which skin friction coefficient mount by . And, Nusselt number of fluid surge by increasing volume fraction of , , nanoparticles respectively. Additionally, the temperature increases with increment in the radiation parameter . An increase in the slip parameter's value results in a reduction in both radial and axial velocities.

Annular Newtonian Poiseuille flow with pressure-dependent wall slip

We investigate the effect of pressure-dependent wall slip on the steady Newtonian annular Poiseuille flow employing Navier’s slip law with a slip parameter that varies exponentially with pressure. The dimensionless governing equations and accompanying auxiliary conditions are solved analytically up to second order by implementing a regular perturbation scheme in terms of the small dimensionless pressure-dependence slip parameter. An explicit formula for the average pressure drop, required to maintain a constant volumetric flowrate, is also derived. This is suitably post-processed by applying a convergence acceleration technique to increase the accuracy of the original perturbation series. The effects of pressure-dependent wall slip are more pronounced when wall slip is weak. However, as the slip coefficient increases, these effects are moderated and eventually eliminated as the perfect slip case is approached. The results show that the average pressure drop remains practically constant until the Reynolds number becomes sufficiently large. It is worth noting that all phenomena associated with pressure-dependent wall slip are amplified as the annular gap is reduced.

Torsional parallel plate flow of Herschel–Bulkley fluids with wall slip

The effect of wall slip on the apparent flow curves of viscoplastic materials obtained using torsional parallel plate rheometers is analyzed by considering Herschel–Bulkley fluids and assuming that slip occurs above the slip yield stress τc, taken to be lower than the yield stress, τ0. When the rim shear stress τR is below τc, the exerted torque is not sufficient to rotate the disk. When τc<τR≤τ0 the material is still unyielded but exhibits wall slip and rotates as a solid at half the angular velocity of the rotating disk. Finally, when τR>τ0, the material exhibits slip everywhere and yields only in the annulus r0≤r≤R, where r0 is the critical radius at which the shear stress is equal to the yield stress and R is the radius of the disks. In the general case, the slip velocity, which varies with the radial distance, can be calculated numerically and then all quantities of interest, such as the true shear rate, and the two branches of the apparent flow curve can be computed by means of closed form expressions. Analytical solutions have also been obtained for certain values of the power-law exponent. In order to illustrate the effect of wall slip on the apparent flow curve and on the torque, results have been obtained for different gap sizes between the disks choosing the values of the rheological and slip parameters to be similar to reported values for certain colloidal suspensions. The computed apparent flow curves reproduce the patterns observed in the experiments.

A state-rate model for the transient wall slip effects in ply-ply friction of UD C/PAEK tapes in melt

Ply-ply slippage is one of the key deformation mechanisms occurring during hot press-forming of thermoplastic composite laminates. Advanced forming simulations, required for defect-free manufacturing, rely on accurate constitutive models for these deformation mechanisms. In this work, we propose a relative simple, yet accurate, transient model to describe the start-up friction response of UD C/PAEK tapes. The model combines a White–Metzner viscoelastic fluid with a state-rate model for the evolution of wall slip near the fiber–matrix interface, describing the disentanglement of surface polymer chains followed by the settlement of these chains in a new equilibrium state. This allows prediction of the stress growth at start-up and the transition from peak to steady-state friction, from smooth to sharp with increasing sliding rate, as well as the magnitude of the peak and steady-state friction. We obtained a good correlation between the modeled and measured friction response for different sliding rates.

Visualizing flow dynamics and restart of Carbopol gel solutions in tube and parallel-plates geometries with wall slip.

The present study examines the impact of slip in Carbopol solutions during the restart flow in pipelines utilizing in situ visualization techniques. Rheological tests were conducted using smooth and hatched parallel plate geometries to obtain the rheological characteristics of the solutions. The behavior of the solutions in the creep tests is compared with those in the experimental unit. Three flow regimes were identified through rheological and experimental setup tests: non-flow, slip, and yielded. The slip regime allowed the establishment of a slip static yield stress value, indicating significant deformation states, and a restart pressure decrease of about 61% when compared to the static yield stress. The flow dynamics under the wall slip effect is captured by velocity profiles, velocity contour maps and velocity gradient. Transient correlations of the scaling law type were determined, with wall slip in proportion to the velocity gradient and wall shear stress. Additionally, the concentration of viscoplastic material in the solution increased the scaling law index. This research seeks to provide valuable findings by quantifying the effects of apparent wall slip through in situ measurements. Such insights are crucial for designing and managing pipeline transport systems that handle yield stress fluids, applicable across various industries including cosmetics, food processing, and the production of waxy oils.

A correction method of the wall-slip effect in a cone-plate rheometer

A correction method of the wall-slip effect in a cone-plate rheometer

Wall slip effects in Rayleigh–Bénard convection of viscoplastic materials

PurposeAccording to the research, viscoplastic fluids are sensitive to slipping. The purpose of this study is to determine whether slip affects the Rayleigh–Bénard convection of viscoplastic fluids in cavities and, if so, under what conditions.Design/methodology/approachThe wall slip was evaluated using a model created for viscoplastic (Bingham) fluids. The coupled conservation equations were solved numerically using the finite element method. Simulations were performed for various parameters: the Rayleigh number, yield number, slip yield number and friction number.FindingsWall slip determines two essential yield stresses: a specific yield stress value beyond which wall slippage is impossible (S_Yc); and a maximum yield stress beyond which convective flow is impossible (Y_c). At low Rayleigh numbers, Y_c is smaller than S_Yc. Hence, the flow attained a stable (conduction) condition before achieving the no-slip condition. However, for more significant Rayleigh numbers Y_c exceeded S_Yc. Thus, the flow will slip at low yield numbers while remaining no-slip at high yield numbers. The possibility of slipping on the wall increases the buoyancy force, facilitating the onset of Rayleigh–Bénard convection.Originality/valueAn essential aspect of this study lies in its comprehensive examination of the effect of slippage on the natural convection flow of viscoplastic materials within a cavity, which has not been previously investigated. This research contributes to a new understanding of the viscoplastic fluid behavior resulting from slipping.

Fully developed opposing mixed convection of a Jeffery tri‐hybrid nanofluid between two parallel inclined plates subjected to wall‐slip condition

AbstractWe analyze the effect of wall slip on the fully developed reverse mixed convection of Jeffery nanofluids between two inclined parallel plates with uniform wall heat flux conditions. The theory of tri‐hybrid water‐based nanoparticles with unique shapes, namely, cylindrical (copper), spherical (titanium oxide), and platelet (aluminum oxide) for heat transfer enhancement is utilized since it has better heat performance applicable in a dynamic of fuels and coolant in automobiles as compared with regular Newtonian fluid and nanofluid. The equations describing the above transport phenomena are nondimensional through appropriate scale transformations. Analytical solutions for velocity, temperature, and pressure distributions are obtained. Four different flow regimes including no reversal, bottom reversal, top reversal, and on both walls reversal are found for different combinations of buoyancy and pressure. Particularly, we notice that the wall slip significantly affects flow reversal. Furthermore, we notice that Magyari 's conclusion that the results of the homogeneous nanofluid flow model can be recovered from the corresponding Newtonian fluid model has great limitations. Besides, the effect of several physical factors on velocity and temperature distributions and important physical quantities, including skin friction coefficient and Nusselt number, are analyzed and graphically discussed.

Thermocapillary thin film flows on a slippery substrate with odd viscosity effects

This study investigates the behavior of a thin liquid with odd viscosity effects as it flows down a uniformly heated, slippery inclined plane, where the liquid’s time-reversal symmetry is broken. The breaking of symmetry results in interesting effects, as the antisymmetric part of the fluid stress tensor does not vanish. Two models, the Benney-type equation model (BEM) and the weighted residual model (WRM), are constructed to account for the combined effects of slip length, thermocapillarity, and odd viscosity. A detailed stability analysis determines both models’ critical Reynolds numbers Rec. For small slip lengths, the first-order WRM is better at capturing the instability threshold than the first-order BEM. While both models account for the effects of odd viscosity and thermocapillarity, only the Rec of WRM incorporates the wall slip effects. Another significant finding is that the BEM effectively avoids the issue of finite-time blow-up by incorporating odd viscosity. Additionally, employing a weakly nonlinear stability analysis with multiple scales uncovers four flow regions in BEM: supercritical stable, subcritical unstable, unconditional stable, and explosive zones. Two separate bifurcation scenarios emerge for various wave numbers: supercritical within a specific range and subcritical for larger wave numbers. The presence of odd viscosity alleviates the reduction of the unconditional stable zone and the increase in the explosive zone, which are caused by the combined influence of slip and thermal effects. Numerical investigation of traveling wave solutions of WRM shows that wave height is promoted by slip and thermal effects but reduced with increasing odd viscosity coefficient. Further numerical simulations of WRM on a larger domain demonstrate the stabilizing effects of odd viscosity and its interaction with destabilizing slip and thermocapillary effects.

Numerical Analysis of Velocity and Thermal Wall Slip Effects on the Boundary Layer Flow Over an Exponentially Stretching Bullet-Shaped Object in Presence of Suction and Injection

A steady two-dimensional axisymmetric incompressible flow over an exponentially stretching bullet-shaped surface has been considered. The present work is mainly focused on fluid flow by the effect of multiple slips. The governing partial differential equations and auxiliary boundary conditions have been converted into higher-order equations by using assisting similarity transformations. These higher-order ODEs are then transformed into a 1st-order system of LDEs by the method of spectral quasi-linearization (SQLM). The validity, accuracy, and convergence of the solution have been performed by using SQLM. The fluid velocity, temperature, skin friction coefficient, and Nusselt number have been depicted graphically for the mentioned parameters as also the numerical values of velocity gradient, and Nusselt number in a table. The numerical investigation shows that the velocity gradient enhances due to the parameter of magnetic, thermal slip, and Prandtl number whereas the remaining parameters have a reverse effect on it. The heat transfer rate reduces for the parameters of magnetic, multiple slip, injection, and viscous dissipation but suction and heat generation have a reverse effect on it. The results of in this work have been justified due to the validity and accuracy of the present problem. Due to the endless application of Newtonian fluids in engineering and industry, no attempt has been taken to inspect the MHD flow with a dual slip effect along with exponential stretching bullet-shaped surface. Also, the current work is of immediate interest to those systems that are highly influenced by the heat transfer process and desired product quality.

Improvements in Drilling Fluid Rheology Predictions Using Rotational Viscometer

Summary The success of an oilwell drilling operation is directly associated with the correct formulation of drilling fluids and their rheological measurements. The goal of this study is to investigate the usage of a Fann 35A viscometer and the methodology for rheological characterization of drilling fluids by comparison with the use of a rotational rheometer. Flow curves and gel strength tests were performed considering classic measurement artifacts such as apparent wall slip, secondary flows, steady-state (SS) regime, and inertial effects, among others. In addition, a study of the relationship between pressure drop and flow rate in a tube and in an annular space was carried out to investigate the influence of the viscosity function and of the rheological properties on the design of pipelines and the correct sizing of pumps. Use of American Petroleum Institute (API) equations and curve fitting were explored as potential choices for viscosity functions. The results indicate that the use of API equation predictions can compromise the effectiveness of the drilling process, while the choice of an adequate viscosity function is essential for the correct sizing of pumps. The gel strength was evaluated in the viscometer and presented divergent results from those obtained in the rheometer. Furthermore, a grooved geometry was developed for the viscometer to avoid the effects of apparent slip at low shear rates. Some recommendations are made based on the results obtained, which lead to better accuracy in the rheological results of drilling fluids and, consequently, better performance of some functions assigned to it. The proposed improvements and methodologies proved to be promising, although in some cases the cost-benefit remained unchanged.

Compounding, Rheology and Numerical Simulation of Highly Filled Graphite Compounds for Potential Fuel Cell Applications.

Highly filled plastics may offer a suitable solution within the production process for bipolar plates. However, the compounding of conductive additives and the homogeneous mixing of the plastic melt, as well as the accurate prediction of the material behavior, pose a major challenge for polymer engineers. To support the engineering design process of compounding by twin-screw extruders, this present study offers a method to evaluate the achievable mixing quality based on numerical flow simulations. For this purpose, graphite compounds with a filling content of up to 87 wt.-% were successfully produced and characterized rheologically. Based on a particle tracking method, improved element configurations were found for twin-screw compounding. Furthermore, a method to characterize the wall slip ratios of the compounded material system with different filler content is presented, since highly filled material systems often tend to wall slip during processing, which could have a very large influence on accurate prediction. Numerical simulations of the high capillary rheometer were conducted to predict the pressure loss in the capillary. The simulation results show a good agreement and were experimentally validated. In contrast to the expectation, higher filler grades showed only a lower wall slip than compounds with a low graphite content. Despite occurring wall slip effects, the developed flow simulation for the design of slit dies can provide a good prediction for both low and high filling ratios of the graphite compounds.

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

AbstractRubber 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.

Dynamics of co-current gas–liquid film flow through a slippery channel

We consider a thin liquid film in a wide inclined channel being driven by gravity and co-current turbulent gas flow. The bottom plate with which the liquid is in contact with is taken to be slippery, and we impose the classic Navier slip condition at this substrate. Such a setting finds application in technological processes as well as nature (e.g., distillation, absorption, and cooling devices). The gas–liquid problem can be decoupled by making certain reasonable assumptions. Under these assumptions, we solve the gas problem to obtain the tangential and normal stresses acting at the wavy gas–liquid interface for arbitrary waviness. In modeling the liquid layer dynamics, we make use of the stresses computed in the gas problem as inputs to the interface boundary conditions. We develop the long-wave model and the weighted-integral boundary layer (WIBL) model to describe the thin film dynamics. We perform a linear stability of these reduced order models to scrutinize the effect of wall slip, liquid flow rate, and the gas shear on the stability of the flat film solution. It is found that the wall slip promotes the instability of the flat interface. Furthermore, we compute solitary wave solutions of the WIBL model by implementing Keller's pseudo-arc length algorithm on a periodic domain. We observe that the wave speed as well as the wave amplitude are attenuated on incrementing the liquid slip at the substrate. We corroborate these findings with the time-dependent computations of the nonlinear WIBL model.

Physical insight into magneto-thermo-migration of motile gyrotactic microorganisms over a flexible cylinder with wall slip, and Arrhenius kinetics

A numerical simulation of magneto-bioconvective DF (Darcy-Forchheimer) transport of gyrotactic microbes using the Williamson nanofluid model over a flexible cylinder under the physical effects of Arrhenius activation energy, thermal radiation, triple stratifications and wall slip is performed in this research communication. The flow dynamics also take into consideration the thermo-migration and random (haphazard) motion's physical effects. The similarity transformations are opted to translate the governing system of non-linear coupled PDEs into ODEs, which are then numerically tackled using the sophisticated MATLAB function named bvp4c. The significant effects of developing emergent physical factors on the accompanying fields are exploited via graphical sketches and numerically constructed tables. It is determined that strengthening the Williamson, porosity, magnetic parameters, and Forchheimer number causes considerable slowing of transport profiles. Thermal enrichment can be seen by increasing thermal radiation and thermophoresis parameters. Microbe concentration rises as a response to activation energy and reaction parameters. The current model may be used to solve various biological, biomedical, bioengineering, architectural thermal insulation, geophysical activities, and ecological problems.

Effects of wall slip on hydrodynamic performances of water-lubricated bearings under transient operating condition

Effects of wall slip on hydrodynamic performances of water-lubricated bearings under transient operating condition

Effects of Wall Slip on Hydrodynamic Performances of Water-lubricated Bearings Under Transient Operating Condition

Effects of Wall Slip on Hydrodynamic Performances of Water-lubricated Bearings Under Transient Operating Condition

Thin film evaporation: New insights with nanofluid inclusion and component of the electrostatic interactions

To assess the implications of the evaporating meniscus in microfluidic channels, extensive explorations have been going on to simulate the fluid flow behavior and the transport phenomena. The present work explores new insights into the evaporating meniscus after including the nanofluid (alumina + water) as a working fluid. This work first emphasizes encapsulation of the different components of the disjoining pressure that arises due to the interactions between the nanoparticles (Al2O3) and the nanoconfined polar liquid including the wall slip effect and later delineates the physics of the results obtained. The investigation will provide crucial insights through a comprehensive enumerated theoretical model comprised of the Young–Laplace equation, kinetic-theory-based mass transport, and the lubrication theory in the purview of evaporating nanofluid meniscus. This study also highlights the selection of the thin film thickness and the dispersion constant at the inception of the evaporation, as they cannot be chosen arbitrarily. A nondimensional approach is opted to explicate different facets of the thin film evaporation region. The results revealed that the nanofluid inclusion increases the overall heat transfer and the thickness of the evaporating meniscus. However, nullifying the combined effect of the electrostatic component of the disjoining pressure and wall slip will exaggerate the net increase in the heat transfer process and understate the increase in the thickness of the evaporating thin film, primarily if a polar liquid is used to unveil the characteristics of the evaporating nanofluid meniscus.

Three‐dimensional numerical simulation on fiber orientation of short‐glass‐fiber‐reinforced polypropylene composite thin‐wall injection‐molded parts simultaneously accounting for wall slip effect and pressure dependence of viscosity

AbstractOn account of the inherent features of the thin‐wall injection molding process, a three‐dimensional numerical model, which accounts for wall slip effect and pressure dependence of viscosity (PDoV), was proposed for a more accurate simulation of the fiber orientation in thin‐wall injection‐molded parts of short‐glass‐fiber‐reinforced polymer composites (SGFRPC). First, the fiber orientation was simulated using the three‐dimensional and mid‐plane models, respectively. The comparison between the simulated and experimental results verifies that the three‐dimensional numerical results were in better agreement with the experimental measurements. Secondly, the influences of wall slip effect and PDoV on fiber orientation in thin‐wall injection‐molded parts of SGFRPC were analyzed based on the three‐dimensional numerical model. The results show that the three‐dimensional numerical simulation simultaneously accounting for wall slip effect and PDoV can better predict the fiber orientation in thin‐wall injection‐molded parts of SGFRPC, suggesting the validation of the proposed model. Finally, five main processing parameters, that is, injection rate, melt temperature, mold temperature, packing pressure, and packing time, were also studied in terms of their influences on the fiber orientation in thin‐wall injection‐molded parts of SGFRPC.

Effect of wall slip on laminar flow past a circular cylinder

A numerical study of two-dimensional flow past a confined circular cylinder with slip wall is performed. A dimensionless number, Knudsen number ($Kn$) is used to describe the slip length of cylinder wall. The Reynolds number ($Re$) and Knudsen number ($Kn$) ranges considered are $Re = [1, 180]$ and $Kn = [0, \infty)$, respectively. Time-averaged flow separation angle ($\bar{\theta_s}$), dimensionless recirculation length ($\bar{L_s}$) and the tangential velocity ($\bar{u_{\tau}}$) distributed on the cylinder's wall, drag coefficient ($\bar{C_d}$) and drag reduction ($DR$) are investigated. The time-averaged tangential velocity distribution on the cylinder's wall fit well with the formula $\bar{u_{\tau}} = [\frac{\alpha}{1+{\beta}e^{-{\gamma}({\pi}-{\theta})}}+{\delta}]sin(\theta) $, where the coefficients ($\alpha$, $\beta$, $\gamma$, $\delta$) are related with $Re$ and $Kn$. Several scaling-laws are found, $log(\bar{u_{{\tau}max}})\sim{log(Re)}$ and $\bar{u_{{\tau}max}}\sim{Kn}$ for low $Kn$, ($\bar{u_{{\tau}max}}$ is the maximum tangential velocity on the cylinder's wall), $log(DR)\sim{log(Re)}$ ($Re\leq45$ and $Kn\leq0.1$), $log(DR)\sim{log(Kn)}$ ($Kn\leq0.05$). At low $Re$, $DR_v$ (the friction drag reduction) is the main source of $DR$. However, $DR_p$ (the differential pressure drag reduction) contributes the most to $DR$ at high $Re$ ($Re>\sim60$) and $Kn$ over a critical number. $DR_v$ is found almost independent to $Re$.