We investigate experimentally the effects of a pipe axial rotation on buoyant miscible displacement flows in an inclined pipe. The displacing Newtonian fluid (salt-water solution) is heavier than the displaced viscoplastic one (Carbopol solution). Via image processing techniques and ultrasound Doppler velocity measurements, we analyze the key flow features such as the flow patterns, the velocity and

Retraction dynamics of viscous drops and sheets depend on the relative magnitude of the viscous force over the inertia-capillary force. The dynamics are more complicated in the case of viscoplastic drops/sheets because the yield stress of the fluid also comes into play. The retraction of slender viscoplastic drops and sheets depends on the relative magnitude of the yield stress over the capillary stress

This paper reports on the multiplicity of steady state solutions and the effect of buoyancy ratio due to both heat and mass transfer on natural convection in a horizontal rectangular cavity filled with a power-law non-Newtonian fluid. The short vertical sides of the cavity are submitted to horizontal thermal and solutal flux densities, while its horizontal walls are impermeable and adiabatic. The problem

We present an experimental study using mixtures of aqueous superabsorbent polymers (SAP) where we systematically investigate the influence of the size of grains that make up the fluid structure on the mixture effective rheology and its domain of validity. In water, SAP powder grains can swell up to 200 times and form gel grains, dg, whose sizes (typically between 1 and 8 mm) can be controlled by choosing

In this paper, we present result from a direct numerical simulation (DNS) of turbulent flow in a converging T-junction for both Newtonian (water) and non-Newtonian inelastic fluid (dilute Xanthan Gum solution). Based on experimental data, the Bird-Carreau law is used to capture the inelastic shear thinning property of the solution. For the Xanthan solution, the viscosity at rest is about 100 times

Fluid flow inside nano-channels coated with a polyelectrolyte brush layer (PEL) is dictated by the brush structure and its interaction with the counter-ion dominated electrical double layer (EDL) near the walls of the PEL channel. In this work, we bring out the confluence of spatial permittivity variation, the influence of proximity between ions in charged PEL channels and non-Newtonian constitutive

The relation between the drag reduction (DR) performance of several water-soluble polymers and their viscoelastic properties was investigated. Polymers with a flexible molecular structure including three grades of polyacrylamides (PAM), and a polyethylene oxide (PEO) were investigated. Xanthan gum (XG) and carboxymethyl cellulose (CMC), each with a rigid molecular structure, were also considered. The

Shear-thickening and thinning behaviors are often observed in the rheological measurements of dilute surfactant solutions with drag-reducing ability in wall-bounded turbulent flows. This study proposes a simple rheological modeling method based on combining constitutive equations, such as Giesekus and FENE-P models, with a fluidity equation to determine both thickening and thinning behaviors in simple

We present a method for speeding up equilibrium simulations of liquid crystals for two related models that are degenerate with respect to defects: the Ericksen model and the uniaxially constrained Landau-de Gennes model. The degeneracy induces a non-linear/non-smooth coupling between the two order parameters in both models that makes the discrete problems very stiff to solve. The technique described

Electro-elastic instabilities in electro-osmotic contraction/expansion flows (EOF) of viscoelastic fluids are experimentally investigated in this work. Several microchannel configurations are used, including the cases with hyperbolic-shaped contractions followed by an abrupt expansion, or abrupt contractions followed by a hyperbolic-shaped expansion. Such cases were selected to assist in the understanding

The relevance of upstream contraction for extrudate swell behavior of polymer melts is numerically investigated for slit dies with an aspect ratio of 10 and a length-to-height ratio ranging from 2.5 to 40. Three-dimensional (3D) flow simulations are performed with ANSYS Polyflow software at different flow rates and a constant temperature of 200°C, selecting a differential multimode Phan-Thien-Tanner

Wall slip quantification using the classical Mooney slip analysis has produced physically unreasonable results for many complex fluids. Over the past decades, the assumption that the slip velocity is solely dependent on the wall shear stress has therefore been questioned. In this contribution, the influence of the radius of cylindrical dies on the wall slip velocity of highly concentrated non-Brownian

This work is concerned with time-dependent axisymmetric free surface flows of Oldroyd-B fluids for any value of β, the ratio of solvent to total viscosities. The Oldroyd-B constitutive equation is dealt with by employing a novel technique to calculate the conformation tensor while an EVSS transformation allows the solution of the momentum equations coupled with the free surface stress conditions: this

In this note, we investigate through scaling laws and direct numerical simulations the development of inertia-dominated coiling instabilities in power-law fluids. Our numerical results are based on an adaptive variational multi-scale method for multiphase flows. In short, when inertia is balanced by viscous forces in the coil, both the coiling frequency and the coil radius are given by a power-law

The performance of supercritical carbon dioxide (scCO2) foams in aquifer remediation and Enhanced Oil Recovery is negatively affected by the foam instability at underground conditions (elevated temperatures and pressures). In search of solutions, viscoelastic surfactants are considered as potential stabilizers beyond traditional surfactants. There are limited studies on the effect of viscoelasticity

We consider the impact of periodical finite-amplitude perturbations induced by oscillations of the supporting plane on the natural instability of a falling film. The oscillations change the basic state of the flow from steady to periodical; for non-Newtonian liquids, the mean parameters of the basic state depend on the plane’s oscillations. We solve the eigenvalue problem for linearized generalized

Buoyant Marangoni convection of a power-law fluid confined in a shallow cavity heated from below is investigated. The free upper surface of the system is assumed to be flat and underformable. A simplified analytical model, valid for an infinite layer, is derived on the basis of the parallel flow approximation. The criteria, for the onset of convection, are predicted for both shear-thinning and shear

A detailed numerical study on the flow and heat transfer phenomena from a rotating cylinder submerged in a streaming viscoelastic FENE-P fluid has been carried out. The governing equations, along with the FENE-P viscoelastic constitutive equation, have been solved using OpenFOAM over the following ranges of conditions: Reynolds number, 10 ≤ Re ≤ 100; Weissenberg number, 0 ≤ Wi ≤ 10; non-dimensional

An analytical model capturing the effects of mean-field considerations on the orientation evolution of a plurality of rigid spheroids suspended in a Newtonian matrix is developed. Three approaches are taken with increasing sophistication: a mesoscale view involving the analysis of several distinct layers of material subjected to simple shear flow, a traditional micromechanics inspired approach involving

A 3D transient non-isothermal finite element code is developed to predict the extrudate shape of viscoelastic fluids emerging from an asymmetric keyhole shaped die. The corner-line method is used to model the movement of the free surfaces. The code is tested using two benchmark problems. First the corner-line method is tested using a trumpet shaped object in a 3D uniaxial extensional flow. Secondly

The present work studied the rheological properties of concentrated non-colloidal aqueous suspensions of graphite particles together with carboxymethyl cellulose (CMC) having various molecular weights, especially focusing on the applicability of the modified Cox-Merz rule. These suspensions were investigated as model slurries to produce anode electrodes of lithium ion batteries. In the case of suspensions

Systematic rheometric measurements are carried out to explore the nonlinear responses of carbon black-filled polyisoprene/squalene solutions with the polymer concentrations ϕ in the matrix ranging from the coil overlapping state (ϕ =ϕ*) to the melt state (ϕ =1). At the coil overlapping state, when ϕ <<1, the system typically shows the classic nonlinearity, where the storage modulus G’ decreases as

The squeeze flow of a viscoplastic material between two parallel coaxial disks with yield slip condition at the wall is examined. The governing equations are solved employing the accelerated augmented Lagrangian method for both the viscoplastic model and the yield slip equation. We compute the shape of the yield surface, the velocity and stress fields using the finite difference method. The effect

In this paper, a Helmholtz-potential-based thermodynamic approach was developed for modelling fluids that exhibit both yielding and thixotropic behavior. The yielding behavior was captured using a framework of multiple natural configurations. The thixotropy was described using a structural parameter. The Helmholtz potential is made a function of a structural parameter and a stretch quantity, and the

The parallel between non-equilibrium dynamics in time-dependent systems and ``the eagle and the rat'' problem is explained, justifying the use of this problem as a metaphor.

This paper presents a numerical approach to predict the rheology of dense non-colloidal suspensions with a biviscous matrix. A biviscous matrix is characterized as a fluid with two shear rate dependent viscosities i.e. one above and below a critical shear rate γ˙c. The methodology is based on the lubrication dynamics which dominantly influence the suspension properties at high values of particle concentration

Although there are many studies in the literature concerning viscoelastic fluids, it remains a challenging subject in the field of polymer rheology to determine which is the most appropriate model and parameter set to describe the rheological behavior of a given viscoelastic fluid under real flow. The aim of this work is to present an optimization procedure for the estimation of nonlinear parameters

Shear thinning is fundamental to a broad range of particle suspensions, both in nature and in industrial applications. Yet the mechanisms governing it remain unclear. In particular, the distinct, and often competing, roles of the interparticle, particle-fluid interactions and the particle surface morphology need clarity. By using non-Brownian silica particles with different morphologies, surface functional

Modeling blood rheology remains challenging in part because of its multiphase, aggregating colloidal nature that gives rise to complex viscoplastic and time-dependent (thixotropic) behavior. Here, we demonstrate that a multiscale approach incorporating a direct coupling of coarse-graining particle-level modeling to the macroscopic phenomenological modeling can provide new insights and a promising methodology

In this paper the generation of Newtonian microdroplets in both Newtonian and non-Newtonian carrier fluids through a commercial micro T-junction under an opposed-flow configuration is analyzed experimentally. Pure deionized water and 0.2 wt% aqueous Xanthan gum solution in presence or absence of surfactant (Tween 20) have been considered as carrier fluids and the silicone oil is employed as the dispersed

This paper presents a current view of non-Brownian (non-colloidal) suspension rheology; experimental and computational works are compared where possible. The matrix fluids are either Newtonian or viscoelastic; the rigid particles are compact and close to spherical. Volume fractions of 0.5 and below are considered. It is important to move beyond steady simple shearing, so unsteady shearing and uniaxial

Pressure drops in flows through a small slit were experimentally measured at constant flow rates to investigate flows with an abrupt contraction and expansion. The flow properties of water, 50 wt% glycerol solution, and two types of surfactant solutions (Lipoquad and Lipothoquad) with a counterion (NaSal) were examined. The slit heights used were 480 µm, 222 µm, and 129 µm, with estimated hydraulic

We study experimentally the penetration of a projectile into a two-dimensional granular bed composed of magnetic repelling grains. The projectile can experience either repulsive, attractive or neutral interaction with the particles generating different dynamics: i) the repulsive intruder compresses the granular bed without contact and experiences rebounds before stopping; ii) the attractive intruder

We present a comprehensive 3D numerical study of particles with imposed velocities relative to the local bulk flow (termed “slip velocities”) in a viscoelastic shear flow. We consider the force on a spherical particle sedimenting, a spherical bubble rising, and a spherical neutral squirmer swimming in an imposed viscoelastic shear flow. We demonstrate that any particle moving with a slip velocity in

We derive an expression for the velocity profile of a pressure-driven yield-stress fluid flowing around a two-dimensional concentric annulus. This result allows the prediction of the effects of channel curvature on the pressure gradient required to initiate flow for given yield stress, and for the width of the plug region and the flux through the channel at different curvatures. We use it to validate

In view of better understanding the properties of waxy crude oils of great practical importance, we study the rheological behavior evolution of model waxy suspensions during transient shear tests, and its variation with concentration in a wide range. Macroscopic tests show a strong destructuring process with the increasing imposed shear rate (starting from rest), while negligible restructuring is observed

In this work we develop a theoretical analysis for the mass transfer of an electroneutral solute in a concentric-annulus microchannel driven by an oscillatory electroosmotic flow (OEOF) of a fluid whose behavior follows the Maxwell model. The annular microchannel connects two reservoirs that have different concentrations of the solute. For the mathematical modeling of the OEOF, we assume the Debye-Hückel

Taylor-Couette reactors may offer an alternative treatment method for ballast water treatment or for flocculation of small size particles to be removed in water treatment processes due to created high energy dissipation and momentum transfer by Taylor vortices occurred during transitional flow regimes. In this study, the effect of shear-thinning behaviour on flow structures and transition thresholds

A recently proposed Lagrangian-Eulerian method for viscoelastic flow simulation is extended to high performance calculations on the Graphics Processing Unit (GPU). The two most computationally intensive parts of the algorithm are implemented for GPU calculation, namely the integration of the viscoelastic constitutive equation at the Lagrangian nodes and the interpolation of the resulting stresses to

This study aims to investigate the elastic properties of blood for pulsatile arterial hemodynamics in terms of their effects on velocity, vorticity and stress fields, as well as the aneurysm rupture risk indicators. The blood flow in a developed fusiform aneurysm is numerically simulated using the modified Oldroyd-B viscoelastic fluid model which includes shear thinning effects, and the results are

Three local self-similar solutions are obtained for the laminar planar jet flow of viscoelastic fluids, described by the FENE-P constitutive equation, through an order of magnitude simplification of the governing equations. The more general solution is shown to be more accurate than two further simplified solutions, here called the delta and the Olagunju-type solutions, at least for the profiles of

In this paper, the influence of non-Newtonian material properties on the draw resonance instability in film casting is investigated. Viscoelastic models of infinite width film casting are derived systematically following an asymptotic expansion and using two well-known constitutive equations: the Giesekus model and the simplified Phan-Thien–Tanner model. Based on a steady state analysis, a numerical

This study presents an analysis of laminar motion of an oscillatory flow of second grade fluid under a harmonic pressure gradient in a rectangular duct. Exact solutions are obtained for the velocity profile, phase difference and the corresponding shear stress. In particular, the flow singularities at the boundaries and corners of the duct are taken into account. In comparison to Newtonian fluid, the

Polymer melts filled with rod-like particles like glass and carbon fibers have high practical importance. Here we numerically investigate the properties of power-law fluids filled with rigid rods of different aspect ratios. For that we compute the rheological coefficients of the transversely isotropic fluid (TIF) equation and compare our results with analytical models, specifically with the model of

The moving contact line of a thin fluid film can often corrugate into fingers, which is also known as a fingering instability. Although the fingering instability of Newtonian fluids has been studied extensively, there are few studies published on contact line fingering instability of non-Newtonian fluids. In particular, it is still unknown how shear-thinning rheological properties can affect the formation

The thin film lubrication approximation has been studied extensively for moving contact lines of Newtonian fluids. However, many industrial and biological applications of the thin film equation involve shear-thinning fluids, which often also exhibit a Newtonian plateau at low shear. This study presents new numerical simulations of the three-dimensional (i.e. two-dimensional spreading), constant-volume

Drug delivery of topical microbicidal molecules against HIV offers promise as a modality to prevent sexual transmission of the virus. Success of any microbicide product depends, in an interactive way, upon its drug (the microbicide active pharmaceutical ingredient, API) and its delivery system (e.g. a gel, film or intravaginal ring). There is a widespread agreement that more effective drug delivery

A recent study in South Africa has confirmed, for the first time, that a vaginal gel formulation of the antiretroviral drug Tenofovir, when applied topically, significantly inhibits sexual HIV transmission to women [10]. However the gel for this drug, and anti-HIV microbicide gels in general, have not been designed using full understanding of how gel spreading and retention in the vagina govern successful

The classical oscillatory shear wave model of Ferry et al. [J. Polym. Sci. 2:593-611, (1947)] is extended for active linear and nonlinear microrheology. In the Ferry protocol, oscillation and attenuation lengths of the shear wave measured from strobe photographs determine storage and loss moduli at each frequency of plate oscillation. The microliter volumes typical in biology require modifications