Concentrated Suspensions Of Solid Particles Research Articles

Shear Jamming and Fragility of Suspensions in a Continuum Model with Elastic Constraints.

Under an applied traction, highly concentrated suspensions of solid particles in fluids can turn from a state in which they flow to a state in which they counteract the traction as an elastic solid: a shear-jammed state. Remarkably, the suspension can turn back to the flowing state simply by inverting the traction. A tensorial model is presented and tested in paradigmatic cases. We show that, to reproduce the phenomenology of shear jamming in generic geometries, it is necessary to link this effect to the elastic response supported by the suspension microstructure rather than to a divergence of the viscosity.

Features of the flow of concentrated suspensions of solid particles

Concentrated suspensions of solids, widely used in the pharmaceutical, cosmetic and food industries, exhibit complex rheology. In the rheometric one-dimensional flows of concentrated suspensions, a smooth or abrupt increase in stresses with a smooth increase in the strain rate intensity can be observed. This is related to the appearance of a first-order phase transition. In our previous work, a phenomenological rheological model of a concentrated suspension of solid particles in a Newtonian dispersion liquid has been developed. This model is characterized by an S-shaped flow curve and describes both continuous and abrupt increases in the stress intensity with a uniform increase in the strain rate intensity. In this work, exact analytical formulas are obtained for the flow velocity profiles of suspensions measured using rotary viscometers. The model proposed before is modified to take into account the non-Newtonian properties of the dispersion medium, which demonstrates pseudoplastic properties at low stress intensities and dilatant properties at high stress intensities. Based on the developed numerical model, the features of the flow of highly concentrated suspensions in plane and axisymmetric channels are analyzed. It is shown that in a flat diffuser, in contrast to Newtonian and pseudoplastic fluids, the longitudinal velocity of the suspension slows down near the walls, where the stresses are maximum, and accelerates in the central part of the channel. Calculations for the submerged jet in the area bounded by the walls show that, with an increase in the average velocity of the incoming pure liquid by more than 0.01 m/s, there occurs a local velocity vortex bounded by a layer with high particle concentration and more viscous medium; particle concentration inside the vortex is minimum.

Rheometric flows of concentrated suspensions of solid particles

Publications on experimental and theoretical studies of the rheological properties of concentrated suspensions of solid particles have been analyzed. According to the currently accepted ideas, the rheology of suspensions is considered as a result of contact interaction of their constituent particles caused by the action of external forces, the formation and destruction of various types of conglomerate structures. A new rheological model of a highly concentrated suspension of solid particles in a Newtonian fluid is proposed, which describes both a continuous and discontinuous increase in the effective viscosity with a uniform increase in shear stresses. Accurate analytical formulas are obtained for the velocity profiles of suspensions in rotational viscometers “cone-plane” and “cylinder-cylinder”, as well as in a slit viscometer. The proposed model is modified to take into account the non-Newtonian properties of a dispersion medium, which exhibits pseudoplastic properties at low strain rates, and dilatant properties at large strain rates. The effective viscosity of such a suspension is presented as the sum of the contributions from the dispersion medium and the solid particles of the dispersed phase. To describe the rheology of the dispersion phase, the Ellis model was used. The velocity profiles in a pressure driven flat channel are obtained numerically by the finite element method. It is shown that, depending on the parameters of the model, the velocity profiles in a flat channel can take various complex forms.

Discontinuous shear thickening in concentrated suspensions.

The flow of concentrated suspensions of solid particles can be suddenly blocked by the formation of a percolated network of frictional contacts above a critical value of the applied stress. Suspensions of magnetic particles coated with a superplastifier molecule were shown to produce a strong jamming transition. We find that, for these suspensions with an abrupt discontinuous shear thickening, a model using the divergence of the viscosity at a volume fraction that depends on the applied stress does not well describe the observed behaviour both below and above the critical stress. At a constant applied stress above the critical one, we have a stick-slip behaviour of the shear rate whose period can be predicted and scaled as the square root of the relaxation time of the frictional contacts. The application of a small magnetic field allows us to continuously decrease the critical shear rate, and it appears that the yield stress induced by the magnetic field does not contribute to the jamming transition. Finally, it is shown that this jamming transition also appears in the extrusion of a suspension through a die, but with a much slower dynamics than in the case of stress imposed on a rotational geometry. This article is part of the theme issue 'Heterogeneous materials: metastable and non-ergodic internal structures'.

Effect of surface active agents on the rheological properties and solubility of layered double hydroxides-modified asphalt

Layered double hydroxides (LDHs) modified asphalt is a typical solid-liquid mixture that is concentrated suspensions of solid particles in solutions. The influence of dodecyl benzenesulfonic acid (DBSA) and polyvinyl alcohol (PVA) on the rheological properties and solubility of LDHs modified asphalt (LMA) were investigated by dynamic shear rheometer, molecular dynamic simulations and optical microscopy. Research results indicated that the addition of DBSA or PVA to LDHs modified asphalt resulted in enhancement of the cracking resistance, stress relaxation and creep behavior at lower temperature. The solubility parameters of surface active agent and LMA showed that PVA and DBSA can contribute to the solution of LDHs in asphalt. The effect of PVA was better than DBSA. The morphology of LMA implied that the distribution of LDHs was uniform when 0.5wt-% DBSA or PVA were added and increasing DBSA contents under certain levels increased the uniformity of LDHs..

Rheology of suspensions of solid particles in power‐law fluids

The viscous behaviour of concentrated suspensions of solid particles in non‐Newtonian power‐law fluids is discussed here. After a brief review of the existing models, new models are presented for the constant shear‐rate relative viscosity of concentrated suspensions with power‐law matrices. To validate the models, experimental work is carried out on the rheology of suspensions of glass beads in aqueous polymer solution using a controlled stress rheometer. The volume fraction of particles is varied from 0 to 44.9 %. The experimentally measured flow curves of suspensions are described satisfactorily using the proposed models.

Particulate Stresses in Dense Disperse Flow

We review and discuss the progress as achieved to date in the matter of describing particulate stresses of different origins that occur in concentrated suspensions of solid particles. A few physical mechanisms of generating such stresses are explicitly recognized. First, these stresses appear as a result of direct momentum transport over a transient network of particles separated by thin lubricating films of the intervening fluid, so that a part of the apparent suspension viscosity must be attributed to its dispersed phase. Second, normal and tangential particulate stresses originate because of random fluctuations of particles caused by (1) their pair interactions as the particles are brought closer together and pass one another in mean shear flow, (2) the relative fluid flow and an external body force field as they interact with random fluctuations of suspension concentrations, and (3) random macroscopic flow patterns, such as bubbles rising in fluidized beds that produce a system of Reynolds-like stresses

Investigation about Electrorheological Squeeze FilmDamper Applied to Active Control of Rotor Dynamic

Electrorheological (ER) fluids, discovered in 1947 by W. WINSLOW, are concentrated suspensions of solid particles in an oily base liquid. Exposed to a strong electric field, their resistance to flow increases very greatly and this change is progressive, reversible and occurs very rapidly. Nowadays, ER fluids, made of lithium salt and fluorosilicon got rid of their old abrasive characteristics and are able to provide a good interface between electronics and mechanical components. A bibliographical study on ER fluids and ER technology has been carried out. The aim of this study is adapting ER technology to Squeeze Film Damper. In order to provide an active control on a flexible rotating shaft so as to command the whole shaft/bearings device in case of high rotating speed or heavy load trouble. Results of numerical computation of a shaft bearing assembly with a Squeeze Film Damper using negative ER fluid are showed in order to see the possibility of avoiding critical speeds by natural frequency shifting. A technical study of ER Squeeze Film Damper design is also presented, taking into account ER fluid properties and ER technology requirements.

Rheological studies of Ratawi vacuum residue at 366 K

Ratawi vacuum residue is a typical bottom-of-the-barrel fraction from an asphaltenic sour crude oil, and previous work indicates that Ratawi asphaltenes are typical petroleum asphaltenes. The rheology of Ratawi vacuum residue is analysed in this work by employing theories given by Pal and Rhodes, Eilers, Campbell and Forgacs, and Grimson and Barker to describe the rheology of concentrated suspensions of solid particles. The excellent and self-consistent description provided by these theories shows that Ratawi asphaltenes are a distinct species in vacuum residue. Information about the macrostructure of asphaltenes in their natural environment, the crude oil or residue, is also obtained. Ratawi asphaltenes are solvated spheres of different sizes in the vacuum residue. Their solvated volume is two to three times the dry volume at 366 K. Direct interparticle interactions between solvated asphaltenic particles are weak at 366 K. These forces are repulsive, and account for the stability of Ratawi vacuum residue with respect to asphaltene precipitation. A method of employing the Grimson-Barker theory suggests that the Ratawi asphaltenes are charged. The solvation effect arises because polar molecules in the non-asphaltenic fraction surround the particles and screen the charge.

VISCOUS PARTICLE INTERACTIONS AND THEIR EFFECT ON KINEMATIC WAVE ROPAGATION

Abstract This paper addresses the one-dimensional stability of non-Brownian concentrated suspensions of solid particles in a viscous, Newtonian host fluid. Recent developments have shown the particle phase pressure to strongly affect suspension stability, but a concensus on the representation of this quantity remains a subject of some controversy. Here, attention is focused on the particle phase pressure that has a viscous origin. The form of this viscous particle interaction is developed for suspensions using an energy dissipation approach, and it is included in the conservation equations for the suspension to determine its effect on sedimenting or fluidized particles at very high concentrations. By means of a linear perturbation analysis, its affect on stability is analyzed, and it is shown to have a highly altenuative and dispersive effect on concentration waves.

EFFECTS OF LIQUID VISCOSITY ON RHEOLOGY OF CONCENTRATED SUSPENSIONS

ABSTRACT This paper presents the experimental results on the effects of liquid viscosity on the rheology of concentrated suspensions of solid particles in Newtonian liquids. Specifically, the relative viscosity of a pseudoplastic suspension decreases as the viscosity of the suspending liquid increases, indicating excess energy dissipation in a less viscous liquid. In contrast, the relative viscosity of a Newtonian suspension is only slightly affected by the liquid viscosity. It is in excellent agreement with the value predicted from the rigid sphere model which neglects nonhydrodynamic interactions, and assumes zero particle-to-liquid relative velocity. The flow behavior indices of both concentrated suspensions are independent of the liquid viscosity.