scholarly journals Influence of the Polarity of the Electric Field on Electrorheometry

2019 ◽  
Vol 9 (24) ◽  
pp. 5273 ◽  
Author(s):  
J. García-Ortiz ◽  
Samir Sadek ◽  
Francisco Galindo-Rosales
Keyword(s):  
Shear Flow ◽  
Electric Field ◽  
Simple Shear ◽  
Flow Direction ◽  
Extensional Flow ◽  
Electrorheological Fluid ◽  
Stable Configuration ◽  
Simple Shear Flow ◽  
Rheological Characterization

Uniaxial extensional flow is a canonical flow typically used in rheological characterization to provide complementary information to that obtained by imposing simple shear flow. In spite of the importance of having a full rheological characterization of complex fluids, publications on the rheological characterization of mobile liquids under extensional flow have increased significantly only in the last 20 years. In the case of the rheological characterization of electrorheological fluids, the situation is even more dramatic, as the ERFs have been exclusively determined under simple shear flow, where an electrorheological cell is attached to the rotational rheometer generating an electric field perpendicular to the flow direction and that does not allow for inverting the polarity. The very recent work published by Sadek et al., who developed a new electrorheological cell to be used with the commercial Capillary Breakup Extensional Rheometer (CaBER), allows for the very first time performing electrorheometry under extensional flow. By means of the same experimental setup, this study investigates the influence of the polarity of the imposed electric field on the filament thinning process of a Newtonian and an electrorheological fluid. Results show that a polarity against the gravity results in filament thinning processes that live longer or reach a stable configuration at lower intensities of the applied electric field.

Numerical study of electric field effects on the deformation of two-dimensional liquid drops in simple shear flow at arbitrary Reynolds number

2009 ◽  
Vol 626 ◽  
pp. 367-393 ◽  
Author(s):  
STEFAN MÄHLMANN ◽  
DEMETRIOS T. PAPAGEORGIOU
Keyword(s):  
Steady State ◽  
Shear Flow ◽  
Electric Field ◽  
Electric Fields ◽  
Simple Shear ◽  
Simple Shear Flow ◽  
Physical Parameters ◽  
Shear Stresses ◽  
Two Dimensional ◽  
Liquid Drops

The effect of an electric field on a periodic array of two-dimensional liquid drops suspended in simple shear flow is studied numerically. The shear is produced by moving the parallel walls of the channel containing the fluids at equal speeds but in opposite directions and an electric field is generated by imposing a constant voltage difference across the channel walls. The level set method is adapted to electrohydrodynamics problems that include a background flow in order to compute the effects of permittivity and conductivity differences between the two phases on the dynamics and drop configurations. The electric field introduces additional interfacial stresses at the drop interface and we perform extensive computations to assess the combined effects of electric fields, surface tension and inertia. Our computations for perfect dielectric systems indicate that the electric field increases the drop deformation to generate elongated drops at steady state, and at the same time alters the drop orientation by increasing alignment with the vertical, which is the direction of the underlying electric field. These phenomena are observed for a range of values of Reynolds and capillary numbers. Computations using the leaky dielectric model also indicate that for certain combinations of electric properties the drop can undergo enhanced alignment with the vertical or the horizontal, as compared to perfect dielectric systems. For cases of enhanced elongation and alignment with the vertical, the flow positions the droplets closer to the channel walls where they cause larger wall shear stresses. We also establish that a sufficiently strong electric field can be used to destabilize the flow in the sense that steady-state droplets that can exist in its absence for a set of physical parameters, become increasingly and indefinitely elongated until additional mechanisms can lead to rupture. It is suggested that electric fields can be used to enhance such phenomena.

Evidence of magmatic flow by 2-D image analysis of 3-D shape preferred orientation distributions

2004 ◽  
Vol 175 (4) ◽  
pp. 331-350 ◽  
Author(s):  
Patrick Launeau
Keyword(s):  
Image Analysis ◽  
Shear Flow ◽  
Simple Shear ◽  
Flow Direction ◽  
Preferred Orientation ◽  
Simple Shear Flow ◽  
Shear Direction ◽  
Thin Sections ◽  
Passive Deformation ◽  
Shape Ratio

Abstract The 3-D Shape Preferred Orientation (SPO) ellipsoid can be obtained by image analysis on a minimum of three perpendicular sections, when the 2-D measurements can be assimilated to ellipses. As numerous phenomenons can modify the SPO in magma (boundary condition effects, crystal interactions, joint migrations, etc.), the ellipsoid calculation is first tested on a set of digital models of simple shear flow. Those models, made of scattered shape ratio distribution, show that a suspension of crystals in a simple shear flow of the magma produces SPO parallel to the shear direction with an intensity given by the average shape ratio of the crystals, without any link with the amount of shear flow. This steady state SPO along the flow direction is particularly useful to study magma emplacement even if it is also shown that a critical shear rate γ between 4 and 8, for crystal shape ratio between 2 and 5 respectively, is sufficient to completely reorient a SPO. Therefore the SPO does not record magmatic strain as may do an enclave, which is an interface between two magmas with low viscosity contrast, that can record the whole strain of the magma by its passive deformation along the flow. An infinite strain is necessary here to parallelize the enclave on the shear flow direction. The application to a natural case (gabbronorite of the Bushveld, South Africa) shows that we must take care of the mineral chosen to describe a flow in a magma and that a careful classical study of the structures observed in thin sections is always required. To allow anyone to test the quality of the 2-D/3-D conversions, a web site is associated to this publication with a free access to all the image analysis and ellipsoid programs presented below.

Observations of fibre orientation in simple shear flow of semi-dilute suspensions

1992 ◽  
Vol 238 ◽  
pp. 277-296 ◽  
Author(s):  
Carl A. Stover ◽  
Donald L. Koch ◽  
Claude Cohen
Keyword(s):  
Shear Flow ◽  
Simple Shear ◽  
Fibre Orientation ◽  
Flow Direction ◽  
Orientation Distribution ◽  
Index Of Refraction ◽  
Simple Shear Flow ◽  
Flow Gradient ◽  
Dilute Suspensions ◽  
Rotary Diffusion

The orientations of fibres in a semi-dilute, index-of-refraction-matched suspension in a Newtonian fluid were observed in a cylindrical Couette device. Even at the highest concentration (nL3 = 45), the particles rotated around the vorticity axis, spending most of their time nearly aligned in the flow direction as they would do in a Jeffery orbit. The measured orbit-constant distributions were quite different from the dilute orbit-constant distributions measured by Anczurowski & Mason (1967b) and were described well by an anisotropic, weak rotary diffusion. The measured ϕ-distributions were found to be similar to Jeffery's solution. Here, ϕ is the meridian angle in the flow-gradient plane. The shear viscosities measured by Bibbo (1987) compared well with the values predicted by Shaqfeh & Fredrickson's theory (1990) using moments of the orientation distribution measured here.

Negative Viscosity Due to Magnetic Properties of a Semi-Dense Colloidal Dispersion Composed of Ferromagnetic Rod-Like Particles With Magnetic Moment Normal to the Particle Axis

2007 ◽  
Author(s):  
Yasuhiro Sakuda ◽  
Akira Satoh
Keyword(s):  
Magnetic Field ◽  
Shear Flow ◽  
Simple Shear ◽  
Magnetic Moment ◽  
Flow Direction ◽  
Colloidal Dispersion ◽  
Magnetic Interactions ◽  
Simple Shear Flow ◽  
Magnetic Field Direction ◽  
Negative Viscosity

We have investigated the negative viscosity of a colloidal dispersion composed of ferromagnetic rod-like particles, which have a magnetic moment normal to the particle axis. A simple shear flow problem has been treated to clarify the particle orientational distribution and rheological properties of such a semi-dense dispersion, under circumstances of an external magnetic field applied in the direction normal to the shear plane of a simple shear flow. The results obtained here are summarized as follows. For the cases of a very strong magnetic field and magnetic interactions between particles, the magnetic moment of the rodlike particles is significantly restricted in the magnetic field direction, so that the particle approximately aligns in the shear flow direction. Also, the particle can easily rotate around the axis of the cluster almost freely even in a simple shear flow. Characteristic orientational properties of the particle cause negative viscosity, as in the previous study for a dilute dispersion. However, magnetic particle-particle interactions have a function to make such negative viscosity decrease.

Torsional Shear Flow of Nematic and Cholesteric Liquid Crystals. Part I: Nematic Phase

1979 ◽  
Vol 34 (7) ◽  
pp. 818-831 ◽  
Author(s):  
J. Wahl
Keyword(s):  
Liquid Crystals ◽  
Shear Flow ◽  
Electric Field ◽  
Simple Shear ◽  
Nematic Phase ◽  
Simple Shear Flow ◽  
Cholesteric Liquid Crystals ◽  
Material Constants ◽  
Torsional Shear

The simple shear flow of a homeotropic nematic layer in an electric field normal to the layer is studied theoretically and experimentally. Several material constants of MBBA are determined as a function of temperature.

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