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

Stover, Carl A.; Koch, Donald L.; Cohen, Claude

doi:10.1017/s002211209200171x

Cited by 182 publications

(100 citation statements)

References 3 publications

(8 reference statements)

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…It has been report 15 that the transport properties of these ellipsoidal particles remain close to those of spherical particles. However, certain interesting concentration and orientation trends were observed which were in agreement with experimental observations [19][20][21][22][23][24] . Similar to spheres, therefore, prolate spheroids were found to accumulate in the viscous sub-layer and preferentially concentrate in regions of low-speed streaks, with a strong dependence on their inertia ) (  p and a minor dependence on their aspect ratio.…”

Section: Introductionsupporting

confidence: 89%

Simulation of inertial fibre orientation in turbulent flow

Njobuenwu

Fairweather

2016

Physics of Fluids

View full text Add to dashboard Cite

The spatial and orientational behaviour of fibres within a suspension influences the rheological and mechanical properties of that suspension. An Eulerian-Lagrangian framework to simulate the behaviour of fibres in turbulent flows is presented. The framework is intended for use in simulations of nonspherical particles with high Reynolds numbers, beyond the Stokesian regime, and is a computationally efficient alternative to existing Stokesian models for fibre suspensions in turbulent flow. It is based on modifying available empirical drag correlations for the translation of non-spherical particles to be orientation dependent, accounting for the departure in shape from a sphere. The orientational dynamics of a particle is based on the framework of quaternions, while its rotational dynamics is obtained from translational dynamics, in terms of preferential concentration, is strongly dependent on their inertia and less so on their aspect ratio. However, the contrary is the case for the fibre alignment distribution as this is strongly dependent on the fibre aspect ratio and velocity gradient, and only moderately dependent on particle inertia. The fibre alignment with the flow direction is found to be mostly anisotropic where the velocity gradient is large (i.e. viscous sub-layer and buffer regions), but is virtually non-existent and isotropic where the turbulence is near-isotropic (i.e. channel centre). The present investigation highlights that the level of fibre alignment with the flow direction reduces as a fibre's inertia decreases, and as the shape of the fibre approaches that of a sphere. Short fibres, and especially near-spherical 001 . 1  particles, are found to exhibit isotropic orientation with respect to all directions, whilst sufficiently long fibres align themselves parallel to the flow direction, and orthogonal to the other two co-ordinate directions, and the vorticity and flow velocity gradient directions.2

show abstract

Section: Introductionsupporting

confidence: 89%

Simulation of inertial fibre orientation in turbulent flow

Njobuenwu

Fairweather

2016

Physics of Fluids

View full text Add to dashboard Cite

show abstract

“…This leads to an asymmetry about the flow direction in aggregate orientation distribution. Similar effect has been observed experimentally in shear flows of semi-diluted fiber suspensions [Stover et al (1992)]. The asymmetry of fiber orientations with respect to the streamlines was attributed to collisions between fibers, which were accounted for by an effective rotary diffusive process [Folgar and Tucker (1984)].…”

Section: Resultssupporting

confidence: 64%

Rotational diffusion may govern the rheology of magnetic suspensions

Kuzhir

Magnet

Bossis

et al. 2011

Journal of Rheology

View full text Add to dashboard Cite

SynopsisThis paper is focused on the theoretical modeling of the rheological properties of the magnetic suspensions in shear flows under an external magnetic field aligned with the streamlines. The conventional theory postulates that the field-induced aggregates of magnetic particles are highly anisotropic and aligned with the flow direction. Therefore, no substantial variation in suspension viscosity would be expected in the presence of field. However, experiments reveal a strong Bingham rheological behavior of the suspensions with a dynamic yield stress of the same order of magnitude that the one measured in the magnetic fields perpendicular to the flow. We explain the high level of shear stress, generated in longitudinal magnetic fields, by stochastic rotary oscillations of the aggregates caused by many-body magnetic interactions with neighboring aggregates. The inter-aggregate interactions are accounted for by an effective rotational diffusion process with a diffusion constant proportional to the mean square interaction torque a net magnetic torque exerted to a given aggregate by all the neighboring aggregates. Using the equations for the orientation tensors coupled with the balance of forces acting on aggregates, we find the orientation distribution and size of the aggregates as function of the magnetic field intensity and shear rate. Our theory, developed for semi-dilute regime, reproduces the Bingham behavior observed experimentally and fits the 2 experimental data reasonably well in a wide range of particle concentrations. We find that the yield stress increases quadratically with the magnetic field strength and exhibits a cubic growth with respect to the particle volume fraction. A part from resolving a particular rheological problem, the new concept of magnetically induced diffusion reveals the importance of long-range non-hydrodynamic interactions in the rotary diffusion process and could probably contribute to the understanding of this process in other concentrated systems subject to non-hydrodynamic interactions.

show abstract

“…Methods to align nanowires in group include shear alignment of nanowires suspended in fluids, [101][102][103][104][105] including wafer-scale alignment in bubble-blown films; [106] brushing suspensions of nanowires over a lithographically patterned substrate to create highly aligned regions of nanowires on exposed areas; [107] and alignment of nanowires in a Langmuir-Blodgett trough. [108] Methods of positioning single nanowires include optical tweezing [109] and opto-electronic tweezing; [110] methods of manipulation by direct contact with scanning probe tips [111] and micromanipulators; [112] and electrophoretic alignment of over pre-patterned electrodes.…”

Section: Arranging Nanowires Of Different Types Using Magnetic Mooringmentioning

confidence: 99%

Use of Thin Sectioning (Nanoskiving) to Fabricate Nanostructures for Electronic and Optical Applications

2011

View full text Add to dashboard Cite

Lead-InThis paper reviews nanoskiving-a simple and inexpensive method of nanofabrication, which minimizes requirements for access to cleanrooms and associated facilities, and which make it possible to fabricate nanostructures from materials, and of geometries, to which more familiar methods of nanofabrication are not applicable. Nanoskiving requires three steps: i) deposition of a metallic, semiconducting, ceramic, or polymeric thin film onto an epoxy substrate; ii) embedding this film in epoxy, to form an epoxy block, with the film as an inclusion; and iii) sectioning the epoxy block into slabs with an ultramicrotome. These slabs, which can be 30 nm -10 µm thick, contain nanostructures whose lateral dimensions are equal to the thicknesses of the embedded thin films. Electronic applications of structures produced by this method include nanoelectrodes for electrochemistry, chemoresistive nanowires, and 4 heterostructures of organic semiconductors. Optical applications include surface plasmon resonators, plasmonic waveguides, and frequency-selective surfaces.

show abstract

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

Cited by 182 publications

References 3 publications

Simulation of inertial fibre orientation in turbulent flow

Simulation of inertial fibre orientation in turbulent flow

Rotational diffusion may govern the rheology of magnetic suspensions

Use of Thin Sectioning (Nanoskiving) to Fabricate Nanostructures for Electronic and Optical Applications

Contact Info

Product

Resources

About