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TECHNICAL PAPERS

Dynamics of Electrorheological Suspensions Subjected to Spatially Nonuniform Electric Fields

[+] Author and Article Information
J. Kadaksham, P. Singh, N. Aubry

Department of Mechanical Engineering, New Jersey Institute of Technology, University Heights, Newark, NJ 07102

J. Fluids Eng 126(2), 170-179 (May 03, 2004) (10 pages) doi:10.1115/1.1669401 History: Received March 04, 2003; Revised October 06, 2003; Online May 03, 2004
Copyright © 2004 by ASME
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Figures

Grahic Jump Location
(a) The initial particle positions, on the midsection normal to the y-direction, are shown. The domain dimensions along the x-, y-, and z-directions are 1.6 mm, 0.8 mm, and 2.4 mm, respectively. The potential is prescribed on the electrode surfaces and the normal derivative of the potential is assumed to be zero on the rest of the boundary. The electrodes on the left are grounded, while the electrodes on the right are activated. (b) Isovalues of the log(|E|) and the direction of E on the domain midsection are shown. (c) Isovalues of log(|E.∇E|) and the lines of dielectrophoretic force are shown.
Grahic Jump Location
The top view of the particle distribution for β=+0.297. (a) t=0.20 s. The particles get divided into three groups. Those on the left move toward the left electrodes, those on the right move toward the right electrodes and those near the center stay near the center. The particles near the domain center come together and form horizontal chains. (b) t=0.7 s. Notice that the particles near (x=0.8 mm, z=0.6 mm) and (x=0.8 mm, z=1.8 mm) form vertical chains and the horizontal chain which was at (x=0.8 mm, z=1.2 mm) moves upwards along the unstable branch of the saddle point. (c) t=11.0 s. The particle chain, in the upper-left part of the domain, is moving toward the electrode. (d) t=13.3 s.
Grahic Jump Location
(a) An oblique view of a typical domain used for simulations. (b) The domain midsection normal to the y-axis is shown. Also shown are the electrode locations and the initial positions of the two particles. The potential is prescribed on the electrode surfaces and the normal derivative of the potential is assumed to be zero on the rest of the boundary. The velocity is assumed to be periodic in the z-direction and zero on the other domain surfaces. (c) Isovalues of log(|E|) and the direction of E at the domain midsection are shown. The electric field is maximum on the electrode tips and does not vary with y. (d) Isovalues of log(|E.∇E|) and the lines of dielectrophoretic force are shown. E.∇E does not vary with y. (e) The z-coordinate of the second particle is plotted as a function of time for four different time steps. (f). The z-coordinate of the second particle plotted as a function of time for three different mesh sizes.
Grahic Jump Location
The top view of the particle distribution for β=−0.297. (a) t=0.2 s. Since β<0, the particles collect in the regions where the electric field strength is locally minimum, i.e., on the domain walls at the center of the domain and the domain walls at the top and bottom of the domain. (b) t=0.85 s. The chains collect in the regions where the electric field strength is locally minimum and that the chains between the lower pair of electrodes are horizontal and those near the domain center are vertical. (c) t∼12 s. (d) t=16.4 s. There is no noticeable change in the particle structure after t=12 s.
Grahic Jump Location
The top view of the particle distribution for β=0.297. (a) t=0.45 s and dp/dz=1 dyne/cm3. The particles collect near electrodes. (b) t=0.8 s and dp/dz=1 dyne/cm3. Notice the curved, concave down chains near the center. (c) t=1.5 s and dp/dz=1 dyne/cm3. Notice the curved, convex up chains. (d) t=0.5 s and dp/dz=5 dynes/cm3. The white particles close to the electrodes were collected in the case of small or no pressure gradient flow described before. (e) t=1.0 s and dp/dz=5 dynes/cm3. The white particles are pushed downstream by the flow. (f) t=1.40 s and dp/dz=5 dynes/cm3. The white particles are moving away from the electrodes, while getting closer to each other because of interparticle attraction and the dielectrophoretic force, which in this region pushes them toward the domain center. (d) t=2.0 s and dp/dz=5 dynes/cm3. The white particles are now captured by the lower electrodes.

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