Levich Institute Seminar Announcement, 02/24/2009
Steinman Hall, Room #312
(Chemical Engineering Conference Room)
Dr. Ehud Yariv
Technion-Israel Institute of technology
"Electro-Hydrodynamic Particle Levitation on Electrodes: Asymptotic Analysis"
This talk is motivated by the observed interactions between colloidal particles which are suspended in an electrolyte solution and are allowed to deposit onto a planar electrode. When exposed to either DC or AC electric currents, the initially dispersed particles appear to attract each other and form planar crystalline aggregates (Trau et al., Science, 272 1996). It has been long realized that this interaction is mainly due to the action of the particle-induced perturbation to the applied electrode field on the charged polarization layer adjacent to the electrode. Use of the thin-Debye-layer model has led to convenient bulk-scale formulations which were solved numerically (Ristenpart et al., J. Fluid Mech. 575 2007).
A common feature in the experimental observations is the small thickness of the particle-electrode gap separation. While this smallness was indeed reflected in the numerical values used in the numerical analyses, it was never used directly so as to obtain an asymptotic approximation.
We here exploit the narrow gap thickness using singular perturbation methods. Thus, the fluid domain is separated into an "inner" gap region, where the electric
field and flow strain rate are intensive, and an "outer" domain, consisting of the remaining fluid domain, where they are moderate. The inner region is analyzed using standard lubrication
approximation, and the outer region is investigated using tangent-spheres coordinates. The inner solution provides an analytic approximation for the hydrodynamic force that keeps the particle
levitating against the action of gravity; the outer solution furnishes an analytic formula for the far-field flow that engenders long-range inter-particle migration. The flow decay with the fourth
power of distance agrees with the numerical results of Ristenpart et al.
CURRENT RESEARCH INTERESTS:
Fluid mechanics, asymptotic methods, electrokinetics,
magneto-hydrodynamics, ionic transport