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The Dynamics of Accumulating Ferrofluid Aggregates

[+] Author Affiliations
Alicia M. Williams, Pavlos P. Vlachos

Virginia Polytechnic Institute and State University, Blacksburg, VA

Paper No. FEDSM2008-55101, pp. 333-342; 10 pages
doi:10.1115/FEDSM2008-55101
From:
  • ASME 2008 Fluids Engineering Division Summer Meeting collocated with the Heat Transfer, Energy Sustainability, and 3rd Energy Nanotechnology Conferences
  • Volume 1: Symposia, Parts A and B
  • Jacksonville, Florida, USA, August 10–14, 2008
  • Conference Sponsors: Fluids Engineering Division
  • ISBN: 978-0-7918-4840-1 | eISBN: 0-7918-3832-3
  • Copyright © 2008 by ASME

abstract

The physics of steady and pulsatile flows laden with superparamagnetic nanoparticles in a square channel accumulating under the influence of a 0.5 Tesla permanent magnet are studied by means of focused shadowgraphs. The accumulation physics of these nanoscale particles is explored as functions of the flow type (steady and unsteady) and accumulation type (injected from the top of channel versus bottom of channel). Ferrofluid is accumulated by the steady injection of a streakline that enters the test section upstream of the magnet, where an aggregate forms. The interfacial phenomena resulting from the interaction of the ferrofluid with the bulk flow is resolved using shadowgraph imaging, where a digital camera captures the side view of the aggregate. Ferrofluid aggregate physics is examined both visually in the raw frames as well as by post-processing to determine the aggregate size evolution in time and couple that bulk information with interfacial behavior using the Proper Orthogonal Decomposition (POD). The shadowgraphs show that the aggregate exhibits different regimes based on bulk flow Reynolds number, which is varied between 100 and 1000, based on the mean flow rate. The aggregate exhibits stable behavior at low Reynolds numbers, where it stretches as it grows and minimal decay of the aggregate occurs. At moderate Reynolds numbers above 400, inertial forces dominate the dynamics, and aggregates do not attain the same size and height as in low Reynolds number cases. Therefore, the interaction of the aggregate with the bulk flow is diminished. The accumulation of ferrofluids is positively impacted by increased magnetic field gradients for some Reynolds numbers, while very high or low magnetic field gradients result in smaller, unstable aggregates. This work is the first to study the accumulation of ferrofluid aggregates over such a large parameter space, which reveals many physics that were previously unexplored in ferrohydrodynamics.

Copyright © 2008 by ASME

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