By Stefan Odenbach
Suspensions of magnetic nanoparticles or ferrofluids might be successfully managed by means of magnetic fields, which opens up a desirable box for uncomplicated learn into fluid dynamics in addition to a bunch of functions in engineering and drugs. The introductory bankruptcy presents the reader with easy details at the constitution, and magnetic and viscous houses of ferrofluids. the majority of this monograph is predicated at the author's personal learn job and bargains with ferrohydrodynamics, in particular with the magnetoviscous results. specifically, the writer stories intimately the interparticle interactions to date frequently overlooked yet of significant significance in targeted ferrofluids. the fundamental concept and the latest experimental findings are provided, making the booklet fascinating analyzing for physicists or engineers attracted to shrewdpermanent fabrics.
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Extra info for Magnetoviscous Effects in Ferrofluids
15. Thus thermomagnetic convection may be used to pump a ferrofluid employed as cooling agent in a high power transformer. 5 Applications and the magnetoviscous effect The second aspect for future applications mentioned above is the change of the properties of the fluids by means of magnetic fields. In the context of the present work especially the magnetically induced change of their viscous properties will have to be discussed. During the past 30 years strong effort has been undertaken to produce liquid materials which undergo strong changes in their viscous properties under the influence of an electronically controllable signal.
To make our further discussion independent from the fluids’ zero field viscosity we define the relative field-induced change of viscosity R as R= h( H ) - h( H = 0 ) h( H = 0 ) = hr Dh = h0 h0 . 34) For large values of H, the Langevin parameter a = (momH)/kBT becomes large and thus for the limit H®¥, tanh(a) goes to zero leading to a high field limit of rotational viscosity only determined by the volume fraction of solid material in the suspension R ( H ®¥ ) = 3 f¢ < sin 2b > 2 . 35) 44 3. The magnetoviscous effect in highly diluted ferrofluids Thus for perpendicular alignment of field and vorticity we end up with an absolute maximum of the relative change of viscosity R°" = y f .
Generally speaking one can state, that the viscosity of a suspension will vary from that of the carrier liquid due to the presence of the suspended particles. 3 Viscous properties in the absence of magnetic fields 23 usual the first approach for a theoretical treatment of such changes has been given for highly diluted suspensions. 20) will hold for suspensions of noninteracting spherical particles. Here hc means the viscosity of the carrier liquid, ho the viscosity of the suspension in the absence of a ~ magnetic field and f denotes the volume fraction of all suspended material.
Magnetoviscous Effects in Ferrofluids by Stefan Odenbach