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Q & A: ferrofluid magnetization

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Most recent answer: 09/11/2013
Hello Van, I have a question regarding magnetic induction. Is it possible for a ferrofluid (something like hydrogen peroxide and iron oxide) to induce a current when passed through copper coils around its pipe? In other words, if a strong magnet is placed along the pipe right before the coil, will the dissolved iron molecules become micro magnets for long enough to induce a current back through the following coils? Will the fluid velocity slow? Thanks, Chris
- Chris C (age 31)
Broomfield, CO, USA

The key question here is whether the ferrofluid keeps its magnetization long enough to induce eddy currents in the coil. I don't think it will.

The magnetic particles will lose their alignment by simple thermal rotational diffusion. In other words, just plain thermal energy makes each particle randomly turn.  The characteristic times to keep orientation depend on the particle diameter, the fluid viscosity, and the temperature. () Just grabbing some numbers from Wikipedia, it looks like a typical ferrofluid particle diameter is about 10nm. () If the fluid has viscosity similar to water, the characteristic diffusion time will be of order 10-6 s.

Mike W.

(published on 09/11/2013)

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