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Neglecting brownian diffusion

  1. Dec 9, 2009 #1
    I am going to run an experiment where I have a laminar flow of water with a dye solvent.

    It is necessary that the velocity of the dye particles is mostly in the horisontal directions. Naturally particles will diffuse but my questions is how I can ascertain that this is kept below some prerequisite.

    I assume there should be some dimensional number telling me for example the ratio of convection/diffusion (thinking Peclet?) and using this I can choose my flow rate and channel dimension to keep diffusion below the required number. However, will this work in practice?

    I am looking at particles at a nanoscopic scale where variations in y must be kept below ~5nm over a distance of ~50nm.
  2. jcsd
  3. Dec 9, 2009 #2

    Andy Resnick

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    I think you are going to have a problem because the continuum approximation breaks down at those scales. You can try to use (for example) the Peclet number, but I don't think it will work that well.
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