Can the Peclet Number Control Diffusion in Nanoscale Laminar Flow Experiments?

[ponjavic]

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.

 

[Andy Resnick]

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.