In a laminar flow regime, a fluid separates into streamlines with a parabolic flow profile. Do particles within such a flow tend to become aligned by mass (e.g. lighter molecules travelling together in faster streamlines)? Or are the flow characteristics of the individual particles basically mass-independent under laminar flow?

Another way of asking this question would be: "Considering the flow of a mixture from point A to point B, is laminar flow (a) desirable, (b) undesirable or (c) irrelevant for ensuring that the composition at point B is representative of that at point A?"

For clarity, this is flow inside a circular tube.

(The reason for asking is that I have scoured the internet and several books for many days and cannot find any treatment of this question. Note: A number of references refer to the importance of 'viscous flow' for maintaining the original composition of a fluid, but this term is sometimes used ambiguously according to context and history and moreover it is not made clear whether the mechanism is inherent to the flow regime, or due to interaction with a wider setup. I can provide links to said references if desired.)

Any authoritative comments or links appreciated - thanks!

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    $\begingroup$ I can't answer your question, but I'm quite sure you need to be more specific about your particular case to get any helpful information. For example, the answer would probably be much different if you're asking about the flow around the outside of a streamlined shape, versus the flow inside a circular tube. $\endgroup$ – D. Halsey Jul 16 '19 at 17:02
  • $\begingroup$ Thanks D. Halsey - I have now edited as you suggest, to say that I am referring to the flow inside a circular tube $\endgroup$ – int Jul 17 '19 at 1:19

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