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Q & A: fluid flow and diffusion

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Most recent answer: 02/20/2019
Q:
So is it like, if there was a pipe through which water was flowing for 20 years, would the water molecules at its surface be 20 years old? As there was "no slip" at the contact surface since the beginning?
- Narina (age 20)
Bangladesh
A:

You're thinking of the purely deterministic smooth "laminar" flow of the fluid, which does go to zero at the edges for "stick" boundary conditions. Meanwhile, however, the individual molecules are radomly diffusing around in all directions. So no individual molecule is likely to stay near the edge for long.

Mike W.


(published on 02/20/2019)

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