Neglecting brownian motion for certain particle diameters?

[sina_mech]

Hi,
Imagine we have few particles with different diameters in fluid flow. so, can we neglect brownian forces at certain particle diameters?
Actually I'm looking for a criteria in which we can neglect the effect of brownian forces in fluid flow.

Thanks :-)

 

[mfb]

Sure. You can certainly neglect it for ships, but not for small molecules. The size where you can start neglecting it depends on the other time and length scales and the precision you are interested in.