Talk:No-slip condition

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I think the last sentence of the first paragraph of the "Exceptions" section--"Some highly hydrophobic surfaces have also been observed to have a nonzero but nanoscale slip length."--really should include a citation: if it's known to have been observed, who has reported having observed it, and where did they report it? Additionally, it might be nice to have a sentence describing how such a determination at "nanoscale" was made/measured. — Preceding unsigned comment added by OlyDLG (talk • contribs) 08:41, 21 June 2019 (UTC)[reply]

Justification

Obviously the no-slip condition is fairly accurate or we wouldn't use it in fluid dynamics. Still, I've never seen a physical justification. At that last layer of molecules, why are they necessarily bound to the solid? That implies that the bond strength between them and the solid is always stronger than the fluid to itself, which can't always be true, can it? I'd guess this comes down surface texture, but don't have any sources for this.―BenFrantzDale 23:19, 26 January 2006 (UTC).[reply]

True —Preceding unsigned comment added by 142.104.117.199 (talk • contribs)

Although I'm rather busy at the moment and won't be able to add anything for a while, I have heard a justification before, it's more to do with molecules at the boundary reaching thermal equilibrium with the solid rather then intra molecular bonds.―Andrew.Ainsworth 21:52, 27 April 2007 (UTC).[reply]

For a viscous fluid, the no slip boundary condition can't be justified from first principles. It is still an open question in science. For viscous fluid flow, it fits almost all macroscopic observations and so it is simply accepted in most fluid mechanics texts books but it is still only an empirical observation, not a fundamental law.

Although it can't be derived, it can be understood by comparing the thermal energy of the fluid molecules and the fluid-wall bonding strength to the viscous energy imparted by the fluid. For the strain rates that are currently experimentally accessible, the energy imparted by the fluid is still several orders of magnitude less than the thermal energy of the molecules or the fluid-wall interaction potential of even the weakest fluid-wall bonds (van der waals forces). Van der waals forces are always present and they are still significantly larger than the shear stress that can be imparted by the fluid in current experiments. So the shear stress at the wall from the fluid flow is only a minor perturbation on the fluid-wall interaction potential or the thermal energy of the fluid molecules.

A number of research groups have been able to mimic a slip boundary condition, by placing a gas gap at the solid liquid interface or by inducing shear thinning (reduced viscosity) in the fluid near the wall. These slip effects are still not macroscopic and are only really applicable in the field of microfluidics. —Preceding unsigned comment added by 128.250.204.118 (talk) 10:40, 4 September 2008 (UTC)[reply]

This page for dummies

This page needs a simple and yet complex explanation of no slip condition, as it is only those who know a thing or two about fuild flow will understand this page, and i don't mean know a thing or two as in the water flows down the pipe. —Preceding unsigned comment added by 208.79.15.101 (talk) 21:00, 20 May 2008 (UTC)[reply]