Re: Increase surface tension of water


Joachim Pimiskern wrote:
<randomname12345@xxxxxxxxx> schrieb:
I building a project that requires a liquid to be dripped at the
fastest possible rate. Right now I'm using water coming out of a
little tube, this works pretty well but I'd like to get the most drops
possible per second. When I increase the flow rate, the water will
collapse into a stream.

Maybe you should make the tube opening triangular.
Some articles on droplet physics:
http://www.newscientist.com/article.ns?id=dn4397
http://physicsweb.org/articles/news/7/11/8
http://www.physorg.com/news9547.html
http://focus.aps.org/story/v11/st14
http://www.aip.org/pnu/2005/split/745-2.html
http://www.physorg.com/news75478692.html
http://www.physorg.com/news6312.html
http://www.physorg.com/news8718.html
http://physicsweb.org/articles/news/8/9/3/1
http://physicsweb.org/articles/news/9/7/14/1
http://physicsweb.org/articles/news/10/4/4/1
http://physicsweb.org/articles/news/9/3/14/1

Nice idea. I had not heard of this one before, but you have done your
homework well.

Another phenomenon I have noticed is that when the liquid *fails* to
'wet' (adhere through surface tension) to the material of the orifice
(as aqueous solutions adhere to the tip of a buret), the drops are
significantly smaller. For this reason I used to coat the tip of my
buret lightly with silicone grease (keeping the orifice itself clear)
to insure smaller drops for those titrations with very sharp end
points.

I can't answer to the relative repeatibility of the smaller drops or to
the flow rate, but the smaller drops made for a finer resolution in the
measurements.

I can also add that, at least in the viscous flow regime, the flow rate
varies quadratically with the pressure drop through the orifice (within
reason, of course). Elementary fluid mechanics texts (often found in
the hands of chemical engineers) can provide more explicit equations.

Tom Davidson
Richmond, VA

.

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