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Siphon
Mar 23, 2011 19:42:55 GMT 1
Post by principled on Mar 23, 2011 19:42:55 GMT 1
Was listening to a podcast about how siphon's work (remember last year that the OED had used the wrong description of how it works for over 100 years). Anyway, the discussion about proving how it worked turned to the height of water that can be supported by air pressure. Although this is around 10.3 metres for a normal tube, in small diameter tubes this height can be increased apparently-due to the strength of the atomic bond in water molecules amongst other things, I believe. Question: Is there an optimum internal diameter of tube where the height supported by air pressure is at its greatest? Does the energy required to increase the height of the liquid above that normally supported by air pressure mean that the water temp would be lower? P
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Siphon
Mar 23, 2011 19:50:05 GMT 1
Post by Progenitor A on Mar 23, 2011 19:50:05 GMT 1
Blimey!
Dunno Sorry
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Siphon
Mar 23, 2011 20:10:40 GMT 1
Post by speakertoanimals on Mar 23, 2011 20:10:40 GMT 1
I think capillary action is what you're looking for, but it depends on the surface tension in the fluid, and adhesion with the walls of the tube. Hence depends on what you make the walls out of. In the simplest model, the narrower you make the tube, the higher the liquid creeps. Vitally important to such national passtimes as this: www.teadunking.co.uk/national-tea-dunking-day.html
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Siphon
Mar 23, 2011 20:13:02 GMT 1
Post by speakertoanimals on Mar 23, 2011 20:13:02 GMT 1
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Siphon
Mar 23, 2011 22:12:21 GMT 1
Post by principled on Mar 23, 2011 22:12:21 GMT 1
Hi STA. Ah dunking, those were the days! Don't do biscuits anymore, unfortunately. Too naughty and nice! Getting back to your reply. The Wiki article on superfluids takes some digesting, especially the statement that there can be a movement of mass without a change in energy and that there is NO temperature gradient either. I assume that as there is no friction, the work is totally done by gravity hence no use of energy by or from the fluid itself.(as opposed to ats. pressure and gravity in the conventional siphon). Thanks for your answer about the height of water in a tube. You might be right about the capillary action only, but I'm sure the physicist mentioned something about atomic bonds. Anyway, working back from the idea that the narrower the tube the higher the water will rise, at what diameter does capillary action no longer play any decisive part in the height the water reaches due to ats. pressure? P
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Siphon
Mar 24, 2011 13:12:19 GMT 1
Post by speakertoanimals on Mar 24, 2011 13:12:19 GMT 1
As far as I can see, there is always going to be some sort of meniscus, hence always that slight additional force pulling the water up just a teeny bit!
Superfluids are just mad, granted!
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Siphon
Mar 24, 2011 15:08:51 GMT 1
Post by carnyx on Mar 24, 2011 15:08:51 GMT 1
I think that osmotic pressure is the one to watch, as it is the process that gets water up to the tops of trees that are well beyond the 32 feet limit.
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