5 ms·
The height limit of a siphon
- chadnickbok 11y agoRelevant xkcd what-if: http://what-if.xkcd.com/143/ http://what-if.xkcd.com/143/
- aaron695 11y agoExcept he has gotten it wrong hasn't he? Which I guess is why this is trending.
- gefh 11y agoHis note [5] links to https://www.youtube.com/watch?v=8F4i9M3y0ew https://www.youtube.com/watch?v=8F4i9M3y0ew which is a demonstration of a siphon in a vacuum, so he's covered :)
- Dylan16807 11y agoBut working "a little bit" as the note says is a good way off from working an order of magnitude or two better.
- marcosdumay 11y ago> Sodium action figurine collection Randal surely has some interesting friends.
- emmelaich 11y agoMy summary: the limit is much higher than can be predicted by barometric pressure because of the tensile strength ("surface tension" of water)
- matthiasl 11y agoA longer summary: the maximum height of a siphon pumping water, at sea level, predicted by barometric pressure is about 10m. But the tensile strength of water is nonzero (a surprise to me) and that is enough to allow much higher siphons if you first remove dissolved gases from the water. The paper speculates that several hundred metres may be possible, perhaps even more. The paper also describes an actual experiment where they showed that a 15 metre high siphon works in practice.
- venomsnake 11y agoWhat are the practical implications of higher siphons?
- johnm1019 11y agoIANA fluid dynamics expert, but it seems to me that for certain designs which move water by creating a lower pressure at some point inside of a pipe you've created a "siphon" in a general sense. If that's true, this could affect certain water pump and plumbing designs, albeit this degassing process may be prohibitively expensive.
- Gravityloss 11y agoClosed circulation central heating systems are degassed. Though, the water is hot there so boils much more easily. Maybe closed circulation cooling water systems...
- graeham 11y agoIts more than this - its that the model of balancing the weight of water with the vacuum pressure being the siphon limit is not correct. This paper shows an alternative model is more likely to be correct. It is that the water boils easily at low pressure, and that is the limit of siphon height. By careful preparation (degassing), boiling is prevented. Which here allows the column to be raised about 10m. A 'law of physics' has been modified. This is pretty cool!
- glup 11y agoSo this is why I couldn't siphon (gray) water from my bathtub on the third floor to water plants in the yard, not lack of moral fortitude. Great!
- jeremysmyth 11y agoNo, unless the water had to rise 10m from your bathtub before descending. If it only had to rise enough to climb through a window before descending to your yard, then that is not enough to produce the problem in the article. The problem described is that water cannot be lifted up more than 10m (due to air pressure pushing on the bath side not exceeding the weight of 10m of water in the hosepipe), not pulled down on the far side.
- basicplus2 11y agoyet but no.. 1. bottom of siphon outlet has to be sealed by the surface of water held in a container.. and 2. and height of long side must less that atmospheric pressure in height from said surface of water or water column on down side will break and draw will be lost
- LeifCarrotson 11y agoBut the bottom side of the siphon doesn't have to be the bottom of the system. Run the tube up 1m to the window and back down out the window perhaps 3m to a bucket on the porch roof - an easy, simple, working siphon. From that bucket, you can use a regular positive-pressure bottom drain to go down as far as you like.
- deleted 11y ago[deleted]
- mabbo 11y agoThis is why water is pumped from below pushing up rather than pulling from the top. But perhaps this will open up new ways to make water pumping more efficient.
- iandanforth 11y agoI love this classic science. Theoretically this experiment could have been performed in the 19th century!