Air solubility in water

[JohnWeal]

I am looking at designing a siphon pipeline for draining down a reservoir.

As the pressure reduces towards the high point, so the air is released. Are there any tables in literature that specify the air solubility in water at various pressures?

Also, how is the air released at the high point?

Regards

John

 

[EmmanuelTop]

http://www.engineeringtoolbox.com/air-solubility-water-d_639.html

Dejan IVANOVIC
Process Engineer, MSChE

 

[bimr]

For water at standard atmospheric pressure, the maximum siphon height is approximately 10 m (34 feet); for mercury it is 76 cm (30 inches), which is the definition of standard pressure. This equals the maximum height of a suction pump, which operates by the same principle.

Air pressure is sufficient to sustain a liquid height of about 34 feet for water. Above that height, a near-vacuum forms above the liquid in the closed tube. Actually, the pressure there is the vapor pressure of the liquid. At 20°C the vapor pressure of water is 2.3 pascal, or 17.5 mm Hg.

You would need to evacuate the air to start the siphon. Conversely, you may break the siphon by allowing air to enter.

 

[katmar]

The air can be released at the high point(s) by an automatic air vent, which works on the same principle as a float steam trap but upside down. [Edit: Dumb comment, see below] If you can keep your velocity high enough to ensure that the Froude number is at least 0.5 in the horizontal pipes and 0.65 for vertical down-flow pipes then small amounts of air will be swept out with the water.

Katmar Software - AioFlo Pipe Hydraulics

http://katmarsoftware.com

"An undefined problem has an infinite number of solutions"

 

[cvg]

be careful venting a siphon, you might break the flow. better to keep the flow steady and size the lines for higher velocity to move the air pockets that might form. keep air out of the inlet, use a anti-vortex plate.

http://www.smvlv.com/pdf/Air-in-Pipelines-HRW-Report.pdf

 

[katmar]

Thanks to cvg for catching my mistake. An air vent is not a good idea on a siphon as the pressure inside the pipeline at the highest point could well be below atmospheric. When the air vent opens because there is air accumulating in it, more air could be sucked into the line rather than venting the air that is already inside. Better to go with my alternate suggestion above and make sure the air is continuously flushed out.

Katmar Software - AioFlo Pipe Hydraulics

http://katmarsoftware.com

"An undefined problem has an infinite number of solutions"

 

[georgeverghese]

Think you may need to post a sketch of your best shot at how this siphon pipe is set up (at both ends of the line).

 

[SteveWag]

Assuming that both ends are underwater and the apex of the syphon is not higher than about 23-25 feet above the source, put a line size tee with the side outlet facing upward at the high point, add about 1-foot of pipe with a cap. At the very top, connect a 3/8 or ½-inch hose leading to a small peristaltic pump. Run the pump on a time basis as needed, or if this is a 24-inch or larger pipe, let it run continuously. If no power, use solar cells. Be very careful that the supply end has enough cover so that air is not entrained, meaning deep!
Steve

 

[rconner]

You may be interested in the references also made available in the past thread at

http://www.eng-tips.com/viewthread.cfm?qid=261310

(with that OP maybe dealing with a very similar challenge).