Physics question for gas property nerds

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scaupus

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I'm trying to get an idea how long we could run a small 1 1/2" wide 6' long tube airlift using an easily carried air source like a 13cf 3000psi pony bottle.

I'm starting with the premise that we need 75psi air pressure exiting a standard low pressure hose, open at the nether end (where it it goes into the bottom of the tube.) Hopefully we will need less psi, but we're starting with that number experimentally based on some data from larger salvage airlifts.

It's for my son's school project.
 
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Easy to believe. All the pictures I have found so far feature an air hose from surface...

However, this is an interesting question. Surely the air must not be able to lift a 6 feet water pillar? Up it goes in any case. These rising bubbles, they drag along some water, right? And this causes water movement, hence suction? Does anyone have the details? What's the relation between amount of bubbles and suction? I have heard that longer pipe means more efficiency. And indeed, there is more bubble at lower pressure, as it tends to expand...
 
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what BRT said. 13cf is not a lot of gas. You have 0.08cf in the tube itself, so you can cycle the tube 175 times before it is done. Really a bit less than that since you have to suck the tank dry to do that. Even less if you are doing it at depth, i.e. call it 150x for reserve which leaves you 1cf left in the tank, and at 33ft you can only cycle that tube 75x. These types of rigs are supported by surface supplied air compressors for a reason.

The one I'm used to is about 6" ID and something like 20ft long or so and uses 33cfm at the surface, so increase that for each atmosphere of depth. Assuming a linear relationship to this design, you're looking at just over 2cfm at the surface to run it, you need to be at minimum 6ft depth so now you're looking at closer to 3cfm, so I guess if you keep it shallow enough, you can run it for up to 4 mins off of a 13cfm bottle, since it is that small. Question then becomes, what are you lifting with a 1.5" ID pipe other than sand? Keep in mind that you'll want a screen on the bottom of it to keep rocks out
 
https://www.shearwater.com/products/peregrine/

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