Bubbles Escaping from Submerged Container

[gordonb]

Hi
We have a problem at work where we need to store a metal container under water. The container is to have small holes in the lid to ensure that it floods when submerged but we must minimise the size of these holes. Intuitively, if you have more than one hole in the lid then water will enter one while the air escapes through another but when we've tried it, this is not the case. I'm guessing that surface tension is preventing the bubbles from escaping. So I'm wondering if there is a way to calculate the minimum hole size for a given depth of water to ensure that bubbles will escape from the container.

Hope someone can help.

Thanks

Gordon

 

[Borek]

Does the lid have to be flat? I wonder if adding two tubes going in different directions (one inside the container, the other outside) won't help, generating small pressure difference.

But I can be completely off.

 

[gordonb]

Thanks for the reply. Yes the lid has to be flat and we don't really have time to make any complex modifications to the can or lid unfortunately.

 

[AlephZero]

Or, put the container on its side, or tilt it, so the holes are at different levels.

If the two holes are at the same depth in the water, how do the water and air "know" which hole is supposed to be the way in and which is the way out? (there's serious point about the physics and symmetry there, as well as a joke)

 

[JanEnClaesen]

Can't you use straws?

 

[gordonb]

AlephZero, yes, it makes sense that holes would need to be at different heights. That explains why slightly tilting the container causes bubbles to start to appear. We may be able to put a hole in the side as well as one on the top.

JanEnClaesen, no, straws or any similar tube wouldn't be possible.

 

[Baluncore]

Maybe a waxy surface on the can is preventing wetting of the small hole. You might put one drop of detergent on one hole to see if it makes a difference. If you punch the holes, lubricate the punch with detergent, avoid oil.

There are adjuvants or wetting agents, (eg “pulse”), used with herbicides to break the waxy surface of weeds, maybe adding some such agent to the water before sinking the can will solve the problem.

 

[SteamKing]

Why can't you have at least one hole in the container itself?

 

[gordonb]

I'll try and reply again. For some reason my replies aren't showing up here.

AlephZero, you make a good point. This would explain why we see bubbles being released when the container is tilted as it is lowered.
JanEnClaesen, we can't use straws or anything similar, we have to rely on holes.
Baluncore, unfortunately we can't add anything to break the surface tension but we'll ensure that there aren't any residues around the holes.
SteamKing, yes, based on AlephZero's suggestion I think we will have to put at least one hole in the side.

Thanks to all who have replied.