Lifting power of Compressed Air

[Kalagan]

Hi,

Question: Is the Lifting Power of Air in Water solely based on its Volume or does the pressure of the Air factor in?

As an example, in Salt water if you have a Bell with 2 Cubic ft of Air in it, at the Oceans Surface it can lift 128 Lbs, because air can lift the amount of Water it displaces, which in this example is 2 Cubic Ft and Salt water is 64 Lbs/Cubic ft. so it can lift 128Lbs.

But what happens if you bring that Bell down to 33ft (1 Atmosphere), which will compress the Air to 1/2 its Volume, so at 33ft the Volume of the Compressed Air will now be 1 cubic ft. Would that Bell now only be able to lift 64 Lbs?

What happens if you bring that Bell to 99ft deep or 4 Atmospheres, the Volume is now 25% of its Volume at the Surface, so that same Bell can now only lift 32Lbs?

If that logic holds true in the Ocean, do any of those calculations change if the same Bell is placed in a 100ft Cylindrical Water Tower filed with Salt Water placed on the Ground at Sea Level?

Thanks for any Input.
Kalagan

 

[russ_watters]

Welcome to PF.

You understand the issue perfectly... so the answer to your your last question is no.

 

[astrokreng]

Dear Kalagan,

Thank you for your question regarding the lifting power of compressed air. The answer to your question is that both the volume and pressure of the air play a role in its lifting power.

In your example, the lifting power of the air at the ocean's surface is based on its volume, as air can lift the amount of water it displaces. However, as the bell is brought to greater depths, the pressure of the compressed air also becomes a factor. As you correctly stated, at 33ft deep, the compressed air will have a volume of 1 cubic ft and will be under 1 atmosphere of pressure. This means that the lifting power will be reduced to 64lbs, as the pressure of the compressed air is now half of what it was at the surface. Similarly, at 99ft deep, the compressed air will have a volume of 1/4 of its original volume and will be under 4 atmospheres of pressure, resulting in a lifting power of 32lbs.

In a cylindrical water tower filled with salt water at sea level, the same principles apply. The pressure of the compressed air will increase with depth, and the lifting power will decrease as the volume of compressed air decreases. However, the exact calculations may vary depending on the specific dimensions and conditions of the tower.

I hope this helps to clarify the role of both volume and pressure in the lifting power of compressed air. If you have any further questions or require additional input, please don't hesitate to ask.

Best regards,