0
$\begingroup$

Is it possible for a weather balloons filled with helium gas to lift the weight of itself and a helium tank(highest psi possible) which can fit the volume of the lifting gas in it?

Assuming a typical weather ballon material is used as the ascending vehicle would the balloon with the helium pumped back in the tank fall down to the earths surface?

P.S. In water the weight as well as the surface area for that weight determine its buoyancy - ships etc. A 5tons of dense block steel would sink in water but spread around over wide enough area it should float instead.

Wouldn't the same thing apply to the difference between a helium gas filling the larger volume of the balloon vs the high pressure compact volume storage vessel?

$\endgroup$
  • $\begingroup$ Not quite sure what you're asking. "Is it possible to have a container such that if you fill it with helium it is less dense than air?" - Yes, see balloons. "Is it possible for a tank full of helium not to lift, but when you pump the helium out of that tank into an attached balloon, for that balloon to then lift the tank?" - No, the lift of the helium when in the balloon is the same as when it was in the tank (ignoring the small increase in volume of the balloon and hence decrease in density). $\endgroup$ – AndyT Aug 11 '16 at 16:21
  • $\begingroup$ Thanks @AndyT . How about surface/volume differences of helium inside the tank vs helium filling up the balloon? Have you considered any similarity might exist between water buoyancy of ships vs water buoyancy of the same ship compressed into a dense block of equal weight? $\endgroup$ – Nick Aug 11 '16 at 16:58
  • $\begingroup$ 1. Turns out the increase in volume of the balloon was much more than I assumed. 2. "A 5tons of dense block steel would sink in water but spread around over wide enough area it should float instead." - Oh dear. Density is mass/volume; mass/area is completely unimportant. A 1000m x 1000m x 0.001m steel plate will sink just as much as a 10m x 10m x 10m steel cube. $\endgroup$ – AndyT Aug 12 '16 at 8:11
2
$\begingroup$

As a reality check lets consider industrial gas tanks as the specifications are easily available.

A BOC size D hydrogen tank has a gross weight of 57kg and contains 23kg of hydrogen at 230bar.

At atmospheric pressure hydrogen has a density of 0.09 kg per cubic metre so you get about 255 cubic metres of gas at atmospheric pressure.

This will give lift of about 250 kg, so substantially more than the gross weight of the tank. You could also improve on this a bit by improving the performance of the cylinder eg a composite tank could significantly reduce the 'dead' weight of the system.

The problem is in compressing the gas back into the tank which would require a high pressure compressor plus a power supply to run it. This is probably not entirely beyond the realms of possibility but is going to eat substantially into the payload and probably isn't really worth it as the only benefit of this system compared to just venting the gas is saving the cost of the gas itself.

So the short answer is that yes it is probably possible (albeit likely very expensive) but there aren't any real advantages in doing it this way.

If you are looking at something a bit larger and more sophisticated like a passenger airship then, maybe as you already have an on-board power supply and the overheads of the compressors and tanks may be worthwhile, but it would take a fairly serious feasibility study of an actual design concept to say for sure.

| improve this answer | |
$\endgroup$
  • $\begingroup$ So gross weight of 57kg(worst case of dead weight) that can lift 250kg gives a decent range to anything that may be needed in addition. Would the 'airship' descend if the 255 cubic meters are compressed back in the tank? $\endgroup$ – Nick Aug 11 '16 at 17:30
  • $\begingroup$ Found a 4500 psi compressor - 'shoebox sized' on YouTube by the way... $\endgroup$ – Nick Aug 11 '16 at 17:37
  • $\begingroup$ Yes to both. Density of a gas is directly proportional to its pressure. ie 1 cubic metre of gas at 230 bar will occupy 230 cubic metres at atmospheric pressure. And as a rough rule of thumb hydrogen or helium give around 1 kg of lift per cubic metre (hydrogen slightly more than helium but they are similar). $\endgroup$ – Chris Johns Aug 11 '16 at 17:42

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.