lfin said:
thanks for all your replies.
So from the last answer it looks that only about 1 litre can be compressed in a cartridge, so not very useful at all, as as far i can understand, that could only lift less than a gram.
I was trying to figure out if it was possible to build a inflatable personal beacon for signalling/ rescue, but it looks unpractical at best..
Let's not discard it out of hand just yet. There's definitely some challenges here, but they're still worth looking at from a thought experiment/learning opportunity perspective.
Issue #1: Sealing the cartridge. Every CO
2 cartridge I've ever seen has a puncture disc as the seal. It's a single-shot option that works quite well. No moving parts to leak or fail, so it's great for extended storage. But it does make recharging the cartridge impractical. Any helium cartridge would not be able to make use of that kind of a system, unfortunately, as they seal the CO
2 cartridge at ambient pressure using dry ice pellets in the cartridge. So you'll need a valve system, or an alternate means of charging the cartridge. For your particular case, it will also need to be able to be triggered without needing to turn a valve multiple rotations, correct? That will also add to the challenge.
So, what could be your options to do this?
Issue #2: Pressure. As others have pointed out upthread, running at standard CO
2 cartridge pressures doesn't provide enough helium for a practical balloon. Unfortunately, the kinds of pressures needed to fit a reasonable amount of helium is going to be more than twice that of the cartridge, which will absolutely burst the cartridge casing. You'll need to have a dedicated cylinder to handle that. Probably a composite overwrapped cylinder for weight savings. I know from first-hand experience that bottles like that can fit 88 cubic feet of oxygen gas at 1800psi, coming in at the size of a large handheld fire extinguisher... about 1 foot in diameter and 2 and a half feet long without regulator. They
do have a 5 year inspection cycle, though. Something to keep in mind for your design.
Issue #3: Size. Do you know how much your beacon is going to weigh? That will help size your balloon, which then determines your gas volume that you need to store. Furthermore, is the lift gas canister intended to stay on the ground, or go aloft with the beacon? That weight would need to be accounted for if it's going aloft, too. Otherwise, it can stay on the ground and be your anchor weight.
How compact are you trying to make the assembled package?
lfin said:
it looks that the other alternative may be to use hydrogen, but it would be too dangerous for the average person to use.
Certainly an option, and a fairly valid one, actually. You'll get about double the lifting force out of hydrogen, from my understanding, and it should be noticeably cheaper, too.
The biggest issue would be leaks through whatever seals are used... molecular hydrogen is a slippery bastard, willing to straight up diffuse into and through certain metals. Helium isn't
quite as bad, as it's not going to diffuse through the metal quite so aggressively, but it will absolutely slip through seals if not done extremely well.
lfin said:
I wasn't looking to compress the helium myself, but to find someone who would do it commercially.
Probably for the best. I've worked with 1800psi nitrogen and oxygen before, and it does require specialist equipment to reach those pressures, as well as care in setting things up, especially the oxygen. But that was on equipment
designed for easy use, such as recharging the emergency oxygen on business jets and the emergency nitrogen bottle for the landing gear and brakes on same. I'm not familiar with helium or hydrogen handling, so that would require some research.