19

Related to this previous question: Could a city be built out of Balloons?

Remember in Oz where the witch is riding in on a bubble. enter image description here I began to think how could I make this as real as possible.

You can breathe helium in place of nitrogen to have an 85% helium to 15% oxygen ratio. Could a person be put inside a clear balloon with enough buoyancy to ride in a bubble?

Would there be any practicle use for this?

enter image description here

Muze
  • 1
  • 1
  • 11
  • 36
  • 1
    Winning answer should calculate bubble size to suspend 70 kg passenger at sea level. Calculate for one bubble using hydrogen and one using helium, each w 15% O2. I am tempted to do it but enough of me already. – Willk Apr 22 '18 at 23:18
  • 1
    Hydrogen is not toxic. Experimentally it has been tried for sick people breathing high O2 levels because H2 is such a good oxygen radical scavenger. Generally, a combination of hydrogen and oxygen for breathing poses an explosion risk and so is not usually done. But H2 is half the weight of He and so your bubble could be smaller. – Willk Apr 22 '18 at 23:28
  • 4
    so basically a blimp with added oxygen. – John Apr 23 '18 at 00:58
  • 8
    Question doesn't appear to have anything to do with World Building per se. This is basically a math / physics question and might best be moved to one of those forums. – elemtilas Apr 23 '18 at 01:11
  • 1
    I'll assume this is ruled out by the way the question is framed, but you could have a mask+hose and breathe outside air. Given how light the helium-oxygen mixture is, that may be pointless though. – JollyJoker Apr 23 '18 at 09:42
  • @Willk Replacing He with H2 will improve your lift by about 10%. That's a nice saving to have but maybe not at the cost of flying around inside a bomb that can be detonated by a spark... – GB supports the mod strike Apr 23 '18 at 10:48
  • 3
    @elemtilas OP is often banned from physics, as is currently the case, which may be one reason for the question being posted here instead. – pipe Apr 23 '18 at 11:26
  • 1
    How is this about building fictional worlds, exactly? – Mołot Apr 23 '18 at 12:34
  • Kinda. Now it looks like you are repeating yourself, this time omitting any part that could be considered worldbuilding. – Mołot Apr 23 '18 at 14:38
  • 2
    @pipe I really don't see how the OP being banned from another SE forum makes it okay to ask a purely physics / science question here. Might as well try the luck over on SE.Music! Also, one wonders why the OP is banned from SE.Physics in the first place... – elemtilas Apr 23 '18 at 23:21
  • 1
    @Muze I see. Well, I guess, lessons learnt and all that! It seems rewriting the above question so that it is on topic for SE.Worldbuilding is in order! – elemtilas Apr 24 '18 at 01:39
  • 1
    @elemtilas is this better? – Muze Sep 09 '18 at 22:15
  • @Muze --- No, not really. – elemtilas Sep 10 '18 at 02:53
  • @elemtilas I think this question is on topic. The fact that I got suspended elsewhere should not affect my ability to participate here. This question is a part of the City built out of balloons – Muze Apr 18 '19 at 00:43
  • @a CVn can you tell me what I need to do to have this question reopened? – Muze Apr 18 '19 at 00:44
  • @Muze -- Long time no see! You're correct, your being banned elsewhere does not prohibit you from participating here. You're still not excused from following the rules of WB.SE, and the community is not beholden to you to let you ask off topic queries. As I said a whole year ago (well almost!): It seems rewriting the above question so that it is on topic for SE.Worldbuilding is in order! Do that and I'll happily nominate it for reopening! – elemtilas Apr 18 '19 at 01:30
  • @Muze -- In order for this query to be reopened it needs to demonstrate worldbuilding context at the very least. Right now, your question is purely real world. And the answer is, such devices already exist. You can get one for $300 or so. Pump some He and O2 in there, roll into the pool and Bob's your uncle. – elemtilas Apr 18 '19 at 01:32
  • @Muze -- Also, why do you want this query reopened? You've already gotten your one best answer and you've chosen it as such! – elemtilas Apr 18 '19 at 01:34
  • @elemtilas because it is in topic and should be open – Muze Apr 18 '19 at 04:01
  • @Muze -- I wonder if this is the kind of attitude that got you banned elsewhere. You don't have to take my advice if you don't want to; I can't force you after all! – elemtilas Apr 18 '19 at 16:13
  • How can you "make this as real as possible" when these things are already actual things!? Your question is still off topic for all you slapped a picture of Oz in the text. – elemtilas Apr 23 '19 at 01:43
  • 2
    It sounds like the only objection to this question is that it isn't connected enough to WB. I don't see that as a problem. It's as connected as many other (still open) questions about what could or could not happen in a particular world, real or not. The edit is a lot clearer as well. I VTR. – Cyn Apr 23 '19 at 02:18

1 Answers1

26

A cubic meter of air weighs about 1.2kg. A cubic meter of 15% O2 and 85% He would weigh about 20% of that or about .25 kg. so a cubic meter of the O2/He mixture would lift about 1kg.

Ignoring the weight of the bubble itself, a 70kg person would need a 70 m3 bubble, which would be about 5 meters in diameter. Since the bubble material would have to be pretty strong to support an adult standing on it, let's call it as needing a 6 meter diameter bubble to also lift the bubble's weight.

Note: While floating in a bubble will attract media attention, it would be most unkind to ask the floatee to do interviews...

According to hosstuffworks:

The average adult at rest inhales and exhales something like 7 or 8 liters (about one-fourth of a cubic foot) of air per minute. That totals something like 11,000 liters of air (388 cubic feet) in a day.

The air that is inhaled is about 20-percent oxygen, and the air that is exhaled is about 15-percent oxygen, so about 5-percent of the volume of air is consumed in each breath and converted to carbon dioxide. Therefore, a human being uses about 550 liters of pure oxygen (19 cubic feet) per day.

So a human needs about 1 cubic meter of pure oxygen/day or about 5 cubic meters of the O2/He mixture. This website says that people can comfortably breath air that is 25% depleted of O2 (equivalent to 10,000 feet which by experience is no particular problem for healthy people.)

Given that, an adult needs about 20 cubic meters of the O2/He mixture/day so as to not deplete it below 75% of its original oxygen. The 6 meter sphere has about 120 cubic meters of the gas mixture, so it will last about six days without any difficulty and would probably work for double that in a pinch.

Hydrogen works the same as helium within the accuracy of these calculations, but a no smoking policy is advised.

Community
  • 1
Mark Olson
  • 14,268
  • 1
  • 43
  • 54
  • 3
    Build your "bubble" from a selectively permeable material which allows carbon dioxide to pass one way, and oxygen to pass the other way, while not allowing hydrogen to pass the same direction as carbon dioxide. – Bob Jarvis - Слава Україні Apr 23 '18 at 02:41
  • 4
    @BobJarvis : that won't work because hydrogen is much smaller than carbon and oxygen. – vsz Apr 23 '18 at 04:06
  • 1
    @vsz: Could be made to work. Consider the way cell walls are selectively & actively permeable to some ions & molecules, but not others, regardless of size. See e.g. ion channels, glucose transporters, &c. – jamesqf Apr 23 '18 at 05:32
  • 1
    Carbon dioxide should be removed somehow, otherwise it could poison/suffocate the person even with adequate oxygen present. – Setsu Apr 23 '18 at 05:49
  • 3
    @jamesqf : then it won't just be a thin and light membrane, but a heavy and complex machinery. Or do you know of any membrane which can do this? – vsz Apr 23 '18 at 06:06
  • 2
    @vsz just add a small chemical scrubber that captures CO2. No need for heavy or complex. – tucuxi Apr 23 '18 at 09:16
  • 4
    @vsz: this is perfectly simple to handle. You use a microcrystalline honeycomb of handwavium filled with liquid unobtanium. Not ONLY does this handle the "selectively permeable" thing, but it ALSO sharpens razors, causes hair to grow WHERE YOU WANT IT, cures warts, makes you smarter, better looking, taller (or shorter - your option), AND if you ACT NOW, it comes with a LIFETIME SUPPLY of GINSU-KNIFIUM!!! AS SEEN ON TV!!!!! :-) – Bob Jarvis - Слава Україні Apr 23 '18 at 11:09
  • @vsz: Animal cell walls are ~20 nm thick, though you'd need some supporting structure as well. As for a membrane that can do this, ever thought about how your lungs transfer oxygen into your blood, while removing carbon dioxide? – jamesqf Apr 23 '18 at 19:11
  • 1
    @Muze replacing oxygen with CO2 when the C comes from the body will change nothing - every 1.8 liters of O2 that gets converted will see the atmosphere getting one gram heavier, the passenger getting one gram lighter, and the buoyancy remaining the same. – LSerni Apr 25 '18 at 20:36
  • 2
    @Muze also, as soon as CO2 levels increase enough, the sphere will become "stuffy" and it will be increasingly difficult to breathe, even if enough oxygen is still there. You need some sort of chemical CO2 scrubber - lithium hydroxide would do great. – LSerni Apr 25 '18 at 20:39
  • @jamesqf "As for a membrane that can do this" -- that's not done by a membrane, that's the hemoglobin molecule at work. Almost no organic membranes are impermeable to hydrogen gas (not single protons), and they rely on active transport, which requires powering the membrane by drenching it in a suitable intercellular fluid, lymph, or blood. The resulting weight would be excessive even if you used it only in a small section of the sphere. – LSerni Apr 25 '18 at 20:54
  • @LSerni: So hemoglobin isn't contained within red blood cells, which have cell walls? And those red blood cells don't travel within vessels, which are in turn composed of cells? – jamesqf Apr 26 '18 at 04:20
  • @jamesqf Yes. And those walls do not stop diffusion of either oxygen or carbon dioxide. To keep the hydrogen inside against a concentration gradient you need a gas-impermeable membrane (see e.g. https://nvlpubs.nist.gov/nistpubs/jres/25/jresv25n3p309_A1b.pdf ). To also let oxygen and carbon dioxide flow, you need that, plus an active transport mechanism which is insensitive to hydrogen. – LSerni Apr 26 '18 at 04:59
  • reopen please thanks and Merry Holidays. – Muze Sep 09 '18 at 22:38
  • I'll be the guinea pig and ride a hurricane at sea. – Muze Sep 09 '18 at 22:52