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Can helium be mixed with hydrogen to form a non-explosive mix? (2003)

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Re: Can helium be mixed with hydrogen to form a non-explosive mix? (2003)

#51

Post by nousermane »

jodrellblank wrote: post #47
ravenstine wrote: post #31

Earlier quoted context omitted.

How could hydrogen be a feasible approach to lifting any amount of cargo if aerogel of all things is too heavy? I just find it hard to believe that even the volume of aerogel required to support enough hydrogen to lift a useful amount of cargo would approach even a tiny fraction of the weight of the cargo itself, but perhaps I'm not imagining things correctly.

Airship Hindenburg had 200,000 cubic meters of lift gas[1]. Air masses 1.2 Kg per cubic meter, so 240,000Kg of air in that volume normally. Helium masses 0.18Kg per cubic meter[2], so replacing that volume with Helium gets it down to 36,000Kg. Hydrogen masses 0.08Kg per cubic meter[2], so replacing that volume with Hydrogen gets it down to 16,000Kg. Huge balloons containing almost-nothing, as soon as you replace the…

This. Also, even if aerogel tech improves drastically, there is another, more insidious problem.

Small-molecule gases diffuse through solid matter (search for "helium leak iphone" if you haven't read that fascinating story), so hydrogen will be slowly leaking out of aerogel, much like it does leak from a normal balloon.

Air diffuse back inside at a much, much slower rate - with net effect that pressure inside drops. This will crush/crumple aerogel, with no easy "top it off" option available for normal balloons.

Re: Can helium be mixed with hydrogen to form a non-explosive mix? (2003)

#52

Post by ncmncm »

voakbasda wrote: post #45
nwah1 wrote: post #43

Earlier quoted context omitted.

But they are still flying bombs, even without crew.

Flying bombs that are being controlled remotely. And we know there’s no possible way that a hacking or ransomware group could exploit that channel and fly it into a couple of towers, right? Inconceivable!!

A gas bag that bumped into a building would bounce off. Or rip and the hydrogen shoot up to the sky.

So, no, not especially conceivable. Or plausible.

Re: Can helium be mixed with hydrogen to form a non-explosive mix? (2003)

#53

Post by lenzm »

ravenstine wrote: post #31
dTal wrote: post #16

Earlier quoted context omitted.

Aerogel is too heavy. The resulting infusion will achieve neutral buoyancy at best.

How could hydrogen be a feasible approach to lifting any amount of cargo if aerogel of all things is too heavy? I just find it hard to believe that even the volume of aerogel required to support enough hydrogen to lift a useful amount of cargo would approach even a tiny fraction of the weight of the cargo itself, but perhaps I'm not imagining things correctly.

The basic principle at work is the square-cube law. The mass of an airship enclosure grows 2-dimensionally while the volume and lifting power grow 3-dimensionally. If you use any 3-d structure to support the airship you will have problems.

https://en.wikipedia.org/wiki/Square%E2%80%93cube_law

Re: Can helium be mixed with hydrogen to form a non-explosive mix? (2003)

#55

Post by ravenstine »

dTal wrote: post #35
ravenstine wrote: post #31

Earlier quoted context omitted.

How could hydrogen be a feasible approach to lifting any amount of cargo if aerogel of all things is too heavy? I just find it hard to believe that even the volume of aerogel required to support enough hydrogen to lift a useful amount of cargo would approach even a tiny fraction of the weight of the cargo itself, but perhaps I'm not imagining things correctly.

Usually when you lift cargo, the volume of the cargo is tiny compared to the volume of the lifting gas. Picture a huge blimp with a tiny gondola underneath. With an aerogel infusion, the volume of the aerogel is the same as the volume of the lifting gas. Picture a huge blimp lifting a huge-blimp-sized lump of something underneath. Even aerogel, light as it is, adds up. In other words - it's barely useful, and the onl…

> The fact that an aerogel-filled blimp might still conceivably be neutrally buoyant is actually testament to how incredibly light aerogel is.

True!

I've always had a soft spot for aerogel. I discovered it as a kid back around 2000 when Disneyland had this NASA/JPL Mars rover exhibit and they had a piece of aerogel on display. When I got home I researched it and was really impressed by all its properties. My mom got me some broken pieces of it off eBay (at the time this was way cheaper than buying an intact slab). My parents were pretty cool in nurturing my nerdiness. hah

The more I think about it, the more it seems like aerogel in a hydrogen balloon isn't the best idea for other reasons. If any moisture makes its way into the balloon, I bet it wouldn't take long for the density to suddenly drop catastrophically.

Re: Can helium be mixed with hydrogen to form a non-explosive mix? (2003)

#56

Post by aaron695 »

The original question was wrong, airships have never used this mixture.

You will get a ~8% reduction of cost, but you get other large costs like dealing with hydrogen onsite and dealing with contaminated helium. How does that re-compress? How do you make sure your mixture stays at the right percentage.

What is the purpose here?

Venting helium is expensive, but venting hydrogen is not. You can't do this with a mix but you could vent hydrogen if it's in separate internal bags. That's a possible use, but again you'd need to look at total costs.

Read up properly here for this mixing idea, but there seems little purpose -

Flammability limits of hydrogen-diluent mixtures in air https://prism.ucalgary.ca/bitstream/handle/11023/164/ucalgar... (2012)

"Hydrogen-helium mixtures fail to propagate a flame at 92% helium in the fuel mixture under atmospheric pressure (Calgary, 89k Pa) and ambient temperature. Therefore, only a small percentage of the helium in dirigibles can be safely offset with hydrogen. This is in agreement with previously reported data.

The lean flammability limits of hydrogen binary mixtures with argon, carbon dioxide, and nitrogen diluents in air for upward flame propagation appear to be very close to the limits predicted using the adiabatic flame temperature concept"

Re: Can helium be mixed with hydrogen to form a non-explosive mix? (2003)

#57

Post by simongr3dal »

ncmncm wrote: post #52
voakbasda wrote: post #45

Earlier quoted context omitted.

Flying bombs that are being controlled remotely. And we know there’s no possible way that a hacking or ransomware group could exploit that channel and fly it into a couple of towers, right? Inconceivable!!

A gas bag that bumped into a building would bounce off. Or rip and the hydrogen shoot up to the sky. So, no, not especially conceivable. Or plausible.

What's to stop the hackers from running the halt and catch fire instruction?

Re: Can helium be mixed with hydrogen to form a non-explosive mix? (2003)

#59

Post by goohle »

nousermane wrote: post #51
jodrellblank wrote: post #47

Earlier quoted context omitted.

Airship Hindenburg had 200,000 cubic meters of lift gas[1]. Air masses 1.2 Kg per cubic meter, so 240,000Kg of air in that volume normally. Helium masses 0.18Kg per cubic meter[2], so replacing that volume with Helium gets it down to 36,000Kg. Hydrogen masses 0.08Kg per cubic meter[2], so replacing that volume with Hydrogen gets it down to 16,000Kg. Huge balloons containing almost-nothing, as soon as you replace the…

This. Also, even if aerogel tech improves drastically, there is another, more insidious problem. Small-molecule gases diffuse through solid matter (search for "helium leak iphone" if you haven't read that fascinating story), so hydrogen will be slowly leaking out of aerogel, much like it does leak from a normal balloon. Air diffuse back inside at a much, much slower rate - with net effect that pressure inside drops.…

But we just need a thick but lightweight shell, which is hard to puncture, not a whole volume made with aerogel.
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