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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)

#31

Post by ravenstine »

dTal wrote: post #16
rini17 wrote: post #11

Anyone thought about using aerogel infused by pure hydrogen, wrapped in plastic? In case the wrap is breached it should make mixing with air slow, preventing explosion. (I am aware that aerogel is absurdly expensive in needed quantity. Just a thought experiment.)

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.

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

#32

Post by ravenstine »

giantg2 wrote: post #5

Hydrogen is non-explosive. If you prevent oxygen from mixing in, then it's also not going to rapidly deflagrate.

So perhaps a decent enough oxygen barrier, say mylar, combined with something like iron oxide to absorb any oxygen contamination, might provide a decent safety profile? Interesting to think about.

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

#33

Post by blippage »

iamthemonster wrote: post #23

Until I got to the last line I assumed this was about safer transmission of hydrogen, not lift gas. Of course it would be uneconomic for pipelines to have 91.5% inert carrier gas but I wonder if you could use an inert refrigerant gas to make "non-flammable hydrogen mix" within piping that runs to consumers through non-zone-rated or even residential areas, and then refrigerate the gas at point of use, to leave a pure…

But if you lower the temperature, the hydrogen increases in density.

I haven't read the article, but I presume that the use of hydrogen is a non-starter. No-one wants a flaming fireball raining down on them.

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

#34

Post by FlyMoreRockets »

ncmncm wrote: post #24
trutannus wrote: post #15

Earlier quoted context omitted.

It's not random detonation that is the problem, the issue is containment failures, or anything that causes one. A collision, or stress fracture for example will allow oxygen into the tank. In an atmosphere with enough oxygen in it like ours, that's always a risk.

Oxygen leaking in is not an explosion risk. As noted, it takes 25% O / 75% H before it can ignite. Above 75% H it cannot. With positive airflow around possible leaks, sufficient H2 to sustain a flame can be prevented. In a collision, gas released goes up and out of trouble.

As noted, the lower explosive limit for hydrogen in air is 4%. Significantly lower with pure oxygen. https://www.safeopedia.com/definition/2205/explosive-flammab...

The problem is that hydrogen is a very small molecule and readily escapes containment. It can even travel along grain boundaries through solid metal.

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

#35

Post by dTal »

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.

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 only reason it works is because of the square-cube law: the weight of the envelope goes up as the square of the dimension, while the lifting power goes up as the cube. If you want to fill the volume with something, you lose the scaling advantage.

The fact that an aerogel-filled blimp might still conceivably be neutrally buoyant is actually testament to how incredibly light aerogel is. If you filled the Hindenburg with water, it would be more than half the weight of the Empire State Building.

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

#36

Post by ravenstine »

egberts1 wrote: post #28

Let us ignore the Helium shortage.

Although it's a resource we should avoid using as much as possible, since it's difficult to renew, the crisis is somewhat averted.

https://phys.org/news/2021-10-helium-south-africa-gold.html

https://us.eitidc.com/new-helium-reserve-discovered/

It seems the situation isn't nearly as bad as was purported back when the helium crisis was the hot new story.

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

#38

Post by chriswarbo »

jrexilius wrote: post #10

It got me wondering if the increase lift capacity would be added factor, but quick calculation shows that it would only gain an extra ~1% of lift. So it would really just be a cost question: https://en.wikipedia.org/wiki/Lifting_gas

Unfortunately, Hydrogen doesn't lift as much compared to Helium as we might expect, since it occurs as H2 molecules rather than isolated atoms.

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

#39

Post by FlyMoreRockets »

jrexilius wrote: post #10

It got me wondering if the increase lift capacity would be added factor, but quick calculation shows that it would only gain an extra ~1% of lift. So it would really just be a cost question: https://en.wikipedia.org/wiki/Lifting_gas

I've often wondered if a double envelope would be worthwhile. Use a thin outer envelope containing He, and an inner lifting envelope with H. The outer envelope would contain any H that leaked through the inner membrane.

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

#40

Post by Sporktacular »

beervirus wrote: post #19
bernulli wrote: post #12

Earlier quoted context omitted.

Why would the hydrogen not escape?

Diatomic hydrogen is bigger than helium, less prone to diffusing through a membrane.

Leading to an increasing percentage of hydrogen that will exceed the danger threshold. Helium level will need to be monitored and replenished.
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