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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)

#41

Post by ncmncm »

FlyMoreRockets wrote: post #34
ncmncm wrote: post #24

Earlier quoted context omitted.

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.

Exactly, the lower limit, when hydrogen has escaped into the air, not when air has leaked into the contained hydrogen. The article makes clear that above 75% H2, ignition is impossible (but only if you read it).

"Traveling along grain boundaries" can only leak trace amounts. With, as I said, positive airflow, trace leaks can be constantly diluted below the concentration where ignition is possible.

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

#42

Post by FlyMoreRockets »

dr_dshiv wrote: post #27

This is making me curious about hot air balloons combined with hydrogen/helium. I don’t know whether the heat would affect the balloon lift in a meaningful way, but would be nice to have control.

It has been one before. https://en.wikipedia.org/wiki/Rozi%C3%A8re_balloon

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

#43

Post by nwah1 »

ncmncm wrote: post #25
h0l0cube wrote: post #17

This article popped up on HN a few months ago advocating 100% hydrogen airships for 'crew-less' cargo shipping https://www.thecgo.org/benchmark/bring-back-hydrogen-lifting...

This is the winning strategy. There is no need for crew on cargo craft.

But they are still flying bombs, even without crew.

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

#44

Post by bryant »

blippage wrote: post #33
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.

> I haven't read the article,

lol. tl;dr (apropos in this case): "So, 8.5% hydrogen in helium appears to be non-flammable, whereas anything above 8.7% is flammable. Eight percent hydrogen really doesn't provide much in the way of cost savings. You probably ought to consider another question concerning your airship business. Are the cost savings by using a 8.5% mixture of hydrogen worth all the trouble and effort it will take to convince your customers that the mixture is safe, as opposed to avoiding the safety questions altogether by using 100% helium?" [implied: probably not]

> but I presume that the use of hydrogen is a non-starter. No-one wants a flaming fireball raining down on them.

it'll probably work just fine on coastal or oceanic automated shipping routes. And oceanic routes would slightly mitigate the risk of someone catastrophically holepunching one with a Class IV laser.

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

#45

Post by voakbasda »

nwah1 wrote: post #43
ncmncm wrote: post #25

Earlier quoted context omitted.

This is the winning strategy. There is no need for crew on cargo craft.

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!!

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

#46

Post by 3pt14159 »

nwah1 wrote: post #43
ncmncm wrote: post #25

Earlier quoted context omitted.

This is the winning strategy. There is no need for crew on cargo craft.

But they are still flying bombs, even without crew.

So are airplanes? And other things, like literal bombs and missiles?

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

#47

Post by jodrellblank »

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.

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 inside with something it gets heavier. Aerogel is 1Kg per cubic meter without the air in it, says Wikipedia. So adding AeroGel to Hydrogen it would be 216,000Kg in that volume displacing 240,000Kg of air. Hardly buoyant at all.

Wikipedia has something called AeroGraphene mentioned[4] which is down to 160g per cubic meter. If that could be scaled up to the same volume with vacuum in it, it would be 32,000Kg and filled with the mass of Hydrogen, 48,000Kg, but that's still less buyoant overall than using Helium lift gas. Hydrogen isn't really "a feasible approach to lifting any amount of cargo", if it was then airships would be everywhere. The rest of the structure of the ship was heavy in the Zeppelin days, leaving little extra lift for people or things. Out of a Whitehouse sized vehicle it could lift low hundreds of tons. Maybe better today with carbon fibre and lightweight engines and such.

[1] https://www.airships.net/hindenburg/size-speed/

[2] https://www.aqua-calc.com/calculate/volume-to-weight

[3] https://en.wikipedia.org/wiki/Aerogel

[4] https://en.wikipedia.org/wiki/Aerographene

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

#48

Post by ncmncm »

trutannus wrote: post #26
ncmncm wrote: post #24

Earlier quoted context omitted.

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.

> In a collision, gas released goes up and out of trouble Except for the cases when there's an open flame nearby or sufficient heat, as is the case in a non-insignificant number of collisions. What if a hydrogen engine collides with a standard petrol engine? Or if the gas becomes exposed to hot surfaces during the oxygen mixing? The gas expansion is also a major cause of explosion. You essentially pull oxygen into th…

What leads you to think that anything would "pull oxygen into the fuel"? H2 under pressure moves outward, and in a containment breach tends to, instead, increase the H2 fraction above the 75% that can sustain a flame until most of the gas has escaped and leapt skyward. H2 explosions are a concern in enclosed, unventilated spaces.

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

#49

Post by ravenstine »

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…

Wow, great explanation! Kind of disappointing since it sounds like an awesome solution, but now this makes sense to me.

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

#50

Post by ncmncm »

nwah1 wrote: post #43
ncmncm wrote: post #25

Earlier quoted context omitted.

This is the winning strategy. There is no need for crew on cargo craft.

But they are still flying bombs, even without crew.

Except, they are not flying bombs. Notably, the only people killed when the Hindenberg blew were on board. And, fewer than half of them. The flames in the film were the (very flammable!) gas bag itself and the kerosene fuel. The escaping gas went up and away.

A modern craft would not be made of readily flammable material.

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