5 ms·

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 ex

by rini17 5y ago

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.)

dTal 5y ago
Aerogel is too heavy. The resulting infusion will achieve neutral buoyancy at best.
- ravenstine 5y ago
  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.
  - dTal 5y ago
    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.
    - ravenstine 5y ago
      > 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.
  - jodrellblank 5y ago
    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/ https://www.airships.net/hindenburg/size-speed/ [2] https://www.aqua-calc.com/calculate/volume-to-weight https://www.aqua-calc.com/calculate/volume-to-weight [3] https://en.wikipedia.org/wiki/Aerogel https://en.wikipedia.org/wiki/Aerogel [4] https://en.wikipedia.org/wiki/Aerographene https://en.wikipedia.org/wiki/Aerographene
    - ravenstine 5y ago
      Wow, great explanation! Kind of disappointing since it sounds like an awesome solution, but now this makes sense to me.
    - nousermane 5y ago
      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.
  - lenzm 5y ago
    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 https://en.wikipedia.org/wiki/Square%E2%80%93cube_law
dreamcompiler 5y ago
Or you could skip the aerogel entirely and use a hard, incompressible shell and pull a partial vacuum inside. Of course we don't currently have any materials both strong and light enough to do that. Neal Stephenson proposed such vehicles made from thin shells of diamond in The Diamond Age.
- rini17 5y ago
  Right and when one shell breaks, the shrapnel breaks the other ones and everything around:)
  - dreamcompiler 5y ago
    Well, they'd implode (the gas inside is at a partial vacuum) so most of the shrapnel would travel inward. But yeah, diamonds are hard but not tough. It's possible that a kid with a BB gun could shatter such a craft with one shot. But they'd certainly look cool.

by rini17 5y ago

dTal 5y ago

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

ravenstine 5y ago
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.
- dTal 5y ago
  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.
  - ravenstine 5y ago
    > 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.
- jodrellblank 5y ago
  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/ https://www.airships.net/hindenburg/size-speed/ [2] https://www.aqua-calc.com/calculate/volume-to-weight https://www.aqua-calc.com/calculate/volume-to-weight [3] https://en.wikipedia.org/wiki/Aerogel https://en.wikipedia.org/wiki/Aerogel [4] https://en.wikipedia.org/wiki/Aerographene https://en.wikipedia.org/wiki/Aerographene
  - ravenstine 5y ago
    Wow, great explanation! Kind of disappointing since it sounds like an awesome solution, but now this makes sense to me.
  - nousermane 5y ago
    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.
- lenzm 5y ago
  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 https://en.wikipedia.org/wiki/Square%E2%80%93cube_law

dreamcompiler 5y ago

Or you could skip the aerogel entirely and use a hard, incompressible shell and pull a partial vacuum inside. Of course we don't currently have any materials both strong and light enough to do that. Neal Stephenson proposed such vehicles made from thin shells of diamond in The Diamond Age.

rini17 5y ago
Right and when one shell breaks, the shrapnel breaks the other ones and everything around:)
- dreamcompiler 5y ago
  Well, they'd implode (the gas inside is at a partial vacuum) so most of the shrapnel would travel inward. But yeah, diamonds are hard but not tough. It's possible that a kid with a BB gun could shatter such a craft with one shot. But they'd certainly look cool.