6 ms·

Good, thoughtful, comment, but the statement that ammonia is more "energy dense than H2 is innacurate and misleading. Ammonia has very slightly higher Volumetri

Good, thoughtful, comment, but the statement that ammonia is more "energy dense than H2 is innacurate and misleading. Ammonia has very slightly higher Volumetric Energy desnity than H2, but it has an extremely lower Gravimetric (mass) energy density.[1] The difference has significant implications for the intended application. 1. https://commons.wikimedia.org/wiki/File:Energy_density.svg https://commons.wikimedia.org/wiki/File:Energy_density.svg

Turing_Machine 5y ago
Hmm... I don't think that takes into account the weight of the tankage. 700 bar tanks aren't light, especially not ones that can resist hydrogen embrittlement.
- coderenegade 5y ago
  The best metric is %-wt of hydrogen. Compressed hydrogen tanks go from 4.5-7% hydrogen by weight. I've read state-of-the-art vessels can get as high as 10%. Liquid ammonia is 17% hydrogen by weight, so as long as the tanks don't erode this too much, you're still doing better than compressed H2.
- ncmncm 5y ago
  LH2 tanks may be very lightweight. Given good insulation, that is much preferred, particularly for aviation.
  - lambdatronics 5y ago
    Right, for large aircraft LH2 might be the way to go. General aviation is more likely to be looking at pressurized H2 due to boil-off.
    - ncmncm 5y ago
      LH2 will not be practical for most small aircraft, although "business jets" will probably take it up. Most of the rest will continue to rely on gasoline or propane. Eventually it will be cheaper to synthesize this from atmospheric CO2 than to mine it.
      - lambdatronics 5y ago
        Right, boil-off is a problem for general aviation, so compressed H2 is the hydrogen option there, which is less attractive. Although, Universal Hydrogen[0] has a wild idea: "... the development of a state-of-the-art uncooled liquid hydrogen storage system that will be able to store liquid hydrogen without venting for over two days. This storage life will be achieved through the use of a specially insulated dual- walled aluminium capsule that allows the pressure inside to build up without exhausting the boil-off." Yikes. [0] https://hydrogen.aero/career-list/?gh_jid=4150445004 https://hydrogen.aero/career-list/?gh_jid=4150445004
lambdatronics 5y ago
I think it's generally understood that densities are per unit volume, and if you want to refer to gravimetric density, you would talk about the 'specific energy.' [0] That said, you make a good point. The energy density advantage isn't huge when comparing to liquid H2, although it's more significant vs compressed H2. [0] https://en.wikipedia.org/wiki/Specific_energy https://en.wikipedia.org/wiki/Specific_energy

Turing_Machine 5y ago

Hmm... I don't think that takes into account the weight of the tankage. 700 bar tanks aren't light, especially not ones that can resist hydrogen embrittlement.

coderenegade 5y ago
The best metric is %-wt of hydrogen. Compressed hydrogen tanks go from 4.5-7% hydrogen by weight. I've read state-of-the-art vessels can get as high as 10%. Liquid ammonia is 17% hydrogen by weight, so as long as the tanks don't erode this too much, you're still doing better than compressed H2.
ncmncm 5y ago
LH2 tanks may be very lightweight. Given good insulation, that is much preferred, particularly for aviation.
- lambdatronics 5y ago
  Right, for large aircraft LH2 might be the way to go. General aviation is more likely to be looking at pressurized H2 due to boil-off.
  - ncmncm 5y ago
    LH2 will not be practical for most small aircraft, although "business jets" will probably take it up. Most of the rest will continue to rely on gasoline or propane. Eventually it will be cheaper to synthesize this from atmospheric CO2 than to mine it.
    - lambdatronics 5y ago
      Right, boil-off is a problem for general aviation, so compressed H2 is the hydrogen option there, which is less attractive. Although, Universal Hydrogen[0] has a wild idea: "... the development of a state-of-the-art uncooled liquid hydrogen storage system that will be able to store liquid hydrogen without venting for over two days. This storage life will be achieved through the use of a specially insulated dual- walled aluminium capsule that allows the pressure inside to build up without exhausting the boil-off." Yikes. [0] https://hydrogen.aero/career-list/?gh_jid=4150445004 https://hydrogen.aero/career-list/?gh_jid=4150445004

lambdatronics 5y ago

I think it's generally understood that densities are per unit volume, and if you want to refer to gravimetric density, you would talk about the 'specific energy.' [0] That said, you make a good point. The energy density advantage isn't huge when comparing to liquid H2, although it's more significant vs compressed H2. [0] https://en.wikipedia.org/wiki/Specific_energy https://en.wikipedia.org/wiki/Specific_energy