For The Hydrogen Skeptics

Discussion in 'Off-Topic' started by Chuck, Apr 26, 2006.

  1. Chuck

    Chuck just the messenger

    Recently, I brought up Pres Bush touting Hydrogen as the fuel of the future. I agree - it won't be a viable option until the mid-21st century.

    A few days ago, the Wikiapedia had a feature article on an ill-fated Swedish balloner that was going to be the first to the North Pole by sailing in an untested hydrogen ballon in 1897. The party of three crashed on pack ice, then walked to a deserted Artic island in Svalbard and died of inadequate supplies, exposure, and exhaustion. :( (story)

    The article is no longer of the main page, but the quote was funny: "...he put his faith and life in the untested hydrogen technology with far too much optimism."
  2. springkitten

    springkitten New Member

    And this....

    From the San Fran Chronicle...

    And also...

    "Ignitability. A flammable concentration of hydrogen-air mixture can be ignited either by a spark or by heating the mixture to its autoignition temperature. The minimum spark energy required for ignition of hydrogen in air is about an order of magnitude (i.e., by about a factor of 10) less than that for methane or gasoline vapor. However, in absolute terms, the ignition energy for all three gases is low so that exposure to weak sparks, hot surfaces, or flames (matches) is sufficient to ignite them. A static electricity spark produced by the human body (in dry conditions) is sufficient to ignite hydrogen.

    Hydrogen has a higher autoignition temperature compared to that of gasoline (see Table 2-1). However, the low ignition energy characteristic makes it more readily ignitable. The hot air-jet ignition temperature for hydrogen is 943 K (compared to 1,493 K for methane and 1,313 K for gasoline). Hence, hydrogen can easily get ignited by a jet of hot combustion products emitted from an adjacent enclosure.

    Burning Velocity. The value for this property (also called the "laminar flame velocity") is high for hydrogen (2.7 to 3.3 m/s at STP) compared to that of methane (0.37 to 0.45 m/s) or gasoline (0.37 to 0.43 m/s). The burning velocity influences the severity of explosion and, together with the flame quenching distance (6.4 x 10 -4 m for hydrogen, 2 x 10 -3 m for both methane and gasoline), determines the design of flame arrestors to prevent flame flashback into a hydrogen tank.

    Explosion/Detonation. Hydrogen has a wide concentration range in air over which it is detonable. In long tubes and tunnels, an ignition of hydrogen-air mixture in the detonable range will result in an initial "deflagration" flame which will transition to a "detonation" front after a certain induction" length. The induction distance is least for hydrogen compared to the induction lengths in methane-air or gasoline-air mixtures. The detonation velocity in a hydrogen-air mixture can be as high as 1.5 km/s to 2.2 km/s. The energy of' explosion of hydrogen, expressed in kg of TNT per kg of fuel is 24, compared to 11 for methane and 10 for gasoline. Hence, on an equal mass basis, hydrogen explosions will be more destructive than those from gasoline.

    Characteristics of Leaks and Dispersion. The relatively small molecular diameter of hydrogen (1.58 D ), compared to those of all other gaseous fuels, makes fuel lines and fuel systems more susceptible to a hydrogen leak (Hansel et al., 1993). The occurrence of hydrogen leaks from properly mated metal-to-metal seals (flared or compression joints) in a hydrogen line is remote. However, non-metal seals, such as gaskets, packings, and pipe thread compounds, present a high probability for leaks. While catastrophic failure of metal joints is highly unlikely, large sudden failures in non-metal seals can occur due to the embrittlement of the materials."
    Last edited: May 3, 2006

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