From: The Butterfly (salsbury_at_sculptors.com)
Date: 05/28/02
Date: Tue, 28 May 2002 12:13:12 -0700 From: The Butterfly <salsbury_at_sculptors.com> Message-Id: <200205281913.g4SJDCm30103@bootstrap.sculptors.com> Subject: Re: GM demonstrates first gasoline-fed fuel-cell vehicle
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Note: CC'd to airships. Original thread is at:
http://reality.sculptors.com/~hyprmail/fuel-cells/0205.html
In article <3CF2DE4B.34D18C39_at_HyperInfo.CA> Simon writes:
>Gasoline-fed fuel cells are not pollution-free. Pure hydrogen-fed fuel
>cells are pollution-free, but have storage problems (low density,
>explosiveness, etc.). Methanol-fed fuel cells are not carbon-free.
>
>Ammonia (NH3) is a high-density hydrogen carrier. Ammonia-fed fuel
>cells are pollution-free and carbon-free.
>
True enough. I think we all agree that hydrogen is the way to go
for zero emissions, and overall eco-friendliness. Methanol, Ammonia, and
Gasoline, as well as other liquid based fuels, provide good energy
density, but are poisonous and spills can cause ecological damage.
Gaseous hydrogen leaks out and floats away, so while there's an
immediate risk of fire upon a tank rupture (in case of accident), that
danger passes within minutes. A gasoline/propane tank rupture becomes
more dangerous as time goes by, as the heavier-than-air fumes spread
across the ground. (I heard of a propane truck rupture years ago out in
the southwest. New Mexico or Arizona or somesuch. The fumes slid down
gullies and across lowlands for *miles*, and eventually found a
campfire, and an entire region suddenly exploded and caught fire.
One technical point about Hydrogen. It doesn't explode. It
burns, certainly. Very hot, and with a dangerous, invisible flame.
However, when hydrogen burns, it combines with oxygen to form water. You
would combine 2 moles of H2 and 1 mole of O2 (6 moles of individual
atoms) to get 2 moles of H2O - water vapor. Going from 3 moles to 1 mole
of volume means that burning hydrogen IMplodes, not explodes.
I was considering an experiment to counter the common
misconception (probably brought on by the Hindenburg disaster) that
hydrogen explodes, and it might be a useful thing for both the fuel-cell
and airship communities, since both are plagued by the bad press about
hydrogen.
I was thinking that a visual demonstration of the implosion
factor might help dispel the myth, so possible a metal foil balloon
(provided the heat from the burning doesn't incinerate the metal
instantly, which might be the real trick) filled with H2 and O2 in the
proper amounts, and then filmed as a spark is ignited inside. If it
works as planned, the balloon should crumple as the internal volume is
reduced and external air-pressure pushes in the non-permeable sides of
the foil.
It doesn't change the fact that hydrogen burns (and I fear it
may only torch the foil and demonstrate how hot it gets), but it could
dispel the explosion misunderstanding in a way that's readily graspable
by non-scientific people. (Burning in a closed environment or glass
chamber with atmospheric pressure meters could also "prove" this, but it
wouldn't necessarily be understood by as many people as seeing the visual
of the crumpling, imploding balloon.)
Another good way to store gaseous hydrogen for fuel cells, without
dealing with lots of pressure tanks, is to use metal hydrides. We've
discussed this on the list before, and there's a bit of a thread here:
http://reality.sculptors.com/~hyprmail/fuel-cells/0082.html
Also, you can search the full archives at the bottom of that
page for "metal hydride" and find a few other posts.
For those who haven't heard of these, they look sort of like
iron filings. The metal-hydride acts like a molecular sponge. You can
put hydrogen in at about 45 psi, and it soaks into the hydride, then
stays there, even at normal atmospheric pressure. To get the hydrogen
back out, you heat the hydride. (Yet even holding a flame to the hydride
won't release it fast enough to sustain burning.)
Just a few thoughts...
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