Re: Global Warming: Junk science at it's [best] worst

On Sun, 16 Sep 2007 21:06:35 +0000 (UTC), don@xxxxxxxxxxxxxx (Don
Klipstein) wrote:

In article <46EA3F1B.E5C9BEC0@xxxxxxxxxxx>, Eeyore wrote:

bill.sloman@xxxxxxxx wrote:

One could design aircraft that used liquid hydrogen as avaiation fuel
- no carbon emission there, though they would dump a lot of water in
the stratosphere, where it hangs around a bit before finally hitting
the surface as rain.

Liquid hydrogen is appreciably less dense than kerosene, so you'd
probably need to go to a blended wing-body design

What do you mean by that ? How will it help ?

to get enough room
for the fuel tanks, which means that such aircraft are going to take
some time to develop, but my guess would be that this is eventually
going to happen.

The problem is that hydrogen is so much less dense than kerosene that
you actually have to make the aircraft structure much larger to be able
to carry enough LH fuel. That results in more weight of course, so you
have to make it larger still and so on.

I suspect you'd have to forget the idea of aircraft with 8000 mi ranges.

Liquid hydrogen has about 8.5% of the density of kerosene, and about 3
times the heat of combustion (in per unit mass terms) as kerosene.

To have equal energy content, a quantity of liquid hydrogen would have
almost 4 times as much volume as kerosene, but 1/3 the mass.

- Don Klipstein (don@xxxxxxxxx)

Last year, I was helping prepare a few slides for my son in high
school on the subject of hydrogen as a fuel supply for transportation.
Two tables from that report are interesting:

Fuel Energy Comparison
--------------------------------------------------------------
MJ/kg Total MJ/liter H2 MJ/liter
--------------------------------------------------------------
H2, 20K cryogenic 120 8.4 8.4
H2, 150K cryogenic 120 3.5 3.5
H2, 5000 psi, ambient 120 2.75 2.75
H2, 3600 psi, ambient 120 2.0 2.0
Methane 50 21.0 12.6
Ethane 47.5 23.7 12.0
Propane 46.4 22.8 10.6
Gasoline 44.4 31.1 13.2
Ethanol 26.8 21.2 12.3
Methanol 19.9 15.8 11.9

The last column in the above chart represents the H2 portion of the
available energy. Obviously, for hydrogen, the last two columns are
identical since 100% of hydrogen's energy is hydrogen. In the case of
the carbon based fuels, hydrogen is only one part of the total energy
from burning with O2.

This chart below, too:

Energy Density Chart
-----------------------------------------
MJ/kg MJ/liter
-----------------------------------------
Batteries 1 1
Pressurized H2 2 2
Hydrides 5 4
Liquid/20K-cryo-H2 8 8
Gasoline 38 27

This one was actually used to make an illustrative graph. It shows
clearly the difficulty we face in replacing gasoline for vehicles.
Carbon is very effective at helping to pack hydrogen into smaller
containers and it provides its own source of energy, as well. It is
tough to beat.

Some web sites for those interested in Hydrogen-energy comparisons:

http://www.nrel.gov/hydrogen/proj_production_delivery.html
http://www1.eere.energy.gov/hydrogenandfuelcells/mypp/pdfs/storage.pdf
http://hypertextbook.com/facts/2003/ArthurGolnik.shtml
http://en.wikipedia.org/wiki/Steam_reforming
http://en.wikipedia.org/wiki/Hydrogen_technologies
http://www1.eere.energy.gov/hydrogenandfuelcells/pdfs/storage.pdf
http://www.physicstoday.org/vol-57/iss-12/p39.html
http://entropyproduction.blogspot.com/2005/09/hydrogen-what-source.html
http://www.getenergysmart.org/Files/HydrogenEducation/6HydrogenProductionSteamMethaneReforming.pdf
http://www.h2wales.org.uk/Assets/Documents/Hydrogen%20Energy%20Basics.pdf

Jon
.

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