Fuel cells producing *liquid* water?

G. R. L. Cowan wrote:
Robert Clark wrote:

G. R. L. Cowan wrote:
...
Hydrogen is one-ninth the mass of the water it is in ...
but if you want to bring water to somewhere it isn't,
9 kg of it in a 0.5-kg tank beats
1 kg of liquid hydrogen in a 15-to-40-kg tank,
even if oxygen is free at the destination.

(Very big liquid hydrogen tanks able to contain
tens or hundreds of tonnes of it can have more favorable
containment-to-payload mass ratios. 15.3 is the lowest I've
heard of at car scale, however.)



The hydrogen won't be in liquid form otherwise I would have no problem
getting the water to liquify. Perhaps mildly pressurized, 4 bar.


4 bar?! That makes the choice (a) carry 9 kg of ready-made water
in a 0.5-kg tank or (b) carry 1 kg of hydrogen in, like, a 1.8-m-dia
spherical tank, maybe 160 kg if walled with 2-mm steel.

But I suppose if you never let the pressure get down near 1 bar,
it can have a tension wall, and not be rigid. Not quite so heavy.


--- G. R. L. Cowan, former hydrogen fan
Boron: internal combustion, nuclear cachet:
http://www.eagle.ca/~gcowan/Paper_for_11th_CHC.html

(Nice boron article. I've been looking for high energy fuels for space
propulsion apps.)

Specialty ultra high strength steels might be able to contain 4 bar of
hydrogen at light weight - especially when you use the fact that
hydrogen is lighter than air.
The wall thickness to radius ratio of a spherical pressurized tank is
given
by:

h/r = Δp/(2σ) ,

where h is the wall thickness, r the radius of the sphere, Δp the
overpressure, and σ the tensile strength of the material.

This page gives the tensile strength of "Maraging steel" as up to 3.5
GPa = 35,000 bar:

Maraging steel
http://en.wikipedia.org/wiki/Maraging_steel

At a hydrogen pressure of only 4 bar, we can use the ideal gas law to
give its density as .32 kg/m^3 at 300K. For a pressure of 4 bar, the
overpressure is 3 bar, so h/r = 3/(2*35,000) = 1/23,333. Take the
radius of the sphere as 1 meter. The mass of hydrogen is the density
times the volume: .32 *(4/3)*Pi*r^3 = 1.34 kg.
For a thin wall the volume of the wall is 4*h*Pi*r^2 = 4*(1/23,333)*Pi
= 1/1856.8 m^3. At a density of maraging steel of 8100 kg/m^3, the mass
of the wall is 8100*(1/1856.8) = 4.36 kg.
The upward buoyant force is the weight of the displaced fluid, air in
this case. Using the density of air at sea level of 1.2 kg/m^3 the mass
of air that would be contained in a sphere of radius 1 meter is
1.2*(4/3)*Pi = 5.03 kg. So the upward force is (5.03 kg )*(9.8 m/s^2) =
49.3 N.
The total mass of the hydrogen and the steel container is 1.34 + 4.36
= 5.7 kg. This would have a weight of 5.7*9.8 = 55.86 N. Then because
of the buoyant force it would feel like it had a weight of 6.56 N if
you were lifting it, i.e., it would feel like you were lifting a mass
of only 6.56/9.8 = .67 kg.
This compares to the mass of water of 9*1.34 = 12.06 kg that would be
produced.
Of course, for accelerating it you would have to use the true mass of
5.7 kg total mass of the hydrogen and steel.


Bob Clark

G. R. L. Cowan wrote:
Perhaps you could take a cue from the Levitated Dipole Experiment,
for fusion plasma confinement, and find a way
to bond hydrogen to the *outside* of a diamond nanofilament.
Less carbon would be required
if it were on the inside, pulling on the hydrogen,
rather than on the outside pushing.


--- G. R. L. Cowan, former hydrogen fan
Burn boron in pure oxygen for vehicle power:
http://www.eagle.ca/~gcowan/Paper_for_11th_CHC.html

An interesting suggestion. Amorphous diamond is commonly made
containing hydrogen, though it can be made to remove the hydrogen.
Hydrogen is known to desorb from the amorphous diamond at raised
temperatu

THERMAL STABILITY OF DIAMOND LIKE CARBON THIN FILMS PREPARED USING
PLASMA ENHANCED CHEMICAL VAPOUR DEPOSITION.
http://www.physics.muni.cz/~jzuda/skola/J05385.doc

The report states the desorption becomes significant at 250C and
increases to a high rate at 400C.
According to the report the amount of hydrogen can be 50 at.%. This
means the number of hydrogen atoms is half the total number of atoms,
or the same as the number of carbon atoms. Then since carbon is 12
times as massive as hydrogen, the hydrogen amounts to 1/13th the total
mass, or 7.7%. This exceeds the DOE weight percentage requirements
assuming all the hydrogen could be desorbed.
For the volume requirements, the mass of hydrogen has to be .07 kg per
liter total storage volume, or 70 kg per cubic meter. Assuming the same
density for the amorphous diamond as diamond at 3500 kg/m^3, the mass
of the hydrogen would be .077*3500 = 269.5 kg.



Bob Clark

wrote:

G. R. L. Cowan wrote:
Perhaps you could take a cue from the Levitated Dipole Experiment,
for fusion plasma confinement, and find a way
to bond hydrogen to the *outside* of a diamond nanofilament.
Less carbon would be required
if it were on the inside, pulling on the hydrogen,
rather than on the outside pushing.


--- G. R. L. Cowan, former hydrogen fan
Burn boron in pure oxygen for vehicle power:
http://www.eagle.ca/~gcowan/Paper_for_11th_CHC.html

An interesting suggestion. Amorphous diamond is commonly made
containing hydrogen, though it can be made to remove the hydrogen.
Hydrogen is known to desorb from the amorphous diamond at raised
temperatu

THERMAL STABILITY OF DIAMOND LIKE CARBON THIN FILMS PREPARED USING
PLASMA ENHANCED CHEMICAL VAPOUR DEPOSITION.
http://www.physics.muni.cz/~jzuda/skola/J05385.doc

The report states the desorption becomes significant at 250C and
increases to a high rate at 400C.
According to the report the amount of hydrogen can be 50 at.%. This
means the number of hydrogen atoms is half the total number of atoms,
or the same as the number of carbon atoms. Then since carbon is 12
times as massive as hydrogen, the hydrogen amounts to 1/13th the total
mass, or 7.7%. This exceeds the DOE weight percentage requirements
assuming all the hydrogen could be desorbed.
For the volume requirements, the mass of hydrogen has to be .07 kg per
liter total storage volume, or 70 kg per cubic meter. Assuming the same
density for the amorphous diamond as diamond at 3500 kg/m^3, the mass
of the hydrogen would be .077*3500 = 269.5 kg.

You said you liked the boron paper I link in my signature,
but then you mentioned space propulsion,
which IMO boron is not well suited for.

It doesn't sound to me as though any elemental-hydrogen
storage system can beat a Dewar flask. Consider these numbers:

Per 300 driveshaft kWh, volumes (L) and masses (kg):

108 L 96 kg · Gasoline
448 L 516 kg · Hydrogen, -253°C liquid
972 L 1,222 kg · Hydrogen, 10-kpsi gas
666 L 1,533 kg · Zinc pellets
245 L 331 kg · Boron pellets
208 L 323 kg · Aluminum pellets
??? L 7,880 kg · GM EV1 NiMH battery pack
??? L 12,700 kg · GM EV1 lead-acid battery pack
? 1050 L 2,100 kg · AC Propulsion T-zero Li-ion battery*


If you want to carry energy for energy and hydrogen for water,
I think you'll find the mass saved by going from liquid hydrogen
to boron or aluminum pellets is enough that you can add a
fairly large water tank and still be ahead.


--- G. R. L. Cowan, former hydrogen fan
Burn boron in pure oxygen for vehicle power:
http://www.eagle.ca/~gcowan/Paper_for_11th_CHC.html





* http://www.acpropulsion.com/EAASV_101803.pdf , p. 17 of 42

On 22 Aug 2006 11:12:00 -0700,
wrote:

G. R. L. Cowan wrote:
Perhaps you could take a cue from the Levitated Dipole Experiment,
for fusion plasma confinement, and find a way
to bond hydrogen to the *outside* of a diamond nanofilament.
Less carbon would be required
if it were on the inside, pulling on the hydrogen,
rather than on the outside pushing.


--- G. R. L. Cowan, former hydrogen fan
Burn boron in pure oxygen for vehicle power:
http://www.eagle.ca/~gcowan/Paper_for_11th_CHC.html

An interesting suggestion. Amorphous diamond is commonly made
containing hydrogen, though it can be made to remove the hydrogen.
Hydrogen is known to desorb from the amorphous diamond at raised
temperatu

THERMAL STABILITY OF DIAMOND LIKE CARBON THIN FILMS PREPARED USING
PLASMA ENHANCED CHEMICAL VAPOUR DEPOSITION.
http://www.physics.muni.cz/~jzuda/skola/J05385.doc

The report states the desorption becomes significant at 250C and
increases to a high rate at 400C.
According to the report the amount of hydrogen can be 50 at.%. This
means the number of hydrogen atoms is half the total number of atoms,
or the same as the number of carbon atoms. Then since carbon is 12
times as massive as hydrogen, the hydrogen amounts to 1/13th the total
mass, or 7.7%. This exceeds the DOE weight percentage requirements
assuming all the hydrogen could be desorbed.
For the volume requirements, the mass of hydrogen has to be .07 kg per
liter total storage volume, or 70 kg per cubic meter. Assuming the same
density for the amorphous diamond as diamond at 3500 kg/m^3, the mass
of the hydrogen would be .077*3500 = 269.5 kg.



Bob Clark


I believe the ideal carbon containment would use a single
nanorod carbon chain with two hydrogens bonded at each
carbon position, and an additional hydrogen at each end to
terminate the chain. By adjusting the number of carbons in
the chain, physical properties such as density and vapor
pressure could be tailored to suit the individual
applications.

The hydrogen energy could be extracted by thermal
decomposition and oxidation, with a boost from the carbon
atoms.

Bill Ward wrote:


I believe the ideal carbon containment would use a single
nanorod carbon chain with two hydrogens bonded at each
carbon position, and an additional hydrogen at each end to
terminate the chain. By adjusting the number of carbons in


There are already two ideal carbon containment systems.
These are called heptane and iso-octane.

No other hydrogen storage scheme comes remotely close.

http://www.tinaja.com/glib/energfun.pdf


--
Many thanks,

Don Lancaster voice phone: (928)428-4073
Synergetics 3860 West First Street Box 809 Thatcher, AZ 85552
rss: http://www.tinaja.com/whtnu.xml email:

Please visit my GURU's LAIR web site at http://www.tinaja.com

Dan Bloomquist wrote in
:



Eeyore wrote:


Don Lancaster wrote:


dave e wrote:

Don Lancaster wrote:


You have to recognize that converting water vapor to liquid
consumes energy and has to be charged against the fuel cell
efficiency budget.

Wow, you got that completely backwards.

Not really.


Yes you did.

No, he didn't, in context. The guy is in the Sahara....


What is the context about the statement "converting water vapor to
liquid consumes energy". That statement is in fact backwards. Water
vapor contains more energy than liquid water - about 9.8 kcal/mole, if
memory serves me.


Yours,

Bill Morse

William Morse wrote:
Dan Bloomquist wrote in
:



Eeyore wrote:


Don Lancaster wrote:



dave e wrote:


Don Lancaster wrote:



You have to recognize that converting water vapor to liquid
consumes energy and has to be charged against the fuel cell
efficiency budget.

Wow, you got that completely backwards.

Not really.


Yes you did.

No, he didn't, in context. The guy is in the Sahara....



What is the context about the statement "converting water vapor to
liquid consumes energy". That statement is in fact backwards. Water
vapor contains more energy than liquid water - about 9.8 kcal/mole, if
memory serves me.


Yours,

Bill Morse


The energy IS consumed and charged against the fuel cell.

Conceivably, if the fuel cell system output liquid water, it would be
more efficient by the latent heat difference.

Throwing away the heat --- throws it away.





--
Many thanks,

Don Lancaster voice phone: (928)428-4073
Synergetics 3860 West First Street Box 809 Thatcher, AZ 85552
rss: http://www.tinaja.com/whtnu.xml email:

Please visit my GURU's LAIR web site at http://www.tinaja.com

William Morse writes:

Water vapor contains more energy than liquid water - about 9.8
kcal/mole, if memory serves me.

Which is why car exhaust is such a fine energy source, second only to LBE
(liquified bovine eructations).

[Say, I've coined a new Google triple in those parens.]

Don Lancaster wrote in news:4l4oggF8btoU1
@individual.net:

(Don originally wrote)

You have to recognize that converting water vapor to liquid
consumes energy and has to be charged against the fuel cell
efficiency budget.

(snip in between)

What is the context about the statement "converting water vapor to
liquid consumes energy". That statement is in fact backwards. Water
vapor contains more energy than liquid water - about 9.8 kcal/mole, if
memory serves me.

The energy IS consumed and charged against the fuel cell.

The energy isn't consumed, unless you are stating that the fuel cell
originally produces liquid water and then subsequently turns it into
vapor - which AFAIK is not what happens.

Conceivably, if the fuel cell system output liquid water, it would be
more efficient by the latent heat difference.

Which is one reason why stationary fuel cells are potentially a good
solution for some applications - e.g. hospitals that need heat, need a
backup source of power, and use enough energy to repay capital costs. I
say potentially because current stationary fuel cells are way too
expensive to repay the investment. And no, I don't think the fuel is
going to be hydrogen, at least not anytime soon.


Throwing away the heat --- throws it away.

Agreed, but it isn't charged against the fuel cell budget, it just isn't
credited to the budget. This might be considered a quibble, but there is
enough nonsense on this newsgroup without adding to the confusion by
stating that "converting water vapor to liquid consumes energy".


Yours,

Bill Morse

"William Morse" wrote in message
...
Don Lancaster wrote in news:4l4oggF8btoU1
@individual.net:

(Don originally wrote)

You have to recognize that converting water vapor to liquid
consumes energy and has to be charged against the fuel cell
efficiency budget.

(snip in between)

What is the context about the statement "converting water vapor to
liquid consumes energy". That statement is in fact backwards. Water
vapor contains more energy than liquid water - about 9.8 kcal/mole, if
memory serves me.

The energy IS consumed and charged against the fuel cell.

The energy isn't consumed, unless you are stating that the fuel cell
originally produces liquid water and then subsequently turns it into
vapor - which AFAIK is not what happens.

It doesn't matter what the mechanism is, whether it first forms liquid and
evaporates it, or whether it initially forms vapor. Energy is a state
function, independent of path. What *does* matter is how you calculate the
denominator in the expression for the efficiency--i.e., whether you use the
reaction

H2 (g) + 1/2 O2 (g) -- H2O (g)

or the reaction

H2 (g) + 1/2 O2 (g) -- H2O (l)

to calculate the ideal amount of energy it can deliver. These two reactions
have very different deltaHs.


Conceivably, if the fuel cell system output liquid water, it would be
more efficient by the latent heat difference.

Which is one reason why stationary fuel cells are potentially a good
solution for some applications - e.g. hospitals that need heat, need a
backup source of power, and use enough energy to repay capital costs. I
say potentially because current stationary fuel cells are way too
expensive to repay the investment. And no, I don't think the fuel is
going to be hydrogen, at least not anytime soon.

Sort of the fuel cell equivalent of co-gen. Interesting idea. I agree with
other posters that comment that water vapor, at least at the T, P, and
concentration we're talking about, is relatively low-value heat, and
converting it to useful work would be difficult and inefficient. I think
Don's original point is that usually, to convert warm moist air to cool dry
air and liquid water, you need to use some sort of refrigeration--i.e., it
costs energy. High efficiency furnaces are able to recover some of the heat
of vaporization of water, but much of the water vapor still does go out the
stack, in 100 % RH air at ambient temperature. Converting it to electricity
would be extremely difficult and inefficient, since the ideal (Carnot)
efficiency is limited by the deltaT. However, in the fuel cell case, using
the water vapor to heat a building is a good idea, since you would then get
to take credit in the fuel cell efficiency not just for the heat you are
able to extract, but for replacing (essentially for free) all of the energy
content of the fuel you would otherwise burn to heat that building
(realizing that even combustion heating is never 100 % efficient).


Throwing away the heat --- throws it away.

Agreed, but it isn't charged against the fuel cell budget, it just isn't
credited to the budget. This might be considered a quibble, but there is
enough nonsense on this newsgroup without adding to the confusion by
stating that "converting water vapor to liquid consumes energy".

Agreed.

Eric Lucas