Fuel cells producing *liquid* water?

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.


Bob Clark

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

Robert Clark wrote:


Batteries would not give you *liquid* water while carrying 1/8th the
weight of the water in fuel. That's an important part of my
application.

Are you building a space vehicle?

wrote:
...
Batteries would not give you *liquid* water while carrying 1/8th the
weight of the water in fuel. That's an important part of my
application.


Bob Clark


Why not just dump the water vapor to the atmosphere (global warming
gas! ack! haha) and just load up on liquid water, somewhere else,
later on?

Otherwise, as someone else mentioned, you have to invest in a heavy,
expensive condensing solution (for example, a radiator or heat
exchanger).

Michael

Proton exchange membrane fuel cells (PEFC) might work since they
condense the water automatically.
From reading some references they appear to have some problem with the
liquid water clogging the membranes, impeding hydrogen flow.
I want to get as much water exhaust out as possible for my
application. Still the PEFC cells might be sufficient for my purposes.
I'm sure you can imagine scenarios where neither fresh water nor
electrical power is freely available. The commonly stated "8 glasses a
day" water per person amounts to 2 liters, or 2 kilos, about 4 1/2
pounds. Over a 10 day trek or a 10 day period without power or fresh
water, that would be 45 pounds that would have to be carried along or
transported to an effected area per person.
There would be significant weight savings if that could be reduced to
5 pounds of hydrogen that had to be carried by each person or
transported to an effected area for a large number of people,
especially if the hydrogen also could provide electrical power,
assuming the fuel cells could be made lightweight.
That raises the question, how lightweight can the fuel cells be made
per electrical power output, not including the hydrogen?


Bob Clark

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.


Bob Clark

The more you describe your ap, the less sense it makes.

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

Robert Clark wrote:
For my application I need a hydrogen/oxygen fuel cell to produce the
H2O in liquid form. But in addition to the electrical energy, the
reaction releases a significant proportion of the energy as heat.
Enough heat in fact to turn the H2O released into steam. I know on
space missions they use fuel cells to produce liquid water but I assume
they use the cryogenic fuels onboard to liquify the water.
Is there a way to insure the water released is in liquid form for the
H2 and O2 at room temperature?

Try using the cell's output to power a refrigerator to cool it.

Less facetiously, you might try condensing the water in a radiator.
The heat has to go *somewhere*.

Tom Davidson
Richmond, VA

Robert Clark 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.

Batteries are almost certainly more cost effective.

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

Batteries would not give you *liquid* water while carrying 1/8th the
weight of the water in fuel. That's an important part of my
application.

You specifically need/want the water ?

I liked the liquid N2 idea for the condensor btw. Dry Ice would be another
possible and easier to handle.

Graham

Don Lancaster wrote:

The more you describe your ap, the less sense it makes.

I've been thinking that too. Unless it *is* a spacecraft !

Graham

tadchem wrote:

Try using the cell's output to power a refrigerator to cool it.

I'm *so* glad that was a joke ! You nearly had me going there. ;~)

Graham

On Wed, 16 Aug 2006 22:48:27 GMT, Dan Bloomquist
wrote:
Robert Clark wrote:
Batteries would not give you *liquid* water while carrying 1/8th the
weight of the water in fuel. That's an important part of my
application.

Are you building a space vehicle?

I think he is, yes! I do hope he isn't planning on using the power
from the fuel cells to drive a great big fan at the back...

--
Posted via a free Usenet account from http://www.teranews.com