Fuel cells producing *liquid* water?

"Robert Clark" wrote in
oups.com:

Don Lancaster wrote:
Eeyore wrote:

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?


Cool the water vapour.

His question shows a profound lack of understanding thermodynamics.

He should start with http://en.wikipedia.org/wiki/Latent_heat

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


Proton Exchange Membrane Fuel Cells.
"Hydrogen from the fuel gas stream is consumed at the anode, yielding
electrons to the anode and producing hydrogen ions which enter the
electrolyte. At the cathode, oxygen combines with electrons from the
cathode and hydrogen ions from the electrolyte to produce water. The
water does not dissolve in the electrolyte and is, instead, rejected
from the back of the cathode into the oxidant gas stream. As the PEFC
operates at about 175°F (80°C), the water is produced as liquid water
and is carried out of the fuel cell by excess oxidant flow."
http://dodfuelcell.cecer.army.mil/proton.html

So you have solved your problem, unless I am missing something. Do you
not want to use a PEM fuel cell for some reason?

Yours,

Bill Morse

"Robert Clark" wrote in
ups.com:

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?

Not very.

In almost all environments save space and maybe the Sahara desert, it is
easier to get water from local sources and purify it, no matter what the
power needs. There are methods for producing water by condensation using
day-night differences in temperature in the desert.

If weight is an overriding concern and volume is not a problem, you could
transport the hydrogen by balloon, and use the balloon to carry the fuel
cells - and you could also use the balloon to carry water.

To summarize, I am having difficulty in seeing any reason to use fuel
cells to produce water.

Yours,

Bill Morse

William Morse wrote:

"Robert Clark" wrote in
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

In almost all environments save space and maybe the Sahara desert, it is
easier to get water from local sources and purify it

But maybe he plans to fly a zeppelin through the Sahara and throw bodies
over board for ballast. Now he has hydrogen to make water and drive
those fans against his sails...

Ben Newsam wrote:
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...


You put the fan in the front, not the back.
First to chop holes in the clouds so the pilot can see.

And second to keep the pilot cool.
If the fan stops, the pilot immediately starts sweating.

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:
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?


;-)

- Bob

Converting vapor to liquid releases energy. Power source for
thunderstorms and hurricanes.


Don Lancaster wrote:
Robert Clark wrote:
Eeyore wrote:

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?

Cool the water vapour.

Graham


A heat exchanger (radiator) might do it. Or quickly exapnding it into
a larger volume.
For my application I want the system to be lightweight.

Bob Clark

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


--
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

Huh?

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

Huh?

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

dangerdoc wrote:
Huh?

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

I meant using cryogenic liquid hydrogen would make it easy to liquify
the water.
As noted by Cowan, 4 bar might be too high for a lightweight system. I
got this number from high performance fuel cells. They would work at 1
bar just not as efficiently.


Bob Clark

dangerdoc wrote:
Converting vapor to liquid releases energy. Power source for
thunderstorms and hurricanes.


Don Lancaster wrote:

Robert Clark wrote:

Eeyore wrote:


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?

Cool the water vapour.

Graham


A heat exchanger (radiator) might do it. Or quickly exapnding it into
a larger volume.
For my application I want the system to be lightweight.

Bob Clark


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


--
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



What I thought I said is not what you think I meant.

If the latent energy is "thrown away" such as through a radiator, it has
to be charged against the fuel cell efficiency.

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