Robert Clark wrote:

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


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.

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.)


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