Ebba Leaci wrote:24kg of hydrogen would be roughly 12,000 moles of hydrogen gas. Completely burning this with 6000 moles of oxygen gas results in 12,000 moles of water vapor. Oxygen gas and hydrogen gas both have a free energy of formation of 0 kJ/mol. Water vapor, meanwhile has a free energy of formation of -228.61 kJ/mol. To find out the total energy released, you multiply the number of moles of each of the reactants (the hydrogen and the oxygen) by their free energy of formation. Because both of their free energy of formations are 0, this results in 0kJ. Then multiply the number of moles of the product (the water vapor) by it's free energy of formation, and subtract that result from the first result of 0kJ, to get 2,743,320kJ of energy output. (If this value was negative, it would require that much energy to cause the reaction to happen: For example, splitting water into hydrogen and oxygen)
If the energy is being generated at a rate of 1440kW, the hydrogen would be used up after 2,743,320kJ/1440kW = 1905 seconds, or about 31 minutes and 45 seconds. And that is assuming 100% efficiency... You'd get a little less than 34 minutes of power if the fuel cell emitted liquid water instead of water vapor, again assuming 100% efficiency.
Unless there's a fusion reactor in there, or you drastically lower power output, you're not going to get 40 hours out of 24kg of hydrogen.
Thanks for putting numbers up for that. I'm recovering from a flu and still half dizzy and two-thirds stupid. Wasn't really up to rummaging through my old thermodynamics textbooks and trying to remember how to do all that. Muhh...
Daistallia wrote:Heh - that's several years old and hasn't really been used in years - I'll have to go have a look at it again before commenting... (It's probably full of flaws.)
I didn't mean to be critical. Well, at least not in an unconstructive way
. Your tank may still work essentially as is. If we assume it is otherwise similar to a slightly larger M-1, we could say it has a capacity of 2000 liters of liquid hydrogen. At a density of 70kg per cubic meter and understanding that there are 1000 liters to a cubic meter, this gives us a capacity of 140kg. Using Ebba Leaci's numbers, that gives you 11 hours and about seven minutes of power. Taking various inefficiencies into account, I figure that amounts to 9 or 10 hours in practice. That, at least seems more reasonable.
I'm not sure what the cubic capacities of the various hydrates are. Is it possible that 2 cubic meters of some sort of hydrate storage could contain more than 140 kg of hydrogen? I may look into that in the future if some smart person doesn't beat me to it
Heh - having had a look at it again, and some of the source material where I got it, yes. Given the time lapsed, I'm not sure of exactly where the calculations went awry - probably multiple places.
Surprised nobody jumped on 12*2=100 before:
12 alkali-modified fullerene nanotube lattice hydrogen canisters, containing 2kg of hydrogen each (100 kg)
I just assumed the 100kg was the total weight of the loaded cannisters