Closed Cycle Hydrogen Fuel Cell Question

[Anaraxes]

There's quite a lot of hydrogen storage in the real world, pressurized and cryogenic. There are hydrogen pipelines (over a thousand miles worth in the US). Trucks to deliver the stuff commercially. There are solar-hydrogen power plants that have to store hydrogen on a seasonal basis (six months or so). It's not quite that bad, even at TL 8.

[Fred Brackin]

Originally Posted by Anaraxes

There's quite a lot of hydrogen storage in the real world, pressurized and cryogenic. There are hydrogen pipelines (over a thousand miles worth in the US). Trucks to deliver the stuff commercially. There are solar-hydrogen power plants that have to store hydrogen on a seasonal basis (six months or so). It's not quite that bad, even at TL 8.

Yes, but what are their loss rates? The hydrogen for he Shuttle came by barge from Mississippi but a rather large percentage of loss (half maybe?) was simply accepted as unavoidable and workable due to a low base cost.

[malloyd]

Originally Posted by Fred Brackin

Yes, but what are their loss rates?

There are two quite different issues here.
Hydrogen atoms will leak through most containers eventually, but not really all that fast. This is a problem that makes it hard to hold hydrogen under pressure for years, but is pretty negligible on the scale of days.

The other is the rate at which heat leaks into containers full of liquid hydrogen and boils it, which requires you to vent the gas to prevent the container from bursting. The best anybody can do there is in the percent or two boil off per day range, and it's way faster than that for stuff like the shuttle tank, which is after all not well insulated since insulation would add weight.

[Flyndaran]

Aerogel wouldn't add that much weight and insulate much better than any other modern material.

[Flyndaran]

I consider fuel cells' main advantages to be reliability, efficiency, safety, and relative simplicity, with weight already sailed away compared to most other ways to produce energy.
I would have no problem with some loss for reusable hydride storage.

[DaltonS]

Murphy’s Rules: I’ve heard of fuel efficiency, but…
Blurb: In GURPS Spaceships, at TL7 a Chemical Refinery (p.19) can produce 4× the rocket fuel that a Fuel Cell (p.20) needs to power it.
Details:
In GURPS Spaceships, a TL7 Fuel Cell (p.20) using hydrogen and liquid oxygen rocket fuel can produce 1 Power Point for three hours on internal fuel plus four times that (12 hours) for each fuel tank … which can filled by a Chemical Refinery (p.19) in 3 to 3 1/3 hours for 1 power point and a tank of water. Thus, each Power Point Hour of fuel cell energy can process up to four Power Point Hours worth of fuel. Since this is a closed system, if the fuel cell’s tanks are filled it can operate indefinitely and still provide power for other systems 72%-75% of the time. (And this is just at TL7; fuel cell efficiency doubles for each of the next three tech levels.)

Dalton “Yeah, I know it's unrealistic, but that's the point!” Spence

[Flyndaran]

That's an "artifact" of the Spaceships' rules. Factories produce at a far more than realistic rate, while the sub-optimal energy sources, like fuel cells, produce at a far more than realistic rate. Combining the two always results in obvious physics violations.

Fuel cells produce on the order of 1/10th what the real plants should, and solar should produce around 1/100th.
Factories of all types should use rules like the 1/24 rate suggested in one or two supplements to keep from slamming out mega projects in absurdly short time frames.

[DaltonS]

Originally Posted by Flyndaran

That's an "artifact" of the Spaceships' rules. Factories produce at a far more than realistic rate, while the sub-optimal energy sources, like fuel cells, produce at a far more than realistic rate. Combining the two always results in obvious physics violations.

That's what makes them Murphy's Rules!

Originally Posted by Flyndaran

Fuel cells produce on the order of 1/10th what the real plants should, and solar should produce around 1/100th.
Factories of all types should use rules like the 1/24 rate suggested in one or two supplements to keep from slamming out mega projects in absurdly short time frames.

Using these rules, a TL7 Fuel Cell should work for 18 minutes on internal fuel or 72 minutes per tank (with doubled efficiency for each of the next three TLs), and solar panels would be completely impractical for powering high energy systems. Employing the Slower Industrial Systems Design Switch (SS7 p.23), a Chemical Refinery could fill a fuel tank in 72-80 hours. (This by itself could keep fuel production behind standard fuel cell consumption until TL10!)

Note: Closed Cycle tanks for fuel cells should cost twice as much as regular fuel tanks, as they'd represent separate tanks for the Hydrogen-Oxygen fuel and the water produced. (Mass would remain the same, as one would empty as the other filled.)

Dalton “BTW, what is a Power Point in kw/ton of ship?” Spence

[Jonas]

Originally Posted by malloyd

Mind you while I think GURPS has always gotten it right, there have been science fiction games that messed it up.

I've seen rules that assume fuel cells run on water for example, and there are plenty of gullible people apparently believe that you can run an engine on water (and more think watering down your gasoline works) in the real world. So I wouldn't be too surprised if you had seen something like that in print somewhere.

The irony being there is a kernel of truth to it though not as depicted. Using metered water injection directly into a combustion chamber CAN boost crankshaft output by flashing to steam in the resulting hot environment at the cost of additional complexity and potential long term corrosion issues. Mainly by scavenging a percentage of the thermal energy that would have otherwise be dumped as waste heat via the cooling system/exhaust.

[Anaraxes]

Originally Posted by Jonas

Using metered water injection directly into a combustion chamber CAN boost crankshaft output

Used in a number of WW II fighter aircraft, for instance. But, as you say, not as fuel.