Amusing Hydrogen tankage thoughts
- Thread starter infojunky
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Of course, the volume (and mass) of the tank (as in the material, not the overall volume), being related to the surface area, will reduce proportionally as the volume of hydrogen it holds increases.
Good question about the ton of hydrogen or ton of tankage. It could be taken either way, but the latter would make more sense as it would account for the necessary insulation, pipework, baffles and reinforcement. But the lack of any cost for all of that is the sticking point, unless you assume that it is included in the cost of the hull.
Good question about the ton of hydrogen or ton of tankage. It could be taken either way, but the latter would make more sense as it would account for the necessary insulation, pipework, baffles and reinforcement. But the lack of any cost for all of that is the sticking point, unless you assume that it is included in the cost of the hull.
| Temperature | Pressure | Density | Specific weight |
|---|
| [K] | [°C] | [°F] | [MPa] | [bara] | [psia] | [mol/dm3] | [g/l], [kg/m3] | [lbm /ft3] | [sl/ft3 *10-3] | [N/m3] | [lbf /ft3] |
|---|
| 20 | -253 | -424 | 0.1 | 1 | 14.5 | 35.29 | 71.14 | 4.441 | 138.0 | 698 | 4.44 |
| 300 | 26.9 | 80.3 | 0.1 | 1 | 14.5 | 0.04006 | 0.08077 | 0.005042 | 0.1567 | 0.792 | 0.00504 |
1 cu.m. = 1000 Liters, so 71.14 kg/cu.m. x 1cu.m./1000 Liters = 0.07114 kg/L
1 metric tonne = 1000 kg, so 1000 kg/tonne x 1 cu.m./71.14 kg = 14.0568 cu.m/tonne
So for GASEOUS Hydrogen at [1 psia] and [26.9 C], the density = 0.08077 kg/cu.m.
1 cu.m. = 1000 Liters, so 0.08077 kg/cu.m. x 1cu.m./1000 Liters = 0.00008077 kg/L = 0.08077 grams/L
1 metric tonne = 1000 kg, so 1000 kg/tonne x 1 cu.m./0.08077 kg = 12,380 cu.m/tonne
[Link to source table]
It has been one of those things I noticed a while back. Rockets are generally fueled up to the point of launch to make up for how light their tanks are, while traveller ships assume longer storage times.
Note my figures above assume a 1% loss rate per day.
Baffling.
Most liquid-carrying trucking trailers have baffles to keep the liquid from rocking back and forth when the truck moves. Without those internal baffles in the tank, a truck stopping at a stoplight could get rocked back and forth and pushed right into the middle of the intersection.
Any ship with gravity plating could possibly set the plates to counteract any movement. But if you lose gravity, L-Hyd fuel would rock the ship around from inertia unless there were physical baffles in the tank, keeping the fuel from moving as much.
Heating the Hydrogen to gaseous form would eliminate the problem, I think.
So leaving the Hydrogen in a gas form until it is used would kill two birds with one stone, as you wouldn't need the equipment, or the weight/mass of the equipment, to keep it cooled. But that does change it's volume.
Please note I am talking about the mass required for the tank at 1atm....
Ships carrying liquid cargoes have them too; I would imagine that aircraft with large fuel tanks would have them as well.
You'd also be likely to get free surface effect as soon as some liquid H2 from the tank has been used, even with inertial compensation. It will be less than you'd see with water or oil, due to the lower density, but it's still there - most LNG/LPG tanks on ships have baffles.
Assuming you aren't increasing the volume but keeping the same mass of H2, you'd then have a very highly pressurised gas needing containment.
In some ways it would be easier to just feed it to the power plant as gas rather than cooling it to liquid.
I eventually figured that out, but it was THIS ...
... that confused me at first. The origin of 1 dTon = 14 cubic meters seemed clear (a ton of liquid hydrogen).
Spinward Flow
SOC-14 5K
You remove the refrigeration cycle and now need VASTLY larger volume tanks.
How much bigger?
Try 1 : 848 (according to the US Department of Energy) on for size and then ask yourself if the refrigeration equipment is "worth it" so you can have SMALLER hydrogen tanks. Wikipedia lists the expansion ratio at 1:850.
To put this in a Traveller context ... you can either have 1 ton of liquid hydrogen fuel ... or 850 tons of gaseous hydrogen fuel ... as direct equivalents in your construction system for Big Craft (emphasis on BIG), since those two tonnages are equivalent.
That Type-S Scout/Courier with 40 dtons of liquid hydrogen fuel?
Try building the same thing with a 40*850=34,000 dtons of gaseous hydrogen fuel tank and see how far you get.
Think that might "do anything" to the spec sheet for how to engineer stuff?
I do.
Game artifact. If Traveller's spaceship rules were based on mass instead of volume....
They aren't.
They aren't.
Still would be prohibitive to go gaseous state as now you have to push/jump all that hull that carries and protects the fuel.
I would think going solid hydrogen instead, various hydrides or other capture mechanisms.
Or my fave, metallic hydrogen, made possible by all that gravitic tech.
Course that interferes greatly with the feed all the jump fuel in 40 minutes or less tropes.
Its really hard to wrap your head around just How. Much. Volume of hydrogen needs to be moved and consumed in a short time on the large ships. Its literally like Niagra Falls volumes of water.
Yes, and no, kinda.
All I am pointing out/asking is that 14 m^3 just the fuel or the included tankage.
Realistically in Traveller the question doesn't matter, as the equipment to access volumes have always been Kina fuzzy.
Amusingly if one assumes that is the tankage volume, the rule of thumb of 10 tons per dTon is much less nebulous.
It sort of HAS to be the fuel (no tankage) because 1 tonne [14 cu. m.] of LH2 will require a LOT more TANK (as a percentage) than 1000 tonnes [14,000 cu.m.] of LH2. That whole volume increases with the cube and surface increases with the square thing.
IMO it's meant to resemble chemically-propelled-rocket levels of fuel use. Antigravity and magic maneuver drives mean launch & landing are solved and easy problems. It's the hyperspace part of it that's the Big Rocket Launch part of the trip.
At least metaphorically.
If we had to do it with such volumes, ejecting tanks would be a necessity for each jump.
mike wightman
SOC-14 10K
You mean like in the Imperial core worlds where jump 6 x-boats and drop tank equipped megacorporation ships are now common?
Does it? Meaning there is a lot of ambiguity in Traveller ship design, defining it one way or another doesn't affect play other than the Narrative. Well and maybe deckplan design...
To be clear Traveller goes out of its way to be a strictly linear design system. While I toy around with more complex ideas and choices when I am farting around designing ships, hint, I am a big fan of using surface area and power as constraints for number and sizes of weapons... (Ok, I must state with my recent dip into Starfield I am trending to an available power model over the surface area model right now. But really that is an entire different topic).
Too be blunt, this thread is just about observations I have made on a topic, not any sort of demand for change... Well no more than the charges we all make to make Traveller work in our heads.
heh, only if your game needs them.
Imperial need and density of business speed in developed areas is one thing, every jump on the frontier is another.
