Ratio of LOX tank to LH2 tank?

[Zatnikitelman]

I'm still plodding along with the lunar base and I need to know the approximate ratio of the volumes of a LOX tank to a LH2 tank given two times the number of hydrogen atoms to oxygen atoms. Would it be 1:2 LOX:LH2 based on size, or not? It's not for a specific ratio of fuel to oxidizer, but for a supposed extraction of lunar ice.
Thanks,
Zat

 

[pattersoncr]

I would say that depends on what temperatures/pressures you intended on using. For reference the shuttle ET has (from wikipedia):
LOX:
Volume (at 22 psig): 19,541.66 cubic feet; 146,181.8 gallons (553,358.2 liters)
LH2:
Volume (at 29.3 psig): 52,881.61 cubic feet; 395,581.9 gallons (1,497,440 liters)
If the tanks are not going to be flown as part of a spacecraft (and therefore weight is not a significant concern, you could use higher pressures, smaller volumes and thicker tank walls.

 

[Zatnikitelman]

Not sure if this makes a difference, but I was planning on using the density values of 1141 kg/m^3 for LOX and 70.8kg/m^3 for the LH2. I keep getting odd values when I check my math so I was hoping someone could help me a bit.

 

[pattersoncr]

You should end up with 8 times (by weight) more LOX than LH2. Using that, I get twice the volume of H2 that you have for O2. That sounds about right.

 

[Zatnikitelman]

Cool thanks! I can get the sizes of the containers myself, but still needed the ratio.
THANKS!

 

[Urwumpe]

By mass, the ideal mixture ratio for hydrolox rocket engines is between 4 and 6 times more oxygen than hydrogen. The stochastic mixture ratio (8) is not the most effective, as the exhaust has a pretty high molecular mass - with 4.8 (where the maximum is), more unburned hydrogen is in the exhaust, reducing the temperatures, but still increase specific impulse.

 

[pattersoncr]

By mass, the ideal mixture ratio for hydrolox rocket engines is between 4 and 6 times more oxygen than hydrogen. The stochastic mixture ratio (8) is not the most effective, as the exhaust has a pretty high molecular mass - with 4.8 (where the maximum is), more unburned hydrogen is in the exhaust, reducing the temperatures, but still increase specific impulse.

See the first post. He wants the stoichiometric ratio.

 

[spcefrk]

I wonder if you could squeeze more pressure into a tank if it were under say 6 feet of lunar soil... I know hydrogen as a gas has a problem of leaking out of every tiny crack and seam, but if you had a good tank, I wonder if you could bury it in [X] feet of lunar soil and get away with say 5% more max pressure because of the increased maximum longitudinal and hoop stress on a typical tank.

 

[JamesG]

Hydrogen molecules are so small and reactive that they can actually defuse thru and leak out of even solid aluminum or other tank material, no matter how well its made.

There is probably a chemical way of creating a coating or barrier to prevent this "porosity", either by blocking them or by binding the leakers up so they don't escape, but I'm not aware of any thing thats been developed.

For long term storage, best bet is to just leave it as water and then only crack it as needed.

 

[Urwumpe]

There is probably a chemical way of creating a coating or barrier to prevent this "porosity", either by blocking them or by binding the leakers up so they don't escape, but I'm not aware of any thing thats been developed.

There are aluminum alloys, which don't let hydrogen leak so easy. It is pretty well possible storing liquid hydrogen in pressure spheres for a long time, but the ratio of dry mass to liquid mass is pretty bad for them, thats why they are no option for rockets.