low and high temperature radiators? - Page 2 - Orbiter-Forum

jedidia · 03-25-2012, 07:18 PM

After some more searching, I can't find enough data to make much sense of it all. I'm still looking for LH2 storage methods.

For space, I think compressed storage seems to be the only real option, as everything else means lots of dead weight. Still, the only thing I learned with certainty is that the liquid hydrogen is stored at 20.3 K. What I didn't find out is how the pressure is kept when the tank gets emptied (carrying the same volume of some other liquid or sufficient amounts of gas with you seems very unpracticle).

The other thing I still don't quite get is how to take heat out of it when it heats up. Ok, I have to run a gas by it that is obviously lower in temperature than 20.3 K (a challenge in and of itself, I guess Helium would be used, but I have really no Idea). This gas takes heat from the hydrogen, then gets directed back to the cooling system where it is liquified by pressure, releasing its evaporation heat (on second thought, Helium has an awfully low evaporation heat. Maybe not suited so well after all), which goes... where? Just into the surroundings despite them having a higher temperature?

I assume so, since this is strictly speaking an energy release and not a heat transfer, so "travels from higher to lower temperature" probably doesn't apply. I'd like to have confirmation for that before starting to code, though... Did I get that bit right?

**Capt_hensley** · 03-26-2012, 03:16 PM

Space Station uses circulated ammonia. I figured on using roughly the same system for my liquid storage facilities. I'll be compressing and cooling on the same order as an earthbound cryogenic storage facility, except hardened for space operations. \

Insulation will provide the bulk of the work, and a stir system will keep the fluid in motion to prevent solidification.

Boil off will not be preventable, but at the resupply rate I have in mind, it will not be a problem either.

I ran into another problem though, if the tank capacity is not kept at at least 85%, expansion perpetuates boil off. Two ways to reduce this are a. Use smaller tanks with more insulation, b. change the size of the tank on the fly with a flexible bladder.

The radiators for the cooling system have a limitation as well. Efficiency of evaporation(which is different in space) depends on the entire system working at a constant rate. The radiators must remain out of the sunlight to remove the heat from the emerging coolant, thus dissipating the heat collected. Efficiency is about 15% with this method, but you must have a system with at least 65% to work effectively to keep the temp of the coolant down enough to make a difference. A pre-cooler in multiple stages can work, but at this point the mechanical equipment starts to become more complicated and increases you failure points along with a higher chance of failure.

The cooling game in space is a trade off, the more complicated the system, the higher the cooling rate, but also the higher chance of failure. Good luck.

MaverickSawyer · 03-26-2012, 04:08 PM

Quote:

Originally Posted by jedidia

After some more searching, I can't find enough data to make much sense of it all. I'm still looking for LH2 storage methods.

For space, I think compressed storage seems to be the only real option, as everything else means lots of dead weight. Still, the only thing I learned with certainty is that the liquid hydrogen is stored at 20.3 K. What I didn't find out is how the pressure is kept when the tank gets emptied (carrying the same volume of some other liquid or sufficient amounts of gas with you seems very unpracticle).

Have you considered mixing in a bit of methane to gel the LH2? It will prevent convection losses.
Hell, switch to methane entirely, and you just need to deal with a fuel that is about the same temperature as LOX.

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03-25-2012, 07:18 PM	#16
jedidia shoemaker without legs	After some more searching, I can't find enough data to make much sense of it all. I'm still looking for LH2 storage methods. For space, I think compressed storage seems to be the only real option, as everything else means lots of dead weight. Still, the only thing I learned with certainty is that the liquid hydrogen is stored at 20.3 K. What I didn't find out is how the pressure is kept when the tank gets emptied (carrying the same volume of some other liquid or sufficient amounts of gas with you seems very unpracticle). The other thing I still don't quite get is how to take heat out of it when it heats up. Ok, I have to run a gas by it that is obviously lower in temperature than 20.3 K (a challenge in and of itself, I guess Helium would be used, but I have really no Idea). This gas takes heat from the hydrogen, then gets directed back to the cooling system where it is liquified by pressure, releasing its evaporation heat (on second thought, Helium has an awfully low evaporation heat. Maybe not suited so well after all), which goes... where? Just into the surroundings despite them having a higher temperature? I assume so, since this is strictly speaking an energy release and not a heat transfer, so "travels from higher to lower temperature" probably doesn't apply. I'd like to have confirmation for that before starting to code, though... Did I get that bit right?

03-26-2012, 03:16 PM	#17
Capt_hensley Captain, USS Pabilli	Space Station uses circulated ammonia. I figured on using roughly the same system for my liquid storage facilities. I'll be compressing and cooling on the same order as an earthbound cryogenic storage facility, except hardened for space operations. \ Insulation will provide the bulk of the work, and a stir system will keep the fluid in motion to prevent solidification. Boil off will not be preventable, but at the resupply rate I have in mind, it will not be a problem either. I ran into another problem though, if the tank capacity is not kept at at least 85%, expansion perpetuates boil off. Two ways to reduce this are a. Use smaller tanks with more insulation, b. change the size of the tank on the fly with a flexible bladder. The radiators for the cooling system have a limitation as well. Efficiency of evaporation(which is different in space) depends on the entire system working at a constant rate. The radiators must remain out of the sunlight to remove the heat from the emerging coolant, thus dissipating the heat collected. Efficiency is about 15% with this method, but you must have a system with at least 65% to work effectively to keep the temp of the coolant down enough to make a difference. A pre-cooler in multiple stages can work, but at this point the mechanical equipment starts to become more complicated and increases you failure points along with a higher chance of failure. The cooling game in space is a trade off, the more complicated the system, the higher the cooling rate, but also the higher chance of failure. Good luck.

03-26-2012, 04:08 PM	#18
MaverickSawyer Field Tester	Quote: Originally Posted by jedidia After some more searching, I can't find enough data to make much sense of it all. I'm still looking for LH2 storage methods. For space, I think compressed storage seems to be the only real option, as everything else means lots of dead weight. Still, the only thing I learned with certainty is that the liquid hydrogen is stored at 20.3 K. What I didn't find out is how the pressure is kept when the tank gets emptied (carrying the same volume of some other liquid or sufficient amounts of gas with you seems very unpracticle). Have you considered mixing in a bit of methane to gel the LH2? It will prevent convection losses. Hell, switch to methane entirely, and you just need to deal with a fuel that is about the same temperature as LOX.