Cryogenic bladder material

[ccarleton]

Would anybody know the following or be able to point me to a web resource?
Thanks

Do you know of any materials that retain some elasticity at cryogenic temperatures in the 20 degrees Kelvin range?

This would be for a bladder that would hold liquid nitrogen in a bath of liquid Hydrogen or helium under pressure. The bladder could either stretch or fold. So it does not necessarily need to stretch, just not crack while it was folded.
Could there be any type of Silicon, plastic or rubber compound that might work?

 

[iainuts]

Nitrogen will solidify at -340 F (aprox) regardless of pressure, so in a bath of LH2, you have other issues. At liquid helium temperature, even hydrogen is a solid.

Teflon will get hard, though if it's thin enough (ie: a few micron) it might work.

I'd suggest trying Kapton film, especially the reinforced variety that has fibers interwoven. Don't know what the fibers are made of though. I've experimented with Kapton film by dunking in liquid nitrogen, and it holds up surprisingly well. If it krinkles up, it will develop holes at the points where 2 folds come together. The key to retaining flexibility with Kapton (and most materials in this circumstance) is to get them as thin as possible to minimize bending stresses.

I've also tried various plastics including nylon, all of which failed miserably.

If you can explain your intented use, it would help.

 

[ccarleton]

Thanks for the response iainuts.
Yes, there are 2 problems to overcome the bladder and someway to insulate or at least reduce the heat transfer across it.
It would be for a small scale LOX/LH2 rocket engine. What I'm trying to determine is if there is a way to use one tank to hold both LOX and liquid hydrogen and use the evaporative gas from the LOX to pressurize both. So the LOX would be contained in the bladder. The chilled LOX actually is good. It improves the performance. But, obviously, frozen LOX is bad. I could get away with a small percentage of it freezing on the bladder surface though.

Before I try experimenting, I'm trying to see if this is even feasible.

 

[iainuts]

The Centaur upper stage uses LH2/LO2. Between the tanks is a relatively thin bulkhead made of a stainless steel shell (2 layers) and layers of MLI between. The bulkhead is purged with nitrogen prior to tanking. During tanking with LH2, the nitrogen freezes out, leaving a vacuum. The combination of the hard vacuum and MLI makes a great insulator.

For stability/strength, the bulkhead is eliptical with the internal pressure (concave side) higher than the external pressure (convex side). Reversing the pressure will reverse the bulkhead, which is generally catastrophic.

If you wanted to do something similar, but using layers of Kapton instead, it might work. Any small amount of nitrogen between the layers of the 'bulkhead' probably wouldn't be a problem as they would just crystalize, making a few snowflakes between the layers. You'd also need both reflective and non-thermally conductive layers. Generally, aluminized mylar or aluminum foil is used, but I believe Kapton can be obtained aluminized as well. For the non-thermally conductive layer, a woven fiberglass matt is what I believe is used in Centaur. Building up layers of this might actually work, but I suspect it would be difficult and of course, very dangerous since any tear could easily lead to a catastrophic explosion.

 

[ccarleton]

Thanks again for your help iainuts,
That's a good idea. That those sound like it could work. It definitely gives me something to start with. Do you think that using the Kapton sandwich would allow the pressure transfer from the LH2 evaporation to the LOX?

I forget where I read this, but some one did experiments and determined that if LOX and LH2 were to mix due to a leak in a bulkhead, that it would not necessarily be catastrophic as it would still require a spark. Do you think that is possible?
If so, then a certain amount of leaking could be acceptable. This of course would be for less valuable payloads where you could afford an occasional failure. The goal, in this particular exercise, is to try and simplify and lower the cost as much as possible

 

[iainuts]

couple thoughts.
- Why use LOX for pressurizing? You then need to carry extra LOX. LHy is much less weight. That's why helium is conventionally used.

- Small amounts of one in the other (ex: by diffusion or extremely small pin-holes) probably isn't a big deal. As you say, there's no spark.

- Regarding a flexible bulkhead between the tanks, I suppose given enough time and research it could be made to work. Seems very risky though - test, test, test...

- Heat source for vaporization is from the engines, but a pump may be required to force liquid through fast enough during the burn to maintain pressure.

- To minimize cracking/tearing in Kapton, it needs to be as warm as possible (preferably in contact with H2 vapor, not liquid) and it needs to roll as opposed to folding. 2 corner folding is especially damaging.

Talk to these folks about your ideas:

http://www.aerospacefab.com/index.htm

I've worked a bit with them in the past, but they weren't very interested in the project I had and eventually we just dropped it. They do seem to have the kind of experience you're looking for though.

 

[ccarleton]

Putting the LOX bladder on top and having it contact the H2 vapor instead of the liquid h2 is a really good idea. I'll consider that.

I miss-spoke earlier, it's the LH2 vapor that pressurizes the system. The goal is to not have a separate gas or system for pressurizing.

I read some reports where they did tests without any external heating and just using the boil off pressure. The system maintained a pretty constant pressure till it got to about 75% through tank consumption, then the pressure started falling off. This was with Propane and Hydrogen peroxide though.

Thanks for the link, I'll check them out.

Did you purchase your Kapton from Dupont? Or is there another source?

 

[iainuts]

The Kapton samples I had were all from Aerospace Fabrication. They also modified the film with reinforcement. They can also heat seal (stitch) however you need it. To make this work, you might consider having some kind of 'quilted' pattern made (heat seal seams) from numerous layers to create a torturous path in the event pinholes develop.

 

[ccarleton]

So at temperatures of LOX (-183C), does that give me more choices of materials I could use for the bladder at this higher temperature?