The only elastomer material that I found to be fully compatible with N2O
was Kalrez. Everything else either burned merrily or got the bends.
On Thu, Jul 23, 2020 at 6:02 PM Henry Spencer <hspencer@xxxxxxxxxxxxx>
wrote:
On Thu, 23 Jul 2020, mark.spiegl@xxxxxxxxx wrote:
A small thin axle with paddles, a corkscrew, whatever..bulkhead.
The axle traverses the entire length of the tank, and out the top
I think you'd want some sort of simple bearing -- a Teflon ring? -- at the
bottom to make sure the axle stays roughly concentric with the tank. The
long thin tank means the axle doesn't have to go very far off center
before things start rubbing on the walls down at the bottom, and
especially if it's metal-on-metal, that's not a good idea in an oxidizer
tank.
Seal the top bulkhead with a standard oring, EPDM Fluorosilicon whatever
Possible alternative: there are magnetic couplings that can carry
rotation through a wall (within a torque limit) without a dynamic seal.
Some pumps use them, especially for applications like food handling.
Might be a bit heavy to put in a rocket, though.
Another idea is building a static heat pipe. Heat pipes work well in
electronics, but I seriously doubt they scale.
They can scale up quite a bit, provided they're *horizontal*. Alas, for
this you'd want vertical, and there gravity becomes an obstacle. The
liquid return flow is by capillary action in the pipe liner, and that can
go *up* only a limited distance. Fine if you're moving heat up (so the
return flow is down), not so fine if you're moving heat down, which is
what you're after if you're fighting stratification in a tall thin tank.
(Some high-powered satellites use complex three-dimensional heat pipes for
internal heat transfer, and it's not uncommon to build "flattened"
versions of those -- with all pipe runs horizontal -- for ground testing.)
If your tank wall is reasonably heat-conductive, conceivably you might be
able to do something external: a heat exchanger wrapped around the upper
end of the tank and another around the lower end, with a ground-equipment
pump circulating fluid around in a loop. (Or just a cooling jacket around
the upper end, cooled by ground equipment.)
Henry