[AR] Re: Portland State Aerospace Society
- From: Henry Spencer <hspencer@xxxxxxxxxxxxx>
- To: arocket@xxxxxxxxxxxxx
- Date: Mon, 25 Apr 2016 15:15:02 -0400 (EDT)
On Tue, 19 Apr 2016, Kyle Meeuwsen wrote:
The senior design team before me also selected relief valves and
solenoids for venting on the top of the LOX tank that are not cryo
rated. I have concerns that heat transfer from the tank to the LOX might
freeze these components that are attached to the top of the LOX tank...
As others have said, non-cryo-rated stuff can be okay for this; there's
nothing particularly magic about cryo rating. Solids don't freeze. :-)
There's an issue with different coefficients of thermal expansion perhaps
causing things to bind, and the absence of that really has to be verified
by experiment -- do some initial flow testing with LN2, not LOX! (LN2 is
not a perfect simulation of LOX, but it's close enough to catch most cryo
issues, and rather less hazardous if something goes wrong.)
The bigger issue is the one Ben mentioned: make sure the materials are
okay for cryo use. In particular, ordinary steel is flat out unacceptable
for anything that *might* get cryo cold, because it goes brittle. Brass,
bronze, stainless, nickel alloys are all generally okay. And most
elastomers stop being elastic at cryo temperatures, so things like seals
generally need to be Teflon aka PTFE (which retains some flexibility).
...a way to safely fill the LOX and Ethanol tank from a great distance
away.
Filling is not a seriously hazardous operation, provided it's done more or
less at atmospheric pressure and you observe appropriate precautions for
the fluids involved. Pressurization is the hazardous part that needs to
be done remotely.
Henry
Other related posts:
