Hi Brett,
From my experience with LOx, using thermocouples along the height of the
tank is the easiest, surest way to go. I've tried differential pressure
sensors probing at the top and bottom of the tank, but first they seem very
prone to failure during pressure spikes and second they tend to end up
giving very noisy signal as LOx in the bottom pressure tap will boil off.
The way tou can fix the latter is to inject some of your pressurant gas in
the bottom tap to create a buffer, but since you're going with the piston
approach this might not work. I've heard of people using ultrasonic sensor
I believe at the top of the tank but again, with the piston, it might not
be possible.
Has anyone ever tried to use the paramagnetic properties of LOx as a
sensing mechanism?
Cheers,
Miguel
On Aug 26, 2018 7:52 AM, "Brett Coles" <brettcoles@xxxxxxxxx> wrote:
I love how posts on this list can randomly reappear later.
Lars,
Thanks for the advice about the piston. I have been a little nervous about
whether or not we will be able to get it to seal. Sutton does have piston
expulsion listed as an option (Though it is pressure driven rather than
mechanically driven). Perhaps some small-scale tests are in order with LN2.
Also, I think we are just going to buy purpose-made Cryo ball valves and
actuate them using servos like Bob has done. We thought about using the
check valve as a main ox valve, but I wanted to make sure we could shut the
motor off if something happened to the piston actuator.
Henry,
Thanks for the emphasis on not using carbon steel. I have no interest in
having our test setup fail like a dropped glass bottle. We are currently
planning on using 6161 and Stainless 304.
Also, is there a way we can measure the fill level in the LOX tank? The
best idea I have so far is just to put a whole bunch of Thermocouples on
the side and watch the cold climb up the tank as it chills in.
On Sat, Aug 25, 2018 at 12:43 PM Lars Osborne <lars.osborne@xxxxxxxxx>
wrote:
Henry,
Thank you for pointing that out. I had forgotten to mention the caveat
that the materials themselves must be cryo compatible!
Thanks,
Lars Osborne
On Sat, Aug 25, 2018 at 11:01 AM Henry Spencer <hspencer@xxxxxxxxxxxxx>
wrote:
On Sat, 25 Aug 2018, Lars Osborne wrote:
I'm surprised no one else has pointed this out, but any valve can be a
cryo valve if you have enough torque...
Well, no, there are issues that aren't solved that easily. Most
especially, any valve with parts made of ordinary steel is *NOT SAFE* for
cryo use, because the steel will go brittle at cryo temperatures. That
alone will take an awful lot of non-cryo valves out of consideration for
cryo applications.
Seals can naturally have similar issues, and differences in thermal
contraction between different materials can cause trouble even if the
materials are individually okay.
Henry