A well vented and insulated LOX tank just after filling will be
sitting right near 1 bar absolute, which puts its temperature at 90K.
http://encyclopedia.airliquide.com/images_encyclopedie/VaporPressureGraph/Oxygen_Vapor_Pressure.GIF
You inject nitrogen at ~35 bar, and the nitrogen has a boiling point
of ~125 K.
http://encyclopedia.airliquide.com/images_encyclopedie/VaporPressureGraph/nitrogen_vapor_pressure.gif
It doesn't dissolve, it liquefies, until the surface of the LOX is
warm enough for it to stop.
At 90 K the vapor pressure of nitrogen is about 3.5 bar, which is why
the Russians can get away with pressurizing LOX tanks to low pressures
with nitrogen without problems.
I would suggest having one regulator per propellant. Ideally dome regulators.
Good luck with your upcoming ignition test. Are you testing at FAR?
Ben
On Mon, Sep 12, 2016 at 9:10 PM, Dillon Wessing <dillonwessing@xxxxxxxxx> wrote:
What are the concerns with using N2 for pressurizing? Dissolving into the LOX?
We’ll go ahead and double up the check valves, they’re inexpensive.
Would you suggest having 1 reg for each side? We’d still end up having 2 regs
but both would have to reg down from high pressure.
Haven’t found the necessary solenoid valves for the main valves but still
looking.
As for an ignition system we are testing one this weekend. If we use it in
our system we’d need to tap off a couple lines from fuel and ox for it.
Best,
Dillon
On Sep 12, 2016, at 4:58 PM, Ben Brockert <wikkit@xxxxxxxxx> wrote:
At risk of restarting a sleeping conversation, I still would not
recommend pressurizing 500psi LOX tanks on a pressure fed stand with
nitrogen on your first test stand.
If you do pursue the current PID, it is standard to put double
checkvalves in situations where propellant could cross, such as the
pressurant lines upstream of the tanks.
The two regulators in a row will cause interesting pressure coupling,
and also mean that both regulators will be about twice as large as
would be necessary if each regulator fed one tank. The first is twice
as large because it's feeding both tanks, the second because it is
operating at such a low inlet pressure compared to outlet pressure.
Have you found solenoid valves that can flow at the necessary rate for
the main valves? They would be big solenoid valves.
Is there an ignition system?
Ben
On Mon, Sep 12, 2016 at 6:57 PM, Dillon Wessing <dillonwessing@xxxxxxxxx>
wrote:
Hi all. I am the lead of the USC Liquid Propulsion Lab. We’re developing a
LOX / IPA engine and wanted some input/advice on our ground testing P&ID.
Just some general specs for the engine. 10 kN of thrust. Total mass flow
4.2 kg/s (fuel: 1.91 kg/s, ox: 2.29 kg/s). Chamber pressure 350 psi.
Pressure going into the injector 437. 5 psi.
We are having channels milled into our combustion chamber for regen cooling
with the IPA and will have a separate reg for the ox since the IPA will
have higher pressure drops. Please comment on the validity of this design
and any concerns that we should keep in mind.
Best,
Dillon Wessing
