Hi,
One thing to note is the dissolving process takes time and is proportional
with pressure. Copenhagen Suborbital conducted testing using N2 instead of
He, found only a few percent lost of Isp. The trick to using N2 is don't
wait too long before firing. Once the LOX and fuel are loaded, pressurize
the system and fire. Our procedure is once LOX is loaded everything else is
already set to go. Wait for LOX to boil down to the desired mass, close
fuel & lox vents, and open the N2 pressure valve. Once proper ullage
pressure is reached, fire igniter and open main propellant valves. The
longer the wait the greater the lost.
I like Henry's approach to figuring out the amount of gas absorbed by the
liquid fluid. The static ullage pressure drop is proportional to the gas
amount absorbed by the liquid. The slope of the pressure vs time curve is
the rate of absorption. In my research days, I would have drawn a sample
and ran it through our lab's gas chromatograph.
Be safe,
Rick Wills
Huber Heights, Ohio
-----Original Message-----
From: arocket-bounce@xxxxxxxxxxxxx <arocket-bounce@xxxxxxxxxxxxx> On Behalf
Of Henry Spencer
Sent: Sunday, 1 August, 2021 4:40 PM
To: Arocket List <arocket@xxxxxxxxxxxxx>
Subject: [AR] Re: GH2 pressurization
On Sun, 1 Aug 2021, William Claybaugh wrote:
How will you assure that there is no air / oxygen in the tank / lines
before pressurizing?
