guys,
There was a project for a mixed monopropellant that I was reluctantly
involved with. N2O and C2H5OH. Sound nuts - it was.
The concept was to use a clear PVC pipe (Schedule 80) to hold the room
temperature liquids. Quick and easy to glue together.
If the concept of mixing alcohol and nitrous didn't set off red flags,
then the idea of putting 750 psi in a 300 psi pipe, that is dissolved
by the liquids, should.
This was a *feature*. The tank was guaranteed to explode in two hours.
(experimentally determined with crazing).
The whole system was *really* remote controlled. Doors to the vented
test cell were locked before anything was enabled. Unlocked when
pressures were zero, through successful dumping or explosion.
This was the test series that we started painting over all the dings in
the concrete after each time.
Rocket ran well with 'record breaking performance' (HA!). Some of the crew
retired to the "Diamond Cabaret" for dinner. The next day, repeating the
previous experiment blew everything up upon ignition. It occurred
that perhaps the fluids were not quite mixed. Inspection of video showed
the division in the tank. So a mixer was developed. A simple magnet inside
the tank and an additional magnet outside. The outside magnet was moved
up and down the tank with an air cylinder (bimba) and some simple
air lines and valves run off a compressor. (the valves and everything else
were already remote so this was relatively easy to add)
The engine blew itself, the valves, the lines, and the tank up quite
reliably after the mixer was installed.
Flame arrestors, corners and crosses, 10 thou injectors, nothing seemed
to prevent complete destruction. The very last test was of a powder based
liquid injector. It may have worked once on the very last test of the
series. This led to some of the firstar work in the Mojave. (I think)
But the manually cycled, air operated, magnetic mixer in the clear tube tank
worked quite well on video. And it was easy to rebuild after the
tank failed.
-Gar.
Subject: [AR] Re: Continuation of small hybrid motogr desin
From: Peter Fairbrother <peter@xxxxxxxxxx>
Date: Sat, 25 Jul 2020 12:42:27 +0100
On 23/07/2020 22:02, mark.spiegl@xxxxxxxxx wrote:
ken mason wrote:
>> [N2O thermal equilibrium]
Very interesting.. you are the first person other than myself to
acknowledge this issue as serious.
I have struggled with N2O temperature striations over and over and over
again. Almost always, my goal is heating the N2O, not cooling it.
Isn't that easy? Just an electric warmer, or warm water if you want
overtemperature control? If it is on the right place you could get
convective mixing?
Or am I missing something?
I have
played with a few possibilities:
-A collapsible rain barrel filled with ice for the supply tank.
-Paint the rocket or static tank black to get help from the sun.
-A magnetic object inside the tank, moved by an external magnet. (like a
chem lab magnetic stirrer on steroids)
Two thoughts here: first, most tank materials are non-magnetic, so you
could make an eg ptfe rotor for a brushless motor to go inside the tank,
with the stator outside the tank. As the power requirements and speed
are minimal a large gap or some Al sheet between stator and rotor won't
matter.
The rotor should have a hole in the center so it doesn't affect
operation of the rocket. It could also have fan blades on the inside and
outside to stir things. You could also move it up and down the tank by
moving the stator up and down.
You could also attach it to a long thin stirrer. No seals required.
Or, for very tall thin tanks, just put any tank-safe magnetic object
inside the tank. To stir, simply move an external magnet up and down the
tank, a bit like using a fishtank cleaner. Not perhaps as effective, but
simpler.
Peter Fairbrother