This is an answer from Henry Spencer on this list 10 years ago to a similar
suggestion:
[quote]:
Assuming you mean *regenerative* LOX cooling, it's been done, but it's quite
rare. The problem is that it works reasonably well only in the supercritical
regime, which for LOX requires quite high pressures, maybe 1000psi to have some
margin. (You don't want your coolant to pass close to its critical point as it
heats, because many properties change very sharply just there and it's easy to
get violent flow oscillations.)
Regen cooling with LOX at subcritical pressures just doesn't work very well.
The temperature range over which it is liquid is short, and the latent heat of
boiling is small, so it *will* boil. And unless you do something tricky and
unusual, you'll almost certainly get into the film boiling regime, where heat
transfer is greatly impeded and wall temperature soars, usually to the point of
self-destruction. Even if you somehow get it past the boiling transition, the
volume flow rate is orders of magnitude higher as a gas, so pressure drop in
the cooling passages will be large and flow resistance will be high, and things
get still more awkward if gas flow starts to approach Mach 1... Basically, you
really want a regenerative coolant to stay (at least mostly) liquid.
There is also some long-standing superstition about oxidizer cooling being
unwise, but there have been a number of successful oxidizer-cooled rockets
(mostly using more cooperative oxidizers) and this *is* just superstition.
The temperature is a very minor issue by comparison. Liquid hydrogen makes a
wonderful coolant despite being even colder, thanks to its very low critical
pressure and some other helpful properties. (People have seriously proposed
unbalanced-tripropellant systems which are mostly LOX/kerosene, but also burn a
small amount of LH2 so they can cool the chamber with it.)
[end quote]
Troy
From: arocket-bounce@xxxxxxxxxxxxx [mailto:arocket-bounce@xxxxxxxxxxxxx] On ;
Behalf Of Yucca Works
Sent: Tuesday, 20 October 2020 11:32 AM
To: arocket@xxxxxxxxxxxxx
Subject: [AR] Hypothetical Lox cooling
I want to get this group's thoughts, experience stories, and possibly advice on
regenerative cooling with liquid oxygen at the small scale (<500lbf)? I have
read the public NASA paper that concerns cracking in the chamber and local
hotspots and have looked into (what little has been released to the public)
Launcher's work with their small 3d printed copper engines. On paper at least,
it seems like one can get away with cooling from the throat up (the entirety of
the combustion chamber). This is just curiosity-sparked research, nothing
beyond that yet.