Tungsten melts at 3,400 K; it looks like peroxide motors should stay
under that, LOX/Kero at Pc of say 150-250 PSI might be under it (but not
much), LOX/alcohol should stay under it.
Rhenium is around 3,150 K, you could find propellant combinations that
would stay under that as well, so perhaps a W/Re TC?
But yes, this is edging into the "You just can't do that" trade space,
when we're having to look at the lowest temp propellants people here
might use and the highest temp metals available on the face of the
earth...
On Fri, Oct 18, 2013 at 3:08 PM, Henry Vanderbilt
<hvanderbilt@xxxxxxxxxxxxxx <mailto:hvanderbilt@xxxxxxxxxxxxxx>> wrote:
I think the most ambitious thing we were talking about so far is
directly TC measuring chamber wall temperature, which is merely
really really hard. Direct measurement of chamber gas temperature
with a TC is pretty much impossible, since the chamber gas in any
halfway efficient rocket motor tends to be hotter than the melting
temperature of just about any material you can name.
Henry
On 10/18/2013 1:54 PM, johndom@xxxxxxxxx <mailto:johndom@xxxxxxxxx>
wrote:
I wonder what commercial TC can measure the inside of a firing
chamber where
uncooled stainless sensor protection tubing simply melts. Yes
soldering it
to the regenatively cooled wall is an option, but that is not
the chamber
gas temperature at all.
jd
-----Oorspronkelijk bericht-----
Van: arocket-bounce@xxxxxxxxxxxxx
<mailto:arocket-bounce@xxxxxxxxxxxxx>
[mailto:arocket-bounce@__freelists.org
<mailto:arocket-bounce@xxxxxxxxxxxxx>]
Namens Norman Yarvin
Verzonden: vrijdag 18 oktober 2013 21:00
Aan: arocket@xxxxxxxxxxxxx <mailto:arocket@xxxxxxxxxxxxx>
Onderwerp: [AR] Re: Best Practices for Measuring Engine Temps
with a
Thermocouple
On Fri, Oct 18, 2013 at 08:11:18AM -0400, Ed Kelleher wrote:
A Swagelok 1/8" tube fitting, with 1/8" diameter
stainless steel shell thermocouple (TC) will seal
up nicely, though part of the fitting remains
permanently attached to the TC. You can remove
the TC and use it on other thrust chambers, but
it will be locked into that initial position/extension.
One thing to remember about such setups, though, is the limits
of the
theory behind why it's okay to weld a thermocouple to the
chamber in
the first place (as opposed to keeping it electrically isolated
like a
normal sensor). The theory is that as long as all the hot-end
junctions between dissimilar metals are at the same
temperature, it
doesn't matter how many junctions there are: their effect nets
out to
zero. So if you have part of the current going from
thermocouple lead
A directly to thermocouple lead B, and another part of it going
through the chamber wall C, it doesn't matter how much current
goes by
which path, because all the junctions between A, B, and C are
all at
about the same temperature. Or at least they are, to a
decent first
approximation, when you're measuring the outside of the chamber.
If you're trying to measure the temperature of the inside of the
chamber wall, on the other hand, you need to electrically
isolate the
thermocouple from the outside of the chamber wall. Otherwise
you'll
get some mix of inside and outside temperatures, the details
being
dependent on exactly what currents are flowing where. (Well,
the heat
equation being what it is, you'll be getting a mix anyway,
not the
temperature of the very innermost micron of the surface. But
this
will make it much worse.)
--
-george william herbert
george.herbert@xxxxxxxxx <mailto:george.herbert@xxxxxxxxx>
