At 04:31 PM 10/21/2013, Pierce Nichols wrote:
My google-fu is weak -- what's the curve for W/Re TCs? -p
By "curve", I assume you mean EMF vs. temperature: http://www.omega.com/temperature/Z/pdf/z246.pdfNote that there are a few different W/Re alloy pairs in common use. I've never personally encountered a "Type G", since unalloyed tungsten is supposedly quite brittle and a pain to work with.
Eric
On Mon, Oct 21, 2013 at 1:27 PM, Eric Boyer <<mailto:jeb19@xxxxxxx>jeb19@xxxxxxx> wrote:At 01:22 PM 10/21/2013, you wrote: On 10/21/2013 7:20 AM, Eric Boyer wrote: At 07:36 PM 10/18/2013, Henry Vanderbilt wrote: Yes, I was careful to weasel-word that and not say it was outright impossible, because I *knew* someone would take that as a challenge <grin> But until Omega lists W/Re TC's as a stock item, I think I'm fairly safe in calling it thoroughly impractical. <http://www.omega.com/pptst/www26_w5w26_w3w25.html>http://www.omega.com/pptst/www26_w5w26_w3w25.html :-) We actually use W/Re TCs (Type C or D) fairly frequently in combustion research. We get them either pre-made or spark-weld them ourselves (especially the really small ones for better time/spatial resolution). Gotta make sure they don't get even a whiff of anything oxidizing when at high temperature, though--ever see how fast the filament of a broken incandescent light bulb disappears? Yeah, it's like that. EricI'm having to back down from "just about impossible", through "thoroughly impractical", to just "mostly impractical". Sounds like if you pick your propellants, and accept low performance, and take a lot of care to run reliably fuel-rich throughout, you could measure chamber gas temp with off-the-shelf Omega Catalog hardware.I'll definitely agree with "mostly impractical". Most of our applications for the W/Re TC measurements involve potting them in sort of ceramic (hafnia for the highest temps), using them to measure a subsurface temperature of something like graphite, or accepting that they're a sacrificial measurement device for a transient event (e.g., temperature-distance profile of a solid propellant flame).Eric Dang, ain't modern industrial resources something else? Henry V On 10/18/2013 4:27 PM, George Herbert wrote: 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<<mailto:hvanderbilt@xxxxxxxxxxxxxx>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. HenryOn 10/18/2013 1:54 PM, <mailto:johndom@xxxxxxxxx>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: <mailto:arocket-bounce@xxxxxxxxxxxxx>arocket-bounce@xxxxxxxxxxxxx<mailto:arocket-bounce@xxxxxxxxxxxxx> [mailto:<mailto:arocket-bounce@>arocket-bounce@__<//freelists.org>freelists.org <mailto:arocket-bounce@xxxxxxxxxxxxx>] Namens Norman Yarvin Verzonden: vrijdag 18 oktober 2013 21:00Aan: <mailto:arocket@xxxxxxxxxxxxx>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<mailto:george.herbert@xxxxxxxxx>george.herbert@xxxxxxxxx <mailto:george.herbert@xxxxxxxxx>_____________________________________________________________Eric Boyer <mailto:jeb19@xxxxxxx>jeb19@xxxxxxx------------------------Eric Boyer Assistant Director, High Pressure Combustion Lab Research Associate Department of Mechanical and Nuclear Engineering <tel:%28814%29%20863-2264>(814) 863-2264 Penn State University<mailto:jeb19@xxxxxxx>jeb19@xxxxxxx University Park, PA 16802
------------------------Eric Boyer Assistant Director, High Pressure Combustion Lab Research Associate Department of Mechanical and Nuclear Engineering
(814) 863-2264 Penn State University jeb19@xxxxxxx University Park, PA 16802