Thermal resistance of plywood

Aaaaah! Life is wonderful... I've been promoted to "asshole"! Are there grades of "asshole", like "lieutenant asshole", or "rear admiral asshole"... ?:-)

...Jim Thompson

--
| James E.Thompson, P.E.                           |    mens     |
| Analog Innovations, Inc.                         |     et      |
| Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
| Phoenix, Arizona  85048    Skype: Contacts Only  |             |
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  |
| E-mail Icon at http://www.analog-innovations.com |    1962     |
             
    Obama: A reincarnation of Nixon, but without ANY scruples, 
           masquerading in politically-correct black-face.

the=20

The standard unit of thermal conductivity (inverse of thermal resistance) is W/(m*K), no "ohms" involved. So much for your "fun fact"

QED

--=20 Transmitted with recycled bits. Damnly my frank, I don't give a dear

----------

path

And google John Larkin for occasional very sloppy math/physics/units.

We also use phosphor-bronze alloy, but I think its main advantage is high electrical resisitivity (while still being reasonable to handle), and thus low thermal conductivity, rather than a deviation from the theoretical (Lorenz) proportionality. IOW, electrically and thermally it just behaves as a very (impractically) thin copper wire.

Best regards, Spehro Pefhany

--
"it\'s the network..."                          "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com

Cite?

Do you think that characterizing a material for thermal resistance per ohm of electrical resistance is somehow "sloppy"? Or maybe a mortal sin? I've found the concept to be useful a number of times. The cryo folks deal with this all the time.

All sorts of metrics can be fun, like transformer watts per pound [1], degress C per foot of altitude, dollar value of Virtex FPGAs per cubic meter, raindrops per square mile per second, stuff like that. I suppose you'd disapprove of the associated engineering units.

Come on, quit being so Slomanesque and have a little fun with math.

John

[1] Grab a couple of catalogs and do a scatter graph on that one. Interesting, at least for people who find things interesting.

What a doofus you are determined to be. One can certainly define a material property Z = thermal conductivity per ohm of electrical resistance. For most pure metals, it's about 150,000 (K/W)/ohm.

Among other things, it's a quick way to convert wire tables into values of thermal resistance for copper wires or rods.

What you're proving is how rigid your thinking is constrained by "standard units." Lighten up a little.

John

This isn't as goofy as it sounds - I've actually used this parameter, albeit it was spec'd as "volt-amps".

Back in my HAM days (ca. half a century ago), this was mentioned in more than one article on rewinding surplus transformers. Well, more like the cross-section of the middle leg of the E, but it translates quite well into VA/lb. (or lb/VA, depending on your POV.)

In fact, I once had a boss make a fool of himself over this - I was tasked to spec a replacement transformer, because they'd changed the requirements for one of the secondaries.

In this box, they had a selector switch to choose one of two secondaries, but NEVER both (DPDT Switch); and I only had to change one, and the VA didn't change much. The moron boss overrode me and spec'd it as if BOTH secondaries would be running at once, which they were guaranteed (in this box) to never do.

This was a retrofit, i.e., an ECO.

The new tranny came in and it didn't even fit in the original box! I almost felt bad for the guy, he was so embarrassed, but I secretly gloated inside because the guy was like The Fourth Stooge - worse than Dilbert's PHB.

After I got myself fired and collected a few months' unemployment, I got a new job, which was about the best job I'd ever had, and at the new company, I ran into two - count'em - TWO former co-workers who had worked under TFS. ;-)

Thanks! Rich

I thought this was because they stand up to the cryo temps better than other alloys.

This (thermal :: electrical) kinda breaks down with diamond. ;-)

Cheers! Rich

in

..

wer

You are only a major asshole.

No, 4K doesn't really hurt most materials.

Strength vs. thermal conductivity is an interesting ratio too. Very important for constructing hot runner injection molds where you have hundreds of degrees temperature differential and rather large forces (that cycle every few seconds).

Since when is diamond a metal?

Sorry, I thought we were just comparing thermal conductivity with heat conductivity. But then there's beryllia, borides, nitrides, etc.

Sorry if I spoiled your day. ;-P

Cheers! Rich

ath

Phosphor bronze is a nice material for this also. It=92s also non- magnetic.

George H.

Magnetically couple power into the chamber, and use bluetooth to radio the data out. :-)

Multi-dimensional...

Diamond is carbon, which is conductive, based on how it is organized, and diamond is pretty dense.

Archimedes' Lever a écrit :

That's what makes you our nice jewel...

--
Thanks,
Fred.

He's a real 'Diamond in the roughage'. :)

--
You can\'t have a sense of humor, if you have no sense!

If you had diamonds in your roughage, you'd be dead from the lacerations by now.

After all, we can't have that brain you sit on being denied its blood supply.