Underhood Temperatures

[bernie at innovative.iinet.net.au]

Garfield Willis tapped away at the keyboard with:

> On Fri, 26 May 2000 08:38:52 +0800 (WST), bernie at innovative.iinet.net.au
> wrote:
> >Garfield Willis tapped away at the keyboard with:
> >
> >> The only definitive way to go about this is to shoot the engine
> >> compartment with a well-focused infrared gun, or better yet, mark it up
> >> with some templsticks to see what kind of temps you're dealing with,
> >> with the hood down, and following heat soak. You can get those
> >> indicators from 125degF all the way up to 2500degF!!, but they have a
> >> nice set from 125degF to 800degF. Take a look at:
> >> 	http://www.tempil.com/tempilstik.htm
> >
> >Hasn't anybody heard of Heisenberg? 

> Nice try, Bernie, but no cigar, not even a light :), doesn't apply here,
> certainly not even theoretically, with the temp sticks. They *record*
> the highest temps achieved in situ, so they're not affected by the
> "experimenter".

You can keep the Cubans.

You change the system in order to observe how it performs. 
All you'll onserve is how the changed system performs. Or
don't the temp sticks have any physical properties at all?

If I crack open a chip and paint the surface with the pen then try
to observe the temperature - I'll probably get very misleading
results in relation to a practical application.

It's the same situation as placing a strain-gauge on a mechanical
component - the strain-gauge carries part of the load. All you can
do is assume that the strain-gauge isn't significant. Your
measurements should tell you that so that you can estimate your
error i.e. the degree of uncertainty.

The Heisenberg principle applies to all systems which are observed.
It's an early awareness of chaos.

> Besides, I'd wager you've never shot underhood temps with a gun either;
> otherwise, you'd know things don't cool off all that fast when you
> suddenly open the hood. The AIR temps change rapidly, but the temps of
> objects do not. You can very effectively scan an area for hotNcold spots
> with a gun for at least a couple minutes before things begin to chill

A couple of seconds to a minute more likely; on my engine a couple
of minutes makes a world of difference to the inlet manifold (which
is directly above the exhaust manifold).

The relative temperature changes are most significant and depend
hugely on engine layout and the operation of ancillaries. (Electric
cooling fan.)

You might get more time with a mechanical cooling fan.

> appreciably. If for example you wanted to know how some piece of
> equipment would fair in a particular place, you take a bit of aluminum
> about it's size and mass, and place it in that spot. If you don't want
> it to pick up from conduction (say you plan on isolation mounting it),
> just lay it on a wad of fiberglass cloth you've folded up underneath it.

You're assuming that the thermal capacity of the piece of aluminium
is the same as for the components. It might be applicable for
steady-state application, but then again, your piece of aluminium
isn't generating any heat either. All you'll get is a baseline
ambient temperature before your own thermal contribution.

> Run the engine up to peak temps, then let soak (or not; both tell a diff
> story), then open the hood and shoot the sample. Those guns can be a
> godsend, and the better ones you can get to focus down onto an area the
> size of a dime.

Yeah... pretty neat gadgets. I saw one which had a laser pointer but
the sales guy couldn't verify that the laser spot was even pointing
at the spot being measured. I didn't even ask about the power output
of the laser. :-)

It's not a tool I'd personally use often though. Not in the
immediate future anyway.

> Oh, to answer your question, *I've* heard of Heisenberg. Wasn't he the
> guy that built that blimp that crashed? So, what about him? :)

Perhaps what he was saying was lost in the translation.

-- 
Bernd Felsche - Innovative Reckoning
Perth, Western Australia
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