2 wrote:
>An IR thermometer, a manometer, and some horse sense are more
>trustworthy than computer modeling -- i. e., if the thermometer says
>it's too damn hot, and the computer app says it's not, it is.
>
They used to say that about antennas too, until MININEC and NEC became
available free to anyone who wants them. Certainly there are big
pitfalls in computer modeling, but antenna modeling has also shown that
"horse sense" isn't always reliable either. In the end, you need both,
in order to check each against the other.
Exactly the same would apply to thermal/flow modeling if we had the
tools to try it.
Unfortunately IR thermometers are notoriously UNtrustworthy, unless they
are calibrated for emissivity and - for this application - also have a
very small spot measurement size.
The temperature readings depend on the emissivity of the surface. Cheap
IR thermometers assume a fixed emissivity of 0.95, which is a poor guess
for bright metal and even worse for glass. IR thermometers with a
variable emissivity setting need to be calibrated against the same
material at a known temperature (otherwise you can change the emissivity
setting and make the temperature read whatever you like).
And then there's spot size. Even a good $500+ IR thermometer has quite a
large spot size, typically 0.5-0.75in across, and that's much too big
for a small object such as a tube pin. Specialized instruments with a
smaller spot size are going to be much more expensive.
Also the covers of the amp affect the air flow pattern, so they need to
be in pace for valid temperature readings. You point the IR thermometer
at the hot surfaces inside... exactly how?
Sorry, IR thermometers have their uses, but determining tube pin and
seal temperatures probably aren't two of them (unless you're in the
giant tube league).
I'm afraid it's back to temperature-sensitive paints, crayons and labels
- try Omega Corp in the USA for a very good selection.
Earlier, I'd asked:
>>> Steve, do you know if there is anything freely available on the net for
>>> heat and mass transfer modeling, equivalent to the way NEC-2 is freely
>>> available for antenna modeling?
>>>
>>> //Ian, no I don't. I honestly doubt there's anything very good available,
>>> or my company probably would not have invested $60K in Flowtherm!
>>> -WB2WIK/6
Sorry to hear that...
--
73 from Ian G3SEK Editor, 'The VHF/UHF DX Book'
'In Practice' columnist for RadCom (RSGB)
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