[time-nuts] Thunderbolt stability and ambient temperature
bruce.griffiths at xtra.co.nz
Fri Jun 12 00:11:25 UTC 2009
Tom Van Baak wrote:
>> Most people thought it was coincidence of heat propagating up the bar
>> just at that time, or steam. Could be, but I still think it is real.
>> The cold end of the bar was slowly getting warmer as I carried it,
>> but after the sudden cooling of the hot end, the cold end seemed to
>> get hot fast.
> We know each material has it's own thermal conductivity. Copper
> is 401 W/m-K and steel only about 1/10th that, etc. It would appear
> from conductivity tables in books that these are fixed constants.
> But I wonder if near-liquid (red hot) steel has a different (e.g., even
> lower) value than warm or cold steel? Is metal thermal conductivity
> actually a fixed constant or is it a function of temperature over a
> wide range of temperature?
> If so, not only is the temperature changing when you drop the
> steel in water, but also the thermal conductivity of the steel. Thus,
> depending on how fast or slowly you cool it vs. how non-linear
> the conductivity is as a function of temperature, I imagine you
> could observe the very effect you describe.
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The thermal conductivity isnt constant with temperature.
It also varies between different crystalline forms of the same material.
This can be seen in more comprehensive tables of thermal conductivity.
In particular at cryogenic temperatures the thermal conductivity can
change dramatically (eg in superconductors)
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