[time-nuts] Thunderbolt stability and ambient temperature

RFSPACE pieter.ibelings at gmail.com
Thu Jun 11 23:33:34 EDT 2009


----- Original Message ----- 
From: "Bruce Griffiths" <bruce.griffiths at xtra.co.nz>
To: "Discussion of precise time and frequency measurement" 
<time-nuts at febo.com>
Sent: Thursday, June 11, 2009 10:36 PM
Subject: Re: [time-nuts] Thunderbolt stability and ambient temperature


> Perhaps the answer is somewhat more prosaic.
>
> Radiation and convective losses from the hot end of the bar are 
> significant.
> In particular the radiative loss is (as a first approximation)
> proportional to the difference of the 4th powers of the bar temperature
> and ambient temperature.
> When one modifies the model to include radiative losses near the hot end
> that are in effect switched off by cooling then some overshoot can occur
> at the hand held end of the bar.
>
>
> Bruce
>
> Bruce Griffiths wrote:
>> John
>>
>> That doesn't appear to reproduce what was claimed to have been observed
>> at all.
>> The input is more like a step function that switches from hot to cold.
>> This allows the simulated bar to reach a steady state temperature
>> distribution before decaying smoothly to a lower temperature.
>>
>> Bruce
>>
>> J. Forster wrote:
>>
>>> The effect that was described was absolutely NOT a result of thermal
>>> conductivity being a function of temperature.
>>>
>>> It was a dynamic effect... a transient condition. The result of applying 
>>> a
>>> short heat pulse to a long Time Constant, distributed system.
>>>
>>> Do the simulation I suggested hours ago.
>>>
>>> -John
>>>
>>> ==============
>>>
>>>
>>>
>>>
>>>>> Tom
>>>>>
>>>>> 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)
>>>>>
>>>>> Bruce
>>>>>
>>>>>
>>>> Excellent. Not constant; and perhaps not even linear?
>>>>
>>>> If you run across a thermal conductivity table for steel
>>>> from say 0 to 1000 C let us know. From that graph we
>>>> should be able to calculate what Rex felt when he put the
>>>> red hot (1500 F?) end of the 1 inch bar into cold water.
>>>>
>>>> Better yet, if some metal or material has an even more
>>>> pronounced thermal conductivity function it would make
>>>> a great party trick.
>>>>
>>>> /tvb
>>>>
>>>>
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>>>>
>>>>
>>>>
>>>
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>>
>>
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>
>
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