[time-nuts] Double ovened 10811-60158 on ebay
Bruce Griffiths
bruce.griffiths at xtra.co.nz
Sat Jul 12 23:19:19 EDT 2008
Rick Karlquist wrote:
> Bruce Griffiths wrote:
>
>> Mark Sims wrote:
>>
>>> Remember that heat flow is proportional to the FOURTH power of the
>>> temperature difference. Insulation is generally a linear function. The
>>> combination makes thermal stabilization over even small ambient
>>> temperature ranges rather problematic.
>>>
>>>
>>>
>>>
>> Nonsense.
>> The radiative transfer between 2 bodies at different temperatures is
>> proportional to the difference between the 4th powers of their absolute
>> temperatures.
>>
>
> And this quantity is approximately equal to the THIRD power of
> the temperature difference for small temperature differences.
> (A simple calculus problem!)
>
> Rick Karlquist N6RK
>
>
The Taylor series expansion gives:
(T+h)^4 - T^4 = 4*h*(T^3) + 6*(h^2)*(T^2) + 4*(h^3)*T + h^4
The largest term of which is 4*h*T^3 for small h, and large T(absolute
temperature).
where ^ denotes the power of and * denotes multiplication.
That is for small temperature difference the radiative heat transfer is
proportional to the PRODUCT of the temperature difference and the THIRD
power of the absolute temperature.
Bruce
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