Environment-resistor temperature

well... to be honest he is not an engineer, I'm an engineer.. I am deeply ashamed...

distrust an engineer so easily, (that's what I

I suspect that the approximation attributed to Massimo's boss is the most useful one to be made. However, it must be recognized as nothing more than an approximation. The heat loss mechanisms do not have an inherently linear relationship between heat flow and temperature differences. For example, convection loss partially depends on radiation which varies with the 4th power of absolute temperature. Chimney effect can cause more air flow and thinner boundary layers through which the heat must flow for convection cooling.

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--Larry Brasfield
email: donotspam_larry_brasfield@hotmail.com
Above views may belong only to me.

distrust an engineer so easily, (that's what I

Should be: total heat loss partially depends on radiation which

--
--Larry Brasfield
email: donotspam_larry_brasfield@hotmail.com
Above views may belong only to me.

About the most I can say is that Tr will not rise more than Te does, though it is possible that Tr will rise almost as much as Te does. At low temperatures (low not being defined) heat is transferred primarily by by conduction and convection. Conduction is a fairly linear process that passes energy with a temperature rise about proportional to the energy flow. Convection is also fairly linear. But in parallel with these two mechanisms is radiation, and it is decidedly nonlinear. Radiation passes energy in proportion to the 4th power of absolute temperature difference. So as the temperature of box and resistor rise, there is some absolute temperature at which radiation will overtake both conduction and convection as the dominate transfer mechanism. I don't know if that temperature is any where near the temperatures you are talking about, however.

So your is correct, in the limit for low temperatures, and you are right above some particular temperature. An experiment is the best way to settle this argument.

Massimo, your boss is right, what counts is the temperature difference. You shouldn't distrust an engineer so easily, (that's what I suppose he is). :-))

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ciao Ban
Bordighera, Italy

Unfortunately you cannot rely on the radiation, it will be a miniscule amount compared to the convection, because he says the box is closed, so radiation can only be from the outer surface, which he didn't report. I presume it will be half way between inside and outside, if the surface is

0.1mq and e=0.8, then with 338K 0.55W is radiated and with 408K 1W is radiated, hardly much in comparison to the total power, but it makes a good excuse to the boss. THX to Larry The formula to impress the boss: surfaceArea(m^2) * e(0.5...1) * constant 5.67e-8(W/(m^4 * K^4)) * (emitterK^4 - ambientK^4)/(emitterK - ambientK)

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ciao Ban
Bordighera, Italy

Yesterday I've tried to test Tr with Te variable (from 20 degrees to 35 degrees). I can say that, with a tollerance of one degree, approximately the variation of Te is the same of the variation of Tr.

Thanks to everybody, Massimo