Heat Transfer at different ambients vs thermal efficiency
Heat Transfer at different ambients vs thermal efficiency
(OP)
I am a EE and had 1 heat transfer class 29 years ago so bare with me.
If I test a transformer in a 25C ambient and a 50C ambient. In both cases to equilibrium. Will the temperature rise be different? My memory is telling me that the higher temperature will yield a lower rise.
Thanks
If I test a transformer in a 25C ambient and a 50C ambient. In both cases to equilibrium. Will the temperature rise be different? My memory is telling me that the higher temperature will yield a lower rise.
Thanks
Neil





RE: Heat Transfer at different ambients vs thermal efficiency
Tobalcane
"If you avoid failure, you also avoid success."
RE: Heat Transfer at different ambients vs thermal efficiency
The thermal conductivity of air is roughly proportional to the square root of absolute temperature, so the amount heat removed at a higher ambient temperature will be higher, but it's not even a percent for the temperatures cited.
TTFN
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RE: Heat Transfer at different ambients vs thermal efficiency
I have a customer who is demanding we test our product in a 50C ambient. They don't believe our test in a 25C ambient even though we had more than 40 deg of head room in the rise. They feel parts could still faile a full temperature.
Any thoughts on how to convince this person that so long as the temp rise over ambient is at least 25 deg below the rise limit, we are not likely to have thermal failures?
Neil
RE: Heat Transfer at different ambients vs thermal efficiency
RE: Heat Transfer at different ambients vs thermal efficiency
Neil
RE: Heat Transfer at different ambients vs thermal efficiency
Tobalcane
"If you avoid failure, you also avoid success."
RE: Heat Transfer at different ambients vs thermal efficiency
You may have other, hidden, thermal problems unrelated to the heat dissipation, per se. Issues with thermally induced noise, race conditions, etc., would certainly be more evident at 50ºC.
TTFN
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RE: Heat Transfer at different ambients vs thermal efficiency
Tobalcane
"If you avoid failure, you also avoid success."
RE: Heat Transfer at different ambients vs thermal efficiency
As far as other problems go. Noise would not be an issue in this application anyway. Don't know what "race conditions" refers to. In the end it just seems we have such a large amount of head room between the max rises (for 40C) and tested rises that to add another 10C should not cause serious consequence. If we were within a few deg of the max rise under room ambient conditions I might be more concerned.
Neil
RE: Heat Transfer at different ambients vs thermal efficiency
Tobalcane
"If you avoid failure, you also avoid success."
RE: Heat Transfer at different ambients vs thermal efficiency
rate of heat generated - rate of heat loss = increase in internal energy of all components in the cabinet.
You already have an idea of the heat generatyed being an EE.
Heat loss will be time dependent when starting cold and basically will have this general appearance:
qloss=UA(Tb(t)- Ta)
Increase in internal energy of components+air will have this general appearance:
u(t)= m*Cp*(Tb(t)-Tb(t-1))/ dt
There is a lot to consider in these equations: shape of components and cabinet, coefficient of heat transfer inside and outside of cabinet, perhaps infiltration, mass of components and cabinets, and a selection for dt.
After identifying all relevant items then you want to itinerate with a spread sheet to determine a steady value for Tb(t).