Final temperature Calculation

[NAYAB AHMAD]

Dear Sir,

We have a electrical equipment Tripping Unit for which we would like to calculate the final surface temperature of components extrapolated to 50 °C from the actual reading of 27.2 °C . We understood the below procedure from the internet but in order to verify we need to know any reference of IEC standard or other is available.

e.g. measured value 60.2°C at 27.2°C ambient gives a temperature rise of 33K.



The temperature at 50°C ambient temperature is the ambient plus the temperature rise.



e.g. 33K plus 50°C are 83°C

Please advise the final temperature calculation.

Nayab Ahmad

 

[NAYAB AHMAD]

Dear Sirs,

Does there is any change on surface temperature of any body with the change in ambient temperature? if yes, how we corelate the temperatures?

Suppose a body measures the final temperature 60.2°C at 27.2°C ambient temperature.
Temperature Rise- 33K

In the same way the is the below calculation is possible?

The final temperature at 50°C ambient temperature is the ambient + the temperature rise.



e.g. 33K plus 50°C are 83°C

 

[Compositepro]

Your procedure is correct. Heat flow is proportional to delta T, not the actual temperatures.

 

[NAYAB AHMAD]

Could you please elaborate and be requested you to provide us any references?

 

[IRstuff]

However, while the heat flow is indeed proportional to delta T, the proportionality is not constant, and depends somewhat on the average air temperature. That said, electronics do not necessarily have a constant power dissipation as a function of ambient temperature; component values are dependent on temperature, so even with constant voltage, transistor thresholds decrease at higher temperatures, although the general trend is a reduction in power dissipation at higher temperatures, since other things tend to make transistors slow down at higher temperatures. This is why PC overclockers are always looking for the coolest possible ambient they can apply to a CPU.

You can find the derivation in any decent heat transfer textbook.

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