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# Max Internal Temperature

## Max Internal Temperature

(OP)
Hello everyone,

I have a question, if someone can please guide me.

I am calculating airflow of a closed enclosure, so need Max internal temperature from below details:

External ambient temperature is 40 degrees
Power dissipation of electrical component (Circuit breaker) is 57.6 watts
Dimensions of the enclosure (1827mm, 560mm, 600mm)

Can someone please guide me if there is an equation to calculate max internal temperature inside the enclosure, or how can we do that?

Best Regards,
Replies continue below

### RE: Max Internal Temperature

Not with that information. It's pretty easy to make a test setup and try it - the temp rise will be roughly linear with ambient temperature, so if it rises 10 degrees above ambient of 30 then it will still rise 10 degrees above an ambient of 40.

Insulation, external airflow, how well sealed the enclosure is, what the orientation of the enclosure is, whether there is any sunshine onto the enclosure, and so forth, would be required along with more than a little effort - it's about even for the effort to do a test where you can vary things like, what else is in the enclosure and where the circuit breaker is in the box and what the thermal path from the breaker to the enclosure wall.

I would not expect 60 watts in as large an enclosure as that to increase by much unless it is well sealed and very well insulated.

### RE: Max Internal Temperature

My approach
> calculate exposed surface area
> use 5 W/m^2-K for heat transfer coefficient
> solve for surface temperature in Q = htc * area * (T.surf - T.amb)
> depending on thickness of walls, calculate interior air temp from Q = k * (area / thickness) * (T.int - T.surf) or assume that it's one the order of 5 deg above surface temp. k is thermal conductivity in W/m-K

End result should be a temperature that's warm to the touch, but not hot, which is reasonable; consider the heat of a 60W bulb spread over a 200x surface area

TTFN (ta ta for now)
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### RE: Max Internal Temperature

What is "air flow of a closed enclosure"

Doesn't make sense.

But I tend to agree with the posters above. I can't see the temp rising much more than 5 to 10 C above external ambient air temp.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

### RE: Max Internal Temperature

Sounds like homework.... use the resources your teacher gave you.

### RE: Max Internal Temperature

(OP)
That's a valid question, not homework. What else do you need to know?

### RE: Max Internal Temperature

You need to know the U-value of the enclosure and if there is airflow (surface heat transfer). Also if there are any vent holes.

Is the enclosure made of copper and with big holes and a fna blowing on it, or made of 5" poly-iso and air-tight in stale air?

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