# Cooling capacity of sealed aluminum electronics enclosure

I need to design a sealed electronics enclosure that also functions as a heat sink. The main component I need to cool generates max 15W. This component will directly contact the walls. The remaining components inside generate 4 watts. For some of the components on the boards inside it is not practical to have them directly touching the outer walls of the enclosure. I am having difficulty finding a good way to calculate how much heat can be dissipated from the air inside the enclosures by the external walls. I have looked into a vent membrane plug to allow hot air to escape but they seem to be hard to find for a small enclosure which needs to be about 80x110x45mm. I have designed electronics enclosures in the past but I was able to use fans and rated heat sinks. Is it even practical to try and dissipate this amount of power from sealed a enclosure. The environment the enclosure will be in could be as high as 50 C. Any advice would be appreciated.

• What is the max temperature your electronics will endure?
– Abel
Commented Mar 31, 2023 at 2:01
• I suggest that 20W in an enclosure that small is too much, but you need to model 50C to ambient heat flux from your box. If the flux is less than 19W you have a problem. Commented Mar 31, 2023 at 5:55
• 89C is the max temp. my calculations show the heat sink/enclosure needs a thermal resistance less than 2.85 C/W. this is just based on the main chip I'm cooling. i'm not sure if it is practical do this with natural convection. most heat sinks that I see that have a thermal resistance that low with natural convection would be incredibly expensive to machine. so I am trying to figure out if having the whole case as the Heat sink could allow me to reduce the fin height.
– pdfj
Commented Mar 31, 2023 at 17:01
• i'm not sure how to calculate the spreading resistance from the small chip to the entire enclosure
– pdfj
Commented Mar 31, 2023 at 17:07

The temperature of your heat sink depends on the total power, and the ambient temperature, and the thermal resistance from the outside of the enclosure to the "air"

The thermal resistance of the outside depends only on the shape and size of the outside.

This is the starting point of the analysis. Consideration of the inside comes only after you've got an idea of how hot the enclosure gets.