Thermal properties of spray paint

Boards are typically coated with clear lacquer. That is an indication that for most applications a coating or two will not effect the outcome.

I would say that unless you are enclosing the thing hermetically you need not ever worry about small temps.

Actually, it will be enclosed - not quite hermetically but certainly water tight. It's not a major issue - and this is only a hobby project, but it raises a interesting engineering question.

I have seen this problem before. As in what color should I paint my equipment cabinets to run as cool as possible? NASA has evaluated paints and finishes for emissivity. You can find their results on the web. For the small temperature rise you are dealing with, I don't think radiation heat loss is a significant factor, so basically I don't think it matters much what you paint the parts with.

hmmm - I did a bit of googling before asking the question, and I didn't see the NASA stuff. I know we generally wrap everything with that white MLI material you always see. I did find some scholarly papers, but they are rather obtuse.

"The more reflective the color, the less emissive the material" is basically true, but you must consider the wavelength range within which you are working.

White paint is a reflective coating in the visible range (in fact, it appears white, as it reflects the whole visible radiation), but it is a high absorber in the infrared-region, which is the common range for thermal emission (unless you heat a body above 600°C).

Therefore, in the thermal radiation range, white paint behaves in the same manner of black paint, showing a slightly lower emissivity: we may assume, as reference figures, that the IR emissivity may be 0.90÷0.95 for a black paint, 0.85÷0.90 for a white paint (1 for an ideal black body).

Then, the radiant thermal emission will remain quite unchanged for black coated components, whilst it will be increased for metal coated parts.

However, as for my own experience, these evaluations may be important for equipments working in vacuum environment, or for lack of gravitational effects. If you operate on ground conditions, natural convection presents a very higher impact on heat transfer than mere thermal radiation.

Thanks - that's the answer I was looking for.

Interesting question bhankiii.

My thoughts are that your concern about emission and dissipation would only be relevant during the dynamic heating or cooling phase of equipment operation (Or shutdown) and thus affect how quickly the components reached equilibrium.

Once thermal equilibrium is achieved, the colour would have little to do with the direction of heat flow, only the thermal resistance of the material and temperature difference across it would impact direction and extent of heat transfer.