What will be the Combined value of solar absorptivity?

[chetanladha]

Hi.

Can anyone please tell me what would be the solar absorptivity of a steel plate painted black?
Steel has got solar absorptivity of 0.65, and black paint is around 0.97.
So what will be the cumulative effect of this? Is taking average of them a logical step?

 

[cjl]

Assuming the paint is done properly, it will probably be the same as the paint alone. That's usually the purpose of paint - to completely cover a surface and give the surface the same optical properties as the paint. So, I would guess pretty close to 0.97.

 

[chetanladha]

Ya that's true.
But the other side of it is if you consider any massive steel structure, the fact that steel has got a high thermal conductivity which will tend to keep the temperature of the paint lower than what it would have been otherwise.

 

[cjl]

That has nothing to do with the absorptivity though. The absorptivity just says how much energy is absorbed, not how much that affects the structure.