# How to quantify a color's effect on heat transfer.

by Indychus
Tags: color, effect, heat, quantify, transfer
 P: 11 Hey, I am working on a thermodynamic design problem, and am trying to come up with some coefficients to modify Qin through a metal surface that is painted different colors. I know that there would be a significant difference in heat through the surface if it were black as opposed to a lighter color, but i need some way to actually quantify it for use in a thermodynamic analysis. I would greatly appreciate any input on the subject.
 Mentor P: 11,837 This is only true in visible light. It could differ wildly in infrared. A good example is a regular black kitchen trashbag, It's black, yet it passes infrared light completely!
 P: 11 That's very interesting with the trash bag, I have never considered that! Basically, i am designing an A/C system for a small vehicle. I am trying to calculate Qin through the various surfaces, i.e. windows, roof, etc. I have no idea how to take color into account for the qin through the roof.
 P: 11 How to quantify a color's effect on heat transfer. Would it be correct to use the surface's emissivity coefficient? Where can I find emissivity values for different colors?
Mentor
P: 11,837
 Quote by Indychus Would it be correct to use the surface's emissivity coefficient? Where can I find emissivity values for different colors?
That I cannot help you with. If you've already done a thorough google search then perhaps someone else here will be able to assist you.
 Mentor P: 11,831 Even with the same color (as seen by your eye), the coefficients can be different. If you want to do it properly, measure the emissivity for the full spectrum of relevant light. If some approximation is enough, measure the total emissivity in your relevant environment.
 P: 11 Well thanks for the input :) I'm pretty sure i can calculate the Qin and use the emissivity coefficient to modify it based on color and material, but I'd like a confirmation of that from someone who knows more about the subject than myself. Hopefully someone will chime in.
P: 11
 Quote by mfb Even with the same color (as seen by your eye), the coefficients can be different. If you want to do it properly, measure the emissivity for the full spectrum of relevant light. If some approximation is enough, measure the total emissivity in your relevant environment.
The number does not have to be exact, a ballpark will work. Just wanting confirmation that I am approaching this the right way. Do I have to consider both the emissivity of the paint AND the underlying material?