Effect of paint on solar absorption of carbon fiber shell 1

[benjaminc]

I'm designing a portable geophysical instrument to be enclosed in a carbon fiber shell. This shell will have a cross-sectional shape and area similar to a 5" square, with a 1/8" wall, a 2' length, and will be closed on both ends. As the instrument will be used in hot desert conditions, and is sensitive to high temperatures -- perhaps above 140F -- some colleagues are concerned about creating an unintentional solar oven (the hot car effect). I don't really have enough experience with this effect or material to evaluate their concerns, though my impression is that it shouldn't be a big problem.

There are two real questions: how concerned should we be about heating well above ambient temperature due to solar absorption, and how helpful would it be to paint the shell some lighter color (other than its native shiny black)? Any input is highly appreciated.

Thanks,
BC

 

[CoryPad]

Is your shell sealed to prevent air movement? That is the hot car effect - energy (solar photons) enters the vehicle, heats the air, but the air cannot escape due to a sealed environment.

It will be very helpful to paint the outer surfaces a light color, or even use a reflective metallic coating/plating/foil/whatever.

 

[IRstuff]

If you can get away with it, a mirror or polished surface would at least cut down on the solar absorption. How much heat is internally generated? That would affect the overal heat load as well.

Just bear in mind that without active cooling, you will not be able to get below the ambient temperature. If that's going to be 140°F, then that's the coolest you can possibly get inside the box using passive means.

TTFN

FAQ731-376

 

[srjchemist]

You can coat this structure with a two component aliphatic
polyurethane very similar to auto paint.
You will need to contact your paint supplier and ask for IR reflective pigment only to be added to the paint. You will only have about 12 choices of color, most in earth tones or black.
These pigments mirror the chlorophyll molecule. It will help keep the temperature down by eliminating heat build up within the part. Pigment used to be manufactured by a company called DMC2, technology sold to Ferro. Not sure who
holds technology currently. Some automakers have toyed with it trying to keep auto temperatures minimized and upholstery
from burning your back side on a summer day. It works and you can have a black substrate feel as cool as a white substrate.

 

[jedward]

why are natural gas tanks located in the sun painted white ?
-to keep them cool since excess heating could be catastrophic.
-their environment seems to be similar to yours
-look for a source of white paint used for these tanks

 

[benjaminc]

Thanks, srjchemist -- interesting technology I was not aware of.