Which Paint Color for Maximum Heat Dissipation?
Which Paint Color for Maximum Heat Dissipation?
(OP)
What would be the best color to paint an iron or steel object that would benefit from quick heat dissipation?
Specifically, I'm talking about things like brake calipers and exhaust manifolds on automobiles. They rust if you don't paint them, and they build up heat and become very hot which isn't conducive to good performance.
I understand that you would want to use a reflective metallic paint to keep heat away, but what color would you paint an object that produces heat which you want to keep cool?
Specifically, I'm talking about things like brake calipers and exhaust manifolds on automobiles. They rust if you don't paint them, and they build up heat and become very hot which isn't conducive to good performance.
I understand that you would want to use a reflective metallic paint to keep heat away, but what color would you paint an object that produces heat which you want to keep cool?





RE: Which Paint Color for Maximum Heat Dissipation?
Truth be told, you're probably better off giving the object some cooling fins.
TTFN
RE: Which Paint Color for Maximum Heat Dissipation?
I won't comment on whether you should paint. If you are painting, then the emissivity of the paint is the key factor in heat removal by radiation. Most paints will have a high emissivity, generally independent of color. If the parts are not exposed to high temperature radiating sources, like sunlight, and it sounds like they are not unless this is a stripped down dune buggy
Jack M. Kleinfeld, P.E. Kleinfeld Technical Services, Inc.
Infrared Thermography, Finite Element Analysis, Process Engineering
www.KleinfeldTechnical.com
RE: Which Paint Color for Maximum Heat Dissipation?
athomas236
RE: Which Paint Color for Maximum Heat Dissipation?
If the parts will be exposed to the sun, then "the plot thickens"...you would then need to determine the solar absorptance (= 1 - solar reflectance for opaque materials). In this case, your candidate finishes would have the highest ratio of emittance to solar absorptance.
Try
www.electro-optical.com/bb_rad/emissivity/matlemisivty.htm for the emittances. If you need solar absorptances, good luck finding them! If you run into a good database, I'd appreciate it if you'd let me know about it!
RE: Which Paint Color for Maximum Heat Dissipation?
Oh, I forgot to mention that there is a weak general rule (I emphasize WEAK) that black finishes have higher IR emittances. It has to do with color AND surface texture and you need to pay attention to both. For example, black anodizing IS NOT THE BEST CHOICE of black finishes because it produces a smooth, shiny surface.
There are white paints that have higher emittances than black paints. Again, a lot has to do with surface texture. For sunlight exposure, white paints are usually better because they have much lower solar absorptances than black paints.
RE: Which Paint Color for Maximum Heat Dissipation?
RE: Which Paint Color for Maximum Heat Dissipation?
I remember seeing a porous infrared radiator which was
made of clay, sawdust and green chromium oxide. After
firing the green Cr. oxide became light gray in visible
light but black in IR.
<nbucska@pcperipherals.com>
RE: Which Paint Color for Maximum Heat Dissipation?
I invite you to do a sample calculation [q=kA*(DeltaT/DeltaX)] on how much insulation value is added by, say, a .001-.010" thick layer of paint of any kind. You will find that the temperature rise is VERY SMALL and not worth further consideration. Paints and finishes have VERY LITTLE influence on insulation (conduction). Also, once any surface is coated with oil, grease, and dirt, it certainly will make NO DIFFERENCE because it's only what's on the outside skin that makes any difference.
nbucska-
As I said, it's not as simple as the color. For example, unfinished diecast aluminum becomes a better emitter as the outside surface oxidizes. This is because IR emission becomes more diffuse (scatters radiation in all directions) the rougher the surface gets. Think about it. I've known quite a few EEs who are stuck with the wives tale that "black is always best." The truth can be seen by reviewing the emittances published in http://www.electro-optical.com/bb_rad/emissivity/matlemisivty.htm
There's a good chance that this link will provide emittance values for oxidized (corroded) bare metals AND for clean, finished surfaces of various color.
RE: Which Paint Color for Maximum Heat Dissipation?
As for minimizing oxidation/corrosion problems, change the materials.
saxon
RE: Which Paint Color for Maximum Heat Dissipation?
Please read my reply to cisco. How do you conclude that paint adds significant insulation? I suggest you do the sample calculation to see for yourself.
RE: Which Paint Color for Maximum Heat Dissipation?
I think the advice that paint and colour has minimal effect is good advice, except that accumulated rust will eventually become a real insulator, and paint will prevent the rust buildup.
You cannot anodise steel or iron. Aluminium and some aluminium allloys are the only materials that respond well to anodising, although, I think magnesium does respond with mediocre results
On the exhaust and brake rotors, you will need a very temperature resistant paint, typicaly called ceramic coatings. you might get away with VHT coatings on the calipers.
Having said all this, I wonder about your original premise that disipating heat will improve performance.
Re Exhaust
I expect that if you dissipate heat from the exhaust, into the engine bay, you will heat up the other components, including fuel and air, thereby decreasing performance. Heat contained within the exhaust does no harm, and is best disposed of via the exhaust pipe outlet, behind the car, hence you should infact insulate the exhaust. This is done by many racers by ceramic coating or by wrapping in fiberglass. creamic coatings protect against rust, while wrapping in fibreglass encourages rust.
Re disk rotors
These will benifit from being cooled, however any coating will quickly be worn of the friction surface. Other surfaces could be coated with a heat dissipating ceramic, but the gain will be very small.
Re calipers.
If they get to hot, the fluid boils.
You want to get the heat out of the caliper, but prevent heat entering the caliper from the pad and rotor, hence, you insulate between the pad and the piston and the piston and the caliper and the piston and the fluid, but you want to dissipate heat from the outside of the caliper, so you aid dissipation between the caliper and the fluid, and the caliper and the air.
Re wheels
The wheels can act as a heat sink for the brakes, as well as influenceing airflow over the brakes. Obviously aluminium is a better conductor than steel, and open designs aids air flow. lotts of fine spokes or a fussy pattern will aid in heat dissipation
Regards
pat
RE: Which Paint Color for Maximum Heat Dissipation?
saxon
RE: Which Paint Color for Maximum Heat Dissipation?
The site you mention has a lot of data, unfortunatelly
they don't tell what wavelength they used for the measurement, so it is not too usefull.
<nbucska@pcperipherals.com>
RE: Which Paint Color for Maximum Heat Dissipation?
TTFN
RE: Which Paint Color for Maximum Heat Dissipation?
If you READ my replies you will see no inconsistencies. The truth is, radiation heat transfer becomes less as the adjoining surfaces become nearly the same temperature (Ta^4-Tb^4). The sheet metal surrounding the engine compartment can do wonders but maybe radiation exchange between engine parts is small because the surfaces are at nearly the same temperatures.