Black Motors vs. Natural Aluminum

[Wingnut1]

For those of us that want black engines, would Renobruce share how it's done? Those parts look fantastic.

[bonanzadave]

Most all electrical heat sinks Ive seen are anodized black.

[tkent02]

Cheapest color to anodize?

[bonanzadave]

Cheapest color to anodize?

There seems to be as much conjecture in the heat sink world as there is in the GS motor world as far as color is concerned............

"Radiative heat transfer (heat transfer by electromagnetic radiation) is proportional to
e*(T1^4 - T2^4)
where T1 is the absolute temperature of the material, T2 is the absolute temperature of the surroundings, and e is the emissivity coefficient.

A black material has a high emissivity coefficient, while a silvery material has a low emissivity coefficient.

However, the emissivity coefficient cuts both ways, so to speak. A black material in thermodynamic equilibrium with its environment absorbs more radiation, true. But it also emits more radiation (this is necessary for equilibrium to hold). Likewise, a silvery material absorbs less radiation, and also emits less radiation.

Conductive heat transfer ensures that the black material on the surface of the heat sink remains hot. The surroundings are at a lower temperature. Therefore T1 and T2 are set, and the heat transferred from the heat sink to the surroundings is simply proportional to e, the emissivity coefficient."

[renobruce]

There seems to be as much conjecture in the heat sink world as there is in the GS motor world as far as color is concerned............

"Radiative heat transfer (heat transfer by electromagnetic radiation) is proportional to
e*(T1^4 - T2^4)
where T1 is the absolute temperature of the material, T2 is the absolute temperature of the surroundings, and e is the emissivity coefficient.

A black material has a high emissivity coefficient, while a silvery material has a low emissivity coefficient.

However, the emissivity coefficient cuts both ways, so to speak. A black material in thermodynamic equilibrium with its environment absorbs more radiation, true. But it also emits more radiation (this is necessary for equilibrium to hold). Likewise, a silvery material absorbs less radiation, and also emits less radiation.

Conductive heat transfer ensures that the black material on the surface of the heat sink remains hot. The surroundings are at a lower temperature. Therefore T1 and T2 are set, and the heat transferred from the heat sink to the surroundings is simply proportional to e, the emissivity coefficient."

My brain just farted.

[tkent02]

Black's purty.

[mriddle]

I'll go with this

Black's purty.

[rapidray]

For those of us that want black engines, would Renobruce share how it's done? Those parts look fantastic.

He COULD show you






















but then he'd have to kill you! Ray.

[renobruce]

For those of us that want black engines, would Renobruce share how it's done? Those parts look fantastic.

Thanks! The key is in the prep. The parts have to be 100% clean. I scrubbed all my parts (some for days) with Simple Green, then used MEK to remove any residual oils. I then masked, etch-primed, painted, and baked. I used Duplicolor Engine Enamel, but if I were to do it again, I'd use VHT engine/caliper paint. It holds up better and seems to resist chemicals better. I've been using that on the carbs I paint and I'm very happy with the results. There are a multitude of other paints you can use, too. Do a search and you'll see what others have done.

[lucabond]

I know I look hotter on a bike with a black motor and thats all that matters.

[posplayr]

I know I look hotter on a bike with a black motor and thats all that matters.

What they say? "Black is Beautiful"

[Dreef1999]

There seems to be as much conjecture in the heat sink world as there is in the GS motor world as far as color is concerned............

"Radiative heat transfer (heat transfer by electromagnetic radiation) is proportional to
e*(T1^4 - T2^4)

So the question is how much heat is actually removed by radiation as opposed to convection?

Couple assumptions 300F engine, 70F air temp
Black engine Emissivity 0.90
Coefficient of convection 100 w/m^2*K (high value for air)

Radiation 1,221 watts
Convection 12,700 watts

So radiation might account for 10% of your engines cooling. The cooler the engine the smaller the role, the hotter the engine the larger the possible role of the radiation.

More importantly the engine would have to run approximately 25F hotter for the convection to more than make up for no effective radiation.

[JMHJ]

Which one sheds water better? Just kidding.

Thanks for the informative replies. I was wondering regarding a special HVAC application. Some outdoor AC units have black coil fins, which would fit with the black cools better scenario (even if just a little bit).

Radiant heat barriers installed near the underside of a roof having the reflective side down doesn't make intuitive sense either.

[chef1366]

You guys are killing me.

[posplayr]

You guys are killing me.

I almost flunked Thermodynamics and stayed in EE so I aint saying nuthin