Post by mj on Jun 6, 2010 8:29:09 GMT -5
Painting something black, for example the engine or tin, does absolutely nothing significant to assist in cooling our engines. It is a myth that a black surface sheds heat better than another color, or no-color (bare metal). Heat is infra-red radiation and there is no color. (Color is a visual phenomena available to us animals. That's all it is. You can even say that as far as heat exchange is concerned, everything is gray.)
Don't be confused by your high-school experiment where you heated two tin cans, one flat black and the other bare metal. The 'color' black can help at low temperatures, for example the temperatures you can bear touching with your fingers (it's why you might prefer a white car rather than flat-black for desert environments), but at the temperatures our engines must cope with, it is a different story because _the hotter something is, the faster it dissipates heat_. In other words, heat transfer is not linear and the _range_ of the radiation of heat we deal with is way beyond the cool factor of black coating.
If coloring surfaces really did help (in our range of concern), then you would find NASA painting their craft with all sorts of patterns to manage heat from various parts just as they design surfaces for the same.
ANOTHER point is that in our exhausts, the heat within the first few inches of the exhaust port is profoundly infra-red, very hot, and the temperature drops hundreds of degrees per inch after that. No amount of air can cool that first few inches because it is radiation. You can not blow away that heat any more than you can blow the beam of a flashlight sideways.
Hard shields can block this radiant heat, and you will find them in most engines. In our ACVW, the heat exchangers serve the same function. If you run 4:1 headers, then note that the rear pipes are probably close to the cylinders. It really helps to wrap headers in fiberglass tape. Tape helps ALOT to keep that area cooler (with headers). There is also a minor performance advantage because the tape insulates to keep the pipes hot and the gasses flowing faster in just that area. BEWARE, however, that just where the tape stops is very hot because cooling has been deferred to that point. So you have to manage that point, too. Don't make the mistake of routing an external oil line, wires, or anything critical close to it.
Finally, sectioning the engine bay as VW did (and as I did shown in my photo) is best to keep heat where it belongs and away from the upper end. It's about the flow of air.
I read a scientist's theory of the function of a Zebra's stripes in which he suggests that the alternating lines of black & white create a convection current at the stripes' boundaries that cools the Zebra's skin. It might. I don't know. But I bring it up to demonstrate the case is of low-temperature dissipation where 'significance' occurs. It is not a significant effect in the temperatures we have to cope with.
Don't be confused by your high-school experiment where you heated two tin cans, one flat black and the other bare metal. The 'color' black can help at low temperatures, for example the temperatures you can bear touching with your fingers (it's why you might prefer a white car rather than flat-black for desert environments), but at the temperatures our engines must cope with, it is a different story because _the hotter something is, the faster it dissipates heat_. In other words, heat transfer is not linear and the _range_ of the radiation of heat we deal with is way beyond the cool factor of black coating.
If coloring surfaces really did help (in our range of concern), then you would find NASA painting their craft with all sorts of patterns to manage heat from various parts just as they design surfaces for the same.
ANOTHER point is that in our exhausts, the heat within the first few inches of the exhaust port is profoundly infra-red, very hot, and the temperature drops hundreds of degrees per inch after that. No amount of air can cool that first few inches because it is radiation. You can not blow away that heat any more than you can blow the beam of a flashlight sideways.
Hard shields can block this radiant heat, and you will find them in most engines. In our ACVW, the heat exchangers serve the same function. If you run 4:1 headers, then note that the rear pipes are probably close to the cylinders. It really helps to wrap headers in fiberglass tape. Tape helps ALOT to keep that area cooler (with headers). There is also a minor performance advantage because the tape insulates to keep the pipes hot and the gasses flowing faster in just that area. BEWARE, however, that just where the tape stops is very hot because cooling has been deferred to that point. So you have to manage that point, too. Don't make the mistake of routing an external oil line, wires, or anything critical close to it.
Finally, sectioning the engine bay as VW did (and as I did shown in my photo) is best to keep heat where it belongs and away from the upper end. It's about the flow of air.
I read a scientist's theory of the function of a Zebra's stripes in which he suggests that the alternating lines of black & white create a convection current at the stripes' boundaries that cools the Zebra's skin. It might. I don't know. But I bring it up to demonstrate the case is of low-temperature dissipation where 'significance' occurs. It is not a significant effect in the temperatures we have to cope with.
