Trying something new:
Senior Member
Posts like a Northstar
Joined: Apr 2004
Posts: 606
Likes: 0
Black body objects are black because they absorb all temperature wave lengths. Yes, some wavelengths are visible light. Radiation is a wavelength thing, not a "physical" transfer like conduction or convection.
Quickly from the internet I pulled this:
I know I did an experiment once where I heated two steal rods of identical diameter and length to the same temperature. One was polished shiny and the other painted flat black. The balck rod cooled significantly quicker than the polished shiny rod. The rods were suspended from thin wire and inside a clear plastic box to limit heat loss through conduction and convection. This only leaves radiation. I can get out my heat transfer book when I get home at the end of this week to verify this and check further. If my memory is serving me wrong than so be it.
Quickly from the internet I pulled this:
Heated bodies radiate by processes just like the absorption described above operating in reverse. Thus, for soot heat causes the lattice to vibrate more vigorously, giving energy to the electrons (imagine them as balls in a pinball machine with strongly vibrating barriers, etc.) and since the electrons are charged they radiate away excess kinetic energy. On the other hand, the electrons in a metal have very long mean free paths, the lattice vibrations affect them much less, so they are less effective in radiating away heat. It is evident from considerations like this that good absorbers of radiation are also good emitters.
Thread Starter
Junior Member
Posts like a Ricer Type-R
Joined: Aug 2002
Posts: 11
Likes: 13
Originally Posted by Chinski
Black body objects are black because they absorb all temperature wave lengths. Yes, some wavelengths are visible light. Radiation is a wavelength thing, not a "physical" transfer like conduction or convection.
Quickly from the internet I pulled this:
I know I did an experiment once where I heated two steal rods of identical diameter and length to the same temperature. One was polished shiny and the other painted flat black. The balck rod cooled significantly quicker than the polished shiny rod. The rods were suspended from thin wire and inside a clear plastic box to limit heat loss through conduction and convection. This only leaves radiation. I can get out my heat transfer book when I get home at the end of this week to verify this and check further. If my memory is serving me wrong than so be it.
Quickly from the internet I pulled this:
Heated bodies radiate by processes just like the absorption described above operating in reverse. Thus, for soot heat causes the lattice to vibrate more vigorously, giving energy to the electrons (imagine them as balls in a pinball machine with strongly vibrating barriers, etc.) and since the electrons are charged they radiate away excess kinetic energy. On the other hand, the electrons in a metal have very long mean free paths, the lattice vibrations affect them much less, so they are less effective in radiating away heat. It is evident from considerations like this that good absorbers of radiation are also good emitters.
I design and build custom laser systems for Hewlett Packard. I know all about light, including those wavelengths that create heat.
Senior Member
Posts like a Northstar
Joined: Apr 2004
Posts: 606
Likes: 0
http://www.jet-hot.com/Pages/coatings.html
If you read the performance advanteges it says:
So the low emissivity of the high luster shiny coating helps to reduce the heat to the engine bay as well as keeping the exhaust gas hot to keep velocities up.
Also they offer:
Now I do realize that the shiny JET-HOT 1300 is also available in black and grey but they do add in that these colors are "the same basic formula". That makes me think that the performace is not exactly the same for the other colors. But the coating specifically for reducing exhaust temps and dissipating heat is only available in black.
The test for this coating may be good. Now that I think about it you can't just point an infrared gun at a point in the air, only at a surface, and 200F is low for a header surface temp.
The ceramic material of the coating is making the difference, it could just be better with a less emissive surface color. Either way it is better than no coating.
JET-HOT 1300™ - Our exclusive formula works beautifully on new or used parts at temperatures up to 1,300°F. Sterling™ is our most popular finish, this high-luster coating, containing silver powder, shares the brilliance of chrome with the subtlety of nickel. It provides the most brilliant appearance in high-temp, high-tech coatings while delivering major performance advantages.
Because of its low emissivity and insulating effect, JET-HOT Sterling creates a thermal barrier to protect headers - inside and out - while reducing heat transfer into the engine compartment.
First, the coating promotes denser, more potent fuel/air charges by insulating the engine bay from exhaust heat. At the same time, it accelerates the pulsed-vacuum effect on “tuned” headers, resulting in more effective scavenging of cylinders. The increased velocity of exhaust gases produced by higher exit inertia not only clears each cylinder more quickly; it also draws in the next fuel/air charge more efficiently.
Also they offer:
JET-HOT TDC™ - In applications where heat must be dissipated rapidly, this rough, black coating (with a temperature tolerance of 1,300°F) combines color and surface profile to lower temperatures within exhaust piping.
The test for this coating may be good. Now that I think about it you can't just point an infrared gun at a point in the air, only at a surface, and 200F is low for a header surface temp.
The ceramic material of the coating is making the difference, it could just be better with a less emissive surface color. Either way it is better than no coating.
Thread Starter
Junior Member
Posts like a Ricer Type-R
Joined: Aug 2002
Posts: 11
Likes: 13
Chinski, I never claimed this stuff was as good as commercial coatings.
But according to Comp Cams, it works as shown in the graph, and I think they have a good enough reputation for me to trust them in my $13 investment.
If it works HALF as good as CompCams tests show, I'll be pleased for that little investment. The advantages of being able to apply it on the car are worth it too. My previous coating looks like ****, and probably isn't very effective.
But according to Comp Cams, it works as shown in the graph, and I think they have a good enough reputation for me to trust them in my $13 investment.
If it works HALF as good as CompCams tests show, I'll be pleased for that little investment. The advantages of being able to apply it on the car are worth it too. My previous coating looks like ****, and probably isn't very effective.
Senior Member
Posts like a 4 Banger
Joined: Mar 2005
Posts: 124
Likes: 0
From: Appleton, WI
Not sure about the color changing the amount of radiated heat, at least in this case. The ceramic element is what stops or retards the heat transfer from inside to outside. If you have tried grinding a ceramic insulator you can actually hold it with bare hands very close to the point where it is glowing red hot, very poor heat transfer. My original stock manifolds were coated inside and out with a titanium gray ceramic and they worked very well, with all heat shields removed from the manifolds. When I inquired about doing the same thing to the to the turbo piping I made, I was told only the black colored stuff would hold up to that amount of heat. Not sure why, but I believe it is a bit thinner coating. All colors except the black must be baked after application, the black is applied and allowed to dry naturally, the exhaust heat finishes the job. It is the only color I am aware of that is readily applied by the home mechanic. What I have is not bumpy, as I heard it described by Jet Hot, must be a different compound? It looks just like flat black paint, but it does not scratch off, has been on the turbo housing and all exhaust manifolding for over 27k miles. No heat shields are used on the piping although the underside of the throttle body is insulated with foil where the pipe runs to exit the engine bay, although it is after the turbine so a fair amount of heat is already disipated. It certainly isn't pretty, but it does seem to work as advertised. Just my experience with it.
Thread Starter
Junior Member
Posts like a Ricer Type-R
Joined: Aug 2002
Posts: 11
Likes: 13
It works, but I'm still collecting 'after' data. In various conditions. Slight delay due to a low-pressure cell over central Oregon, 60° daytime high temps, and rain.
All my 'before' testing was done in 80-90° conditions.
All my 'before' testing was done in 80-90° conditions.
