DirtRider . Net MX, SX, Arena Cross, Off-Road Community
Dirt Rider . Net Text Version Home
Dirt Bike Dirt Bike Dirt Bike Dirt Bike

This is the text version of DirtRider.Net
Click Here for the Full Version


Pages: 1

black vs. unpainted radiators

(Click here to view the original thread with full colors/images)

Posted by: sodhead

Does anyone know what the true story is between painted vs. unpainted radiators regarding their ability to dissipate heat ?

A buddy and I have YZ400F’s that came with black radiators. Another buddy of ours has a YZ426F that came with unpainted radiators. Somehow we were all under the impression (we must have read somewhere) that Yamaha started using unpainted radiators because they are able to dissipate heat better thus able to cool the engine better than black painted ones..

I talked to a guy from a radiator shop who told me that this was not true. He said if two radiators were compared and everything but their colors were identical (one being black and the other unpainted aluminum) the black one would actually cool better than the unpainted one. He said that the only reason the manufacturers are not painting the radiators is that they are less costly to manufacture that way.

I also found some info on the internet from a radiator sales place that said that radiators are painted black because black is the best color to dissipate heat.

Which is actually more efficient,, black, or unpainted radiators??

Thanks,
Bob



Posted by: jake949

I would tend to think that any kind of non matalic coating would work as insulation. therefor holding the heat in. Black obsorbs all wave lengths of light(heat energy). That is why solor panals are black. I was just looking at one of my hotrod mags, all the cars have shiny nonpainted rads. Look at the factory bikes if paint was good they would have it.

just me babbling


Posted by: sodhead

True.

I was thinking the same thing about the paint being a form of insulation.

I wonder why manufacturers of radiators go through the trouble of painting aluminum ones - or used to anyway..




Posted by: jake949

corrosion protection


Posted by: kmccune

Wow this takes me back... Some theory about the perfect absorber being the perfect radiator. The color black did indeed make for better dissipation. But I agree that how the color is applied is important as well, as a thick coating will act as an insulator. I but heat exchangers for work and they come in both black and raw aluminum. They seem to work the same, so I would guess that there are enough inefficiencies other then the color to negate an potential gain of one color over the other. Hope this helps?
Kevin

------------------
McCune's Scottish Pub
Brews That You Can Chew!


Posted by: Kav

I’ve heard that black can dissipate heat better also. How it worked was black absorbs heat, so it could be used to draw extra heat from another source in this case the aluminum. For the most part there is a constant flow of air over the bike and radiators to keep the black paint from being “overloaded” with heat from the aluminum radiators. This allows the aluminum radiators to radiate off even more heat with the help of the black paint then with just the unpainted aluminum radiators. But it may be a small amount of extra heat that is removed from the radiators, and may not be worth the extra cost to paint the radiators.

just my $0.02

------------------
'01 YZ250
'92 DR350S

Lessons will be repeated until there are learned.


Posted by: Dirteater

Perhaps this is a null point, but wouldn't the heat absorbed from outside sources detract from cooling. If the radiator gets 110deg sitting in the sun how is it supposed to help with the engine running?
Just for kicks imagine a white car with the windows rolled up on a hot summer day. You get in and drive without rolling the windows up or turning the A/C on. Do the same in a black car.
The black car is excessivly hot to begin with, and will cool off slower.
Black absorbs all lightwave paterns. Not heat necissarly, just the heat from the solar radiation. Is a black car sitting inside a garage warmer than a white car next to it?
Just rhetorical questions (sp?)


Posted by: SFO

My 01 wr does have painted radiators...
Silver painted radiators...
It has already begun to peel off, this reality makes color, I believe, a cosmetic issue in Yamahas eyes.
Just another viewpoint...


Posted by: jake949

It is matalic paint.


Posted by: will pattison

uh, erm...i are a enguneer, and here is my engineering opinion regarding the myth of painted radiators:

it's a myth.



------------------
will pattison
engineer, racer
ignition
www.ignitioninc.com


Posted by: sodhead

Will,

What is a myth?

The paint inhibiting heat dissipation, or the black color enhancing it?



Posted by: SFO

I remember this debate raging in the early 80's...
The viewpoint then was that the matte finish of sandblasting offered a higher ratio of conductivity...
I think in the end it was covered in dirt and nullified...
6' down deep.
Covered in dirt eventually, I guess...


Posted by: will pattison

sodhead and all,

i'm no expert on heat transfer, but can say a few things in general. where the color of a surface is involved, radiative heat transfer is the mechanism that applies most. however, even though they are called "radiators", radiative heat transfer is not likely to be the most important mode of heat transfer involved on a motorcycle. perhaps they should be called "convectors", because convection is really what's at work. it seems to me that the airflow through the fins would have to be far more dominant than any other effect.

now, as to the insulation effect of the paint. that really applies to the third mode of heat transfer: conduction. while it's technically true that any insulation will have an effect on the ability of the aluminum fins to conduct heat to their surface, we are talking miniscule amounts. paint is typically 0.003-0.005" thick in an application like this. it's just not enough to have a practical effect.

from my product development experience, i believe yamaha painted the radiators strictly for cosmetic reasons. eventually, they either decided that it was too expensive, or the marketing department heard that race teams were stripping radiators to make them cool better, and well...you know what happened then.

hopefully that helps.

wp.


Posted by: MACE

We are most likely to boil when stationary. When we are stationary convection to the air is reduced and radiation to the atmosphere is predominant. In this case the black body is a more efficient "emitter" as well as a more efficient "receiver". If the black body is cooler than the atmosphere it will receive and if it is hotter it will emit.

If you have DeVol guards paint them black. They will "pull" heat out of your rediators at the next trail bottle neck. Leave your radiators black as well. Don't paint your helmet black. Wash your hands well before returning to work. Don't wear a sweatshirt with drawstrings when operating a lathe.

That's all I have to contribute http://dirtrider.net/ubb2/wink.gif

------------------
MACE

One night I was layin' down,
I heard mama 'n papa talkin'
I heard papa tell mama, "you let that boy MOTO,
it's in him, and it got to come out..."


Posted by: jake949

mace is that how you got the silver costume? Those draw stings will do that every time.


Posted by: Boit

What might have been passed over here is that whether the coating is black or white is not the issue. Replika Maschinen in Santa Rosa, Ca. offers a coating that is said to aid in the transfer of heat(BTU). This coating happens to be black. I would contact them for further info. They have a web site at WWW.ReplikaMaschinen.com

[This message has been edited by Boit (edited 02-21-2001).]

[This message has been edited by Boit (edited 02-21-2001).]

I just tried using the URL but I get an internet error. I checked for spelling and punctuation and it IS correct. I don't know what the problem is. Keep trying.

[This message has been edited by Boit (edited 02-21-2001).]


Posted by: RM_guy

OK...here I go (I know Will, I know). I think surface area and air flow makes the most difference in cooling where heat transfer is involved. The more surface area, the more heat that can be dissipated, hence sandblasting as Will had mentioned. Dark colors absorb heat so it would seem counter productive to be absorbing heat from the environment at the same time as you're trying to dissipate heat from the radiator. In any case I don't think the color makes much difference compared to surface area and air flow. If a dark color made that much difference then why doesn't anyone try to paint the inside of the cooling passages in the cylinder black?

------------------
Did I do the double?
Ah,um...Sure did. I was right behind you!
My Pictures


Posted by: MACE

Quote:
Originally posted by jake949:
mace is that how you got the silver costume? Those draw stings will do that every time.


That is on my short list of things that could have turned out much worse. A lesson learned without blood thankfully.

Re: Black
I had a minor problem with burping radiators on my WR until I painted my DeVol guards black. Problem is gone now.




Posted by: will pattison

for some reason, when i clicked the url posted, explorer converted it to repliCamachinen (notice the missing s).

wp.


Posted by: Boit

Will: It was bothering me why that URL wouldn't work. To satisfy my curiosity, I tried all lower case letter and it worked. Try this www.replikamaschinen


Well heck! It only works if I type it in manually. It won't link from here.

[This message has been edited by Boit (edited 02-24-2001).]


Posted by: techman

Here's a brain twister. At low speed in a tight trail, there's low air velocity through the rad. This is of interest because it's a typical overheating scenario. Should one have sandblasted surfaces to get more surface area, but slower air velocity because of increased aerodynamic drag at the surface (hence more backpressure and lesser air flow), or should one keep it smooth so there's less backpressure and more air flow through the rad? I'm sure the words laminar, turbulent and surface-layer mix into the answer to this.

------------------



Posted by: TriPower

Color has nothing to do with heat dissipation ability. Black or aluminum, rads will work the same. Color changes a material's ability to absorb/reflect LIGHT, not heat (although absorbed light will become heat). Black will absorb more heat when exposed to light, but since our radiators are almost always in the shade, this simply isn't an issue. The issue is whether unpainted radiators work better than painted ones in regard to airflow heat transfer; you could paint them pink and they would still work the same http://dirtrider.net/ubb2/smile.gif

So, if you put a black radiator and a white radiator into your oven at 350 degrees for one hour, which one would come out hotter? http://dirtrider.net/ubb2/smile.gif

How about if you left them in the sun for an hour? Get it?

Techman, I believe the bike in your scenario will overheat no matter what type of finish you use http://dirtrider.net/ubb2/smile.gif

------------------


[This message has been edited by TriPower (edited 04-10-2001).]


Posted by: MACE

Quote:
Originally posted by TriPower:
...Color changes a material's ability to absorb/reflect LIGHT



NOT light, radiant energy. Once more, the black body is a more efficient "emitter" as well as a more efficient "receiver". If the black body is cooler than the atmosphere it will receive and if it is hotter it will emit.

Quote:

So, if you put a black radiator and a white radiator into your oven at 350 degrees for one hour, which one would come out hotter? http://dirtrider.net/ubb2/smile.gif


The oven and both radiators will reach the same equilibrium temperature.

If you put them both in for one minute, the black radiator will be hotter.

Heat goes to cool.


Quote:
How about if you left them in the sun for an hour?


Equilibrium between solar recepter and emitter to the air would be a higher temp for the black body.


Now if you heated to 200F two aluminum plates identical except one was black and one was unpainted and set them in the sun, which would be cooler after two minutes?

Black one.

MACE


Posted by: Kramer

Mace, you're a sharp tack, and I believe techman's sandblasted radiator would improve efficiency. By thinning the boundary layer you would improve conductive and convective transfer. (Ask a cook about Al foil, shiny side in or out.) I'm not sure how you'd go about surfacing such thin and delicate material though. Probably not worth the effort.

TriPower, you're right, the overall difference between Al and black's cooling capicty is probably negligible. The portion of that transfer that's due to radiation, well that's a different story. You're talking Quantum Physics, and it's not intuitive. Radiant heat _is_ light. It's just another electromagnetic wave with a different frequency. While I don't know what the emissivity of either the black paint or the bare Al is, I'm sure the black emits more.

Incidently, a black radiator is not a true 'black body'. By definition a black body absorbs and emits all radiation -for it to appear black it only needs to absorb most of the radiation in the visible spectrum. (I think Mace's suit is the opposite, an 'ideal reflector'. http://dirtrider.net/ubb2/cool.gif )

Just remember, energy in - energy out = energy gained. Everything real is always absorbing radiation, and also radiating at the same time regardless of temperature (unless it's at absolute zero, then it has no energy to radiate, and it wouldn't be real either).

It's net heat transfer though, will obey the 0th law and the heat will go from the warm object to the cold.


that's enough, I'm going to paint a "DO NOT PAINT" sign on my helmet -right after I wash my hands. Lucky for me I have neither a lathe nor a sweatshirt with drawstrings!!

------------------
Kramer
member BRC, AMA
98 WR400 Dualsport!


Posted by: JohninKY

In general, blacker is better. It's already been said that darker colors emit and absorb more radiant energy. That's no myth.

Someone said:
"now, as to the insulation effect of the paint. that really applies to the third mode of heat transfer: conduction. while it's technically true that any insulation will have an effect on the ability of the aluminum fins to conduct heat to their surface, we are talking miniscule amounts. paint is typically 0.003-0.005" thick in an application like this. it's just not enough to have a practical effect."

Note:
The paint will also impede the overall convection heat transfer.
Even a coating of a few thousandths of an inch can reduce the overall heat transfer coefficient by as much as 50%. That said it would depend on the type of coating.

Make mine an unpainted black radiator.

------------------


[This message has been edited by JohninKY (edited 04-10-2001).]

[This message has been edited by JohninKY (edited 04-10-2001).]

[This message has been edited by JohninKY (edited 04-15-2001).]


Posted by: techman

Sounds like black anodised, rough finish ought to be best, except for cost and the possibility that the oxide might have a poor thermal conductivity. On that issue, the fins may only be 0.020" thick Al and 0.003" to 0.005" of paint coating on each side represents a fair proportion of the overall structure - so that paint better be pretty darn thermally conductive if it's used. My opinion there contradicts Will a bit, but I think he's right about the convection being the majority mechanism for energy transfer to the air. Most of the fins' radiating surfaces face another fin (!) so it radiates back into itself! The globally speaking outer surfaces would radiate outwards, one into the engine and frame and one into the forks, with some portion actually escaping out into the air that comes flowing back into the rad.... Doesn't sound very beneficial except when standing still. Maybe I'm viewing that in a technically pessimistic way - perhaps a majority or at least significant portion of the radiated energy just boogies off into space, not absorbed by the air. That is, once it bounce off those neat little angled plastic rock and roost protectors on the way out... Still sounds pretty pessimistic for radiation as helping much.

So, it seems the overall target is to maximise the convection efficiency and capability.

However, Mace's evidence of painting his Devol rad guards and stopping coolant burping when stopped on the trail suggests that when convection gets shut off, radiation is all you got left and with the rad being much hotter than the surrounding environment, there will definitely be solid outbound heat flow in the absorption/radiation balance - with the evidence agreeing with the principle that black should radiate better. Of course, those originally shiny-surfaced, silver colored Devol aluminum guards were not only previously blocking part of the radiation path and convection airflow, they were reflecting a portion of the radiated heat back into the rad! Mace, paint the inner guard surfaces too! (maybe you already did) Sorry Tripower, black color does give a higher gain of heat radiated per body temperature. (think solar water heaters - in reverse - you can look in a table called emissivity of materials) Mace is right about black and improved radiation capability. My slow trail scenario was still a combination of radiation and convection, but I was only asking about the convection issue in that post.

Back to convection, Will's rougher fin surfaces causing turbulence and a thinner surface layer per Kramer's statement and hence improved convection - I think I can buy that. But, Kramer, when stopped so convection = 0 then Maces black radiation improvement will be better, as per theory and his evidence. When flying down the trail, however, the balance swings to vast majority of convection action over radiant action and the improvement from the black becomes a lot less significant. I agree with JohninKY's statement about the black coating possibly impeding the heat flow from the coolant out through the metal fins to the air contacting the fins - remember the 0.003-0.005 paint vs 0.020 metal fins dimensions? But, 50% seems out of kilter - John, what's your source and details of that 50% example?

So, basicly it would seem that you want to go black on the outer rad surfaces where they can radiate out into space, but use a very thin paint or oxide with a thermal conductivity approaching that of aluminum, which is very high. I don't know whether anodising can be done or is done on rads, or the specifics of good paint to use. The missing link is the thermal conductivities of oxides and paints. Maybe replikamashinen anodises their stuff (?) I think cars use paint just to stop corrosion. I think paint can give a smoother surface if applied a certain way (the way that's desirable to make your car fender shiny), but we would want a "poor" paint job that comes out rough or dull to improve convection. I think lacquer goes on the thinnest, but I don't know it's thermal properties.

Of course, if I could do away with those rad protectors I would get much better cooling. Or I could just stick the bigger WR rads on the bike.

All that said, I don't have a lathe or a sweatshirt with drawstrings http://dirtrider.net/ubb2/wink.gif

------------------



Posted by: JohninKY

Quote:
Originally posted by techman:
the 0.003-0.005 paint vs 0.020 metal fins dimensions? But, 50% seems out of kilter - John, what's your source and details of that 50% example?


We have titanium tubed steam condensers at work. We calculate the actual heat transfer across the tubes (btu/hr-ft2-F) and compare to design on a regular basis. It has been my experience that a thin coating (a few thousandths) of calcium scale will drop the heat transfer rate nearly in half. Both the thickness of material and heat transfer coefficient affect heat transfer. Even between metals the heat transfer coefficient varies greatly. I'm guessing most coatings would not transfer heat well. That said a 50% reduction is an exaggeration for a radiator coating.

For radiation heat transfer temperature, color(blacker is better), surface roughness and area determine transfer rate.

I'm guessing that even sitting still convection heat transfer never drops to zero.

I'd also guess the black coated vs bare metal is a wash. My old KDX has black coated radiators, my newer CR has bare aluminum. I'd like to think engineering design gets better as time goes by, but accountants sometimes screw that up. Which one transfers heat better? I don't know, but both radiators burn my hand at operating temperature. http://dirtrider.net/ubb2/smile.gif




------------------



Posted by: techman

JohninKY, it sounds like you may have a reference book at work with a chart of heat transfer coefficients for differnt materials. Any chance of looking up a few things like Al, oxides, steel, copper etc and posting them? Would that be (watt x meter)/(square meter x delta temperature) ? I think I get one more linear dimension for the thickness of the material, besides surface area.

Your experience with steam condensation may have some of that steam table phase change black magic in it. However, maybe scale inside the rads can be dramatic to liquid state coolant heat exchange as well. I could see it being very significant. BTW, I know air would convect in thermal updrafts around the rad when you're sitting still causing some heat exchange on the outer surfaces, I just meant that the bulk of the active fin surfaces (inside the rad) would see zero thru-flow air velocity vs when the bike is moving.

If you have taken thermodynamics courses, you've probably experienced the situation where even the prof says "there's no definite answer to that question". One of those soft sciences, like measuring atoms with statistics: "so where is it?" "its sort of near here, sometimes" http://dirtrider.net/ubb2/smile.gif

------------------



Posted by: kevkon

With all this discussion about the thermal qualities of radiator finishes,lets not forget to emphise the importance of basic cleaning and periodic coolant flushing. Also,
I know this should be a different thread, but what about the difference between various coolants?

------------------



Posted by: Rich Rohrich

I think kevkon may have hit the major point. Keeping the radiators clean INSIDE and OUT probably has the biggest impact, but ultimately doesn't make for as interesting a discussion http://dirtrider.net/ubb2/biggrin.gif

------------------
Rich Rohrich
==

"Wisdom is not a product of schooling but of the life-long attempt to acquire it."
- Albert Einstein


Posted by: motopuffs

ok, can someone comment on "water wetter" type products? Not on a product review basis, but from a technical standpoint. How does this stuff work (or does it work?)?

also, what about running mostly water in the radiator (just a little a.f. to protect from corrosion). I would predict a gain in heat transfer, but the boiling point would be lower...is this a worthwhile trade off?

------------------


[This message has been edited by kookooformotopuffs (edited 04-13-2001).]


Posted by: wrench

Info provided by BWALKER.


posted 06-27-2000 02:15 PM Staff Use Only:


--------------------------------------------------------------------------------
Ando, Rich. I called redline today and requested msds files on water wetter .

Chemical name: Glycol Ether mixture

Ingredients

DiIsopropyl Alcohol Ether 1-40%, TriIsopropyl Di Ether1-40%, Sodium Molybdate2-10%, Tolyltriazole1-3%, polySiloxane Polymer

specific gravity:1.09
PH 9.5 @ 10% solution
evaporation rate- not determined?
water solubility- miscible @ 25 degrees celcius

Rich, you could you do the chemical analysis on this stuff and let us know if any of the chemicals have useful properties for our application. Hopefully this will clear up some of the bs and non sense. bw

06-27-2000 :Edited

--------------------------------------------------------------------------------


------------------



Posted by: spanky250

Quote:
Originally posted by kookooformotopuffs:
ok, can someone comment on "water wetter" type products? Not on a product review basis, but from a technical standpoint. How does this stuff work (or does it work?)?

also, what about running mostly water in the radiator (just a little a.f. to protect from corrosion). I would predict a gain in heat transfer, but the boiling point would be lower...is this a worthwhile trade off?


All Water Wetter consists of is basically anti-corrosion additives to protect the radiator from corrosion when running straight water. It's cooling benefits come from the simple fact that pure water is a better conductor of heat than anti-freeze/water mix.

------------------
1992 KDX 250-FMF porting,two-stage power reeds, Fatty pipe, Power Core silencer,titanium rod,Wiseco Ultra-lite, Pro-Action suspension...Oh my Gawd, they killed Kenny!


Posted by: Rich Rohrich

Quote:
Originally posted by spanky250:
It's cooling benefits come from the simple fact that pure water is a better conductor of heat than anti-freeze/water mix.


As Ando pointed out in a previous post the idea behind Water Wetter's cooling effects are based in surficant technology. Whether it achieves those goals in an all aluminum engine is open to debate http://dirtrider.net/ubb2/smile.gif



------------------
Rich Rohrich
==

"Wisdom is not a product of schooling but of the life-long attempt to acquire it."
- Albert Einstein


Posted by: motopuffs

the claim on the bottle is that there is an improvement in cooling beyond just that obtained by running straight water.

------------------



Posted by: JohninKY

Quote:
Originally posted by techman:
Any chance of looking up a few things like Al, oxides, steel, copper etc and posting them? Would that be (watt x meter)/(square meter x delta temperature) ? I think I get one more linear dimension for the thickness of the material, besides surface area.

Your experience with steam condensation may have some of that steam table phase change black magic in it.


Ok, everybody's a critic. When I figure the heat transfer coefficient I calculate an overall coefficient taking into account thicknesses, materials and film coefficients for both the inside and outside surfaces of the heat exchanger. Units are Btu/hr-ft2-F. You're right, the individual material's coefficient independent of thickness would be in Btu/hr-ft-F. That said here are some numbers for common materials:

Aluminum 118 Btu/hr-ft-F
Carbon Steel(low C) 31
Copper 223
Stainless 7 to 26

Non metals
Asbestos 0.093
Water 0.364
Ethylene Glycol 0.148

Note:
These are typical, general numbers and don't take into account flow conditions, fouling, alloying, surface finish, any number of different kinds of oxidation etc, etc...
Hopefully this shows that just a few thousandths thickness of the wrong material can dramatically change the heat transfer.
Also, this is only one piece of the puzzle. There is also a film coefficient on each side of the material which depends on flow type (turbulent/laminar), velocity and fluid type. Water wetter would improve your film coefficient. If you figure all that out you're still only coming up with the "clean" heat transfer coefficient. In the real world you also have scale on the inside and mud on the outside, plugged internal paths and low flow areas.
There is no black magic steam table duplicity here. It doesn't matter if the heat is latent or sensible. The simplified overall heat transfer coefficient equation is:
Q=UA(LMTD)
U- coeffient(overall)
A- area
Q- heat transfer rate
LMTD - log mean temp difference.

Sorry, this is too long and probably a totally inadequate explanation. I'll stop here.




------------------


[This message has been edited by JohninKY (edited 04-15-2001).]



This is the text version of DirtRider.Net
Click Here for the Full Version

Text Version Home





vBulletin Copyright ©2000 - 2009, Jelsoft Enterprises Limited.
vB Easy Archive Final ©2000 - 2009 - Created by Stefan "Xenon" Kaeser