corrosion of alloy radiators?

[matty12]

only copper/brass radiators are painted black,its to stop the copper fins from braking down,thats the only real reason.

Its not often that a ally radiator or condensor is actually painted from the factory but some are.Of course some people when servicing a ally radiator will paint them to make them like nice and new again but thats just for apperance sakes.

[Z2TT]

Anyway to tell difference between a painted or anodized radiator?

Wouldn't anodized be better since the layer is thinner and will be able to let it's heat off better?

[Q-Authority]

Anyway to tell difference between a painted or anodized radiator?

Wouldn't anodized be better since the layer is thinner and will be able to let it's heat off better?

I'm not sure about how you tell which is which, but as for which is better, engineering reports show that anodizing is not better than some plain coatings/paint, and especially the better specialized coatings, but does still work quite well. It can tend to be a bit thinner than some other coatings, but this either doesn't appear to be enough of a factor to move it ahead of the others, or perhaps it just isn't actually as effective as the others, per thickness, and the thinner coating actually helps it get the emissivity rating that it does.
Unfortunately, however, they also report that anodizing will tend to wear prematurely, under extreme temperatures compared to specialized coatings, etc., and will then start loosing some of its effectiveness.

[matty12]

i have never ever heard of anodising radiators/condensors they are always painted,if someone was to show me one i would be more than interested to see it.

[twentyEight]

My aluminium JAR radiator is about 2.5 years old now and I just run standard black rubber radiator hoses and Toyota red coolant.

I took it out about a month ago when I was doing some work and the inside of it looks like new still.

I might have to put this on the JAR website as feedback as I'm sure ricey would be pleased to see that up there!

Do you mind?

[YLD-16L]

I might have to put this on the JAR website as feedback as I'm sure ricey would be pleased to see that up there!

Do you mind?

Knock yourself out

[3sgte]

At work we used to get cars with aluminum and brass rads.
Without a doubt the aluminum cores held up better to the salt they put on the roads in Canada.

It was nothing to see 300,000 km on an aluminum core, looking as good as new, but a brass core would have missing and loose fins at that mileage. We had more cracked tanks than actual leaks from the cores themselves.

Edit, they are almost all aluminum core now.

[oldcorollas]

meh .........

[oldcorollas]

It was nothing to see 300,000 km on an aluminum core, looking as good as new, but a brass core would have missing and loose fins at that mileage. We had more cracked tanks than actual leaks from the cores themselves.

Edit, they are almost all aluminum core now.

so what is different between stock alloy rads and aftermarket.. just the alloy end tanks instead of plastic?

oh and dodgy alloy used for the cores perhaps?

[Q-Authority]

interesting points, but a few things to think about...

anodising IS aluminium oxide. aluminium oxide and anodising have the same emissivity, on a small scale... but on a big scale is different

emissivity is arguably not really a factor when it comes to radiators, since much more heat is lost through conduction to the air, than by emission as radiation.
if radiation was a primary or even a significant method of heat loss, then having all those hot tubes facing each other, is the worst possible design for losing heat by radiation,

what is important is the coefficient of heat loss from aluminium etc to moving air.
and the thickness is also important, since the driving force for heat loss is temperature difference divided by thickness....

Good points to ponder. However, what about the following:

Would not emissivity create hot air currents and help to draw heat away from the coated object when there is little or no moving air around, or through, for instance the intercooler fins? And would this type of emissivity possibly be more effective on say, a horizontally mounted intercooler (not one directly on top of an engine, such as many Corollas, but more like an MR2), where upward heat convection would more easily draw up cooler air from below, helping to reduce the temperature of the intercooler in question? Thereby, providing better cooling when there is little or no moving air from the mobility of the car itself.

I'm no engineer, so don't jump on me too hard, if that doesn't seem plausible.

I'm not sure if I can completely trust the figures, but a guy on Naisioc(?) took intercooler outlet temps, of the same intercooler, before and after coating it with a specialized 'heat dispersant' coating, and showed that there was a significant drop in outlet temps when using the coated intercooler. Unfortunately, he also works for a place that does some work with these coatings, so it may not have been entirely unbiased.
But he did include a lot of data, and some that he was a bit puzzled about, which I later determined was more than actually likely to have been caused by the heat dispersant coating. The puzzlement was such: while the car was sitting in the garage, after a long run, the coated intercooler would actually heat up, from heat soak, significantly above the temperature level reached by the uncoated intercooler, under the same conditions. This odd period of time ocurred from about 5-10 minutes after turning off the engine, to about 20-30 minutes later. However, this period of higher heat soak was immediately followed by a much faster reduction in temperature, over the next and final recorded 30-60 minutes, or so.
I believe that the emissivity factor of the applied coating is more than likely accountable for that, as a higher emissivity rated object will heat soak from surrounding higher temperatures, more quickly that a lower emissivity rated object, but as soon as the surrounding temperaturtes drop, the higher emissivity rated object will also cool more quickly.

I'm sure his data could have been fudged, but in looking back at it, and over the entire range of data that he provided, the gains made by the coated intercooler certainly do seem plausible. He also showed that higher driving speeds produced less of a difference between the coated and uncoated intercoolers, though the coated one still produced somewhat cooler temps. However, it was at slow to non-moving speeds (such as at long stop lights) that the coated intercooler produced very significant lower outlet temps, presumably before possible heat soak would have a chance to really take effect.

Does any of that seem to make sense, or bear out?

[oldcorollas]

it really depends how the temp is measured...
try measuring the temps of different materials at same temp, using IR thermometer

to be honest, i don't think emissivity is such a factor in low temperature situations like intercoolers/radiators.
I started to do the calculations last night and just cbf , but maybe someone can be bothered?

re emissivity creating hot air currents etc..
if air absorbed radiated heat enough to make a difference, then infrared temperature monitors would not work unless they were placed in direct contact with the object.. since the air would absorb a significant amount of the radiation... but it doesn't...

However, it was at slow to non-moving speeds (such as at long stop lights) that the coated intercooler produced very significant lower outlet temps, presumably before possible heat soak would have a chance to really take effect.

well.. that depends where the heat soak is coming from... if the IC was on top of motor, there is heat radiated from cam covers.. but maybe it mainly occurs due to air heat...
either way, if the intercooler resists heating up from external effects.. doesn't that indicate that either a) it is being insulated by the coating so that heat conduction into it (and out of it) is slower (ie bad), or b) the emissivity is lower so it absorbs heat slower.. which is also bad when you want heat loss....


edit, all it would take to see the effect of coatings would be for someone to do a reasonable calculation of heat loss from radiator/IC for heat conduction and convection to air, and then do same for heat loss by radiation (and then alter for the emissivity = just multiply by the coefficient) and then you can get reasonable idea of effectiveness..

[eeeyan]

Just went out the back to get a quick photo which you see below.

On the right is "mill finish" aluminium on the left is the same grade aluminium with a "15um" clear anodised coating.



The anodising is usually for a better corrosion, heat dissipation, and aesthetic quality.

[Q-Authority]

to be honest, i don't think emissivity is such a factor in low temperature situations like intercoolers/radiators.

I don't know enough about the physics of it to comment in any depth, regarding its effectiveness in high or low temp circumstances. It certainly is quite effective in high temp situations, however, as it has been unequivically proven to increase furnace efficiency, and reduce fuel costs when the interior of said furnaces have high emissivity coatings applied to them. Even Nasa makes use of them, and the SR-71 Blackbird did as well. They are also used on halogen, and quarts lamps.

re emissivity creating hot air currents etc..
if air absorbed radiated heat enough to make a difference, then infrared temperature monitors would not work unless they were placed in direct contact with the object.. since the air would absorb a significant amount of the radiation... but it doesn't....

Wouldn't the IR frequncy of the radiated heat make a difference when it comes to monitoring it. If the emissivity coating was designed to radiate the heat in a specific spectral range, couldn't you adjust your IR monitor to allow for that.

well.. that depends where the heat soak is coming from... if the IC was on top of motor, there is heat radiated from cam covers.. but maybe it mainly occurs due to air heat...
either way, if the intercooler resists heating up from external effects.. doesn't that indicate that either a) it is being insulated by the coating so that heat conduction into it (and out of it) is slower (ie bad), or b) the emissivity is lower so it absorbs heat slower.. which is also bad when you want heat loss....

I wasn't saying that the intercooler resisted heating up, actually quite the contrary. What I inferring was that once the car had been parked, and the engine turned off for a short period of time, enough heat eventually was generated around the intercooler to heat it up, and until then the temperatures around the intercooler were generally somewhat lower than the air temperature inside the intercooler. That would indicate that the intercooler was not placed somewhere, such as on top of the engine, but in a somewhat more insulated position.

FYI: The testing was done on a turbocharged car, so the temperatures inside the intercooler would have remained relatively high in comparison to say a supercharged MR2, with its electronically controlled sc clutch.

So far I have only been able to find articles, which specifically use the term emissivity, regardng rather hi-temp uses.

[oldcorollas]

all those emissivity examples are in the hundreds to thousands of degrees.
hmm... how close do you need to hold a cup of coffee to your eye, for that temp to make your eye feel like it is warming up.. compare to looking at a candle or into a furnace?

generally, emissivity changes the intensity, but not really the wavelengths of emitted radiation.

for objects near room temperature, the heat emitted will generally be in the infre-red range, but as things get hotter, there is more emission of radiation in the visible spectrum..
ie, "heat" is radiated out at all different kinds of wavelenghts, including the visible spectrum, but for the range in which IR monitors work, the amount of radiation in the IR band is calibrated to the temp reading..
if the emissivity is lower, the surface temp will appear lower.
BUT this does not mean the object cannot lose more heat by conduction/convection, whilst having lower emission of radiated heat...


eh? if the engine is off, NO heat is being generated. without reading the original reference it is hard to see what is going on
actually with turbo, unless the car is on boost, and the air is being heated by compression, the air going through the intercooler will COOL the intercooler from the inside, compared to the engine bay air...


edit:
regarding the relationship between temperature and radiation, the equation looks like this

P~A.T^4
ie, the energy radiated is linearly proportional to the area (assuming none of it is facing each other.. like in radiators/intercoolers) and is proportion to Temperature to the power of 4....

so for example, something at 1000C will radiate 356 times more energy than something at room temperature,
but something at 100C will only radiate 2.6 times more...

Conduction, the heat lost is linearly proportional to the temperature, and same for Convection

in other words, the lower the temperature, the lower the contribution of heat loss by emission

[eeeyan]

The Melting point of Aluminium is 660 degrees.

The average radiator i would hope never goes above 20% of that.

If your thinking that the effecieny of the radiator is changed by the coating i wouldnt think the efficiency is compromised by much at all considering the temperatures involved.

Its clearly a corrosion inhibitor or aesthetics thing only i dont think theres that much engineering gone into it guys. Its not for the space shuttle its for your car.
Its mostly a weight and ease of manufacture thing for using aluminium i would have thought.