Should intercooler be painted/anodized for max heat transfer?

[Viper488]

Which would extract heat better, a grill mounted intercooler in natural aluminum finish, or one anodized black?

 

[Warpspeed]

You have to ask yourself the question, what is the most important mechanism of heat transfer, conduction or radiation ?

If the temperature of the intercooler is extremely high compared to the surroundings, then black would enhance infrared radiation. If it is cooler than the surroundings (sic) it would also absorb infrared radiation more readily.

This is not as silly as it sounds. If the intercooler is "looking" at the sun, or some red hot exhaust pipes, it may well run cooler than the "optical" surroundings.

On the other hand, if the temperature difference is minimal, as it should be, then direct conduction between the metal core and the air will be the main method of heat transfer. So any sort of paint less thermally conductive than the core is a no, no. But black anodizing would be quite o/k, I doubt if it would work measurably better than natural anodizing.

 

[evelrod]

Not to argue theory here but to add a practical point of view---in too many years of fooling aroung with heat exchangers, inter-coolers, after-coolers, oil coolers, etc., color has proven to be a "non critical" point. We painted the air to air intercoolers, grill mounted, to match the color of the race car just for drill and it made no measurable difference in intake air temp (T-Coupe)---flat black anodized, same deal. I admit that thermodynamics is not my area but, I have relied on several of Ford/JBA engineers sugestions in years past and now just mount the heat exchangers as they come out of the box, usually a silver anodized finish. I have been told several times the three basic truths to proper operation is , airflow, airflow, airflow!
One note, though. We did a 'natural fiish' ie, used Easy Off to remove the anodizing---bad idea! By years end the fins were showing signs of corrosion.

Rod

 

[MintJulep]

Anodizing is actually forming a thin layer of oxide at the surface. This oxide layer is an insulator.

From a theoretical stand-point, bare alumunum would be better. Of course bare aluminum quickly oxidizes and gets that white chalky stuff on it.

In my past experience, I have found that an alodine finish on alluminum reduces the effectiveness of an intercooler slightly compared to clan bare aluminum.

Depending on the application, I might try a PTFE-impregnated anodize on the hypothesis that it should stay cleaner / be eaiser to clean, hence reducing the effect of air-side fouling.

 

[patprimmer]

PTFE is a very good insulator, and builds up over the anodised surface as well as keying into the anodised surface. I suspect that it will substantially reduce heat transfer.

Regards
pat pprimmer@acay.com.au
eng-tips, by professional engineers for professional engineers
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[MintJulep]

I realize that PTFE is an insulator. However, the thickness is small. The effect can be compensated for by upsizing the cooler slightly.

I think the main advantage would be that gunk would be less likely to stick, and be eaiser to clean. Therefore fouling would presumably be less of a factor, and the cooler's performance more consistent in actual service.

If I were ever in a position to need to incorporate an intercooler or aftercooler into a dirty-environment design again, I'd give this a test.

 

[patprimmer]

The surface must first be anodised but not sealed to attach the PTFE to the pores in the anodised coating. This gives two insulating layers, and the PTFE is not all that thin a coating compared to anodising or some paints. I will dig out my data on PTFE coatings and quote some actual figures.

I would be interested to see results, but I very much doubt that the results will be beneficial.

Regards
pat pprimmer@acay.com.au
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[evelrod]

Having actually DONE all these finish schemes to heat exchangers in the past, I will stick to what I posted previously, HOWEVER, y'all are missing the point of this paint deal. No one that I know of would "paint" the cooler as I think is being envisioned here. When I said paint, I ment simply a bit of color to the thing, not 3 or 4 mills !!! Less than a mill will give a sufficient coating o forestall corrosion for the season!
Still, all the effort we made was pretty much wasted energy. The "out of the box" finish of most heat exchangers works quite near the best you can expect. I agree that if you need better cooling, get a bigger unit. I also know that oft times that is not possible for a variety of reasons thus creating all these schemes to "improve". If you put as much effort into proper inlet AND exit airflow you'll be money and time ahead, IMO.

Rod

 

[MintJulep]

I suppose a crude experiment could be done at home on the kitchen stove. It would only require two pots that are identical other than for the presence of a PTFE coating on one.

 

[ZoRG]

There are some interresting systems out there, electric intercoolers, some new technology with watercoolers, and some company actually makes copper intercoolers, I've read the Ford patents, but have not yet seen it in practise, the electric coolers seemed promising... as does a enclosed system using co2.

All of these would be worthy alternatives with better gains than painting, I have not yet seen any significant improvement with any painted intercoolers.

 

[Warpspeed]

Beyond a certain point there is probably not a lot you can do with an air to air intercooler, you reach the point of diminishing returns, and that is it.

Air to water cooling offers more possibilities, because of the high specific heat of water (stored cold) and the possibility of cooling the water below ambient by various means.

The system I like, but hardly practical, would be an air to air intercooler to take out most of the sting, then feed the induction air through a down stream air to water heat exchanger, which would then only need to remove part of the total heat load.

It would be more complex, but the cooling water could be used more efficiently.

 

[Warpspeed]

The difficulty of total loss phase change systems, nitrous, freon, or carbon dioxide,is that the cooling effect in BTU per pound of fluid is not that high.

Do not confuse low temperatures with high hear removal.

It's like dropping a very small white hot nail into a bucket of water. That little nail sure is hot, it must practically boil away all that cold water eh ? Well no.

Spraying all that -40 degree gas onto a really hot intercooler must really cool it down ? Well no.

You need to look at how much heat is removed by evaporating away a pound of "stuff". Try looking up the heat required to evaporate a pound of nitrous, a pound of carbon dioxide, and a pound of water. You might be surprised.

Water is rather easier to find and store as well !

 

[IRstuff]

The only way something like that would make sense might be if you had a water/water exchange on the intercooler and a separate water/air exchange somewhere else.

Since the heat transfer is linearly proportional to the temperature difference across the intercooler and its heat transfer coefficient, both could be helped if water was used as the transfer media.

TTFN

 

[ZoRG]

The co2 system I've seen is not a open system, it a completely sealed system, open co2 systems tend to cost you some power as some of the co2 gets into the intake. I have no personal experience in these system though.

Personally I have a zakspeed unit, its black, but that will come off and its being converted to a air/water unit due to its size and mounting issues. I was going to use it like warpspeed suggested by having a air to air unit then air to water, but currently there is no space for that. But water to air is about as good as it gets, especially if you plan on doing some drag racing or making lots of power, im not going to buy into these new technologies(co2, nitrous, electric etc) and find out after that it was a waste of money.

 

[carnage1]

a coating will not help heat transfer.
It doesn't mater what you coat it with it simply can't increase the heat transfer. it can not effect it much but it can't help. it can help prevent corrosion. it can look nifty. it can even distract other drivers giving you the better line into a corner, but it can't help heat transfer.
making the intercoller out of a better material would help though. i like the idea of copper, much better heat sink.

 

[BrianR]

My experience is with cooling electronics where heatsinks are very important and we learned that color is not the big issue, eg. air dried enamel of any color has emissivity of 0.9 or better.

A good emissivity is great provided the surrounding material is a lot cooler as the radiation is proportional to Delta-T. Of course the reciprocity theorem states that it works just as well in reverse so make sure the exhaust is not in view.

 

[nostrayvoltage]

Well in another application flat black paint always enhanced overall cooling over even tarnished copper, aluminum, & steel surfaces. I have done lots of heat rise test...don't know if I really understand all the theoretical whys but..

Radiation cooling is usually more significant than people think....while the paint may or may not be conductive, it is thin, so convective/conductive cooling is not reduced much at all..

Yes, it is more than color, shiny black has poor emissivity compared to flat black, so usually you want a nice dull finish, but flat black seems to be the standard.

no_stray_voltage@yahoo.com

 

[harrisj]

Paint's not such a good idea because it is an insulator and has significant thickness, reducing the size of air passages.

Anodizing also means an insulating layer, but it's very, very thin.

A process called Alochrom is similar to anodizing, but is electrically conductive (anodizing isn't). Often, thermal and electrical conductivity are closely associated, so it might be worth looking into. I don't have any personal experience, though.

All this only makes a difference if you're after the last fraction of a percent.

John