Spray-on solution for heat transfer woes

banjomike · banjomike's Garage

Have an oil cooler? Have a turbo charger? Have an intercooler? What about a Cool Collar? Do you want these to function better?

Since I have left the Porsche fold, I have been delving into the lore of VW tuning. I've already grown tired of the infinite variations on the "cold air intake", "slammed ride", and cat-back exhausts, but I stumbled on this tidbit in the back of European Car magazine. I just wish I still had a trombone to ponder spraying it on. As it is, I am considering spraying it on my intercooler and intake side turbo casing.

http://www.topspin.com.tw/html/hbn/hbn.htm

vwvortex may be a decent forum but there are just too many people to form a true community, and the emphasis is more on things like ride height than handling characteristics.

so I ask... whaddaya think? Which B Grupper is gonna spray thier oil cooler with it? Anybody gonna spray their cylinder fins!?!?

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the real question is, "can you stand the english translated form the japanese grammer at the above website

randywebb · 02-11-2005, 06:26 PM

I don't need to follow the URL to tell you.......

Understand the modes of heat exchange and you know what cannot possibly work.

A continuous spray of water would work - it would evaporate and cool the surface it was on.

banjomike · banjomike's Garage

Oh I don't know, if the air-surface interface of the stuff has a higher coefficient of convection then it could help. I don't think anyone would believe that this stuff will make a trombone better than a carrera cooler, but it might make a trombone a few percent better. Or it could just be gunky stuff that actually ends up insulating the surface and working against you? I'm gonna see how much a can of the stuff is. I have a good idea for testing it.

randywebb · 02-11-2005, 08:00 PM

higher coefficient of convection....

No.

Check out a basic heat transfer text such as Kreith or Karlekar & Desmond.

RoninLB · 02-11-2005, 10:20 PM

hey Randy..
what do you think about a heat sink on a CD box ?
if a yes, then what range cooler, on a wild guess, when the box is about 175degF ?

randywebb · 02-11-2005, 10:59 PM

what range cooler ....? not sure what you mean there

a finned heat sink will greatly increase cooling - is that what you mean?

you can paint it with a non-metallic color to increase radiative cooling a bit

RoninLB · 02-11-2005, 11:17 PM

Quote:

Originally posted by randywebb

a finned heat sink will greatly increase cooling - is that what you mean?

Yes.
So there's a chance that a very warmed up engine, in bumper to bumper traffic, in 110 desert heat, might see 20degF cooler on the CDI box ?

aigel · aigel's Garage

BN is often used for coating metal surfaces in harsh environment. It's the corrosion resistant and heat resistant properties of the material that make it special. It also gives a self lubricating surface, much like graphite.

What they are trying to do here is to use it to increase actual surface area (by increasing surface roughness). It's basically like putting a bunch of small fins. There is no reason to use BN for this. There are other high temperature coatings that should do much better. Thermal conductivity of BN is good, but on the same order than regular metals. Emissivity of the white BN material should be rather poor though, compared to a black material. If I'd chose a coating, I'd go with a black coating any day. And have you noticed, the porsche oil coolers don't come painted white fromt he factory.

It is unclear how they measured the temperature in their tests. I can not see any thermocouples there, between the FedEx boxes.

If they used ain IR thermometer, they certainly introduced a huge error, since the emissivity between the BN and the blank pipe is likely very different.

Anyway, hold back from spraying this on your oil coolers. If the seller claims that the material "draws heat" from the hot surface, that's a bit too much for my taste. I think all this will do is "draw money" from your wallets!

If nothing else, how practical is a rough white surface on your oil cooler? It will attract a nice insulating layer of dead insects, oil and road grime in no time.

George

randywebb · 02-12-2005, 11:18 AM

George has it exactly right. Also, the surface roughness will reduce the air speed near the surface (boundary layer), and that will reduce cooling a bit.

Ron - we are cross-posting and hijacking the original thread (but I will if you will)... is there a chance? well, yes a chance; and it depends on air speeds present while the car is stitting still. There will be air speed from the fan, and from induced (aka 'natutal' or 'free' convection - caused by air moving up away from hot areas and sinking near cool areas).

The convection regime may also be mixed (partly frre and partly forced convection). The best thing to do is to try the fins and use small thermocouples to measure the temperatures inside or on the surface of the box. Don't bet on 20 oF, but there's a chance.

Now, how about a nice 12 VDC blower fan? You could even have it temperature controlled to come on only if the box is hot and can run some plastic tubing from a cool area so it won't just move hot air around. It's complicated, and probably not needed, but I think I know your gadgeteering instincts well enought by now to predict that you are already ... intrigued.

You could also have an electric pump sprayer to spray water mist on the box....

Or you can see if the boys up in nattick (not far from you) have got their artificial skin projects going yet - then the box could have its own sweat glands to cool off like humans do (and pigs too).

Have fun.