I just changed mine. Cost me 900 bucks and took about 10 min to change. The plastic end popped out. It happen the same day I put in my guages, I took it for a test ride to see what the boost will actually hit and it hit just around 42lbs max. And that was the end of that chapter. Now I have the metal one and I have seen 45lbs peak with it. The boost fooler is great only see 30 with it off. Egts are down with it too.

 

"But it is true, black does absorb heat better and it does dissipate heat better. Its just physics."

That would be true as heat applies to light. Since black absorbs all the frequencies of light, that energy must go somewhere. Due to the Law of Conservation, that absorption of light energy is converted to heat energy. This does not apply to an existing heat source.

"An air-to-air CAC's primary mode of thermal energy transfer is conduction (I don't think convection is significant even when dynoing or hooking), but radiant heat transfer is also effective."

The method of heat transfer in this case is indeed primarily convection, or rather forced convection.

I'll explain a few basics of heat transfer here. For you scientifically minded, it will be brief, will skip a lot, and will not cover everything. For those of you quick and dirty types, it will be long. No apologies.

Conduction is acheived wherby materials transfer thermal energy through themselves by excition of lower energy "cooler" molecules, by higher energy "warmer" molecules. This is the process by which the interior of the fins transfers heat to the outter portion of the fins on the intercooler.

Radiation is the transfer of thermal energy in the form of infrared or visible portions of the electromatic spectrum. All materials radiate "heat" at all times, even when it is not apprent. For example, two materials that are at the same temperature have a radiative flux that is in equilibrium, so no heat is transfered.

Convection, or "Forced Convection" specifically for our case, is when two materials are in relative motion, one material drawing heat away from the other. This is acheived through the use specifically of air and fluid. Oil in the engine and transmission lubricates, but also draws heat away from parts that come into contact with each other. This is a type of forced convection. Coolant travelling through the engine and then again through the radiator are other examples of forced convection. The intercooler like the radiator performs two forms of forced convection; once when heat from the compressed air is transferred into the fins, and again when outside air is pulled through the intercooler fins by either the engine fan, or through the ram effect.

Heat transfer is affected by two primary factors, a material's heat coefficient, and thickenss.

Each material has a "heat transfer coefficient", if you will. The aluminum used in our intercoolers has a relatively low heat transfer coefficient. That coefficient represents two main things for our purposes. One is thermal conductivity, and the other is heat retention. Just like copper is a better conductor of electricity than the rubber used to jacket it, aluminum is used for our pots and pans rather than, say, wood. If you heat up one side of a stick, it will be a long time before you feel that heat on the end you're holding. Hold a aluminum rod at one end and heat the other, it won't be long before you're dropping that aluminum rod. Thermal conductivity.

When sand is heated all day by the sun, it becomes hot, but when the sun goes down the sand cools down with it. Take a concrete sidewalk or brick wall in the same scenario. When the sun goes down, ithe sidewalk or brick wall continues to radiate heat for a time. Thermal retention.

The problem with thermal retention is that it is effectively holding that thermal energy, which prevents it from taking in more heat. It needs to release that energy before it can make room for more at a steady energy level.

How does this apply to a painted intercooler? Well when you take the thermal coefficient of the aluminum by itself, that is all the thermal energy has to deal with. Once you paint the aluminum, thermal energy now has to also deal with the heat coefficient of the paint. In addition, it makes the distance the heat has to travel effectively longer before it can be transferred to the outside air. I can also guarentee there are few paints that would conduct heat better than aluminum. I personally don't know of any, but that doesn't change the fact that you are still adding the paint's thermal coefficient to the aluminum.

Once you add the paint, the heat also has to deal with the microscopic layer of air between the aluminum and paint, which is in effect a thermal barrier. The last line of the equation is going to be the boundary layer of air which lies between the outside of the intercooler fins and the air moving through the fins. Due to resistance of air against the fins, the air moves slower against the fins than it does through the center of the channels. No Duh, right? Hence, why we try to put less restrictive airwayson our intakes. The paint may smooth this out, but a highly polished aluminum surface would be the least restrictive. Keep in mind that the boundary layer has it's own thermal coefficient and thickenss.

So.... What does all this have to do with our intercooler? Very, very little. The thin layer of black paint on the intercooler isn't going to affect the heat transfer of our intercoolers a whole heck of alot, when compared to other factors that would be better to consider. So why the long drawn out explanation? Education, my fellow CTD'ers. A intercooler stipped of it's paint might lower your charged air temperature, but probably not enough to make a difference in the big picture. So what factor can we control that will have the largest effect in removing heat from the charged air?

This is where a slightly unrelated aspect of the polished aluminum surface comes in. The polished aluminum surface allows for less friction, a less restrictive surface improving airflow over the fins. This is where we should concentrate our efforts to lower our intake air temperatures. Not by removing the paint, but by increasing the airflow over th fins. The increased airflow will strip down that boundary layer, making it thinner. This will provide cooler air in contact with the fins. The best way to accomplsh this is via the use of a bigger or more efficient fan with a higher volumetric flow rate.

Whew! Done.

 

Thanks for the thoughtful post!

Perhaps it's merely semantics, but we may have to agree to disagree... isn't convective heat transfer a phenomenom self-contained within a fluid medium?
I agree that the model has forced convection modes (i.e. coolant system circuit), but surely the thermal energy present in the surface of the CAC would conduct heat to the molecules of air that touch it.
Or, is it your point that this is accomplished in the boundary layer, beyond which the forced convection mode becomes more apparent as the relative airflow through the heat exchanger increases?

As far as the effect of the aluminum's surface finish, couldn't a case be made that a smoother surface would promote laminar flow separation, inhibiting total system efficiency?

I like your point about the additional thermal energy boundary posed by the layer of paint, but not sold yet on the interleaved air!
Still, good thinking...

Empirically, of course, I've found hot black stuff to hurt more than hot shiny stuff.

 

Ahhh I'm glad I'm an EE!!

Thank you all very much for the excellent posts!

 

You've heard of a forced convection oven, right? Mine doesn't fill up with fluid every time I turn it on.

My point on the boundary layer is that it simply acts as another medium for which thermal energy has to pass through. Figure in all that thermal coefficient stuff and thickness. I simply suggest reducing the thickness of the boundary layer by "stripping" it with faster moving air.

The hot black stuff simply reinforces my point on thermal retention. Because the surrounding material cannot dissipate heat fast enough, that heat is retained within that material.

Here's a different view of the same concept. Imagine two funnels that are the exact same size. One has a large hole at the bottom to let water out, the other a smaller hole. If you fill both funnels with water and unplug the holes, the funnel with the larger hole will drain faster. If you keep filling those funnels up as fast as they can drain water, the funnel with the larger hole will be able to pass more water than the funnel with the smaller hole in 1 minute. Or you can pour water in at the same rate, and the funnel with the larger hole will maintain a lower level of water in the funnel itself, increasing it's capacity to handle more.

Imagine the black painted intercooler as the funnel with the smaller hole. It's hotter because it "cant drain water" or heat, in this case, as fast.

Now imagine if you could liquid-cool the intercooler from the AC system! Imagine your intake temps from that!

 

Please, Hopper - I'm sure you know that air is a fluid...

 

Semantics, aye!

 

so what a good intercooler for around $900????

 

cool twist might be the only one around that price