Don't you mean latent heat of vaporization? I would say the phase change does have a definite affect. Yes, there is no phase change as the water heats up, but once it does, it changes state and as the water evaporates, it cools, then it must be heated up again. It is a constantly occurring cycle until the water is gone.

As further proof, place a volumn of water in a vacuum jar and then lower the pressure inside the jar. What happens? It starts to boil because you have changed the boiling point. As the water boils off{changes state}, it cools down, it seems counter intuitive, but it does. If you could drop the pressure fast enough, create a vacuum quick enough, you can flash freeze the water and stop the process.

That's one of the reasons that it takes so long to dehydrate a system, you have to do it slowly so that you actually draw off the water and not freeze it.

So it is the evaporation of the water that results in the increase in efficiency over a straight water to air intercooler or air to air intercooler. If you poured hot water over the IC, it would not improve the cooling of the charge, but once the water started to evaporate, the cooling affect would begin. I mean if you stood there with a hose pouring hot water over the IC. Does that make sense?

Now I'm getting to far into theory and remembering the long hours of study and discussion at school......many sleepless nights.

 

I'm sure most viewers are pretty bored with this thermodynamics discussion, but I love a good debate. So here goes:

Water, or any other fluid, does not change temp as it boils, even if the boiling point is lowered by decreasing the pressure. You can test this at home with a thermometer and a pot of water on the stove. When the water is boiling, the temp stays constant no matter how much heat is put in from the burner.

The driving force for any heat flow is a temp difference. If hot water were flowing over the outside of the IC at the same temp as the air inside, no heat transfer would take place. For a given temp difference between the inside and outside of the IC, however, an equal mass flow of water would take away more heat than air.
The Alta spray cooler undoubtedly relies on water evaporation/boiling to remove heat. But this is simply a convenience -- less water is needed. It would work just as well, maybe better, if it dumped so much water on the IC that water ran onto the street and very little of it got a chance to evaporate from the IC. In either case the IC efficiency increases dramatically because one of the air - aluminum interfaces has been replaced by air - water. This illustrates that the main resistance to heat flow in an air - air heat exchanger is transport of the heat thru the 2 air streams, not the resistance from conduction thru the aluminum or aluminum + thin oil film.

 

we're all forgetting something. Even if the presence of the oil only cuts the transfer efficiency a few percent, the fact that the air is combined with gas means that the effect is multiplicative. And that for any given operation point, a certain amount of power goes into internall losses. So a 1% change in IC efficiency can really be several more % in power to play with.

As the discussion has show, there's lots going on here. The best way to tell would be with some air temp probes before an after an IC, and then to play a bit. You don't have to wait a few years for the effect, just pour or spray some oil in the IC........ Messy, but would work.

Some of the other effects have to do with how the air flows over the aluminum, and that the oil can smooth a rough surface (this can lower back pressure, and also decrease heat transfer efficiency as turbulence is removed from the air/aluminum interface.

To calculate all of this would be no small task.

But in general, you don't want organic coatings on thing you want to have high heat transfer, and if any of that stuff makes it into the cylender, it's just displacing stuff that can create power.

Matt

 

Matt- In a MCS there is no gas in the intercooler. Gas is injected into the intake runners next to the head, downstream of the intercooler.

 

Yes, that is true as long as you are adding heat. My example, and I probably should have stated it a little more clearly, is when you lower the pressure within a sealed vessel at room temperature, and you are not adding heat, as the liquid boils off the temperature falls. This occurs due to the latent heat of vaporization. This is why when water evaporates, it removes heat better then if you just flowed water over the surface you were trying to cool.

Here is another example to further belabor the point.
Let's say you have a nuclear reactor you are trying to cool.
Lets say your a pumping thousands of gallons per minute over the hot surfaces in the reactor and you are removing the heat. No "boiling" is occurring. Now let's say you manipulate the variables in the system to allow something called "nucleate boiling." This creates small bubbles of steam on the heat transfer surface that are carried away in the fluid and collapse. This is a much more efficient mode of heat transfer and you remove more heat with this process and you increase overall system efficiency.

The change in state (liquid to gas) removes more heat then when you maintain a static state (liquid).

 

it is true as long as it is boiling and the pressure is constant.