hacker-pschorr

Due to a court order, I am not allowed to be within 500 yards of that much tin foil. Long story, yes it was a "dare".

James-man

Not sure I want to know...

Jim Nowak

My twin-turbo Mercedes CL also had an air to water intercooler. The one thing that the air to water intercooler can do that the air to air intercooler can't is the ability of the air to cool below ambiant air temps. However, there are ups and downs to both systems.

I'd say for the street or drag strip that the air to water intercooler is best. However, for endurance racing or on a race track, the air to air intercooler would be the best choice. I say that because the air to air intercooler is more dependable than the air to water intercooler. You don't have to worry about water pump failures with the air to air intercooler. The air to water intercooler is easier to package and is very efficient.

RyanPerrella

James,

I don't know who told you that air to air is more efficient at dropping temps then air to water, but they are wrong.

Your own example of tin foil in a freezer will stay warmer longer then tin foil dipped in water proves just that! Your statement is a total contradiction. The goal of an intercooler is to remove as much heat as possible. Water is a much more effective means of this then ambient air. Why did porsche water cool the 928 anyway? Why did the 911 finally get 4 valves per cylinder with the introduction of the 996 and its watercoolerd engine? BECAUSE WATER IS A MUCH BETTER MEANS OF COOLING!

Simple as that.

There are physics behind these radical ideas i am proposing! I am not a physicist or a chemist but If i must i will look it up and give you specifics.

Water is somewhere in the neighborhood of 14x more effective of cooling then air is. Wether its due to surface tension, or contact or whatever, there is science behind it. A simple experiment will prove just this. Such as Enzo's examples, and yours as well that tin foil will star warmer longer in the freezer. Why are Air/water intercooler cores so much smaller? Because they are much more efficient. You cant get air temps below ambient, so the intercooler that gets them closest to that in the smallest package is thus the most efficient.

Cheers

bernard farquart

I think it would be due to water being much more dense than air, yes?

RyanPerrella

here is some stuff taken from Wikipedia


The advantages of using water cooling over air cooling include water's higher specific heat capacity, density and thermal conductivity. This allows water to transmit heat over greater distances with much less volumetric flow and reduced temperature difference. For cooling CPU cores, this is its primary advantage: the tremendously increased ability to transport heat away from source to a secondary cooling surface allows for large, more optimally designed radiators rather than small, inefficient fins mounted on or near a heat source such as a CPU core. The "water jacket" around an engine is also very effective at deadening mechanical noises, which makes the engine quieter.



I think its odd there are still people running around claiming that air is more effective at cooling then is water. Driving a 928 i would think your a heretic, I think your a die hard 911 fan, but perhaps you just dont know it yet.



for more try some of this stuff.......actually you could spend days looking at this stuff and i could waste hours further researching it. I'll leave that to you, but this may also help.


Convective heat transfer is a mechanism of heat transfer occurring because of bulk motion (observable movement) of fluids. This can be contrasted with conductive heat transfer, which is the transfer of energy molecule by molecule through a solid or fluid, and radiative heat transfer, the transfer of energy through electromagnetic waves.
Convective heat transfer is split into two categories: natural (or free) convection and forced (or advective) convection, also known as heat advection.

hacker-pschorr

That's funny right there, I don't care who you are.

largecar379

OK guys---I'm no engineer.

I only made the comment about the coolers because of my "experience", not any engineering degrees and such.....

if aftercoolers (water/air) were so efficient, the trucking industry would have stayed with them. the trucking industry is by far the largest user of turbo/cooler technology, so my guess is they probably know what they're doing.....

Caterpillar only recently added a water cooler to their ACCERT engines, due to the addition of another turbo (twin turbos in series). The current air to air coolers did not offer enough swept area to sufficiently cool the intake charge,so they had to add a water cooler.

same can be said for oil to water coolers. if they (either intake, engine oil, tranny, etc.) coolers are placed in a cool air flow, they will perform quite well.

I have argued this with other engineers as well, but when you take a oil cooler and subject the oil (temp of 180 degrees) to engine water temps of 240 degrees, the oil gets hotter, not cooler. I have over three million miles of on road testing between 4 trucks that have proved this to be the facts using temp gauges on both sides of the coolers, whether they were oil/water or oil/air. I suspect that air to air would return the same results......

Facts as they are, say that air to air is better.

I made no mention of location, plumbing, or any other related issues except keeping the intake charge "cooler".

The other issue I can relay about water coolers is that if you have an internal leak, the water will be ingested into the intake causing massive damage to the engine.

So you want to take that risk with your very expensive 928 engine????

Sorry I ventured into another argument about "which is best".......but, here we go again.

--Russ

hacker-pschorr

I'm not trying to pull 20,000 pounds with my 928. When I do, I'll look to the trucking industry for ideas.

Until then, I'm sticking with Bugatti, McLaren, and the ZR1 corvette team
A valid point - you could also spend a lot of time and money to design an air / air intercooler system that works so well........it reduces the air flow to the radiator so much the car over heats (true story with a 928 running ONLY 6psi of boost).

Going on four years with my air / water setup - no issues to speak of. Carl going up Pike's Peak with his air / water setup worked pretty damn well.

Neither setup is "the best".

Vilhuer

Air to water IC setup in Murf is brilliant IHMO. Washer fluid stays cooler than coolant and all 928's have container readily installed. Whoever came up with idea of using it is genius.

James-man

I think Jim Nowak has it right. I think that we all can agree that water can transfer heat faster. If you are talking about cars already at speed, the differences between them are probably negligible. A drag racer with water should have a slight advantage over air-air initially, but once down the track I really doubt there would be much difference. The water heats up a bit but flowing air does not.

I am indifferent between the two options, really. I was just hoping that someone would share some tin foil pics. Ooops, I am in the wrong forum.

James-man

I am not suggesting air to air is better. I am pointing out that the examples have other factors involved which reduces the differences between the two options. I will agree with you that the required size of the heat exchanger will favorably impact the efficiency of the charged flow.

The jumper into the lake is supposed to be wearing a thin suit of metal metal for Enzo's story to be accurate, plus an entire lake to jump in would require a tanker truck of water hooked to a car for the intercooler analogy.

I generally get this stuff, I just try (often unsuccessfully) at being at PITA.

Cheers back at ya!

RyanPerrella

Dude, James-man,

what does him jumping in with a metal suit have to do with anything! Where do you get this idea? why cause the intercooler core is made of aluminum he has to jump in in an aluminum foil suit to simulate the intercooler core. Thats stupid. He was saying the human body gets colder faster in water then it does in air. all your doing is substituting the body for the aluminum core. The effect is the same, water transfers heat faster!

Also about the trucking industry, did you ever see the space they have to deal with! They can put a 48' x 60" air to air core in there no problem. So size and packaging ARE OF NO CONCERN AT ALL! Those trucks top out at 80mph, when you care about drag and top speed you can't have styling of a brick, so when you have a sleek body, you have less frontal area which will limit your space for an air to air core.

Now i dont know all the answers to this, i consider myself a just about a novice when it comes to this stuff, but until you can present a valid argument then lay off. The original question had to do with efficency, this has nothing to do with whats "better". Better can be described as anything really. If you consider bigger better then air to air is better. It all depends on what your trying to accomplish. But when you say air to air is more efficient, then i speak up because you obviously dont have a clue what your saying.

At least come up with a logical example to back up your theories.

RyanPerrella

also

you cannot get a closed water to air system below ambient temprature. The water will only get as cold as the outside air. The water is cooled by another radiator which is cooled by air. And the water cant get any colder then the ambient temp. The way you get temps below ambient is when you fill the system with ice or some other cold liquid. Drag racers do this regularly. But their intercooler system probably has a capacity north of 5-10 gallons. On a road car you will most likely have less then 2 gallons and more likely close to a single gallon of water.

Z

That's not necessarily true. It depends on the configuration.

If the intercooler is located after the throttle, it's subject to both boost and vacuum. If there's an internal leak in an intercooler configuration like that, under boost you'll get boost leaking into the water area of the system. At low throttle the intercooler will be subject to vacuum, and the water will get sucked into the engine.

If the intercooler is located before the throttle it's only subject to boost, and never to vacuum. If there's an internal leak in an intercooler configuration like that, under boost you'll also get boost leaking into the water area. With this configuration, at low throttle the intercooler is not subject to vacuum though, so no water gets sucked into the engine. The water is not pressurized, so there's nothing to force it into the intake tract. When at low throttle with the centrifugal setups, the blowoff valve between the supercharger and intercooler is open, and air is blowing out of it. That means that there's actually a slight positive pressure in the intake tract ahead of the throttle and in the intercooler, which would actually help keep any water from getting into the intake tract if there ever was an internal leak.

The ability of water to transfer heat better than air has already been talked about. What hasn't been mentioned yet though is the thermal mass of the water in an air-water intercooler system. There's somewhere around three gallons of water in the air-water intercooler systems. Put three gallons of water in a pot, put it on the stove, and see how long it takes to get warm. That's with it being directly on top of a gas flame. Think the air in the intake is as hot as that gas flame? That gas flame is probably 1,000 degress or more higher than the highest boosted charge air temperature that anyone will ever run on any 928 anywhere.

One more point that gets overlooked is the complete situation on all of the heat transfer occurring in an air-water intercooler setup. Some people mention the water getting warm because the heat exchanger for it has to transfer the heat to the air anyway. Heat to warm the water is only being produced while under boost. How long do you really think that someone making 10, 20, or more pounds of boost is going to be holding their foot to the floor before they lift? Do it for around 11 seconds in Tim Murphy's car, and even if you started from a dead stop, you'll be going somewhere over 130mph, and will still be accelerating almost as hard as a stock S4 does in first gear. How much do you think that the three gallons of water on the stove would have increased in temperature after 11 seconds, even with the gas flame being much, much hotter than Tim's intake air under full boost could ever get, and without any heat exchanger taking heat out of that water on the stove? As soon as you lift, there's no more boost and no more heat being created to warm the water. The heat exchanger is then still removing whatever increased heat there is in the water, but that's not all that's occuring. At least close to ambient temperature air is going through the intake tract while at part throttle and not under boost. That air is going through the intercooler. The transfer of heat in the intercooler has now reversed, and the intercooler is acting like a second heat exchanger, helping to remove any heat that there may be in the water. It's doing that the entire time that there's no boost being made.

Wasn't it our old buddy Normy that said air cooling is for lawn mowers?