air/air vs water/air intercooler?

alfadriver wrote: Sure it does. Just like the water system does. You claim that you can have the fan on- so that cools the heat exchanger to ambient. If you have it on to keep the water at ambient, then the air system can have it on to keep ambient air flowing across it.... Which is fast enough to cool the engine. Why is it the fans are on for the water system to prevent heat soak but off on the air system??? 1-2 seconds of a small increase of air temp isn't going to make much of a difference, anyway.

You can have the fans on in either case. But if you're just farting around in traffic, you're probably not going to think "hmm, maybe I can go WOT when that new lane starts in a 1/2 mile, better turn the fans on", so they may or may not be on when you get to the point of going WOT. If they're on, the performance difference will be minimal. If they're off, the water system will better mitigate the spike when you take off from basically a stop (although it won't be as cold as either case would be if the fans were kept on).

In reply to rslifkin:

Just looking at some data, I have to disagree.

It does not take much air flow across the air-air heat exchanger to have it work effectively. Nor does it take a lot to have the water system be above ambient so that it's not working effectively.

One system is just not that clearly better than the other- it's very dependent on the situation and what the goals are. If I want to keep my intake are no lower than 100F, I'd go water all day long. If I have no package space for an efficient air-air cooler, I'd also go water. If I had space, and have no problem running the cooling down to whatever the ambient is, I'd go air. If I was worried that my water cooler may vibrate to put a hole in it, I'd also go air. If I could run ice and take advantage of the extra cooling, I'd go water.

It all depends on what I need.

In reply to Jumper K. Balls:

For your 850 I'd think a top mount a2a with a louvered decklid(with a beastly fan), or a rear mount a2a with a ram scoop feeding it(bonus points if scoop is through decklid)

I think what I just came up with should be enough of a case for me to NEVER own an 850.....

alfadriver wrote: In reply to rslifkin: Just looking at some data, I have to disagree. It does not take much air flow across the air-air heat exchanger to have it work effectively. Nor does it take a lot to have the water system be above ambient so that it's not working effectively. One system is just not that clearly better than the other- it's very dependent on the situation and what the goals are. If I want to keep my intake are no lower than 100F, I'd go water all day long. If I have no package space for an efficient air-air cooler, I'd also go water. If I had space, and have no problem running the cooling down to whatever the ambient is, I'd go air. If I was worried that my water cooler may vibrate to put a hole in it, I'd also go air. If I could run ice and take advantage of the extra cooling, I'd go water. It all depends on what I need.

I always viewed it as more of an issue with packaging, not efficiency when it came to the choice of which a vehicle got.

In reply to Boost_Crazy:

an intercooler is a heat sink..it must absorb the heat from the charged air then its able to release the heat to the ambient air. water has a MUCH higher thermal conductivity than air, which btw air is often used as an insulator instead of a conductor so you see how WATER cools better than AIR. besides an air to air is only as efficient as ambient temps allow and the big one many people forget, the amount of ambient air that can flow through the intercooler...an ac evaporator and radiator behind it sure impede airflow through an air to air intercooler. this gets real simple for you http://www.turbosmart.com.au/technical-articles/how-an-intercooler-works/

chiodos wrote: In reply to Boost_Crazy: an intercooler is a heat sink..it must absorb the heat from the charged air then its able to release the heat to the ambient air. water has a MUCH higher thermal conductivity than air, which btw air is often used as an insulator instead of a conductor so you see how WATER cools better than AIR. besides an air to air is only as efficient as ambient temps allow and the big one many people forget, the amount of ambient air that can flow through the intercooler...an ac evaporator and radiator behind it sure impede airflow through an air to air intercooler. this gets real simple for you http://www.turbosmart.com.au/technical-articles/how-an-intercooler-works/

Again, the water-air system has to dump it's heat into the ambient air just like an air-air system. It just adds water into the mix. All the issues you say are a problem with air-air are still there with water. The A/C condenser and rad impede the air for a water system just as it does for an air system...

Air does a great job for heat rejection, BTW, since that's where the radiator dumps it's heat into- which tends to be a LOT more heat than an intercooler ever has to deal with.

And since the overall cooling system is designed for the radiator's ability to reject roughly 1/3 the rated power of the engine, getting enough air to reject intake heat isn't normally a big deal- regardless of an air or water system.

In reply to chiodos:

Wow. Just...wow. I checked out your link. It's a parts website, with a very brief overview of intercoolers. I see that it has the same misinformation that you repeated. But it's on the internet, so it must be true...

"Water is more efficient at heat transfer than air and has more stability so it can handle a wider range of temperatures."

To be fair, the sentence is somewhat true. Not sure about the stability part, as water changes from a solid, to a liquid, to a gas in a realatively small temp window. But it's completely out of context in this discussion, for the reasons I've mentioned above. There is a lot of info out there, do some research on your own if you don't believe me. You said do the math- take your own advice, the numbers don't lie. You have x degrees of temperature rise at the compressor outlet. You transfer some of that heat from air to water, and then back to air again. You remove y worth of heat at the heat exchanger, and you end up with z. Somehow you expect the water to do something magical in between (aside from the bump you get before it comes up to temp), but your are really just saying that 1+1=3.

chiodos wrote: In reply to Boost_Crazy: an intercooler is a heat sink..

I may have missed this part the first time around. This isn't true- an intercooler is a heat exchanger. Not a heat sink. It moves heat energy from one medium to another.

In this case, the end result will always be from intake air to ambient air- be it with water in the middle or not.

rslifkin wrote: You can have the fans on in either case. But if you're just farting around in traffic, you're probably not going to think "hmm, maybe I can go WOT when that new lane starts in a 1/2 mile, better turn the fans on", so they may or may not be on when you get to the point of going WOT. If they're on, the performance difference will be minimal. If they're off, the water system will better mitigate the spike when you take off from basically a stop (although it won't be as cold as either case would be if the fans were kept on).

In every air-water system I have installed, the pump and cooler fans (if present - Magnusson's C5 system doesn't have fans) are triggered on by the fuel pump relay. So any time the engine is running, the pump and fans are running.

I'm not saying it does anything magic, just that it transfers heat better because water transfers heat better. But the more I read, the more I find that a heat sink is a heat exchanger. Furthermore! Let's break this down so we are all on the same page, hot air from turbo enters aluminum intercooler that's ambient temp, heat is transferred from the turbo air to the air to air intercooler, which has to keep rising until it is above ambient temp before it can start shedding heat, thus the intercooler is the thermal reservoir, and if we know of thermal inertia we know the intercooler will keep getting warmer as it absorbs heat until it's overcome and outlet temp spikes. Now when you have an air to water intercooler the thermal reservoir isn't the intercooler but the entire contents of the liquid medium, the aluminum absorbs the heat from the charge air, which has water on the other side at a cucumber like 70* and is absorbing all the heat directly into the water instead of the intercooler itself.

Alfa, I maybe getting terms wrong but heat sink absorbs heat from one thing and releases it to a cooling medium where heat exchanger transfers heat between two mediums. That's what I gleaned off my definition search please, if you would tell me what a heat sink is and why an intercooler is not one

going down the thermal dynamics rabbit hole has been enlightening but I still have no idea where you guys are coming from.

In reply to chiodos:

The water in an Air/Water does not transfer heat better. It is impossible, because you cannot divide by zero. The water is a heat transfer- not a cooling- mechanism in an Air/Water I/C system. There is no such component in an Air/Air system. You are comparing something with nothing, a blank space. Look at it this way...

Air/Water 1) Turbo compresses and heats the air charge.

2) Heat is transferred to the water.

3) Heat is transferred to the air cooled heat exchanger.

Air/Air

1) Turbo compresses and heats the air charge

2)

3) Heat is transferred to the air cooled heat exchanger.

You are stuck on trying to compare step two.

The intercooler may function as a heat sink is some instances, but that is not what it is designed for. That is way, way down the list of design parameters. It is a heat exchanger. If it were only a heat sink, a solid chunk of aluminum would do. Your wheels bolt up against your brake rotors, and effectively act as heat sinks for the braking system, but that is not what they are there for. I'm not saying that it doesn't have an effect. But it's very minor in the overall operation of the system, if you compare to adequately designed systems.

In reply to chiodos:

Think of a heat sink as a bucket that can store heat. You can pour heat into it, but it will fill up. Once full, that heat will stick around.

Think of a heat exchanger as the same bucket, but with a spigot at the bottom. You can pour heat in, but it can escape out the spigot.

The size of the bucket is the ability of the system to absorb heat, the size of the spigot is the ability of the system to shed heat.

If you compare an air/water and an air/air system of similar capabilities, the air/water would have a bigger bucket with a smaller spigot.

An ice chest I/C system for a drag car would be an example of a huge bucket with no spigot.

Boost_Crazy wrote: In reply to chiodos: The water in an Air/Water does not transfer heat better. It is impossible, because you cannot divide by zero.

They do transfer heat better, but not because of magical properties of water. You can fit a lot more exposed surface area in the nose with an air/water system. Radiator heat exchangers have much smaller/closer/flatter tubes than an air/air intercooler. That is more surface area to transfer the heat from the working fluid to ambient air.

That is what I mean by being able to fit more cooling capacity into the nose of the car.

Yes, there are some inefficiencies added by the adding of an intermediate step, but the benefits FAR outweigh them!

Now, if you want to join the dark side... imagine for a moment that you could use a gas as the working fluid and instead of a circulating pump, use a compressor to increase the pressure (which adds temperature), THEN cool it off in the heat exchanger, THEN pass it through an orifice (pressure drop - temperature reduces) on its way to the intercooler. For added icing on that cake, use a working gas that will go through a phase change in the different heat exchangers to really transfer those BTUs.

Yep. Use an A/C evaporator as your intercooler. Make it happen. Yeah it may take 5-10hp to drive the compressor, but how much more power will you see from being able to drive intake temps below ambient even under boost?

The only possible downside is that existing systems may not be able to handle large transient changes too well. Solution - use a standard air/water intercooler and build a box around the evaporator and turn it into a water-R-134a heat exchanger. Heck, if you used antifreeze as the working fluid, you could get rid of that pesky 32F limitation and really get things cooling...

I keep trying to go further in depth with the whole heat transfer and thermal resiorvor bit but you keep it 6th grade and ignore that part, that analogy on heat sink doesn't seem correct to me, think of a cpu heat sink, it absorbs all the heat it can and when it's heat is higher than the surrounding air, it dissipates heat and thus draws heat out of the cpu, in your analogy the heat sink would just keep getting hotter until it nukes (bucket overflows) an intercooler acts the same way, it absorbs the heat out of the charged air until it's warmer than ambient air and it can then shed the heat (as we know heat energy only moves with a temp difference). But as I keep trying to say, water cooler has a much larger thermal resiorvor (all the water has to heat before the aluminum core temp can raise) here's a test you can do, stick a lighter under a milk jug and it won't melt because the milk acts as the thermal resiorvor , now drain the milk jug and do the same thing and it melts right through because the air surrounding the plastic isn't enough to cool it below melting. Correct me if I'm wrong here but I go off science and the more y'all tell me to read the more I believe I am correct here, all I have been trying to say all along is that water intercooler is more efficient than air to air. I'm sorry to totally have derailed this thread well kinda, but I'm working on DORK and I'm almost there haha sorry.

We are all dorks here

In your lighter example, with the empty jug, the jug gets hotter faster because air is a poor conductor of heat. With the full jug, the jug itself doesn't get as hot because the liquid is much better at transferring heat. In both cases, you're moving the same AMOUNT of heat. You simply have a choice of heating a fluid or heating the container.

The milk or whatever in the jug doesn't go up in temperature very much because the heat conducts through the liquid very rapidly.

Same reason you can stand outside in freezing temps for quite a long time without getting hypothermia, but go into the same temperature water and your survival is measured in minutes. Or work outside when it is 120F vs. sit in a 120F bath.

Water has a higher specific heat capacity than air. In fact, it has the highest of any naturally occurring molecule. Specific heat is the amount of heat needed to raise the temperature of a certain mass by 1 degree Celsius. The specific heat of water is 1 calorie/gram °C = 4.186 joule/gram °C. Most given figures for air (dry) is 1.05 joule/gram °C.

This means that water takes a lot more energy to heat up. But once hot, it takes much longer to cool down.

Appleseed wrote: This means that water takes a lot more energy to heat up. But once hot, it takes much longer to cool down.

Which is why the air/water setup gives more consistent intake temps. Even assuming that you don't get any extra cooling capacity from the more efficient heat exchanger design it allows, the consistency can sometimes be valued more than slightly better absolute performance under ideal conditions.

In reply to Knurled:

They do transfer heat better, but not because of magical properties of water. You can fit a lot more exposed surface area in the nose with an air/water system. Radiator heat exchangers have much smaller/closer/flatter tubes than an air/air intercooler. That is more surface area to transfer the heat from the working fluid to ambient air. That is what I mean by being able to fit more cooling capacity into the nose of the car. Yes, there are some inefficiencies added by the adding of an intermediate step, but the benefits FAR outweigh them!

You are correct, but you blow the whole apples to apples comparison when you add extra surface area via more/ larger heat exchangers realatively to an air/air system. There is definitely a place for air water, and it is better when you are space limited.

Boost_Crazy wrote: when you are space limited.

If your intercooler isn't big enough to ensure that your charge temps are cooled to exactly ambient temp, then you're space limited, as adding a bigger intercooler would improve performance. So basically, you'll never really encounter a setup that isn't space limited.

In reply to rslifkin:

Which is why the air/water setup gives more consistent intake temps. Even assuming that you don't get any extra cooling capacity from the more efficient heat exchanger design it allows, the consistency can sometimes be valued more than slightly better absolute performance under ideal con

It depends entirely on the situation which one is more consistent than the other. If anything, the air/water would likely have the greatest temp swing, cooler during the initial drive, hottest after a long run.

In reply to rslifkin:

True, but that applies to either set up, and you do reach a point of diminishing returns. This also ignores the fact that internal flow characteristics are just as important as cooling capacity, and bigger isn't always better. This is actually a strong point in air/water's favor, as good internal flow is usually easier with air/water. Let's look at an extreme but common example where the intercooler gets a lot more work than in a typical sports car, and there is no shortage of frontal area- turbo diesel commercial trucks. They are on boost most of the time, at high boost pressures. But since they have plenty of room, they use air/air intercoolers.

In reply to rslifkin:

Radiator heat exchangers have much smaller/closer/flatter tubes than an air/air intercooler. That is more surface area to transfer the heat from the working fluid to ambient air.

While this may be true, this is only one of the two heat exchangers in this system. You just transported the heat to the front of the car. Even if it was 100% efficient, you still have the heat exchanger that transfers the charge air heat to the water. Like I said, the water part just moves and stores the heat, it doesn't remove it.

Boost_Crazy wrote: In reply to rslifkin: True, but that applies to either set up, and you do reach a point of diminishing returns. This also ignores the fact that internal flow characteristics are just as important as cooling capacity, and bigger isn't always better. This is actually a strong point in air/water's favor, as good internal flow is usually easier with air/water. Let's look at an extreme but common example where the intercooler gets a lot more work than in a typical sports car, and there is no shortage of frontal area- turbo diesel commercial trucks. They are on boost most of the time, at high boost pressures. But since they have plenty of room, they use air/air intercoolers.

The big turbodiesels I drove when I was behind the wheel of a truck would dwarf many car's radiators... and I drove cabovers which have smaller grill areas than regular cab trucks

In reply to chiodos:

I think you just added bananas to your apples and oranges comparison. The CPU is an electrical device. If it generates more heat than it can shed, it can melt down. An intercooler does not generate any heat. It doesn't need to shed any heat, it could care less either way, it will still be a collection of tubes and fins. If it absorbs all of the heat it can and can't dissipate it fast enough, it just tells the air charge, "sorry, I'm full," and lets the engine deal with the rest. The intercooler doesn't give a E36 M3. Why are you worried about heat soaking an intercooler in a stationary car? I won't even bother guessing. Probably makes as much sense as a CPU cruising down the highway at 70 to keep cool.