2007 Exige S Intercooler Air Flow Study

[IamBatman]

well, you would not want to spray THROUGH the IC obviously. Not only would you get condensation inside the IC, you would pull heat from the IC to the intake air. In our application, I would put the nozzle right after the IC to finish the job of the IC in cooling the air. Most of the misting coolers are meant to replace intercoolers. Typically you use a mix of alcohol and H2o to enhance the evaporation. Spraying water/alcohol though the intake also serve to reduce detonation and allow you to to run more timing & boost.

[robains]

Want to be clear here, talking about EXTERNAL spray not internal.

[Monsi]

Originally Posted by robains

Want to be clear here, talking about EXTERNAL spray not internal.

same rules apply... when the water turns to steam it is still pulling heat away from the IC

[apk919]

Originally Posted by robains

if you spray water on the IC it converts to steam which is then pushed thru the IC which in turn does NOT cool the IC.

Misting is performed on the incoming air to cool the air which then cools the IC.

I agree with you is some ways but you are removing the air flow from the equation/context -- yes you convert the heat into steam and reduce IC temp, but the steam immediately then flows over IC increasing it's temp.

The Subaru sprayer is manual, not automatic, and it wouldn't be the first time a gimic device has been but on a car...happens all the time.

I do have an idea, the water went thru the IC onto the hot engine which then converted the water to steam which raises up towards the IC which in turn heats the IC, not cools it.

The key here is to mist the air flowing OVER the IC, not to spray water ON the IC. You want the air to be cooled and water free by the time it passes thru the IC.

Wait... what is turning the water to steam? If the IC is hot enough to turn water to steam, then spraying water on it is cooling it, whether the water turns to steam and goes through it or not. Turning water into steam requires adding the latent heat of vaporization to be supplied by the surface that it's in contact with (which I assume is the IC, correct?). If you mist the water, the latent heat of vaporization is supplied by the air it's misted into, cooling the air (which then has more potential to lower the temperature of the IC).

The question is, which has more potential to cool the IC: air that has been cooled by the water's latent heat of vaporization (during misting), or water sprayed directly on the IC. Both of them will cool the IC, but off the top of my head I couldn't say which is more efficient (but it probably would be the misting system).

BTW, real misting systems are high pressure (~1000 psi) so that the droplets can be made very small (<50 microns) and can then "flash evaporate", pulling all the latent heat of vaporization needed from the air and leaving no water residue. Larger droplets will not completely evaporate, and therefore not pull as much heat out of the air. They're also sensitive to humidity, and won't work as well in a humid environment.

[xtn]

The most efficient use of an external mister would be to get the smallest droplet size, and get the mist spread out over the largest possible surface area of the IC, and get those millions of tiny droplets to vaporize during contact with that surface.

Some of you seem to have a bit of a misconception about cooling the air first, and then having the cooling air flow through the IC. Spraying the perfect mist, by itself, does not cool the air. Put your hand in the flow a couple inches down-stream from the nozzle and you will feel cooler air. By the time the air reaches your hand, you will feel a bit of cooling due to evaporation, but the bulk of the cool effect you feel is just the fact that a cool mist is being sprayed on you. The real (most effective) cooling comes from the evaporation. The exact point of evaporation is what pulls the largest hunk of heat energy out of the surroundings. Having the liquid water flash over into steam while it's in contact with the IC will pull a lot more heat out of it than just flowing cooler air over it will.

So you want a fine mist, located just far enough up-stream to spread out and reach the whole width of the IC, but not so far up-stream that a lot of it has evaporated by the time it gets to the IC. So yes, you want the liquid water (albeit in tiny mist droplet form; a single squirt-gun stream aimed at the middle won't be nearly as effective) to reach the IC in the liquid state. Ideally the front of the IC fins would be slightly wet, and as the airflow pushed the droplets across the fins to the exit side, the water would evaporate, and the very back edge of the IC fins would be dry. This would indicate you are pulling out about as much heat as is possible with such a system. In an ideal world your mister system would have sensors to determine this condition, and increase or decrease the mister flow as the IC heated up and cooled down to maintain this ideal condition.

Since nobody is likely to develop that sort of thing any time soon, we set the flow to establish that condition during hot track usage. At other times, if the IC is not hot enough to turn it all into steam, then use less water, or just accept liquid blow-by if there is a means to prevent it puddling up after the IC. Not like you should complain about it. "Awww my IC is too cool to vaporize all the mist," is kind of a silly complaint, don't you think?

xtn

[apk919]

Originally Posted by xtn

The most efficient use of an external mister would be to get the smallest droplet size, and get the mist spread out over the largest possible surface area of the IC, and get those millions of tiny droplets to vaporize during contact with that surface.

Some of you seem to have a bit of a misconception about cooling the air first, and then having the cooling air flow through the IC. Spraying the perfect mist, by itself, does not cool the air. Put your hand in the flow a couple inches down-stream from the nozzle and you will feel cooler air. By the time the air reaches your hand, you will feel a bit of cooling due to evaporation, but the bulk of the cool effect you feel is just the fact that a cool mist is being sprayed on you. The real (most effective) cooling comes from the evaporation. The exact point of evaporation is what pulls the largest hunk of heat energy out of the surroundings.

So you want a fine mist, located just far enough up-stream to spread out and reach the whole width of the IC, but not so far up-stream that a lot of it has evaporated by the time it gets to the IC. So yes, you want the liquid water (albeit in tiny mist droplet form; a single squirt-gun stream aimed at the middle won't be nearly as effective) to reach the IC in the liquid state.

If the IC is not hot enough to turn it all into steam, then use less water, or just accept liquid blow-by. Not like you should complain about it. "Awww my IC is too cool to vaporize all the mist," is kind of a silly complaint, don't you think?

xtn

Hmm.... as long as the droplets evaporate completely, I'm not sure whether it matters whether that happens first in the air going through the IC, or on the surface of the IC itself. The latent heat of evaporation still has to be carried away by the air flowing through the IC. If there's not enough air to remove the water vapor, it will eventually become saturated and additional droplets on the IC will not evaporate. So I think bottom line, it's the air's ability to remove heat from the IC, either by starting at a lower temperature (misting the air), or by removing water vapor from the IC (spraying directly on the IC).

EDIT: Also, spraying directly on the IC would only get mist on the first few mm's of surface area from the front of the IC... theoretically you'd want the entire surface area of the IC to be more efficient (true evaporative chillers are designed to get a maximum surface area wet), and it seems the best way to do that would be to cool the air, which is going to contact the entire surface area.

[robains]

Guess I need to start data logging my results. Unfortunately I can't find a pump capable of efficient misting that is 12V DC that doesn't draw excessive amps. The 40-70psi pumps I've used really just don't mist regardless of the nozzle.

[Chris A]

I put this in a few post ago....it was at the bottom so maybe you didn't see it Seine Systems > MPC

[robains]

Chris, WOW -- you da Man! Just order unit, overnight.

That does look like a viable unit!! Guess I missed your post, sorry.

[Chris A]

Cool.....I'm looking forward to your review!

[robains]

Kit is missing one part, but I think I can work around it as I have a boost/relay trigger. Part is on back order (pressure solenoid that runs inline with the hose).

[xtn]

Originally Posted by apk919

Hmm.... as long as the droplets evaporate completely, I'm not sure whether it matters whether that happens first in the air going through the IC, or on the surface of the IC itself. The latent heat of evaporation still has to be carried away by the air flowing through the IC.

Assume an appropriate mist level that will not waste any liquid water out the back of the IC...

The results will be better getting the water droplets to pull heat out of the IC fins directly than pulling the heat out of the air first. The cold air passing over the fins does not have nearly the heat transfer rate, per unit of surface area, that water has. Liquid water has much better heat conducting characteristics than air. With your method, you'll get cooler air out the back of the IC, having wasted some potential energy absorbtion, than if you had let the water absorb the heat energy at the IC itself.

Are you cooled down more on a hot summer day by an evaporative cooler that is blowing cool, humid air on you (water already evaporated) or by having a mist blown directly on you while you stand in front of a regular fan and letting the water evaporate directly off your skin?

Originally Posted by apk919

EDIT: Also, spraying directly on the IC would only get mist on the first few mm's of surface area from the front of the IC... theoretically you'd want the entire surface area of the IC to be more efficient (true evaporative chillers are designed to get a maximum surface area wet), and it seems the best way to do that would be to cool the air, which is going to contact the entire surface area.

If the water is completely evaporating within the first few mm of fins as the airflow passes through, then you could turn up the volume of water being supplied. Assuming a small enough droplet size, it will all be passing through the IC, coating whatever fins it touches. The only reason it would be coating only the first few mm is if it's evaporating faster than new droplets are coating the fins. If that's the case, you need more water for maximum cooling capacity.

xtn

[robains]

Misting is based on the theory of Evaporative Cooling (or Desert Cooling), which uses the scientific principal of Thermal Dynamics, which states that water requires energy to evaporate, or 600 calories of heat per gram of water, and this heat is taken from the environment.To achieve this water is forced through a very small orifice creating a very fine mist or fog of ultra fine 50 micron water droplets (smaller than the diameter of human hair). Once these very fine droplets of water are exposed to the hot atmosphere, they quickly absorb the heat present in the environment and evaporate in the process. This quick heat exchange is known as Flash Evaporation, it takes heat from the surrounding area, and drops its temperature by up to 35 degrees F, and consequently the air is cooled.

High Pressure misting generates Fog, which is ideal misting, with finest mist. However the cost is way high too, because it uses high pressure pumps, and stainless steel tubing, and metal fittings to handle the high pressure. The finer the mist, the more efficient is the system (due to the larger surface are), and the higher the pressure the finer is the mist produced.

I think the issue I have with misting directly ON the IC rather then trying to cool the air flowing over the IC is that air flows thru an IC more evenly, mist will not. A mist will most likely just contact a smaller surface area so you end up cooling only a small section of the IC. Cooler air will flow better and provide a more uniformed coverage.

But want to be clear, water spray vs. water mist -- with water spray you will go thru water at a very rapid pace for track duty and you'll have a bunch of wasted water that drips on the engine or in my case tires.

Anyway, I think best way to settle this debate is to do some testing -- and that's exactly what I plan to do an submit my findings to you folks. But in all cases, I'm only hoping try and keep IAT at sane levels, not really expecting massive reduction in IAT or big HP gains (just try to minimize).

Kit arrives tomorrow, hope I have time to install before event. I'll check IAT after each track session.

[dmh]

Just curious...What group allows a car that sprays water on the intercooler on a track with other cars?

[qball]

Browser Warning

[robains]

Just got signed off on my LogBook, so apparently it's not an issue.

dmh, you can apply your logic to any fluid used by the car, oil, radiator fluid, gas, water injection, etc. etc. -- a failure is a failure -- just ask FF about the car that dumped oil on the track during cool down and they hit the oil and car went off. But out of all those fluids, water is the most evaporative and least slick.

Also, some professional race series use water injection on the brakes. If it's working right it's not a problem, just like any part of the car. In my case, it wasn't working right.

QBall, went thru that article, apparently that kit would work only for max 9 seconds before the pump would overheat and fail or need a long cool down period.

[dmh]

Just having fun with you...

Speed World Challenge:
2.9.3.16.5: Water Spray Systems
Water may not be sprayed on any intercoolers, radiators, etc. Water spray systems may only be used to inject water into the brake ducts. See the brake section of Article 2.9.9.5 for additional details.

Koni Challenge:
No intercooler spraying is allowed.
7-2.4 Fluid or fan cooling of the brakes is prohibited.

Rolex GT:
Is forced induction even allowed? Water brake cooling is not.

In all forms of racing, at all levels, if the rules don't say you can do something, you can't.

Not to mention...NASA and just about any other form of racing...15.17.10 Engine Coolant
Ethylene Glycol-based antifreeze and other additives that may cause a slippery condition if spilled on track are prohibited. Other water additives such as Redline Water Wetter may be used.

[Smoky]

+1 to dmh's comments. External spraying of any kind will not pass tech inspection at most sanctioned events.

[nak]

There is a way for water spray to spike the temps up instead of down.

If the water hits the IC and is heated but not flashed to steam and it is not forcded by airflow through the IC, you have a problem. The initial hit takes heat out of the IC and warms the water. Then this hot water sticks around and restricts air flow through the IC. These cars are not noted for good IC airflow to begin with.

The key to good cooling is flow rate, period. It could be air or air + mist BUT IT HAS TO FLOW to take the heat away.

A very fine mist, in the right quantity, would lightly and evenly coat the IC, heat up, and then evaporate away in the airflow. THis would boost heat transfer in the expected way.

[Monsi]

Originally Posted by nak

There is a way for water spray to spike the temps up instead of down.

If the water hits the IC and is heated but not flashed to steam and it is not forcded by airflow through the IC, you have a problem. The initial hit takes heat out of the IC and warms the water. Then this hot water sticks around and restricts air flow through the IC. These cars are not noted for good IC airflow to begin with.

The key to good cooling is flow rate, period. It could be air or air + mist BUT IT HAS TO FLOW to take the heat away.

A very fine mist, in the right quantity, would lightly and evenly coat the IC, heat up, and then evaporate away in the airflow. THis would boost heat transfer in the expected way.

water isnt gonna just hangout in your intercooler and restrict airflow(if your intercooler is hot enough to flash boil water you have SERIOUS issues) its going to absorb heat and evaportate and if it doesnt air will push it out

even if the air didnt push it out it would still absorb heat and evaportate

there is no way for water spray to increase charge temps unless the water you are spraying is hotter than your intercooler(and even then it might evaporate fast enough to help), thermal energy only flows from a high concentration to a low concentration...

if water spray increased charge temps then how come you dont start to detonate when it rains?