I wonder how much could be accomplished by spraying a fine water mist on the heat exchangers, like the Porsche GT2RS does under high power demand?
So far, I haven't been able to find detailed information on the Porsche system, including how they ensure that all the water is vaporized, and none ends up on the track.
Any info, experiences or thoughts?

 

It might be windshield washer fluid, that would evaporate faster than water.

 

Mitsubishi and Subaru have also used intercooler sprayers in the past.

 

It seems to be a rather well investigated technology, with some technical papers (mostly in the industrial and AC realm) reporting heat transfer or cooling improvements of 50 to 200%.

 

 

 

If you're going to set up water/meth injection on a supercharged car, is there ANY reason to spray it onto the outside of a HX rather than into the intake tract? Assuming none is lost, I guess the cooling from evaporation would be the same either way, but it somehow feels like you'd get more from the injection approach...

 

I think you're right, but several things come to mind:

1. In some types of racing, like mile events, they have rules that put alcohol-injected engines into a faster category. A buddy had to run in a "fuel" category, though he was using pump gas in the main fuel system. This was a number of years ago, so things might be different now.

2. Lower cost, easier availability. Distilled water can be found in most any grocery or drug store, for about a buck a gallon.

3. Water, once vaporized in the intake tract, will displace some oxygen-containing air. This won't matter, when the water is sprayed outside of the intake tract.

4. Might also be used to cool the main radiator (which would also cool the oil better), and not just the charge air. And that might be fairly simple, having three heat exchanges stacked in a row as we do.

 

Thanks. From the article:

" So anyway, we were struggling with an overheating issue. It was enough of an issue that it slowed my last two runs in qualifying. The first of those runs the car went into limp mode about half a mile from the finish of the qualifying sector, and the last run I aborted completely when the temps jumped substantially not long after the start.....

.....we had absolutely no intake ducting. This one was totally on us, with the compressed timeline forcing us to skip things that we would have normally done. With proper ducting, air coming into the front grill would be forced through the radiator. But with our current lack of ducting the air, as opposed to being forced through the radiator, would instead look for the path of least resistance, which would be around the radiator. Clearly not ideal. With no easy access to fabricate the proper ducting we looked for other solutions. The simplest one was to water spray the radiator. My NRG Motorsport guys raided the local Home Depot for some hoses and lawn sprinkler mist nozzles to MacGyver the system.Using our unneeded windshield wiper bottle as a reservoir, we ran a main hose to the nozzles we installed just in front of the radiator and intercoolers. This had an immediate positive effect. Our temps dropped 20-30 degrees and we were able to get several runs in before we hit redline."

 

this is a great thread, and i was planning on playing with this myself on my car.

As far as drippage onto the track goes, i doubt it, as long as a person has a nozzle that creates a good mist, and sprays it UP or DOWN from the nose intake cavity, all of the heat exchangers in the area will vaporize the water upon contact.

Evaporation is a cooling process, this obviously lowers the temps of the heat exchanger metal, and that in turn is able to offer more heat absorption from the fluids flowing through it. I believe 20-30 degrees cooling is very possible.

What would be very slick is if a person had a type of catch can/res system from the AC condenser and captured the water that drips off of it. Once the can/res was full, the system could be setup to make proactive sprays onto the HX on its own, and then a person would also have a manual override button to spray it onto the HX when they want to spray it, and that can drain the tank completely.

Then another switch could control bringing winsheild washer fluid down to the can/res, IF the can/res went dry (or one could just have a separate pump and nozzle from this washer fluid tank, and keep the nozzles and systems separate. Running the AC or even weaponX etc Chiller for boosted air, would also create water drippage that could be caught by the can/res.

Or, just Keeping it simple with just the washer fluid tank alone, but either way, i think you are correct that this could/should be implemented onto cars Warp.

I don't think it is something anyone needs to advertise to a track that they have. The key is to spray it while they are driving forward, and then all the water would absolutely hit a HX and vaporize. No drippage would occur from the sprayers.

Spraying straight down from above the transmission cooler, would be a great spot. 1 nozzle in the middle would be plenty.

Oddly enough, water could be sprayed onto the supercharger lids themselves from the outside, this would cool them down. The ones that are less insulative like the NX Outlet lid, would be ideal, that lid would be a literal heat exchanger.

I am amazed that no one has created a heat exchanger lid yet, especially callaway cars where the lid is exposed... there could be the return hot water from the bricks going back through the lid, to keep it cool.

Callaway should be using a much more conductive material for their lids either way... like the NX outlet lids are made.

 

Spraying water on heat exchangers is only really effective in low humidity locations. You are depending on the phase change from water to water vapor which extracts 550 or so calories per gram of water evaporated. Problem is the rate of evaporation is highly dependent on the dew point of the incoming air.

I used such a system many years ago on an air to water intercooler system for a turbo charged 425 hp rotary engine drag car. It was effective in the early spring and late fall when the dew point was in the 40-50's. In the summer, when it was really needed, the system was pretty much useless since around here the dew point is in the 70's during the summer.

A good illustration of the effect is that swamp cooling air conditioner systems are only useful in low dew point locations like in the desert.

 

i agree it helps in arid locations even faster, but to say that water would not boil and vaporize right off of the blower lid or right off of the heat exchanger, down here in humid florida, is not true at all... especially when the car is moving and wind is going across the HX. I think our 650hp cars may be a little hotter than the 425hp drag car and its single pass once in a while... was.

 

Ron, I think you'd be spot-on, if evaporative cooling were the only mechanism involved. However, one study found a second factor at play in their tests. They found that spraying ethylene glycol had almost the same benefits as water, despite having double the boiling temperature, and having much lower "latent heat of vaporization". Their conclusion was that a liquid film on the heat exchanger enhanced heat transfer.

That sounds counter-intuitive to me, and I haven't fully digested the entire paper yet, but that's what they came up with in their "conclusions" section at the end of the paper (on the page labeled 316).
I would have guessed that a liquid buildup on the heat exchanger would act as an insulator, but it's looking like it may not, at least not under all situations. Live and learn.

Sometimes, it will take me several reads to fully get my mind around a highly technical paper, so there's also the possibility that I've misinterpreted something.

Here's a link to the paper:
https://deepblue.lib.umich.edu/bitst...pdf;sequence=1

 

 

Why? Just curious.
I can see why it might not be ideal for OEM, with the need to add water periodically, or some other need for frequent maintenance, but Mike's suggestion of recycling condensate from the air conditioning evaporator might take care of that, for light occasional use in warm climates. Unless the condensate has already become contaminated enough, that it would grow slime in the reservoir. Pure distilled water is sterile, and will stay clean indefinitely.

 

 

high end exotics use this, all the way down to porsches. Its a viable solution. 30 degrees of cooling in rough situations is not a bad thing to have. In fact, the hotter the car is, the more benefit this system will have as the hotter and hotter the surface is, the more the water is forced to evaporate at a faster pace.

 

 

 

It's been a long time since I did any heat transfer stuff but one thing I do remember is adding anything in the path to the end heat sink, in this case air, detracts from the heat transfer rate. The only thing that really helps is increasing surface area of the last thing before the external heat sink, in this case air. That is why you see heat sinks in electronics with a lot of surface area provided by multiple fins.even though the mass of the intermediate heat sink is less then a solid piece of equivalent external volume.

As to the paper it would seem this is an engineering student paper/experiment probably done as an undergraduate senior design/ analysis course. Such courses used to be a requirement in most all engineering schools (this paper is from 44 years ago) to demonstrate some actual familiarity with an actual design of something relevant to the degree being sought. My observation is based on not seeing any degrees/experience citations behind he authors names as is/was always the case for such papers.

If you want to spray something on the fins that really cools, maybe to a fault, NOX is an good choice. The bad news is you may crack the core due to rapid thermal contraction and in an actual race possibly trigger the safety crew from the vapor trail down track.

I actually used this method screwing around during a test day. It was effective however not really practical for actual racing where in later rounds you may have to run back to back with no time to refill the NOX bottle.

BTW it did cause the safety crew to roll from the vapor trail. It did however take the intercooler water temperature into the mid 50's F vs 100+ F with just air flow. I was using a 10 oz nitrous bottle marketed in those days as Sneaky Pete for people running in restricted classes trying to hide the nitrous from the tech inspectors. There were some fine explosions from people trying to use these bottles hidden in oil pans.