Lindsey racing air/water intercoolers: Opinions/thoughts

[Tony D]

My reference to the AIR pump was only to illustrate the size of the A/C compressor on a Geo Metro, not that you could actually use an AIR pump for anything that asthetics...

 

As for Air/Air being discounted, industrial stationary compressors use aluminum Air/Air units for cooling interstage air very effectively. Some two-stage units (stainless steel precooler, Aluminum Main Cooler) will have approach temperatures within 5 degrees of ambient. Not bad when you consider it's ingesting 455F air on the inlet side at full load. And this is 24/7 service!

 

Cooper Cameron (Cooper Turbocompressor, or whatever they are called this month) has had a small centrifugal multistage compressor available for close to 10 years now. 125 to 350HP range, supplying 125psi air. Those are AIA Coolers on it, and the air temperature will be very close to ambient on the outlet side of the cooler.

 

Thing is, if you cool too much below 85 degrees F, you will start getting a lot of condensate in the airflow, the more relative humidity the more you will get.

 

Most industrial application will limit first stage intercooling to 120 F inlet temperature to the second stage simply to keep condensate entrained. They just upsize the second stage wheel or compression element to compensate for the lessened air density.

 

The amount of condensate that can be entrained in the air almost doubles from 85 to 120 F. And again as it gets colder, you will get more condensate. As BLKMGK mentioned seeing 'fog' from the BOV, this is totally possible, and indicative of the 100 % Relative Humidity in aftercooled, compressed air. Any object that quickly drops the pressure will experience a JT effect, meaning a quick temperature drop...and the entrained water vapor will condense and turn into fog. In extreme cases, this 'fog' can be what is going into the engine... This can be 'bad' if the condensate is in sufficient quantity to lock a cylinder.

 

In an A/C based system (Freon), this WILL be a consideration as at 35 F you will have condensate running along the I/C piping. The easiest thing for elimination of this, is small pinholes in the bottom of the pipe with a soft rubber flap covering it tightly---under vacuum the hole is sucked closed by the close proximity of the rubber, under boost the condensate is positively eliminated through the holes, free to spew all over underhood components below them! (You can pipe it with flappers like on the old road-draft tubes the VW's had...but...what a pain!)

 

As for scoffing at A/C based systems, the project got a passing grade in Industrial Technology, and was proven in concept, real world, in a hot environment. You have to know what you're doing with the A/C, and one of the big considerations is the accumulator sizing. This goes with any sort of system using compressed anything. With a big enough accumulator, you will get by with progressively smaller and smaller compressors. It is FAR more suitable for a Street Car, than a Bonneville Racer. Street cars will rarely, if ever see more than 15 to 20 seconds of boost where the A/C must cool the charge. At all other times, it will, as mentioned above, eliminate all stored heat in the exchanger for better transient heat elimination.

 

I digress...

[(goldfish)]

Nice, I always guessed it would not cool it well enough to overcome the power required to drive the compressor.

[240hoke]

They did it in Thrust Racing... that enough proof for me!

[BLKMGK]

I do not believe that condensate is an issue, at least not a big issue. Yes, vapor will indeed form when temp drops below the dew point. However the volume and airspeed in the piping is such that any condensate will get blown right into the engine. I've known folks to inject alcohol into the turbocharger intake (sans intercooling I believe) and had no issues with fluid in the piping, certainly that was a greater volume than you'd get with condensate. Indeed the Mustang we tuned didn't care at all about the vapor I'm sure it was ingesting, free water injection IMO I wish I'd gotten video of that thing, it was pretty sick. We left a plug wire off once and freaked when power dropped off by more than 100 from the previous pull but the thing idled and pulled fine on 7 cylinders!

 

As for A/C cooling the airstream... In short bursts yes I'd agree that works, the Lightning concept truck did this actually by cooling a secondary medium like water I think. But continuosly? I don't think so, not in a manner that is feasible. The amount of power to compress the coolant and the size of the heat exchanger(s) do not seem to me to be practical unless it's only a small temp difference you want. There's no free lunch and this reminds me much of the guys who thought putting a computer in a small refrigerator would yield superior cooling. They quickly found out that wasn't so! If it were easy and practical I think it would certainly have been done already, possibly even by the OEMs. Certainly it's not a new idea as I've heard it proposed a few times. Heck, Autospeed might have even tried it once upon a time, I'll have to look.

 

The volume of air an engine ingests (and thus must be cooled) is pretty extreme, I've actually seen people try to dyno test those silly electric bilge pumps as blowers (ahem) and when that didn't work tried feeding a gas powered lawn blower into the intake full blast - the engine was still restricted at WOT (lol). The temp drops we get from A2A intercoolers today are often as good as they are because the intercooler is acting as a heatsink not because it can keep up with the heat going through it - once it's heatsoaked temps climb. The advantage of water is that it's like a MUCH larger mass and easier to package since it's a fluid, that it transfers the heat to the medium so readily is a big bonus. Once it's heatsoaked though the same thing occurs - temps climb. I watercool my computer because of this, temps change slowly as loads are absorbed unlike when I used air and even minor changes in ambient could be noted.

 

Some interesting things I've noted on the dyno in the past... When I'd cool an intercooler with alcohol and then do pulls I found that my intercooler would get warm from the intake side first and that the heat would then slowly creep to the outlet side. When I tested Supra with the smaller intercoolers I often found that after only one or two pulls the entire surface was warm. The difference in the intercooler I ran vs the other was mostly mass - mine was noticably thicker (3row vs 4row Greddy). When you'd start a pull intake temps would often go up and then down, it took a second to clear the warmer stagnant air. I saw that on the street too, temps would be high puttering around or idling, go up as I went WOT, and then drop before slowly coming up. On the drag strip I'd launch with elevated RPMs and warm air, see temps drop, level off, and then go up by as much as 10 degrees or so by the traps. As soon as I let off temps jumped up! That was the intercooler dumping heat it had absorbed into the intake stream. Driving around airflow was slow enough that it seemed to pickup heat from the piping and intake. I'd like to try insulated pipes (plastic maybe?) and ceramic coatings on the intake sometime. One thing I never got to do was put a temp probe at the turbo inletoutlet - I'll strive to do that sort of testing when I've got another car I can play with I really was a data junkie