Here's a little of the math.

A gram of 20C water requires 80 calories to get to 100C, and about another 600 calories to change phase to vapor. So about 680 calories per gram.

A gallon of water weighs 8.351b or about 3.8kg. This represents about 2.6 million calories, or about 10,000 BTU's.

If all of this occurs in an hour. You get about 3000 watts of cooling.

This assumes that 100% of the latent heat to warm the water and evaporate it comes from the oil, and not the ambient air. My guess is that the real efficiency is around 10%.

Now, somebody else will have to figure out how many watts are put out by the item that they want to cool.

Also, somebody check my math, it's been nearly 20 years since I had to take that thermodynamics class.



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Bill Krause
'79 911SC Euro

You go Bill.

If you pulled all those numbers from memory, you are my idol.

The 600 calories / gram you give for phase change though is for boiling. I think the number for evaporation is different (not sure, can someone confirm?), and likely lower. With this product the water will be evaporating.

911pcars, note the relevant units here are BTU / Calories (energy), watts / Joules (power) and not degrees (temerature).

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'86 Cab, '77 Targa, Family Truckster

Aren't boiling and evaporation the same? Just different words for the phase change from liquid to gas.

The only number I pulled from memory is the 600 calories/gram. I'm still trying to verify that number.

I think the best application of this "technology" would be to cool the driver.

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Bill Krause
'79 911SC Euro

Yeah. Boiling and evaporation are the same. This 600 degrees is best described as the heat energy required to change a gram of liquid water into a gram of gaseous water.

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'83 SC

Okay, so let's use the 600 cal / gram. Since it is evaporating we would not add in the extra 80 cal / gram.

1 gal of water would then take 2.28 million calories to evaporate. If at a rate of 1 gal per 1.5 hours (like this product), then it is 1769 watts of cooling capacity (assuming 100% efficiency).

Cooling capacity = 1769 watts

Now, I don't know what the typical oil cooler or brake dissipates, but I do know that Porsche calls the big reds their 2000 HP brakes because that's how much they can dissipate.

2000 HP = 1,490,000 watts so

Big Red heat dissipation capacity - 1,490,000 watts

That means this system has a cooling capacity that is .118% of the heat dissipation capacity of BigReds.

So we could slap this on our big reds and get roughly 1/10th of 1% improvement in braking.

I will give you that big reds are not typical, but even if regular brakes dissipate 10 times less heat than big reds, this system would only garner about 1% improvment. And that assumes 100% efficiency of getting the cooling into the brake, which won't happen.

If the math is correct, I think that should settle any agrument - this system is useless for brake cooling.

Anyone know how many watts a typical oil cooler or intercooler can dissipate?

Anyone want to bet me a dollar how those calcuations will come out?

Chuck

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'86 Cab, '77 Targa, Family Truckster

[This message has been edited by Clark Griswald (edited 05-14-2001).]

I have no idea if a water sprayer would work on an oil cooler (especially a trombone) or if sent over the engine, but I am pretty certain it works in practice on intercoolers.

I base this on a couple of things:

1. Subaru do it, based on the technology trickling down from their World Rally Championship cars, and they know what they are doing when it comes to 4WD intercooled turbo'd cars

2. I searched for 5 mins and found this link to someone who installed a water sprayer on their Audi intercooler and logged the resulting intake temperature changes. Regardless of the physics/maths (of which I have no idea), a product that provides a worthy benefit is worth some money. I mean, what scientific evidence is there to support the fact that Swepco is the nectar of the gods for 915 transmissions.

http://www.audiworld.com/tech/eng22c.shtml

I also note that this product has some pretty cool features, such as automatically monitoring the temperature and spraying accordingly.

Cam

Camb,

No doubt water based cooling can work. But the capacity of the system has to be appropriate for the job.

That Audi system probably had much higher flow rates than this system. If that is the case, it may work very well.

In my first post on this thread I was suggesting that a flow rate around 1/2 gallon per minute might make sense for oil coolers and such. I then raised concerns about hauling the weight of all that water around.

Turns out this product only consumes 1 gallon in 1.5 hours. That just isn't enough cooling capacity for the applications that 911pcars is promoting the product for. The math has proved this.

How much would this product need to flow? Well, if you wanted to double the capacity of your bigreds it would have to flow nearly 1000 gallons in 1.5 hours.

I would speculate that Intercoolers dissipate less heat than oil coolers and brakes, so might better lend themselves to this type of system. I think that Audi system only sprays when the intercooler is hot (under boost), so they can get away with higher flow rates while still keeping the total water consumption down somewhat.

Again, the basic idea is sound, but this particular product is not engineered to meet the needs of the applications it is being marketed for.

Maybe the market for hippy hats will take off.

Chuck

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'86 Cab, '77 Targa, Family Truckster

At the risk of a flame, here goes...

I do not claim to be a math wiz, but even those that are can be mystified at times by why things work when the math says they should not...

Physics and Engineering can not solve everything... not that long ago, it was impossible for a man to fly or go into space... and so on...

Have you ever been in a house that uses evaporative cooling? I have, it lowers the temp of the air very well, and this is the principle that is in use here. Not to cool the metal, but the air that surround it.

Kind of like, your car runs hotter in the summer than in the winter... It is pretty simple... Not cooling metal cooling Air that is cooling the metal....

I have seen and used the Personal Misters that were talked about earlier, and they make one hell of a difference in the air temp around them.

Depending on the cost, I think it is a great idea....

Just my two cents...


Randy


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Get in, Sit down, Shut up and HOLD ON!

1978 911 SC

[This message has been edited by kamikazepilot (edited 05-14-2001).]

I have seen a couple of similar homemade
devices for spraying water into 911
fans for track events here in Rocky
Mt. Region of PCA. It apparently works well
for twenty minute run session, using
the washer bottle reservior and RV sink pump.
One driver claimed it cooled his
'73E 20 degrees. We have the
right conditions for optimal effect here
in Colorado low humidity and hot weather.

Bill

No equations though, just a couple empirical
data points.

Super is right....this device is intended for sun-struck hippies (and racing spectators).
Jack Olsen could easily finance future enhancements of the Black Beauty, by selling these gizmos to the over-heated crowds at Willow Springs.

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Doug
'81 SC Coupe (aka: "Blue Bomber")
Canada West Region PCA
members.home.net/zielke/911SC.htm

Nobody is questioning whether or not a spray mist will cool air. It does, it's easy to understand how, and to figure out how much. The problem is that it's not enough to cool signifigantly large heat producers like brakes or internal combustion engines unless you carry around an incredible amount of water.

Randy, you said that "Physics and Engineering can not solve everything... not that long ago, it was impossible for a man to fly or go into space... and so on..."

Please explain to me how these two tasks were solved without physics and engineering. Did we get to the moon by using gimicks and clever marketing?

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Bill Krause
'79 911SC Euro

You are correct Bill, Physics did get us there, but this is the same physics that said it was not possible.

We are constantly bending the rules.

But not worth arguing over, this board is for fun, not flame...

I will concede on this point...

Randy

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Get in, Sit down, Shut up and HOLD ON!

1978 911 SC

They make alcohol injection devices for forced induction applications. These are for people who don't have intercoolers or want a cheap way to drop the intake temperature and they do this by using alcohol injection. People will also use water or urea (diesel) injection to remove carbon build up in their motors and improve emission but this is risky and could cause hydro-lock.

If I were to spray this thing on anything, it wouldn't be my brakes that's for sure. Talk about dangerous. And to me, there seems to be better ways to cool your motor/oil/brakes than spraying water on them. The application only works in dryer climates where humidity levels are lower. I also wouldn't want salt build up, so filtered/deionized/reverse osmosis water is better.

Just my 2 cents.