Floyd

iTrader: (9)

If you put a red hot poker in water it cools very quickly, much more than waving it around in the air. I thought that's why water cooled engines are better than air cooled (Porsche have switched now).

As John says, even if water spray is not super efficient, it keeps us amused to build these systems and makes us happy!

BTW if you put a cup of boiling water and a cup of cold water into a freezer, which will freeze first? Strange but true....

F

RT

Bruce, I guess this is where our opinions differ. As in my experience, loads of water coming dripping out the underside of the intercooler. Of course, I'm running 4 non-std nozzles and a high pressure pump. To me, its insurance (against det) for the hot climate and slow traffic. Its definitely cheaper than Octane Booster!


So Bruce says: Almost all the water sprayed onto the IC evaporates.

While I say: Almost all the water sprayed onto the IC drips out from the underside.

What do others think?

RT

Quote:
"I had automatic IC spray kits on my previous two Scoobies (MY00 Turbo and MY01 WRX)...How much it helps? I have no idea...I press the Sti's switch every now and again, just for the hell of it...Think an automatic setup would have been so much better... "


Bruce, the JDM STI's have an Auto (on-off position switch) and a Toggle for a 5-sec burst. If you switch the Auto switch to off, you'll get no spray. Believe the Auto function for your Euro-STI is ON all the time? (that's what I've heard)

BruceWarne

Nope. It only has a spray toggle switch..No automatic mode (well, I'd have to check the water-level to be sure).

I there a difference between UK and European spec?
Think we get the UK spec here. Well, it must be, cause we order it off the same brochure that has the Prodrive spec ones in.

Btw, I never said all the water evaporates. I said that the water that doesn't evaporate is not on the IC long enough to have much of an effect.

But I think over here it would be safe to say a LOT of it evaporates, especially in the summer. Why do UK cars have IC sprays anyway? They don't need it. Each and every time I've been over there it was raining (granted, I've only ever been there a couple of hours at a time, travelling between Gatwick and Heathrow, or sitting on Heathrow staring at the rain).

BruceWarne

You're missing the point...

The issue here will be that the amount of energy both cups of water would have to give up to get to 0 C, is very small compared to the energy they'd have to loose to turn into ice.

RT

...If ALL of it turns into ice....

haha!!

BruceWarne

I've never disputed that obviously very informed and well thought out argument of yours.

Let's say only 20% of the water stays on the IC to evaporate. (You think 20% is a bit much, what should it be? 10%? 5%?...read on)
The energy absorbed by that 20% when it evaporates is equal to the energy required to heat ALL (as in 100%, as in everything even that which fell off, so if you could keep all the water on the IC) of the water from 0-100C.

Let's assume the water starts off at 0C.
What are the normal charge temperatures, 40 C? Obviously the water can't get warmer than this. So, if you sprayed 1 litre of water (at 0C) onto the IC, the maximum energy it can absorb, without evaporating is equal to 40% of the energy that will be absorbed if 200ml (20%) of it evaporates and 40% of 200ml is 80ml.

But, as you say most of the water falls off...
So, you can't really heat it to the maximum 40C...let's say you can heat it on average to 20C - which I doubt, but let's say that anyway.

Seeing that heating water from 0-40C is 8% as efficient as evaporating it...heating it to 20C halfs the efficiency of all the water that doesn't evaporate.

This means, if you flood your IC with 1 litre of water at 0C, only 40ml of it has to evaporate to absorb the same amount of energy as the 960ml that fell off.

In the beginning I assumed 20% of the water stays on the IC. It is clear that even if this is 4%, the water that evaporates is still more efficient that all the rest that fell off.

So, you only need 4% of the water to stay on the IC, to outperform the 96% that falls off.

Can I make it any clearer?


[Edited by BruceWarne - 5/31/2002 6:06:08 AM]

[Edited by BruceWarne - 5/31/2002 6:20:05 AM]

RT

Bruce, I don't dispute the power of evaporating water.

But 2 things:

1. Is the front (hot water) mounted tank better than the boot tank (cold water)? I take your point that it is your opinion that the boot tank gives negligible benefits. But it is a benefit right?

2. The bottome line: Is spraying MORE water better than spraying LESS water, assuming temps are the same? Will spraying more water INCREASE the absolute amount (not percentage) of water evaporated? Obviously if you spray 1gram of water, all of it should evaporate. But this "100%" evaporation rate does not remove very much heat!

You've got me pretty darn confused now.


EDIT: But I note that our target is "the highest absolute amount of water evaporated", not "the highest percentage of water evaporated", per unit time. Therefore to an extent, we must supply an optimal spray rate and not use the "1gram-100%" theory.

[Edited by RT - 5/31/2002 7:51:57 AM]

BruceWarne

1. Boot mounted might be cooler (after 2 or 3 sprays). It was probably one of the factors for why it was moved to the boot, but I think space, and accesability played more important roles.

2. Yip. I agree totally on this one. There will be an optimum point. Too little water probably won't be very effective, and too much water won't be very efficient.

GavinP

According to Corky Bell's book, the heat transfer between aluminium/water compared to aluminium/air is 14:1 .....

I experimented with water sprays and fans mounted under the IC before going with a chargecooler - water pressure is key IMHO.

Thanks

Gavin

RT

"According to Corky Bell's book, the heat transfer between aluminium/water compared to aluminium/air is 14:1 ....."


Are you saying that heat will travel from Aluminium to Water 14 times faster than Aluminium to Air? (Assuming the Aluminium is at a higher temp than the water/air.)

Trout...

QUOTE: If you put a red hot poker in water it cools very quickly, much more than waving it around in the air. I thought that's why water cooled engines are better than air cooled (Porsche have switched now).


Yes and the poker cools - not beacuse of conduction - i.e. the heat moves from the red hot poker to the water. The red hot poker makes the water 'boil' and so go a phase transition from water to water vapour - which has been pointed out - needs an awful lot of energy.

The Porks use conduction - rather then phase transfer! Good but different argument!

Trout - who loves water 'cos I swim in it

PS My water tank is in the boot
PPS When I have been driving on track the intercooler gets too wet - needs finer spray and an evapouration effect!

GavinP

Are you saying that heat will travel from Aluminium to Water 14 times faster than Aluminium to Air? (Assuming the Aluminium is at a higher temp than the water/air.)

That's what Corky's book says and his book is treated as a "bible" on turbocharging...

In addition, I have seen on Redline's "Water Wetter" page that thermal conductivity is double and heat capacity is four times as much for water rather than air (no transfer medium specified)....

Thanks

Gavin

RT

Gavin, can I have the title, author and SN# etc of Corky's book?
tks.

john banks

http://www.amazon.com/exec/obidos/AS...435327-6562231

STI05V

on my sti v5 on a dyno......we done two tests....one with the i/c spray on and one with it off

it showed a genuine 5k/w at the wheel increase with it on.......i think it was every bit worth it

RT

Good show! Is your tank boot or bonnet mounted?

Anyone else with solid figures?

Stelios

MoTeC Data Log informs me a 15 C cooler induction temps with w/spray .
Case closed I think.

WREXY

Where's your bottle mounted, Stelios?

Stelios

I use the wiper washer bottle and being a wagon i dont have rear wipers-water . Anybody can point me to a cheapish rear water tank?
Thanx!

BruceWarne

Aha!
It would be very interesting to see what difference mounting a tank in the boot makes...