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Old 08-16-2002, 02:24 PM   #1
jmott
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Default alcohol/water mixes for cooling intercoolers

lots of people spray water on their intercooler to cool it down, either with spray kits or by hand at autocrosses etc

most of the heat transfer is due to evaporation

now, a lot of people reccomend using a mix of alcohol and water when doing this, to get even better cooling.

but, the latent heat of alcohol is about half that of water.

so why use alochol? It takes less heat to make it evaporate.

whats the benefit?
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Old 08-16-2002, 02:43 PM   #2
jmott
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ok so to answer my own question =)


The relative evaporation rate of butyl acetate is 1.0. Other materials are then classified as:

95% Ethyl Alcohol = 1.4
Water = .3

So alcohol evaporates at nearly 5x the rate of water, while having about half the the latent heat.

Soooo, if your current watery spray setup is such that not all of the water is evaporation, adding alcohol could be a plus. OR, you could add alcohol to the mix and increase the volume of liquid going to the intercooler and get a benefit
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Old 08-16-2002, 03:32 PM   #3
thejean
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I think they are adding alcohol to prevent freezing during winter.

I also agree that alcohol, due to its poorer thermal properties, shouldn't transfer heat quicker than water. Water should transfer the heat from the intercooler fins to the water quicker than alcohol and should also transfer it to the air quicker as well. What it won't do is evaporate quicker. However, I don't see this is a disadvantage unless you were using ice water and not water that is already at ambient temps as the water will only cool to ambient temps (plus wind chill) anyway. Ice water would transfer the heat from the intercooler quicker however, the transfer to the air should remain the same for a given temperature. The IAT thread also found that ice water addition didn't really affect IAT's (post intercooler) in terms of making the intercoooler colder, all it served to do was dissipate the heat slightly quicker.

However, since alcohol does evaporate quicker, you would actually reduce the volume of liquid on the intercooler surface quicker, which could have two effects:
1. Force you to use the waterspray more often to keep temps down OR
2. it will result in a slightly higher IAT due to poorer heat transfer.

Therefore, IMO, alcohol should only be added as a means to prevent freezing.

JC

EDIT: Thought about it some more - at very low speeds or idle however, evaporation could be good as the evaporation will carry it away quicker. So to follow your logic above.

Water evaporates at a rate of 0.3. multiply this by a relative heat transfer of 1.0 and you get a heat dissipation factor of 0.3.

Alcohol evaporates at a rate of 1.4. Multply this by a relative heat transfer of 0.5 and you get a heat dissipation factor of 0.7.

So, I guess it could be beneficial however, it would mean that you would use a lot more spray and alcohol is expensive!!!

Last edited by thejean; 08-16-2002 at 03:41 PM.
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Old 08-16-2002, 03:39 PM   #4
BamBooI
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jmott is asking about different water sprayers to cool the ic. I don't think he is worrying about freezing. I would rather use alchol because if poor alchol onto your hand you get a cooler feeling because it evaporates quickly. If you poor water onto your hand it doesn't feel as cool as the alcohol.
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