# Thermal Conductivity of Glycol v Water



## RIPPERTON (Jan 26, 2010)

Just got 40l of Glycol from a friend who works at RAAF in QLD.
He says this stuff came out of a FA-18 and is about 5 years old.
Im planning on using this to cool my Barina motor so need something that is non conductive and cools at least as well as straight tap water.
First I put an Ohm meter across it and it showed 3 megaOhms after 30 seconds ( kept on climbing) compared to tap water, 60 kilaOhms after 30 seconds.
Then I got an old aluminium pot and put 30mm of tap water in it, then I got a smaller steel bowl and put 10mm of tap water in it an floated it in the larger pot. Starting off at 13 degrees C (its winter here) the water / water combo climbed about 10C per minute and took 8 minutes to boil leaving the water in the small bowl at 80C.
Then cooled all the stuff back to room temp and put 30mm of glycol in the aluminium pot and repeated the experiment.
Starting at 12C the glycol boiled in 6 minutes and had the bowl water at 80C.


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## electro wrks (Mar 5, 2012)

Isn't deionized or distilled water less electrically conductive than regular tap water and a better choice, in this application, for cooling?


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## kennybobby (Aug 10, 2012)

Will the system be at ambient or pressurized--the boiling point changes with pressure and may factor in the coolant performance.


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## Duncan (Dec 8, 2008)

Hi Ripperton
Tap water is actually a nearly miraculous coolant
Good conductivity, great specific heat

"_Pure ethylene glycol has a specific heat capacity about one half that of water_"

Your Glycol mix will not cool as well as pure water
The other ingredients are for corrosion control 
And it's those chemicals "wearing out" that normally mean you have to change your coolant


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## samwichse (Jan 28, 2012)

I really hope you'll use distilled water instead of tap in the final product.


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## RIPPERTON (Jan 26, 2010)

samwichse said:


> I really hope you'll use distilled water instead of tap in the final product.


Distilled water is almost a perfect non conductor until you use it.
As soon as it gets poured out of its container into something dirty like a radiator, it gets contaminated like tap water and becomes a conductor.

Kenny Bobby, the system is ambient as it will never produce enough heat to boil water as long as it is running through the radiator.


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## Duncan (Dec 8, 2008)

RIPPERTON said:


> Distilled water is almost a perfect non conductor until you use it.
> As soon as it gets poured out of its container into something dirty like a radiator, it gets contaminated like tap water and becomes a conductor.


Unfortunately true!
A mixture of Ethylene Glycol and water will (I think) just behave like water as far as conductivity is concerned

Pure Ethylene Glycol will be a very poor conductor (of electricity) but also a poor coolant

Which will not be a problem if your system has a lot of excess cooling capacity


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## onegreenev (May 18, 2012)

samwichse said:


> I really hope you'll use distilled water instead of tap in the final product.


If I recall correctly distilled water in a radiator is to help prevent mineral buildup so you don't clog your cooling system.


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## bigmotherwhale (Apr 15, 2011)

the most important factor to consider would be corrosion, maybe more important than specific heat capacity, most cooling system failures happen because of blockages and the insulation that oxides cause. 

the best coolant i have come across is this stuff http://www.evanscoolants.co.uk/
its water free


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## Duncan (Dec 8, 2008)

bigmotherwhale said:


> the most important factor to consider would be corrosion, maybe more important than specific heat capacity, most cooling system failures happen because of blockages and the insulation that oxides cause.
> 
> the best coolant i have come across is this stuff http://www.evanscoolants.co.uk/
> its water free


Interesting site
Trouble is they don't mention the fact that nothing has the heat capacity of water
So any other liquid will have to flow at about twice the rate of water to achieve the same heat dissipation

If your cooling system has plenty of spare capacity then one of these fluids could be an improvement
But if you don't have a lot of excess capacity then it's overheat city


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## bigmotherwhale (Apr 15, 2011)

yes i agree, but i would tend to think that if you design a system around one of these fluids it would be better in the long run than using water based design, just because you can have direct contact between the fluid and the metal without any surface coating or the use of low conductivity metals like stainless steel which are also heavy, i would say heat transfer is more important than heat capacity,
the other advantage is that once the system is set up there is no degradation like a water based system, biological factors are not a concern either, and toxicity is a a big bonus point.

on a side note when i used to run water cooling in my pc, i ended up running pure glycol, diluted glycol would gum up the system and cpu temperatures would slowly climb, the nice shiny cillit bang cleaned copper would go dull and corroded despite the corrosion inhibitors and you would be surprised what can live inside a water cooling loop!

i noticed no differences in CPU temperatures between water glycol and pure glycol on a clean system. 

most industrial coolants are 95%+ glycol based


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## Moltenmetal (Mar 20, 2014)

The trouble with ethylene glycol - water coolant mixtures like Prestone etc. is that a) they're loaded with antioxidants and corrosion inhibitors, all of which are electrical conductors and b) it is much more viscous than water. To remove heat in a flowing (forced convection) system, the heat capacity and thermal conductivity matter a little and the viscosity, which directly affects the Reynolds number, matters a lot. The thermal conductivity and heat capacity of glycol water mixtures are close enough to that of water, but the viscosity is much higher.

As soon as you add oxygenated deionized or distiller water to a mixed metal system like a water coolant radiator, your water will become conductivee as a result of contamination by metal ions due to corrosion. To reduce the amount of conductivity buildup, boil the water or pull a vacuum on it to degas it, then seal it up in the system and don't admit fresh oxygen. Deionized water is only an aggressive corrodent when it is oxygenated. The trouble is, a little corrosion itself may not matter much, but the conductivity of the ions may be enough to cause trouble.


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## bigmotherwhale (Apr 15, 2011)

Moltenmetal said:


> The trouble with ethylene glycol - water coolant mixtures like Prestone etc. is that a) they're loaded with antioxidants and corrosion inhibitors, all of which are electrical conductors and b) it is much more viscous than water. To remove heat in a flowing (forced convection) system, the heat capacity and thermal conductivity matter a little and the viscosity, which directly affects the Reynolds number, matters a lot. The thermal conductivity and heat capacity of glycol water mixtures are close enough to that of water, but the viscosity is much higher.
> .


i agree, this is why the Evans waterless coolant results in higher engine temps, its much more viscous, which is unfortunate.


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## Duncan (Dec 8, 2008)

Hi Molten
I agree the higher viscosity is a problem - but I disagree about the lower heat capacity,

If you are using 70% water then you heat capacity is going to be similar,
But if you are using a waterless system then your heat capacity will be half that of water
meaning that you need to shift twice as much of the more viscous liquid

Water is amazing stuff - not like any other liquid at all


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## Moltenmetal (Mar 20, 2014)

We were talking about glycol- water mixtures Duncan. If you're talking about a waterless system then you're right- actually you have problems with all three thermophysical properties.


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