Cooling by evaporation.

[steve-V8s]

I have a radiator and wish to cool the gas passing through it. Sucking air through it helps, misting it with water helps even more presumably because the water needs to acquire energy to evaporate which it takes from the radiator. If I add some isoproponal alcohol to the water the cooling effect seems better.

Questions are :-

Is the improved cooling with added alcohol directly related to the water alcohol ratio.

Would misting with chilled water add to or hinder the cooling effect as it may have to hang around longer and probably dribble away before it could evaporate.

[Huff]

You've got several things going on: three things to think about/ further reading

https://en.wikipedia.org/wiki/Newton%27s_law_of_co...

Latent heat of evaporation - this is pretty low for alcohol - but so is the temperature at which it vaporises! IOW - you'll use a lot of alchol, but while it can absorb the heat flux you need to get rid of - it will hold temps down towards that temp pretty well.

Specific heat capacity - water has an enormous specific heat capacity, also rather large latent heat of evaporation. but at a rather higher temp.
So cooled water works first in taking a lot of energy to change temperature, then - if you are getting hot enough to lose it as vapour - considerable absorption to evaporate it / small mass flow of water

It's likely you can pretty much look-up a mix to do what you want. Or just throw water at it, to arbitrary effect.

[rxe]

It all depends what temperature the radiator is running at.

If around 100C or more, I would be chucking water at it. If you have loads of water, then you are better off with direct cooling. If you don’t have much water, then misting is so that the water is fully evaporated on the trailing edge is most efficient.

If it is at 50C, then alcohol will be better, but you are going to use a lot of alcohol. Again, if you have loads of water, then direct cooling will be the best approach - dunk the rad in the water.

Also do bear in mind that the flash point for pure alcohol is below room temperature. If you’re vapourising large quantities of alcohol, you’re effectively making a fuel/air explosive.

[steve-V8s]

In an ideal world the rad itself will not get significantly above ambient. What I was perhaps hoping to determine was if a water alcohol mix would be more effective than just water. I don't have a large amount of water available but plenty of air and a fan to suck it through.

[ATG]

I'm guessing that the benefit you'll get from alcohol's lower boiling point means it'll be a more effective coolant to spray on a radiator running at room temp than water, in spite of water having a higher specific heat capacity and greater latent heat of vapourisation. The alcohol will evaporate more readily. Compared to water, you'll have way more of the liquid alcohol molecules straying into the bit of the Boltzmann curve where they boil even though the average temp is below the boiling point. Once boiled, the molecule pisses off, so its heat can't get transferred back into the rest of the alcohol, hence the "magic" effect of evaporation allowing a surface to drop below ambient temp. Think how cold your hands feels if you wet it with meths compared to water, even if both liquids are at room temp. The meths is closer to its boiling temp and evaporates much more readily, and you can feel that carrying loads of heat out of your hand.

[hairy v]

Hi OP, why don't you go for a thermally driven cooling system e.g. Li-Br or Ammonia -water

Admittedly this is new to me, but looks to have a lot of potential:

https://www.semanticscholar.org/paper/THERMALLY-DR...