Much SNIP<

So I agree, the system needs to be balanced, and we absolutely need a

good

enough heat transfer to the air - the final step.  I think that my

point

was

that
nucleate boiling is mandatory to get a high enough heat transfer from

the

very

hot parts of the engine to the fluid, since phase change heat

transfer is

about

3 orders of magnitude higher than conduction.  Regardless of the size

of

the

radiator, if there were no nucleate boiling, the engine would

overheat

locally.

Higher k helps on radiator size, and cannot be ignored, but is not a

show

stopper if it varies moderately.

I think we are really agreeing about 97% here, with a slight

disagreement

on

semantics and "why", both of which are not worth much more effort.

Thanks for the good commentary.  Excellent points.

Bill

Actually we agree 100%.  I absolutely agree on the need for nucleate

boiling

at the hot spots.

There have been proponents on the list asking about other fluids (oils?)

that

had higher boiling points, apparently worrying about boilover.  These

heat

transfer oils, used for industrial processes requiring high temperatures
DON'T make good coolants for engines. Some numbers:

Water  k= 0.392  viscosity = 0.0123  Cp = 1.0  (best)
50/50 WG  0.260              0.0287       0.87 (next best)
glycol    0.135              0.086        0.64

Therminol 0.0753             0.1067       0.52 (Much worse, k= 1/5 that

of

water, viscosity = 8.5x water, and heat capacity ~1/2 that of water.

Clearly water is best but needs antifreeze because of low temperature
exposure, so some mix of water/glycol is what we use.

Bill

marc mularz wrote:

Hello all:
Well its been two weeks of the iron nail sitting in water/ glycol mixtures
and here are the results.
A.  The iron nail in pure distilled water (redundant) is severely corroded.
This began within SIX hours of being placed in the test tube !!!  As I
expected, its not the ions in the water that cause the corrosion, it's the
oxygen dissolved in the water.

B.  The nails placed in the water glycol mixtures show no corrosion that is
visible to the un-aided eye, even in as low as a 10 % solution.  I was
suprised that this low concentration of anti-freeze contained this degree of
anti-corrosive properties.

>From this, I would think that those who want to run a lower than 50/50 ratio
of water/glycol would only have to be concerned with the freezing and
boiling characteristics of their mixture.  OTOH I don't believe that a
difference of 0.12 in the specific heats of pure water vs. 50/50 is
significant in terms of the heat that must be removed by the cooling system.
  Hope this info helps.
Take care, Marc M
 

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