Re: Bob Myers input requested, RE: more heat!

[Robert Myers <rmyers@inetone.net>]

At 10:55 AM 1/3/99 -0800, Avi Meron wrote:
>Fred,
>Correct me if I am wrong but the best heat transfer is 100% water. 50/50
>mix, is a bit of a compromise, but acceptable. If I remember my literature
>correct a 20% mixture supposes to be best for corrosion resistance and
>increasing of the boiling point. Of course a low mixture is not a good idea
>for cold weather.
>Bob could you please put your input in this issue?

Sorry, I have no specific data at hand.  In general the statements above
are correct.  Most materials have a lower heat capacity (specific heat,
cal/gram-degree) than water.  Therefore a coolant higher in water content
(high specific heat) should be capable of absorbing more heat than a
coolant high in ethylene glycol (lower specific heat).  

Calories absorbed = deltaT * mass * specific heat

The exact same equation will do for btu or calories or Joules.  They will
differ only in the units of the specific heat term as is consistent with
the other terms.

Lowered freezing point of the coolant will probably pass through a minimum.
 Coolant either more or less concentrated than this particular mixture is
likely to freeze at a higher temperature.  Exactly what the composition of
this specific mixture is unknown to me.  (Perhaps the 70:30 ethylene
glycol:water mixture?)  Surely someone will have ready access to the phase
diagram for ethylene glycol-water.  If so the composition and freezing
temperature at than comp[osition may be ready directly from the phase diagram.

Corrosion resistance (in a specific cooling system) depends more upon the
"corrosion fighting additives" in the coolant not the water or the ethylene
glycol.  In *very* loose terms, their main function is to scavenge oxygen
from the system.  As, over time, more oxygen is absorbed the capacity for
the corrosion fighters is diminished.  This necessitates the periodic
flush/refill for the cooling system.

HTH, Avi


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   Bob
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