Bill Freeman wrote:

Paul,
Were you disagreeing with my comments on boiling and a
higher boiling temp coolant?  Not sure what to make of your
comment.   I *did* look at the piece you sent to me privately
before you posted it.   I generally agree with your source
(Heinz), I just now saw that the heat transfer increases by
TWO orders of magnitude as nucleat boiling comes on
line rather than "just" one order of magnitude.  I think we are
in general agreement on this, except I contest your comment
on steam creating an "air pocket".   :-)   Russell agrees with
me, but as he says - a nit, not worth much picking.  The only
part of Heinz that I question is the continued existence of the
steam bubbles for large distances away from the hot spot.
I would expect the cooler (sub boiling temp) turbulant gross coolant
would quickly condense the bubbles unless the liquid coolant
was extremely close to the boiling temp itself.  Typical auto coolant
temps are 200-220F and under pressure the EG/water
has something like a 260F boiling temp.  Steam bubbles should
quickly condense when washed into the turbulent stream of
liquid coolant.  Heinz says they stay intact until they reach the
surface in a coolant tank.  The conditions that form the bubble
are only controlled by temp and press, not by any free surface
of trapped air that might exist somewhere in the engine.  Bubbles
would rise, of course, but would not necessarily seek out some
air pocket, whether in the block or in a coolant expansion tank-
just a high point.  And remember I stipulated adequate coolant
flow rates and radiator size plus airflow being adequate.

Bill

 
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