Paul Lamar wrote:

Come to think of it I did not see any -4 bleeds on Power Sports engine
from the front of the block (PSRU end) to the pressure can.
Perhaps when they changed the rad to a single pass from a double
pass they inadvertently got all the air out of the system and it started
cooling better. Things like that can really fool you.

Come to thing of it if you don't have a bleed like this the rotary engine will
build its own [vapor] pocket in this part of the engine block while the
airplane is in a climb . That is because  the water inlet and
outlet to the block are located no higher than the rest of
the block. When it is tilted up in a climb it is generating
a [vapor] pocket in the front of the block due to normal nucleate
boiling. Not to mention an out and out boiling steam pocket.

Russell Kent responded:

[ Nitpick mode = ON ]
Paul,
True nucleate boiling won't cause an "air pocket".  Actually, nothing but
entrailed air can cause an air pocket.  It is possible to have full-tilt boiling
cause a steam pocket, however.  Of course, if you have full-tilt boiling (not
nucleate), then you're seconds away from much bigger issues...

But you are correct in stating that the highest point in the block needs to have a
bleed line.

Paul responded:

I think Heinz Heisler disagrees with you. He calls it "vapor" in
them tiny bubbles and they go to the air space at
the top of the system.

I don't have Heisler's "Advanced Engine Technology".  I think I mis-understood how he
was using the term "nucleate boiling".  I believed this term to describe the heat
transfer mechanism whereby small amounts of coolant at the metal surface flash into
vapor, then depart the surface and quickly re-condense in the coolant. Given that they
quickly re-condense, how can they migrate to the high point of the engine and form a
steam pocket?  Re-reading Heisler, I see that he uses "nucleate boiling" all the way to
film boiling.  I guess his definition is correct: nucleation sites are still involved
the whole way to film boiling.

But there are two distinct sub-phases to nucleate boiling, divided vaguely where the
vapor re-condenses rapidly after departing the surface (before), and where the vapor
remains a bubble long after departing the surface (after).  We want the former since
enormous amounts of heat energy are transferred (i.e. high cooling system efficiency);
we want to stay away from the latter, as it allows steam pockets to form, which are just
as bad as stable films (very bad) because they allow localized hot spots to occur.

BTW, have you seen this paper about adding soap to coolant?
http://www-heat.uta.edu/publications/1995c3.html

Russell Kent

That is probably what Water Wetter is :-)

Paul Lamar
 
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