<< Take another look at that chart I uploaded David. You will not normally
 notice nucleate boiling. I think the point you are referring to is
 where it transitions to "unstable film boiling". I think that is the
 classic radiator boiling over point we have all experienced.

 I don't think anybody is advocating allowing the coolant to do that.
 I think Jeff is referring to the amount of heat transferred during
 the nucleate boiling stage. Note; that nucleate starts at only a
 10 degree C difference in coolant temp to wall temp. As the temp
 difference reaches 50 degrees the rate of heat transferred
 is 100 times higher and we have still not reached unstable film boiling. >>

Actually that chart is over-simplified because the temperature difference
that matters is the difference between wall temp and boiling temp of the
fluid.  You will have nucleate boiing with or without glycol.  The delta T of
wall vs boil will be similar.  By raising the boiling point, the wall temp
follows.  That's why I made the previous comments.  That's why the pure
glycol systems use  Propylene glycol instead of ethylene glycol...the boiling
point is about 30 deg less for propylene IIRC.

Jeff Spitzer

Don't you mean "30 deg less for ethylene"?

Paul Lamar
 
The AirCraft Rotary Engine NewsLetter.              Powered by Linux.

http://home.earthlink.net/~rotaryeng/            http://www.linux.org