irampil@notes.cc.sunysb.edu a crit :
>
> As fluids approach their boiling
> point they start to nucleate small bubbles (look at a pot of
> near-boiling water). These bubbles insulate the walls of the coolant
> path from
> efficient heat transfer from the metal to the liquid.
>
Ira and all,
I'm afraid it is the other way round : nucleate boiling help reject
tremendous amounts of heat from the engine.
Phase change from liquid to vapor absorbs several hundred times more
heat than just raising the coolant temperature just another degree, and
helps convection. This was clearly established by NACA researchers
during the '40s.
See Contrails
http://contrails.free.fr/engine_liquide_refroid.php (only in French at
the moment)
Scroll down to the NACA reports.
Also some basic info at :
http://www.tpub.com/content/doe/h1012v2/css/h1012v2_62.htm
Please note that we are speaking of nucleate boiling, and not of the
"boiling crisis", which is the transition from nucleate to "film
boiling". It is film boiling which tends to isolate the hot walls from
the coolant.
Best regards,
Gilles
http://contrails.free.fr
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