Gilles
I think you have pointed out the difference between theory and testing.
Theory should be used to explain observed facts not the other way round.
The latent heat of vaporization of water is 525 calories per gram,
whereas it only takes one calory to raise the temperature from 99 deg.
to 100, boiling point. It won't boil until it gets the other 524 calories.
Thanks for your clear thinking. It made me think again
Graham
Gilles Thesee wrote:
> <Gilles.Thesee@ac-grenoble.fr>
>
> 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
>
>
>
>
>
>
--
Graham Singleton
Tel: +441629820187
Mob: +447739582005
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