Date:         18 Jul 1995 12:24:39 -0700
Sender:       Vanagon Mailing List <vanagon@vanagon.com>
From:         "Harvey Chao" <Harvey_Chao@smtp.svl.trw.com>
Subject:      Re: fizzix ?

                      RE>>fizzix ?                                 7/18/95

As an EE  (long ago) who was forced to take a manditory course in
thermodynamics that I never partilcularly appreciated, and If I remember
enought thermo (take heat in thermo we used to say)  -  I concur with the
person (AI?) who talked about heat transfers  in the following vein:

o  Coolant temp  is on the order of 200 F.
o  Radiator sheet metal is exposed to local ambient, less than 200 F
o  Xth  law of thermo says heat transfer is from high to low => coolant
transfers heat to radiator sheet metal.
o  yth  law of thermo says heat transfer quantity is related to delta temp
across boundry, therefore the cooler the radiator sheet metal is relative to
the coolant, the higher the transfer rate.
o  If you cool the radiator  sheet metal to  a lower temp, it will transfer
heat from the coolant at a faster rate/higher quantity because of the greater
delta t
o  Therefore:  If you throw cool water at the radiator sheet metal (or for
that matter blow cold are at it instead of local ambient), and assume that the
sheet metal temperature approaches the temp of the coolant on the other
(inside) side, about 200 F, the water will absorb heat from the external side
of the radiator.  This will:
  -  Heat the cool water 
  -  Hasten the evaporation of the applied cool water which because of the
specific heat of evaporation (change of state) absorbes even more heat
  - Remove heat from the outside of the radiator
  - Lower the temperature of the outside of the radiator
  - Increase the delta t between the cooled outside of the radiator resulting
in increased transfer of heat from the coolant to the radiator to the
evaporating water to the external environment.

Regarding the demonstration described with an acutal running engine, I would
be inclined to accept the explation put forth related to the thermostat being
so located that it too was cooled with the radiator, closing in response and
hence the climb in engine temp.