Date:         Tue, 18 Jul 95 16:16:40 PDT
Sender:       Vanagon Mailing List <vanagon@vanagon.com>
From:         Dave Kautz <dkautz@hpsidms1.sid.hp.com>
Subject:      Cooling

 One last gasp on this cooling thread.

 If you think about it, water cooled engines are actually air cooled, in that
 that's where the heat energy ends up. The water is being used as a conductor
 to carry the waste heat of combustion away from areas of intense local 
 heat to a more convenient spot for a large surface area water to air
 heat exchanger. 

 The heat exchanger <radiator> works via heat movement from the hotter
 material on one side <water/antifreeze> to the cooler material <air> on the
 other side. As the temperatures approach each other, less heat flows. 

 In the aforementioned experiment where the radiator was dosed with lots of
 liquid water, this may have decreased the efficiency of the radiator as
 a heat exchanger. The water prevented air from circulating through it's 
 side of the heat exchange circuit. As the water on the air side became hotter
 and hotter, less and less heat was removed from the engine. Not unlike a
 radiator in stopped traffic with no fan.

 Some evaporative cooling of this water was going on, no doubt, but the rate
 at which it was occurring must have been to slow to compensate for the 
 impairment in heat transfer efficiency normally achieved by the radiator.

 Picture immersing the entire radiator in a large tub of water. Probably cools
 real good when you first put it in, but as the water in the tub heats up
 towards the same temperature of the water inside the radiator the heat 
 exchanger gets less and less effective. Pretty soon the water inside the 
 radiator and the water in the tank will be at close to the same temperature,
 your heat exchanger is now worthless and the only cooling you will get is
 the evaporative cooling off the top of the water in the tank  and whatever
 heat is coming off the tank walls. This is taking the radiator experiment
 to a logical extreme but maybe it gets easier to understand this way. 
 Basically, all I'm trying to say is that the water on outside of the 
 radiator decreased the efficiency of the heat exchanger the same way that
 blocking airflow with a piece of plastic would <or that accumulations of
 oil and dirt do on those air cooled heads <VW content!>>.

 'Nuff said, I guess. Sorry to waste time.


 Dave
 n