Date: Tue, 18 Jul 95 11:23:17 PDT
Sender: Vanagon Mailing List <vanagon@vanagon.com>
From: Al Knoll <alf@hpptc38.rose.hp.com>
Subject: fizzix ?
Scott the busman said
>
Ok It works like this. What happens to the cooling fin when it is cooler
than the air around it? It absorbs heat right. If it's absorbing heat
back from the air it isn't radiating heat into the air right. Thermo
dynamics are wonderfull things but kinda tricky. You want to keep the
flow of heat in one direction and cooling the fins externaly just slows
down their heat radiating ability from the internal heat source. As I
said if you can just pump very humid air around the fins then you would
get the efficiency you want. Putting a water jacket around an air cooled
engine makes it a water cooled engine!
>
Lemme see, you're worrying about the air to fin temp? That's the wrong end
of the dog. The operative thermo interface is the coolant to radiator material
boundary. The higher the delta T at this interface the more heat will cross
the boundary. Don't give a hoot in a rainbarrel about the fin to air trick
it's mousenuts compared to the other transfers going on. Yeppo, the heat
will go from the air to the cool fin but bunkie that is a tiny transient
condition if your coolant is at 80C 'cause the fin will absorb one hell of a
lot more Q from the coolant than it will from the ambient. Now back to
keeping that delta T high by cooling the radiator down to as cold as you can
get it. Frinstance if the fin is at 20C the ambient is at 35C (damn hot day)
and the coolant is at 90C which way do you think the heat will go referencing
the coolant? Gotta see the grand scale or the micro features will confuse
even the most diligent. Transients are basically meaningless in the overall
Q transfer in steady state. The coolant doesn't know how hot the air is it
only knows how cold the radiator material is. Insofar as dumping Q that's
all that matters.
--
___ / __ __/ ____/ Al Knoll HP Performance Technology /
/ / / / Center Roseville, CA, USA 95747 /
_____/ / / 916.785.5317 (Telnet 785-5317) /
/ / / email: alf@hpptc38.rose.hp.com /
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