72 Pantera-65 Tiger-96 Thunderbird 4.6
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From: "Rick in Ca." <rwgushue@gte.net>
To: Multiple recipients of list <detomaso@realbig.com>
Subject: Cooling Subject
Date: Sun, 22 Mar 1998 22:36:07 +0000
Message-ID: <3515D862.691E@gte.net>
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This conversation attached was from another list. Anyone want to
provide explanation, comments etc... I ain't no engineer. Also am
very aware of the KISS principle.
FWIW
Rick in Ca.
1582
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> >With no thermostat your engine should of actually been colder because
of
> >the full flow of water circulating.
> (snip)
> Actually, that's not true. The water circulates too quickly which
doesn't
> allow for enough dwell time for heat transfer. If the hot surfaces
aren't
> in contact with the water long enough to transfer heat, then the engine
> will overheat.
(snip)
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> Picture this: You have a closed system, with a constant amount of
cooling > fluid. If you have a flow of X gph, then any given molecule of
coolant > will be able to remove a certain amount of heat during the time
it is > inside the engine, and flush it to the atmosphere when in the
radiator. > > If you double the flow rate to 2X, then yes - the molecule
will only have > half as much time to absorb from the engine and shunt to
air, but since > the flow is twice as high, it will actually pass through
the loop TWICE > when compared to the lower flow rate. So even if it
only
removes half as > much heat on each pass with the double flow rate, the
net extracted will > still be the same.
(snip)
What non-thermal people don't take into account is
that heat transfer is NOT linear with time. It is an asymptotic
relationship. The rate of heat transfer is dependent on the temperature
difference, dT. dT is like the power or driving force behind the heat
transfer. Leave the coolant in contact with the surface long enough and
no heat transfer occurs. Coolant in contact with the surface twice as
long MAY, at best, give 25% more cooling. Probably not even that much.
So, in your analogy, moving the water through twice as fast produces MUCH
better than twice the heat extraction.
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Comments?
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