Randall's explanation makes sense. For me a simplier answer would be
that with the fan in front of the radiator there is a restriction of
air flow, even if the fan blade is spinning. Behind the radiator the
air restriction occurs after the air has passed over the fins and has
had the designed cooling effect.
Aaron Cropley
71 TR6 (Throttle Body Injection!)
http://www.triumphowners.com/108
Topsham, Maine
-----Original Message-----
From: Randall <tr3driver@comcast.net>
To: Triumphs@autox.team.net
Sent: Sat, 27 Aug 2005 18:17:45 -0700
Subject: RE: TR3 running hot
> O Randall, Imparter of Great Knowledge, please explain to this
unworthy Old
> Airplane and TR3 Guy how putting an electric fan in front or behind
the
> radiator would make a difference in how much air would flow through
the
> radiator? Or did you arrive at this knowledge empirically?
>
> Isn't it rather like putting a resistor in an electric circuit in
front of,
> or behind, the load? The flow would decrease just the same?
Let's see if I can echo the explanation given to me by my high school
physics
teacher ...
The critical difference is that electrons have no mass (well, not
enough to
worry about anyway) and hence go around corners better. Air has
inertia,
meaning it does not like to go around corners, and slows down when it
does.
Once the air has been deflected by hitting the fan blades, it is
turbulent and
moving at an angle relative to the radiator openings.
However, once the air has been through the radiator, it becomes
turbulent
anyway. So upsetting the flow at that point makes less difference.
Or I could be all wet on this ... I just know I've seen evidence of
this on my
Stag and so I believe the effect is real. Of course that means I'm
going to
have trouble when I get the original AC condensor & it's fans fitted,
since they
are configured as pushers. Just have to figure out how to keep it cool
even
with the reduced airflow. I'm thinking a "chin" spoiler is the way to
go ...
BTW, not all cars originally had puller fans ... my 1970 Audi 100LS for
example
had a belt-driven pusher fan from the factory. And a tendency to run
hot at
freeway speeds. In 1971, Audi switched to an electric puller.
Randall
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