> Why does a fan block the airflow more when it is in front of the
> radiator than when it is behind the radiator?
I don't know, but my guess is that it has to do with what happens when the
air is deflected by the fan blades. With the fan behind the radiator, the
air spills out to the sides of the blades and eventually finds it's way
through. With the fan in front, the air is more apt to spill out to the
sides and bottom and miss the radiator entirely. The extra turbulence right
in front of the fins can't be good for airflow either. After it's through
the fins, it's going to be turbulent anyway, so adding more doesn't make
much difference.
As a thought experiment, think of a bunch of pipes bundled together and
you're squirting water at them with a hose. If the water hits the end of
the pipes squarely, then it doesn't spread much and you get maximum flow
through each of the pipes being hit. If you angle the water though, it
spreads out over more pipes, and there is less flow per pipe. But having
something deflect the water after it runs out of the pipes has little or no
effect.
Randall
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