cooling fan curious; the solution

[don spence <dspence@oanet.com>]

In front the fan directly obstructs airflow to the "hidden" portions of 
the core, say 30% as an example. In other words the fan blades prevent 
the air from flowing through part of the core.
With the fan Behind, the full 100% of the core is exposed to the 
incoming air. Exit flow is hampered but not blocked by the fan in 
behind as the air can flow around the blades etc. to exit. so maybe 
a10% reduction in efficiency when the fan is "parked".
All numbers are purely for the purpose of illustration.