/tryingto avoid a trick question.
Can to please clarify your post a bit better?
You can mount case fans horizontally (blowhole on a V3 for instance) so they pull air out the top of a case, or vertically (on the front, side, or rear).
Air travels through the fan ...
http://en.wikipedia.org/wiki/Computer_fan
Some centrifugal fans have also been used:
http://en.wikipedia.org/wiki/Centrifugal_fan
Hope this helps.