I can't help with computer fans....
but I decided not to got the computer fan route - instead I used a 12v cig lighter fan for a car. This had three main advantages:
1. It has a guard on it, so you can accidently brush the blades with hoses etc;
2. Its bigger and faster = more wind
3. It has a swivel angle bracket on it, so I can eventually mount it and angle it where I want it
$16 at supercheap.....
I got an onld 12v power supply from a scanner and just hooked it up.
Just another option.
M