The amount of heat generated by the small fans is so low that the air flow direction does not matter.
Someone assumed it blows up or down, but only if installed on a horizontal surface.
I have seen some mounted vertically, so up or down air flow could matter as I would have the air blow away from the TE which on a bench would be up. If blowing in the down direction and wall mounted, the fan would tend to recirculate the warm air exhausted out the bottom of the TE.
SO Greg's response of blowing up to me is the best way to mount the fan!!
PS, I recycle old computer power supply fans into the TE's for myself and friends.
Picture of fan wired to TE and connection. Red is plus 12 volt, black is ground. Some fans have blue wire as ground.
700k hjigh res picture, I posted a link as uninterested dial-up users will not have to download the picture.
Have to tell you guys a funny story, learned about fans and air direction while working at Hewlett Packard.
They were having heat problems in a product and the heat inside was higher than expected.
The conventional wisdom was the "obvious" blow air on the thing that was hot... but it turns out that it just circulated hot air inside, the air just built up. Exhausting the air was not happening. The old time engineers argued "theoretically" you needed to blow as much air on a heat sink as possible. Turns outh that you need very little airflow to transfer most of the heat from a heat sink.
It finally became clear you needed to get the heat out positively, thus an exhaust fan.
The topper was an old xy recorder. The existing fan was inside... the fan was sucking air in from the outside, the heat of the fan was added to the insides. The device ran cooler when the fan was removed!
It was a big deal in the labs, as "common wisdom" at the time was not really founded in the physics of the problem.
OOOOOOOOOOOOOOOOO Snap RJ made a fun fun on me....
HE HE HE watch it buddie i'm on vacation and headed your way to Key West tonight on vacation. my harley was shipped down to miami last week as i am to meet some freinds and we are riding from miami to the keys over the great long bridge for some fun in the sun on Friday.... so you better watch it buddy, im comin rite past you on the way down, and if the weather holds on the way back. i may have to pay you a visit