Make air cooling device?

[The Coolest]

I have a duct from the case side with a 80mm fan on top of the hole and I was wondering how to cool the air in the duct some more? is it possible in any way?

[The Coolest]

BUMP

[Random Nonsense]

converging duct = increase in velocity + decrease in pressure + decrease in temperature. This isnt very noticeable at the size you are thinking of though, but its the only "free" way of dropping the air temp... only thing is it will heat up again as it exits the duct and the pressure equelises.... it may be ok on a heatsink though, as it probably equelises after exiting the 'sink