MKL said:it should be stressed that you have to create an air flow, so besides a fan you also need air vents on the opposite side of the case (think of PC cases):
cool air----->fan---->stuff to be cooled---->vents---->hot air
or:
hot air<----fan<----stuff to be cooled<----vents<----cool air
A fan blowing air into (or out of) a completely closed case will not do.