So I was over at one of my fathers friends house today replacing his case fans with blue ones. when I was done I had a few fans left over and one of them caught his attrition. I replaced his 80mm fan with a 92 mm fan ( because that what he had the holes for on his case.) and he was wondering if I could mound the 80mm on the outside of the case. now I'm sure that you can do that, and it mite even hinder the air flow, but he wanted me to look in to it anyway. so thats my dumb question.
Do you mean mounting a fan on the outside of the case up against a fan mounted on the inside of the case so that the only thing separating them is a case panel? If so, it is a very bad idea. The problem is that the fans will never run in sync. That's impossible to do. The lack of synchronization and the air turbulence would actually produce terrible airflow. One case fan produces better air flow than two fans next to each other. To produce the proper wind tunnel effect two identical fans would have to be at least 1.5 inches apart.
thats what i thought ( i think we covered this last year in my A+ cert class in college) be he wanted me to double check. also he has a CPU duct much like this case. case he also said about mounting it on the outside. but i would have to buy screws and a fan filter. i think it a waste and the filter mite hinder the fan duct. but the man's a business man and he doesn't want to waste anything. and in him being like that i told him i will look for all options.