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ducts & fan location..?

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Jun 29, 2001
Reality, USA
I'm currently experimenting with some small ducts. (to read about it, click here)

Anyway, I was wondering about the best fan location in a duct. Is it easier for a fan to push air through a duct or pull air through a duct? Ideally, for a long duct, you would probably want fans on each end and fans along the length of the duct pulling and pushing air. But, what about a short duct where you are limited to one fan? Would it matter if the duct is for exhaust or intake? For example, if you had a duct located near the heatsink to remove the hot air, should the fan be located on the inside of the duct to push air out? Or should the fan be located on the outside near the case to pull the air through the duct? Or, for a third option, would it be better to have the fan in the center of the duct? Maybe it all depends on the environment, type of duct, etc.

Has anyone ever done tests on this type of stuff? Any HVAC experts know the answers?
My main system runs with a duct. I've got a plastic tube that people put in speaker boxes for their cars mounted on the side of my case, I hot glued it in so there are no screw heads or nuts or bolts showing. The tube has a nice finish on it, looks like a professional modified my case. The tube goes straight to the fan on the CPU's heat sink. The fan is in its original position sucking air in and blowing it onto the heat sink. I've dropped my CPU temperatures by 6 degrees celcius by doing it this way. I think that its better to have the fan at the destination site sucking air in than if you have it at the other end blowing air into the tube because if there is a gap halfway through then at least you're still getting full air pressure at the destination, even if some of it isn't coming from the prefered source. I'm not sure how scientific that logic is but 6c is results enough for me. I will suggest that you keep the number of bends in the tube to a minimum and keep the length short. It may be easier to hide an air hole that comes out the back of the case instead of the side but a straight, short tube from case side to CPU will be more efficient.