I got to thinking about ways to reduce or eliminate unwanted dust from being drawn into a PC case via intake fans. Thus, I would like to proffer a solution that may or may not be well-known or understood in regards to a clean PC operating environment. It has to deal with positive air pressure flow within a PC case.
Sometimes, more is not better. Having oodles of powerful intake and exhaust fans in a case are not going to keep dust from entering a system, and oftentimes, they do a poor job in cooling the system anyway. Simply throwing fans at a dust/cooling problem isn't going to solve it, and more logical and effective methods will need to be incorporated to truly keep the inside of a PC case both clean and cool.
With this in mind, for those serious about clean PC's, you may want to look into the use of positive air pressure in a PC case. Positive air pressure simply means that more intake air is forced into the chassis than air is being exhausted. This might sound contradictory at first, but if you think through it, it will make sense.
It goes something like this: If there is more air entering the chassis than exiting, you have a positive air pressure environment. This happens when your fans are intaking more air than being exhausted. This surplus of air will push air out of the case through the many cracks inside a chassis. This positive air pressure essentially prevents dust buildup where there are no fans. I'm sure everyone has experienced dust buildup in places such as the CD/DVD bays or the PCI slot area. These areas and others are notorious for dust build up where fans are not used.
However, if you have more air being exhausted than taken in, you have a negative air pressure environment. This happens when your fans are exhausting more air than being taken in. What occurs here is dirty, unfiltered air is being drawn through the cracks within an enclosure. This condition creates dust buildup within an enclosure very quickly. The problem is only exacerbated because this unfiltered air cannot be contained or filtered in any way.
If you intend to use a positive air pressure design in your chassis, using fans that offer high static pressure such as Silverstone's excellent Air Penetrator series (http://www.silverstonetek.com/product.php?pid=257
) will help tremendously in this regard. These types of fans have higher mmH20 than most, and can increase the positive pressure inside a chassis considerably while keeping operating temperatures in check at the same time.
The one constraint when employing positive air pressure within a PC enclosure is that the intake fans MUST have good filters installed on them. This cannot be stressed enough! 3M filters meant for HVAC systems that are then cut to size are an extremely good choice and what I use in my own systems.
For more information concerning positive air pressure versus negative air pressure, check out Silverstone's TechTalk link (http://www.silverstonetek.com/techtalk_cont.php?area=en&tid=wh_positive
). It has a nifty animation showing how both positive and negative air pressure interact in a typical PC enclosure.
If any of this was helpful to anyone, please feel free to chime in! Thoughts and comments are always welcome. Thanks!