This node is about air flow in Personal Computers a topic long neglected by mainstream PC companies. With increasing power consumption of core components (CPU, power supply, graphic chipset, northbridge chip) this constantly becomes more important.
Case fans are used to direct cold air into and for sucking hot air out of the PC case. For purposes of cooling, the higher the temperature difference between components and the cooling air the better. This is why it is preferrable to create slight negative pressure with fans directed out rather than blowing air in. Otherwise the trapped air will either just circulate or accumulate in the top of the case and heat it up. Worst place for this is of course under the power supply near the hottest components CPU and graphics processor. A good starting place for creating proper suction is a power supply with 2 fans, one directed out as usual at the top of the tower and another at the bottom of the power supply sucking off the hot air from the CPU and graphics adaptor.
There are quite usable double-fan power supplies available for building a quiet PC using Pabst fans. Just make sure you have enough power for the CPU type / speed you are using. Next you could install a case fan underneath the power supply to suck out even more hot air. Finally make sure you have a useable air inlet at the opposite side of the case, which is on the bottom at the front of the tower, this is where you can also install an air filter.
One should avoid anything obstructing the air flow, including using ribbon cables. You can get rounded cables instead.
You can also improve cooling by using a flexible air shaft leading from the outside, usually bottom of the case, directly to the CPU cooler. Provided there is sufficient negative pressure in the case, the cooler room air will automatically be sucked through the pipe.
Then the cooler can use fresh, unheated air and build up of hot air will be avoided. I had a link for a manufacturer that got lost, if anybody could supply this I would be grateful; this one is actually hard to find, that's why I think it would be useful.
Air flow is also a hot topic in the recording studio where there is quite a bit of electrical equipment. If you are using modules in a rack, always put the hottest equipment on the top, as this is the place which can dispense the hot air most quickly and it does not have to pass through (over) all the other equipment. And, to state the obvious, if its self built case make sure to perforate the top.
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