Cooling is an issue that cannot be ignored, new components run hotter and hotter.
Good cooling is getting more and more expensive, and quiet cooling adds even
more cost. But a little planning and good design goes a long way. Ducting can
increase the efficiency of air cooling by surprising amounts.
Ducts are mostly used in 2 ways, to fit a larger fan to a small fan mount,
and to direct airflow to give better flow over hot areas.
Rules for Fan Ducting
Reducing ducts make the fan work harder, so ducts that reduce too much are
ineffective and noisy. For example, a 120 to 60mm duct is not recommended. Ducts
tend to be most useful when the area of the wide end is about twice the area
of the smaller end, such as 80 to 60 mm, and 120 to 92mm. Case fan ducts are
most effective when they are straight and unrestricted, any curves or corners
should be as shallow as possible, and the walls of any duct must always be as
smooth as possible, rough edges create turbulence, which slows the air down.
You can put a fan at each end of a duct if it is long and restrictive, but both
fans must be the same CFM rating. This kind of duct is very useful for bringing
fresh outside air into the middle of the case.