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RBMODS.COM |
Understanding Case Fans
Considerations that Help You Improve Cooling Performance
by Fantronic.com
Fan Dimensions
Case Fans are available in a wide variety of sizes. There are small 30mm fans
and 40mm fans such as you’d find in a laptop or car audio amplifier, and there
are larger 80mm fans and 40mm fans which are commonly used for cooling computer
cases. All case fans have one thing in common – their outer dimensions are
square, so if a fan is referred to as a 120mm fan, the 120mm is the measure of
the outer length of the fan’s square case. Case fans vary in depth, which is why
you commonly see notations such as “120x25mm Fans” or “40x10mm fans”. The number
following the “x” is referring to the fan’s depth. As a general rule, selecting
the largest fan that fits your application, both in terms of length and depth,
will result in optimal cooling with reduced noise.
Fan Blade Design
There are a lot of misconceptions out there about how the number of fan blades
and their shape affects a case fan’s cooling abilities. Some case fans have as
many as 10 blades, while others have only 3 blades. As more blades are added
to a case fan of a given size, the width of the blades decreases. The narrower
blades can operate at higher speeds without making as much noise, but contrary
to common belief – more fan blades reduce the fan’s overall efficiency. This is
one reason a silent fan is so quiet, even if it is operating at the same RPM as
a louder fan. On the other hand, a case fan with only 3 blades will sound loud and choppy as the
huge blades slice through the air, but the larger blades move more air per
revolution and have a higher overall efficiency. Fan blades are rarely a
consideration for overclockers, but in an application where flow efficiency
outweighs noise levels, a fan with fewer blades will get the job done better.
Airflow and Noise Levels
Fan noise increases proportionally with air flow, and the noise level to air
flow ratio is something that must be considered when the application will be
used in close proximity to yourself or other people. 80mm fans used to be
the most popular size, but in the past few years, people have made more use
of 120mm fans due to their ability to move more air at drastically lower noise
levels. There are some instances where bigger is not better, such as with CPU
cooling. The reason is that the majority of the airflow generated by a fan
comes from its outer edges, and the center part has a much lower flow rate.
The area around the fan’s motor hub has zero airflow. Whenever directional
cooling is required, it is typically better to use a smaller 80mm fan or
even a 92mm fan, even if the noise levels are greater.
Static Air Pressure
The relationship between a PC fan and its static air pressure rating is
a murky topic for many. To simplify and make it easier to understand, a fan
that has a higher air pressure rating can maintain its rated air flow at
higher resistances. A resistance for a fan would be something like a
radiator or having to pull or push air through a fan filter (static
pressure is not an issue with fan grills, which offer no appreciable flow
resistance). Water cooling is a popular application where you need to
consider a case fan’s static air pressure rating. If the pressure rating
of the fan is too low, the fan will not be able to maintain an adequate
air flow through the resistance imposed by the radiator. Yate Loon fans
are a great example of case fans that have high static air pressure, yet
are affordably priced. If you plan to use a foam fan filter, you will
probably want a fan with a higher static pressure rating. Mesh Fan Filters
offer much better airflow but do not filter as well.
Intake Fan or Exhaust Fan
A lot of PC enthusiasts opt to use both intake and exhaust fans to cool
their case, and they refer to that configuration as a push-pull setup.
When it comes to cooling a PC case effectively and without excessive noise,
using one or more high mounted exhaust fans tends to work the best. The
hot air from the components in the cause will rise, and having the fans
mounted in the upper-rear of the case will yield the most efficient flow
of air. Most modern PC cases have front intake fans as well – the front fans are
not so much for lowering the case’s internal temperature, rather they are
directed to cool hard drives. Intake fans can help improve overall case
cooling, however it is possible to achieve fully optimal cooling with
properly placed exhaust fans. A single 120mm fan works great, or on smaller
cases you can use two low noise 80mm fans such as the Panaflo fan or
Enermax Enlobal fan. If you
are building a rackmount server or need powerful cooling in a tight space,
blower fans may be the answer.
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