CPU FANS and CPU FAN SIZES
What size CPU Fan is Better for you CPU
If you have the space, always go with a larger fan.
Larger fans have the following advantages over smaller fans:
1) Higher resistance to static back pressure - in other words, if you have a highly resistive case air flow, a larger fan will more easily pull the pressure, because the blade chord (the width of the blade, essentially) is bigger.
2) CFM at 0" H2O column tells you jack about how the fan will perform in a real application. You need a CFM vs. Inches H2O column chart to REALLY tell if a design is good. That is not typically given anywhere - stick with bigger fans.
3) Tip speed of a fan is the chief overall indicator of noise. Larger fans spin more slowly to generate the same CFM at a given pressure than small fans do. Unless you LIKE a noisy case.
4) Hub ratio. Keep the overall diameter to the hub diameter ratio as high as possible. 3:1 or 4:1 is most preferable. Avoid the "hub and stubs" concept. A shorter fan blade can be stressed more and push higher pressure, but at a poor airflow distribution and hellacious noise.
5) Venturi. I've noticed that the 80, 90, 120 mm fans commonly available have a nice looking Venturi on them. This smoothed inlet really helps with fan efficiency. Don't modify it.
6) When you operate in "suction" mode, the dead air spot in front of the fan is a non-issue. The principal benefit the case fan has on the back side of the case is that it pulls air uniformly out of the case. A "blower" fan, on the other hand, will tend to be influenced by blockages in front of it (cables, cards) and the identical fan in "blower" mode will actually push less air. 6a) Blower in duct - a rule of thumb to eliminate the "hub shadow" is at least five fan diameters for a duct...I doubt anyone could construct this inside a case but at least one fan diameter duct length would minimize this problem.
7) A common rule of thumb to to divide your case up by sides and have as many sucker fans as blowers (front - blower, back - sucker, side - blower, top - sucker). This is a good rule of thumb in my opinion as you do not fan fans to "fight" each other.
I have not done any experiments, but at some point additional case fans will not provide any additional cooling airflow as back-pressure will be far too high and the fans will go into stall, meaning that no additional fans will produce any more CFM (CFM stands for "Cubic Feet per Minute." This is equivalent to the volume of air that a fan will move in one minute at 0 (zero) static presuure") through case. Then it's time to move to centrifugal "squirrel cage" fans that can handle far more back pressure than our trusty axial fans.
Tags: CPU FANS, CPU CASE FANS, FAN SIZES, CPU FAN SIZES, CPU COOLER, COOLING FAN, TOWER FAN,
What size CPU Fan is Better for you CPU
If you have the space, always go with a larger fan.
Larger fans have the following advantages over smaller fans:
1) Higher resistance to static back pressure - in other words, if you have a highly resistive case air flow, a larger fan will more easily pull the pressure, because the blade chord (the width of the blade, essentially) is bigger.
2) CFM at 0" H2O column tells you jack about how the fan will perform in a real application. You need a CFM vs. Inches H2O column chart to REALLY tell if a design is good. That is not typically given anywhere - stick with bigger fans.
3) Tip speed of a fan is the chief overall indicator of noise. Larger fans spin more slowly to generate the same CFM at a given pressure than small fans do. Unless you LIKE a noisy case.
4) Hub ratio. Keep the overall diameter to the hub diameter ratio as high as possible. 3:1 or 4:1 is most preferable. Avoid the "hub and stubs" concept. A shorter fan blade can be stressed more and push higher pressure, but at a poor airflow distribution and hellacious noise.
5) Venturi. I've noticed that the 80, 90, 120 mm fans commonly available have a nice looking Venturi on them. This smoothed inlet really helps with fan efficiency. Don't modify it.
6) When you operate in "suction" mode, the dead air spot in front of the fan is a non-issue. The principal benefit the case fan has on the back side of the case is that it pulls air uniformly out of the case. A "blower" fan, on the other hand, will tend to be influenced by blockages in front of it (cables, cards) and the identical fan in "blower" mode will actually push less air. 6a) Blower in duct - a rule of thumb to eliminate the "hub shadow" is at least five fan diameters for a duct...I doubt anyone could construct this inside a case but at least one fan diameter duct length would minimize this problem.
7) A common rule of thumb to to divide your case up by sides and have as many sucker fans as blowers (front - blower, back - sucker, side - blower, top - sucker). This is a good rule of thumb in my opinion as you do not fan fans to "fight" each other.
I have not done any experiments, but at some point additional case fans will not provide any additional cooling airflow as back-pressure will be far too high and the fans will go into stall, meaning that no additional fans will produce any more CFM (CFM stands for "Cubic Feet per Minute." This is equivalent to the volume of air that a fan will move in one minute at 0 (zero) static presuure") through case. Then it's time to move to centrifugal "squirrel cage" fans that can handle far more back pressure than our trusty axial fans.
Tags: CPU FANS, CPU CASE FANS, FAN SIZES, CPU FAN SIZES, CPU COOLER, COOLING FAN, TOWER FAN,
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