Basic principles of fans (?)

[SpaghettiCarbonara]

I would like to know some basic principles of different kinds of fans.

 

What makes a fan optimised for static pressure or airflow?

 

More specifically, does it have to do with the angle of the fan blades and/or spacing of the blades? What is the best blade angle/spacing for both kinds of fans?

 

Cheers

[ForeseenVisionz]

Noctua nf-f12's. full stop.

[Benjamin G]

Noctua nf-f12's. full stop.

....?

[ForeseenVisionz]

....?

just buy all da noctuas and put them everywhere!!!!

(it was a jk if u didnt get it)

[Constantine]

I would like to know some basic principles of different kinds of fans.

 

What makes a fan optimised for static pressure or airflow?

 

More specifically, does it have to do with the angle of the fan blades and/or spacing of the blades? What is the best blade angle/spacing for both kinds of fans?

 

Cheers

 

Oh buddy, you're asking me to dig up my Fluid Mechanics. Say hello to Bernoulli's Principle: http://en.wikipedia.org/wiki/Bernoulli's_principle

 

But the gist of it is just remember that static pressure and airflow are inversely related to each other. An airway that has lots of resistance will require higher static pressure and will produce less airflow.

 

Linus tested some of the fans in a proper lab and gave some good results on the matter:

http://imgur.com/EcZfQCE

 

Lets look at the two Corsair fans, one is the AF120 (optimised for airflow) and the SP120 (optimised for air pressure)

You'll notice that the AF120 have a leaner plot and has less area under the graph compare to the SP120 but ultimately reaches the same max airflow. This shows that compared to pressure optimised fans, they'll need less power and can run at a slower RPM  compared to the SP120 and thus produce less noise. But what happens when we put it in an environment where there's a lot of resistance? Lets say we put it in an environment where it needs to produce around 1.0 mmAq of static pressure to produce "optimum airflow", the AF120 can only produce around 20 CFM of airflow. This is where the pressure optimised fans would shine like the SP120 where it produces around approx ~48 CFM. 

 

TLDR; Static pressure fans for environments with high resistance i.e. Front Bezels with dust filters and meshes, Radiators and heatsinks.  Airflow fans for open areas with no or little resistance i.e. exhaust ports or side panels

 

btw, any other experts feel free to call me on my shit. Fluid Mech wasn't my specialty

[SpaghettiCarbonara]

Sorry guys, I appreciate the effort, but you've missed the point a bit.

 

I understand the applications for different fans and I understand a bit of how static pressure works.

 

What I'm asking is if anyone knows how the design of a fan affects the amount air it pushes and how it affects static pressure.

 

For example, when comparing the AF120 and SP120 fans, the SP120 fan's blades have a much shallower angle and smaller spacing between the blades when you look directly at them. Can someone please expand on this?

[WoodenMarker]

Sorry guys, I appreciate the effort, but you've missed the point a bit.

I understand the applications for different fans and I understand a bit of how static pressure works.

 

What I'm asking is if anyone knows how the design of a fan affects the amount air it pushes and how it affects static pressure.

For example, when comparing the AF120 and SP120 fans, the SP120 fan's blades have a much shallower angle and smaller spacing between the blades when you look directly at them. Can someone please expand on this?

AF fans like NF-S12a's have a less dense fin array to allow more air to be pushed but just in a general direction. http://www.newegg.com/Product/Product.aspx?Item=N82E16835608038

SP fans like NF-F12's has a more dense fin array to 'force' the air to move in a more specific direction for better focused airflow. http://www.newegg.com/Product/Product.aspx?Item=N82E16835608026

For the record: I'm not an expert on fans. 

[Constantine]

Sorry guys, I appreciate the effort, but you've missed the point a bit.

 

I understand the applications for different fans and I understand a bit of how static pressure works.

 

What I'm asking is if anyone knows how the design of a fan affects the amount air it pushes and how it affects static pressure.

 

For example, when comparing the AF120 and SP120 fans, the SP120 fan's blades have a much shallower angle and smaller spacing between the blades when you look directly at them. Can someone please expand on this?

 

Taken from the Bernoulli's principle wiki page:

 

Applications

Bernoulli's principle can be used to calculate the lift force on an airfoil if the behaviour of the fluid flow in the vicinity of the foil is known. For example, if the air flowing past the top surface of an aircraft wing is moving faster than the air flowing past the bottom surface, then Bernoulli's principle implies that the pressure on the surfaces of the wing will be lower above than below. This pressure difference results in an upwards lifting force.^{[nb 1][25]} Whenever the distribution of speed past the top and bottom surfaces of a wing is known, the lift forces can be calculated (to a good approximation) using Bernoulli's equations^[26] – established by Bernoulli over a century before the first man-made wings were used for the purpose of flight. Bernoulli's principle does not explain why the air flows faster past the top of the wing and slower past the underside. To understand why, it is helpful to understand circulation, the Kutta condition, and the Kutta–Joukowski theorem.

 

Same thing happens on fans, the SP120's have wider blades to force higher air pressure by making air travel along the blades for longer distances. The high airflow blades such as the AF120, don't need as much concentrated air and only need to cause as much turbulence or disturbance as possible. They do this by increasing the number of blades and thinner blade "thickness" or blade width is the result of having to allocate the extra blades. Thinner blades also mean that air pressure wont increase (remember pressure and air flow are inversely proportional) and its insured that you'll achieve good airflow.

 

The angle that you're asking about pertains more into Airfoil design and their optimised angle of attack and becomes a bit hard to explain without asking the engineers that designed them.

Edited January 21, 2014 by Constantine

[SpaghettiCarbonara]

Thanks guys

[rentaspoon]

Thanks guys

Can I just add that a lot of people forget that fans assist in convection heat transfer as to me it very important.