Airflow vs static pressure fans. Are they a scam?

[The red spirit]

As far as I understand this is the formula of fan airflow:
air moved = rpms*volume of air that fan blades catch per revolution*static pressure of fan

It seems that fan static pressure and airflow is very similar to car engine's horsepower, revs and torque. So static pressure in fan is like torque in car and horsepower in car is like airflow in fan. Since fans usually aren't made thicker and most common size of them is 120mm, a hypothetical fan that runs at 1400 rpm, but one is made to be optimized for air flow and other is made to static pressure. That happens if you change blades. However, to achieve higher pressure, some cfm has to be sacrificed, therefore fan is able to provide lower level of air flow, but through more obstructions, meanwhile airflow optimized fan is overall better performing in terms of cfm (and probably in terms of noise, since pressure fans have heavier blades and they vibrate more when spinning), however such fan in theory shouldn't cope well with obstructions. However, from as much as I have observed, a fan blades don't really affect fan performance much. I'm starting to think that higher static pressure fans may have only slightly higher static pressure (makes sense, since a fan isn't a good air pump, due to gaps and due to looking nothing like a proper Archimedes screw) and thus in many practical scenarios higher static pressure just simply fail to deliver any proper advantage over basic airflow optimized fan. Meanwhile air flow fans pretty much always generate enough pressure, so there's no need for any special design. Are these observations true or not?

Side note:
it seems that static pressure optimized fans have a much better laminar flow:

See? Nidec has pretty much ideal straight laminar flow, instead of very turbulent and not straight flow of typical fan, which yo can see here (certainly not the best video, but I have seen that stuff somewhere else, it's just so hard to find such stuff again):

Also I have some generic 7 blades and with hand I can feel that air mostly flows from blade edge and flow isn't straight, but but it is like 25 degrees sideways. Not all of it isn't straight, but a good portion of it. Anyway, I have no idea if laminar flow is preferred and is any better than turbulent flow, as far as I know from car aerodynamics, laminar should be better, but since computer fan isn't pushing out air at high speed, it probably doesn't matter much.

 

[MentalAcetylide]

Maybe you're making this more complex than it needs to be or maybe not. I'm not all that familiar with the physics behind fans as its been a while for me, but in general, more fan blades = less static pressure = less noise. You want more static pressure from a fan if you need to push air through things such as radiators, hard drive cages and/or similarly situated components inside a case. High static pressure usually means more CFM air being moved by a fan that has fewer blades & spins faster, but the tradeoff is going to be more dBs.

This is just a guess, but turbulent flow(depending on how "turbulent") just throws air around in a disorganized manner and is probably more suited for cases that don't have a lot of obstructions inside while laminar would work great for cases that, for example, have 3 fans on the bottom pulling air into the case and 3 fans on the top expelling air out of the case.

 

[Shrek]

Anyway, I have no idea if laminar flow is preferred and is any better than turbulent flow, as far as I know from car aerodynamics, laminar should be better, ...

Turbulent should pick up heat better from a heat sink, but bearing life is also an important consideration in my opinion.

I seem to recall that counter rotating fans are more efficient, but I imagine they are also more noisy.

 

[80251]

Maybe you're making this more complex than it needs to be or maybe not. I'm not all that familiar with the physics behind fans as its been a while for me, but in general, more fan blades = less static pressure = less noise. You want more static pressure from a fan if you need to push air through things such as radiators, hard drive cages and/or similarly situated components inside a case. High static pressure usually means more CFM air being moved by a fan that has fewer blades & spins faster, but the tradeoff is going to be more dBs.

This is just a guess, but turbulent flow(depending on how "turbulent") just throws air around in a disorganized manner and is probably more suited for cases that don't have a lot of obstructions inside while laminar would work great for cases that, for example, have 3 fans on the bottom pulling air into the case and 3 fans on the top expelling air out of the case.

Three bladed refrigeration Delta fans have very little static pressure (and the below fan is 52mm thick):

https://www.delta-fan.com/eub1312me.html

This delta 120x25mm fan produces more static pressure at a lower RPM than the three-bladed fan above:
https://www.delta-fan.com/AFB1212L-F00.html

 

[looniam]

i love that guy

my understanding fwiw, high air flow are more likely to have several more blades than a high static fan 11-9 compared to 7-9 blades and the space between the blades will be larger. i've seen brochures/marketing about pitch and curvature/whatever but i just file that as . .marketing.

 

[MentalAcetylide]

Three bladed refrigeration Delta fans have very little static pressure (and the below fan is 52mm thick):

https://www.delta-fan.com/eub1312me.html

This delta 120x25mm fan produces more static pressure at a lower RPM than the three-bladed fan above:
https://www.delta-fan.com/AFB1212L-F00.html

I think you need to recheck the spec sheets on those fans. The first link for the 3-bladed one shows a static pressure of 32.60 mmH2O vs. the second link for the 7-bladed fan which only has 3.93 mmH2O.
32.60 mmH2O > 3.93 mmH2O, meaning the 3-bladed fan has higher static pressure.

 

[The red spirit]

Turbulent should pick up heat better from a heat sink, but bearing life is also an important consideration in my opinion.

I seem to recall that counter rotating fans are more efficient, but I imagine they are also more noisy.

Eh, bearing life span barely matters in reality. It's not that it doesn't matter, but because even very basic and cheap sleeve fans survive for more than decade and their lifespan could be extended with re-oiling them and keeping them clean. Pretty much anything more than sleeve fan is overkill. Noise and maybe performance are the main factors for choosing certain bearings and the classical orientation problem (you shouldn't mount sleeve bearing fans horizontally, although that observation is more theoretical than empirical. I personally have ATi X800 Pro and ATi X800 XT PE cards, both have sleeve bearing fans and they worked for a long time in vertical position, fans still work).

 

[The red spirit]

i love that guy

I like him too. I legit have golf ball dimpled fans myself (Silverstone Globe 120mm 1200 rpm). I got them with Silverstone Grandia GD05B case. Specs say that they are 20dB loud at 1200 rpm, which is pretty much identical to the most generic 7 blade fan, like Cooler Master Sl1. At least in terms of noise and rpms, they are the same. I haven't noticed anything else either. It seems that golf ball pattern doesn't do anything, other than looking odd.

my understanding fwiw, high air flow are more likely to have several more blades than a high static fan 11-9 compared to 7-9 blades and the space between the blades will be larger. i've seen brochures/marketing about pitch and curvature/whatever but i just file that as . .marketing.

I noticed that too, but then we have outliers like some crazy Noctuas, like this one:

Which, at least according to their specification sheet, is better for CFMs than CM Sl1, but at same time, it's is 2 dB quieter and fails to produce as much pressure, as it improves airflow. And this is just 7 blader with different angle and blade shape.

 

[80251]

I think you need to recheck the spec sheets on those fans. The first link for the 3-bladed one shows a static pressure of 32.60 mmH2O vs. the second link for the 7-bladed fan which only has 3.93 mmH2O.
32.60 mmH2O > 3.93 mmH2O, meaning the 3-bladed fan has higher static pressure.

3 bladed 126mm fan @ 2000RPM from datasheet: 0.139inchH2O (which equates to 3.53mm-H2O according to http://www.worldwidemetric.com/measurements.html)
7 bladed 120mm fan @ 1900RPM from datasheet: 0.154inchH2O (which equates to 3.93mmH2O according to the same website)

32.6mm-H2O of static pressure out of an 126mm axial fan spinning at 2000 RPM is IMPOSSIBLE. If you look at the datasheet the P-Q graph for the 3-bladed delta fan quotes a pressure figure in Pascals of of 34 Pa. Pascals <> mm-H20 as indicated here:
https://www.sensorsone.com/pressure-converter/

 

[The red spirit]

This is just a guess, but turbulent flow(depending on how "turbulent") just throws air around in a disorganized manner and is probably more suited for cases that don't have a lot of obstructions inside while laminar would work great for cases that, for example, have 3 fans on the bottom pulling air into the case and 3 fans on the top expelling air out of the case.

Apparently, CM's static pressure design with long blades is also good at laminar flow. As I understand, turbulent flow is slow flow and in case, disorganization means that it just ends up everywhere, where it shouldn't be, therefore laminar is always preferred. Those two fans are Silencio FP 120 PWM and BladeMaster 120, they don't match in terms of rpms, so for spec comparison I will use blade equivalent MasterFan Pro AP in quiet mode. And for comparison let's add the most generic 7 blade Noiseblocker BlackSilent 120 XL-P:
rpm 2250 vs 2000 vs 2000
cfm 53.5 vs 76.8 vs 75.3
pressure (mmH2O) 3.14 vs 3.90 vs 2.79
noise (dBa) 30 vs 32 vs 31.7

And the conclusion is that, the more cfm fan produces, the higher pressure will be at same noise level. Pressure optimized fan may be more helpful than airflow one at lower rpms, but at 2000 rpms airflow fans are always better.

To test that theory, I will compare Corsair's AF with SP fan spec sheets. Here they are
rpm 1500 vs 1400
cfm 52 vs 47.7
pressure (mmH2O) 1.45 vs 1.46
noise (dBa) 26 vs 28

And while Corsair claims that both are static pressure designs, from pictures you can see that SPs technically should be more pressure oriented. And in every aspect SPs are just worse. (Side note: Corsair has really went downhill fast, they don't seem to be reputable brand anymore).

 

[OneMoar]

two sides of the same coin

 

[MentalAcetylide]

3 bladed 126mm fan @ 2000RPM from datasheet: 0.139inchH2O (which equates to 3.53mm-H2O according to http://www.worldwidemetric.com/measurements.html)
7 bladed 120mm fan @ 1900RPM from datasheet: 0.154inchH2O (which equates to 3.93mmH2O according to the same website)

32.6mm-H2O of static pressure out of an 126mm axial fan spinning at 2000 RPM is IMPOSSIBLE. If you look at the datasheet the P-Q graph for the 3-bladed delta fan quotes a pressure figure in Pascals of of 34 Pa. Pascals <> mm-H20 as indicated here:
https://www.sensorsone.com/pressure-converter/

Ok, sorry about that, they have a typo on their specs sheet. Anyway, try comparing two fans that have the same dimensions, same max. rpm, with different number of blades like this:
7 blades, 120x120x25, 121.8 m^3/hr, 3.94mmH2O: NF-F12 industrialPPC
9 blades, 120x120x25, 102.1 m^3/hr, 2.34mmH2O: NF-A12x25 PWM

Now, I could be wrong since fan blade orientation also plays a role, but comparing the specs between the two fans, the 7-bladed fan spinning at 2k rpm has a higher static pressure than the 9-bladed fan spinning at the same rpm.

Apparently, CM's static pressure design with long blades is also good at laminar flow. As I understand, turbulent flow is slow flow and in case, disorganization means that it just ends up everywhere, where it shouldn't be, therefore laminar is always preferred. Those two fans are Silencio FP 120 PWM and BladeMaster 120, they don't match in terms of rpms, so for spec comparison I will use blade equivalent MasterFan Pro AP in quiet mode. And for comparison let's add the most generic 7 blade Noiseblocker BlackSilent 120 XL-P:
rpm 2250 vs 2000 vs 2000
cfm 53.5 vs 76.8 vs 75.3
pressure (mmH2O) 3.14 vs 3.90 vs 2.79
noise (dBa) 30 vs 32 vs 31.7

And the conclusion is that, the more cfm fan produces, the higher pressure will be at same noise level. Pressure optimized fan may be more helpful than airflow one at lower rpms, but at 2000 rpms airflow fans are always better.

To test that theory, I will compare Corsair's AF with SP fan spec sheets. Here they are
rpm 1500 vs 1400
cfm 52 vs 47.7
pressure (mmH2O) 1.45 vs 1.46
noise (dBa) 26 vs 28

And while Corsair claims that both are static pressure designs, from pictures you can see that SPs technically should be more pressure oriented. And in every aspect SPs are just worse. (Side note: Corsair has really went downhill fast, they don't seem to be reputable brand anymore).

I guess each has their pros and cons. I've heard arguments against turbulent something to the effect of having "warm pockets" in the case & laminar with not enough air hitting everything in the case. If it keeps my stuff at reasonable temperatures, regardless of the workload, I'm a crappy hamper... err, happy camper!

 

[80251]

@MentalAcetylide
Of course the blade design of both those Noctua fans is obviously different. Fewer blades can have a greater pitch, thus increasing static pressure, but that doesn't help the 126x52mm delta 3-blade fan.

I don't know anyone who has personally used one of those three-bladed fans -- they're commonly used in refrigeration. I always thought they would be good exhaust fans because they still have a good CFM rating and are quiet too.

 

[Ominence]

server fans are mostly pressure based fans so that's what you need. high air flow fans are cheap to engineer and do not work in the confines of a case. the 'high air flow' is marketing gimmick to get cheap products to move through the shelves at relatively high margins.
for a low maintenance system, keep two exhaust pressure fans with all the intake ports free of obstructions but with a single layer filter attached. heat extraction is the key to performance. the air will find it's way in, you do not need to go out of your way to get it in your system

 

[Vya Domus]

Ultimately they don't make that much of a difference because once you place a fan over a radiator it will constrict most the air to go one direction anyway, which is through the radiator.

 

[Valantar]

Apparently, CM's static pressure design with long blades is also good at laminar flow. As I understand, turbulent flow is slow flow and in case, disorganization means that it just ends up everywhere, where it shouldn't be, therefore laminar is always preferred. Those two fans are Silencio FP 120 PWM and BladeMaster 120, they don't match in terms of rpms, so for spec comparison I will use blade equivalent MasterFan Pro AP in quiet mode. And for comparison let's add the most generic 7 blade Noiseblocker BlackSilent 120 XL-P:
rpm 2250 vs 2000 vs 2000
cfm 53.5 vs 76.8 vs 75.3
pressure (mmH2O) 3.14 vs 3.90 vs 2.79
noise (dBa) 30 vs 32 vs 31.7

And the conclusion is that, the more cfm fan produces, the higher pressure will be at same noise level. Pressure optimized fan may be more helpful than airflow one at lower rpms, but at 2000 rpms airflow fans are always better.

To test that theory, I will compare Corsair's AF with SP fan spec sheets. Here they are
rpm 1500 vs 1400
cfm 52 vs 47.7
pressure (mmH2O) 1.45 vs 1.46
noise (dBa) 26 vs 28

And while Corsair claims that both are static pressure designs, from pictures you can see that SPs technically should be more pressure oriented. And in every aspect SPs are just worse. (Side note: Corsair has really went downhill fast, they don't seem to be reputable brand anymore).

This post clarifies some of the confusion leading to the initial questions here: the lack of clarity in testing methodology when it comes to fan specs.

Firstly, and by far the most importantly: Airflow is measured when entirely unobstructed (in a wind tunnel or similar), while pressure is measured when fully obstructed, i.e. at 0 CFM/m3h. These number can never be seen as existing together, but as an either/or pair of extreme (and extremely unlikely in real life) situations. In real life there is always some obstruction, but never total. The question for each fan is how it handles various levels of obstruction and whether it's capable of overcoming it to push air through whatever is obstructing flow, and if so, at what rate. These relationships are highly complex and non-linear (if a fan can produce 100cfm unobstructed and 10 mmH2O when fully obstructed, you don't necessarily get 50cfm at 50% obstruction. This would logically mean that "airflow optimized" in fan design parlance should mean "optimized for maximum airflow at zero or near-zero restriction", while "pressure-optimized" would mean "optimized for maximum pressure when fully or severely impeded" - but it doesn't. The difference they indicate is far smaller than that. See below.

Secondly, and nearly equally importantly: aside from the two highly general points above, there are no accepted industry standards for measuring these things in the PC space. As such, specs between manufacturers are fundamentally incomparable.

Thirdly, no fan manufacturer supplies a full flow+pressure graph for their fans, which would provide a lot more useful information than how it acts at full speed, and could highlight how different blade geometries work differently at different speeds.

Remember, airflow is extremely complex, and we can't even really claim to have a complete understanding of all the factors involved from a scientific point of view. Some general principles apply, but the specifics are extremely difficult to ascertain. There's a reason why computational fluid dynamics is a booming field of research, and that findings and methods from this field are widely used on supercomputers and massive computing clusters for designing anything high budget where it might be applicable - aircraft, boats, skyscrapers, and a million different industrial uses.

In the end, airflow is primarily about the transfer of movement energy from a fan motor, through its rotor and blades, to the air. This can obviously be done in many different ways, and is dependent on a host of factors, from blade shape, mass, stiffness/flexibility, speed, size, etc. Server fans create tons of pressure through huge, powerful motors spinning at high speeds, moving thick rotors (i.e. more of a screw shape) with litte room for back-pressure to push air back out between the blades. Case and cooler fans can't be as thick, so they have to try to balance things somehow.

Airflow optimized fans are designed around minimal flow impedance, and rely on the Bernoulli effect (directed airflow dragging along surrounding atmospheric air in the same direction, increasing flow, as demonstrated here) to maximise flow in unimpeded environments. The Bernoulli effect only applies if no significant backpressure exists, which is why these fans can provide fantastic airflow when unimpeded, but need to be planned around to work. Essentially, for low pressure, high airflow fans to work well, your case needs to be built like a wind tunnel. This is quite unlikely. In reality, most "airflow optimised" fans are instead designed as a middle-of-the-road solution. The Noctua pictured above is a relative rare example of a truly airflow optimized fan - and putting that fan on a restrictive radiator might cause the majority of the air it moves to reflect back off the fins and seep out between the blades, resulting in minimal flow through the rad. But it can also provide a staggering 100m3/h (by Noctua's testing methodology) at just 1200rpm in an unrestricted environment. The fancy new A12x25 needs 2000rpm to achieve the same ariflow - but can produce twice the pressure when fully restricted too. And the low noise optimized 1200rpm version of the NF-A12x25 seems out-and-out worse at just 55,7 m3/h/0.82mmH2O - but its design is likely far better optimized for in-between, partially restricted scenarios. Remember, this is a non-linear relationship. A quiet airflow optimized fan might also turn very noisy if excessively impeded, as the back-pressure from whatever is impeding it will mean that the blades, instead of gently guiding a vortex of airflow, are suddenly chopping through a turbulent mass of air instead.

(Btw, also worth noting from the demonstration video above: in the tests shown, the further the airflow source the faster the bag fills with air, but crucially, only the test with the airflow source clamped to the bag is able to increase pressure in the bag significantly above atmospheric pressure, as in the other cases, once the bag is full, air starts being pushed out as new air is pushed in.)

Pressure optimized fans are designed around, put simply, shoving air forward with a lot of force. Think of moving an oar or paddle through water - if you angle it closer to the direction of desired motion for the boat/canoe, the oar will move more easily through the water, but will impart little movement energy on the boat. Angling the paddle perpendicular to the desired direction of motion makes for a more efficient transfer of energy, making moving the paddle heavier, creating more turbulence in the water, and moving the boat further per stroke, especially at low speeds. Turbulence also causes drag, of course, which is quite inefficient, which is why fan blades aren't designed like flat paddes, but rather to combat drag. But this serves to illustrate why pressure optimized fans typically have more swept blades with a larger visible surface area from either side - they're trying to shove air forward rather than create constant flow. This helps them overcome turbulence and impedance, but also means that the blades chop through the airflow constantly, slowing down air being dragged in by the flow created on the opposite side, creating more turbulence. Creating a low noise pressure-optimized fan is thus more difficult than a low-noise airflow optimized one, due to the blades creating more and more complex turbulence.

Of course, all of this is grossly oversimplifying the complexities of fluid dynamics. Which blade design is "best" depends on rotational speed, weight, desired/acceptable noise levels, desired/acceptable noise pitch, power restrictions, distance to the impeding element, and a whole host of other factors.

The vast majority of PC fans fall across the rough middle of this spectrum. As someone said above, they aren't air pumps, so truly optimizing for pressure when fully obstructed is nonsensical, and as there will always be some restriction, optimizing for airflow at near-zero restriction is also pretty silly. Given the constraints on size (25mm thickness in particular, though some exceed that, like the Arctic P14 at 28, and others at 30+) and power draw, plus the desire for low noise, the resulting designs are typically relatively similar. The vast majority of possible fan designs just aren't suitable for PC use. How manufacturers choose to balance this depends on what they're targeting, their budgets, their price targets, R&D capabilities, etc. - but seeing how fans are a commodity, cheapness tends to dominate. The best performing type of design in situations with moderate-to-high impedance, such as radiators or thick heatsinks, tend to be the "shoving" kind - like the NF-A12x25, Arctic P12/P14, Gentle Typhoon, etc. - but that is also due to most radiators and heatsinks being generally clustered around a middle ground of impedance. Each is built to fit the other, so to speak. And crucially, each is built for realistic use cases rather than zero or full flow impedance.

This, in the end, is why most "airflow optimized" and "pressure optimized" designs are a) rather close within the overall range of possible fan designs, and b) thus perform relatively similarly in most cases. Differences aren't huge simply due to the designs overall not being that different. There are obviously differences, but they are mostly relatively small, and are highly complex in how they are different - noise levels, noise pitch, flow linearity/turbulence, flow patterns, how large the dead spot from the motor is, etc., etc.

 

[bug]

As far as I understand this is the formula of fan airflow:
air moved = rpms*volume of air that fan blades catch per revolution*static pressure of fan

It seems that fan static pressure and airflow is very similar to car engine's horsepower, revs and torque. So static pressure in fan is like torque in car and horsepower in car is like airflow in fan. Since fans usually aren't made thicker and most common size of them is 120mm, a hypothetical fan that runs at 1400 rpm, but one is made to be optimized for air flow and other is made to static pressure. That happens if you change blades. However, to achieve higher pressure, some cfm has to be sacrificed, therefore fan is able to provide lower level of air flow, but through more obstructions, meanwhile airflow optimized fan is overall better performing in terms of cfm (and probably in terms of noise, since pressure fans have heavier blades and they vibrate more when spinning), however such fan in theory shouldn't cope well with obstructions. However, from as much as I have observed, a fan blades don't really affect fan performance much. I'm starting to think that higher static pressure fans may have only slightly higher static pressure (makes sense, since a fan isn't a good air pump, due to gaps and due to looking nothing like a proper Archimedes screw) and thus in many practical scenarios higher static pressure just simply fail to deliver any proper advantage over basic airflow optimized fan. Meanwhile air flow fans pretty much always generate enough pressure, so there's no need for any special design. Are these observations true or not?

Side note:
it seems that static pressure optimized fans have a much better laminar flow:

See? Nidec has pretty much ideal straight laminar flow, instead of very turbulent and not straight flow of typical fan, which yo can see here (certainly not the best video, but I have seen that stuff somewhere else, it's just so hard to find such stuff again):

Also I have some generic 7 blades and with hand I can feel that air mostly flows from blade edge and flow isn't straight, but but it is like 25 degrees sideways. Not all of it isn't straight, but a good portion of it. Anyway, I have no idea if laminar flow is preferred and is any better than turbulent flow, as far as I know from car aerodynamics, laminar should be better, but since computer fan isn't pushing out air at high speed, it probably doesn't matter much.

Instead of making up formulas, you can just Google: https://techcompass.sanyodenki.com/en/training/cooling/fan_basic/004/index.html

 

[Valantar]

Instead of making up formulas, you can just Google: https://techcompass.sanyodenki.com/en/training/cooling/fan_basic/004/index.html

Wow, that was a great explainer, thanks for sharing!

 

[The red spirit]

server fans are mostly pressure based fans so that's what you need. high air flow fans are cheap to engineer and do not work in the confines of a case. the 'high air flow' is marketing gimmick to get cheap products to move through the shelves at relatively high margins.
for a low maintenance system, keep two exhaust pressure fans with all the intake ports free of obstructions but with a single layer filter attached. heat extraction is the key to performance. the air will find it's way in, you do not need to go out of your way to get it in your system

Or you can just have two static pressure intake fans and two airflow exhaust fans. That way you already have air in your case brought in and then exhausted easily and maybe faster.

 

[ThrashZone]

Hi,
Static fans are usually made a little stronger so they don't bend or get sucked into the closest object that usually being a radiator....
Some fans are really cheaply made and flex too much if you try and mount it on the back of a radiator as intake.
Nothing worse than having a fan blade hit a radiator and break lol

 

[The red spirit]

Case and cooler fans can't be as thick, so they have to try to balance things somehow.

I don't see any reason why they sometimes couldn't be so. I remember reading that there were 40mm pc fans created, but it was a very niche product, which wasn't advertised much and most people didn't even know that it existed, however, few that have those fans claim that they are great. And for example on tower cooler like 212 Evo, it wouldn't be too difficult to mount 40mm thick fan and it would be possible to have cooler more dense than it already is, so that it performs better. In most cases, you can mount 40mm fans as exhausts too. Intakes are thought due to various obstructions, but I think that 40mm fans certainly could be sold for pc enthusiasts wanting to try something different. And if Corsair, CM or Noctua would release such model, it could gain become a reasonably well known.

The vast majority of PC fans fall across the rough middle of this spectrum. As someone said above, they aren't air pumps, so truly optimizing for pressure when fully obstructed is nonsensical, and as there will always be some restriction, optimizing for airflow at near-zero restriction is also pretty silly.

lol it was me who said that they are not like Archimedes screw (which I think would be reasonable static pressure fan design, but who knows, if it spins too slow, water can just go back and air would be even harder to start moving. Anyway, since you say that computers will always be restrictive (which is definitely true, even more so for high end systems), wouldn't that mean that you would always want to buy only static pressure optimized fans? Because as you said too, there isn't much from where airflow fan would have unimpeded airflow and thus won't performs nearly as well as they are stated in spec sheet.

Hi,
Static fans are usually made a little stronger so they don't bend or get sucked into the closest object that usually being a radiator....
Some fans are really cheaply made and flex too much if you try and mount it on the back of a radiator as intake.
Nothing worse than having a fan blade hit a radiator and break lol

I don't think that this should be a major argument for static pressure fans. I never had a fan hitting something and breaking. I have one cheap brittle translucent Cooler Master Blue LED fan and while it may more easily break, it will never bend or start hitting radiators. All my other fans, including generic 7 blade fans, are much stronger and unsurprisingly don't hit anything. I think that you just got very unlucky.

 

[Ominence]

Or you can just have two static pressure intake fans and two airflow exhaust fans. That way you already have air in your case brought in and then exhausted easily and maybe faster.

from a low maintenance perspective, i've to say no to wasting any fans on the intake side. the moment your airway path immediately before or immediately after (filters or grills) the fan blade is restricted, the cfm of HSP will still be higher than that of the so called HAF fans.

 

[The red spirit]

Instead of making up formulas, you can just Google: https://techcompass.sanyodenki.com/en/training/cooling/fan_basic/004/index.html

Thanks a lot for this, it's really good. However, my made up formulae is about calculating fan performance and it isn't about airflow, pressure curve, thus I included how much air fan scoops in each revolution.

from a low maintenance perspective, i've to say no to wasting any fans on the intake side. the moment your airway path immediately before or immediately after (filters or grills) the fan blade is restricted, the cfm of HSP will still be higher than that of the so called HAF fans.

It's no for you, but for me it works well. Intake fans help a lot too cool GPU, while keeping system quiet. And dust for me somehow doesn't really accumulate fast, so I never care about minimizing it with fan setup.

 

[freeagent]

I think most consumer grade fans are a joke. SP vs AF? Server fans have both. Common misperception is that they are loud.. yes.. yes they are. But only at full speed. What is SP? It’s just air.. but more of it. Thick fans are where it’s at.

 

[bug]

Thanks a lot for this, it's really good. However, my made up formulae is about calculating fan performance and it isn't about airflow, pressure curve, thus I included how much air fan scoops in each revolution.

It's also wrong. But to hell with the countless engineers that have been working on these for ages, surely they haven't thought about computing airflow volume.