Airflow vs static pressure fans. Are they a scam?

[Ominence]

smaller dia fans are generally poor performing due to them having a bigger ratio of the hub sacrificing wind swept volume.

Obviously, the more blade area there is, the more spherical the blades are in shape. Other than that, shaping them in constant overlying flow acceleration is the practical limit, imo. I think altitude matters for this scenario, but cannot tell in which direction.

it's interesting to see noctua have 2 very different fans with one optimised for airflow and the other for static pressure at the same rpm but not the same noise profile? seems to me that AF is noiser than SP??

the SB series is louder, less airflow and more pressure than the SA series, interesting!

 

[mtcn77]

the SB series is louder, less airflow and more pressure than the SA series, interesting!

Those charts aren't p/q curves. Loudness and pressure is against flow in that comparison. We are looking for the plateau.

 

[Ominence]

Those charts aren't p/q curves. Loudness and pressure is against flow in that comparison.

yes, there is no curve there, they are absolute measurements with a few given constants in a lab environment.

 

[eidairaman1]

Higher Static pressure fans help push air through obstructions where as high cfm fan help flow air more quickly, so id say use high flows on less restrictive heatsinks and other areas.

 

[Ominence]

i think the real trick here is that the more absolute airflow you actually have across your system, the louder and potentially cooler it will be (diminishing returns always apply, you will hit the ambient wall eventually). finding that perfect balance is the fine arts science we all have to work towards- balancing noise and temps (and from there, system longevity and performance).

 

[Shrek]

I would like to know if turbulence helps with heat pick-up

 

[Ominence]

I think altitude matters for this scenario

jets, more blades, more thrust- better than props for high altitude performance. haven't seen a high service ceiling propcraft anytime recently.

turbulence helps with heat pick-up

i don't quite catch your query but the more turbulence there is, the more variable restriction would apply to the fan motor torque which could lead to very slow heat buildup. any inconsistencies in the fan speed due to external factors will lead to friction forces/resistance and therefore heat to potentially generate above nominal. however, the design of the motor should take into account such factors and be within the operating range of its engineering spec.

 

[Shrek]

I meant that if the fan output was turbulent, it would pick up heat more efficiently from a surface than if the impinging air was laminar, but I don't know if it would be a significant improvement.

 

[mtcn77]

I meant that if the fan output was turbulent, it would pick up heat more efficiently from a surface than if the impinging air was laminar, but I don't know if it would be significant.

That is at the fin interface.

 

[Shrek]

Such a simple seeming device, the fan, but how complicated in reality.

 

[mtcn77]

Such a simple seeming device, the fan, but how complicated in reality.

Has to do with rotational versus forward velocity me thinks, just like helicopters.

jets, more blades, more thrust- better than props for high altitude performance. haven't seen a high service ceiling propcraft anytime recently.

Jets ignite fuel, cause a thrust. Propfans cannot make a pressure gradient from atmospheric thin air.

 

[Ominence]

fan output was turbulent, it would pick up heat more efficiently from a heat sink than if the impinging air was laminar.

i think turbulence is not the key to better heat pickup. the magic scenario from a fluid dynamics perspective would be laminar flow right across and brushing the fins of the thermal exchange surface. this would ensure maximum constant density of airflow across the fin interface as @mtcn77 puts it and give the maximum effective thermal transference. this could be the reason why the new noctua fanless cooler has only 13fins to space the fins optimally from each other to allow effective convection to occur, whilst at the same time not allow the fins to feed heat off each other before being able to dissipate it to the air thru natural forces at play (potentially getting trapped in turbulence and slowing their escape speed leading to faster heat buildup and/or higher constant retained heat).

Jets ignite fuel, cause a thrust. Propfans cannot make a pressure gradient from atmospheric thin air.

well, they all seem to do something with the fuel so take your pick i guess.

 

[mtcn77]

i think turbulence is not the key to better heat pickup. the magic scenario from a fluid dynamics perspective would be laminar flow right across and brushing the fins of the thermal exchange surface. this would ensure maximum constant density of airflow across the fin interface as @mtcn77 puts it and give the maximum effective thermal transference. this could be the reason why the new noctua fanless cooler has only 13fins to space the fins optimally from each other to allow effective convection to occur, whilst at the same time not allow the fins to feed heat off each other before being able to dissipate it to the air thru natural forces at play (potentially getting trapped in turbulence and slowing their escape speed leading to faster heat buildup and/or higher constant retained heat).


well, they all seem to do something with the fuel so take your pick i guess.

View attachment 207554

200iq stuff right there.

I recently watched a series why propfans are junk. Turns out they don't need Mercedes to produce their junk quality.

 

[Ominence]

they don't need Mercedes

or BMW for that matter!

 

[The red spirit]

i have old noiseblockers as well so the eloops discussion is also somewhat interesting. i tried an interesting experiment some 4 years ago- Noiseblocker black silent pro 140mm 1700rpm. But my 18 fans sound like this on idle, 7v i think, 1 inch distance. this is a push pull arrangement sandwiching a watercool 420 pro stainless rad.

Where do you even put so many fans? Is this an eATX case?

Thicker fans can spin slower and still produce more CFM and static pressure than a thin fan -- at the same RPM. Whether or not it would also produce less noise is anyone's guess.

That's has been debunked. Thicker fans increase pressure, bigger diameter increases airflow. If you want to Google something, Google Feser Triebwerk fans, they were very thick (55mm) and they didn't really do anything special.

I would like to know if turbulence helps with heat pick-up

As far as I know, it seems that turbulence is bad, because turbulence is slower than laminar flow. If anything turbulence may trap heat.

Such a simple seeming device, the fan, but how complicated in reality.

I would like to say that, but nah it's really not. The main problem there is that it's very hard to find a correct and in depth information about such stuff. That and fan manufacturers trying to sell various fan designs as being better and often lying about that or at least not explaining in what specific situations it's the best design. But then again, I don't consider automotive aerodynamics difficult. To be honest, it's far easier to design a sleek car, rather than make 7 spinning blades into most efficient form.

 

[Ominence]

Where do you even put so many fans? Is this an eATX case?

external rad mate. fed into the case with tube grommets on the NZXT phantom OG.

 

[freeagent]

I would like to know if turbulence helps with heat pick-up

I believe it does.. to a point. Lots of people value silence, I do to.. but when it’s time to work you have to make a little noise, or the silence will keep you in the slow lane. And that’s ok..

 

[The red spirit]

I believe it does.. to a point. Lots of people value silence, I do to.. but when it’s time to work you have to make a little noise, or the silence will keep you in the slow lane. And that’s ok..

Or you just build completely passive system and have both performance and silence.

external rad mate. fed into the case with tube grommets on the NZXT phantom OG.

View attachment 207584

Is that car radiator?

 

[Shrek]

I believe it does.. to a point. Lots of people value silence, I do to.. but when it’s time to work you have to make a little noise, or the silence will keep you in the slow lane. And that’s ok..

I'm with you on that; silence is a big deal.

 

[freeagent]

Or you just build completely passive system and have both performance and silence

Not the kind of performance I am used to.

Edit:

I do know a little about running semi passive. I was running my 3770K @ a solid 4500MHz on my Le Grand Macho RT with Linpack Xtreme and no CPU fan installed, case fans @ 5v last winter.. I even tried my old 3600XT passively. It was ok @ 4400.

 

[Ominence]

Is that car radiator?

Watercool MO-RA3 420 Pro Stainless Steel, 269,95 €

 

[formula383]

"Airflow vs static pressure fans. Are they a scam?"​

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No? How would they be a scam?​

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Every fan has its use case and will fit into the market in some way. If you don't find a difference in fan design for your use then just get the fan you like the color of. But for others different types of fans can be of value.​

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Things you need to keep in mind.​

- 1 - We are limited by form factor.​

- 2 - Noise is a large concern for PC fans.​

- 3 - Moving air creates noise.​

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There is only so much you can do in side of these restrictions.​

​

So i'm sure you are asking well WHERE would i use a SP fan. Thick, high FPI rads will do better with a SP style fan. If you use SP fans in a relatively open space they will have no positive effect. IE using a SP fan on a CPU cooler that was created for optimal air flow for low noise in a PC. Putting a SP fan on that cooler is going to show no benefit at all.

(edit: no idea why this post is all in bold its not marked as bold in the tools here..)​

 

[The red spirit]

I have found some good stuff on Reddit about Airflow vs Static Pressure:
https://www.reddit.com/r/buildapc/comments/6c3cla

 

[doyll]

Air turbulence creates resistance to airflow, thus lowering airflow .. and mixing heated air with cooler air flowing through case .. thus increasing air temp .. thus this air can't absorb as much heat from components .. so components run hotter. Every degree warmer airflow is through our cases means components will be same degrees hotter (at same load and fan speed / airflow).
Air temp to component temp is an almost exactly 1:1 ratio (same load & same fan speed).

Higher pressure rated fans work will flow more air in our applications than higher airflow rated fans because higher pressure ratings mean more ability to overcome airflow resistance.

To have "airflow" we have to have a pressure differential .. fans create higher pressure air on exhaust side .. this higher pressure air moves into lower pressure air creating airflow.

If a fan made no pressure (0.0mm H2O) it would have no airflow. The higher the pressure rating the more airflow fan will have in our cases because even a small round wire creates resistance.

The lowest resistance grills are the wire ring kind, and even they restrict airflow of most fans by 25-35% .. and the lower the pressure rating a fan has the less air will flow through grill / case resistance.

Keep in mind a fan rated 1.836mm H2O (only at full speed) has about the same pressure difference between intake side and exhaust side (at full speed) and there is between the pressure on your feet vs on your chest standing at sea level.

Yeah, our fans create almost no pressure differential .. so have almost no ability to overcome resistance.

Best way to understand how airflow works is to think of air as being water .. the science of airflow is named "fluid dynamics" for a reason.

Think of your case as a box under water with holes in box as vents in a case .. propellers in some of the openings are fans in our cases. For water to flow into box an equal amount of water has to flow out.

We cannot move more air into our cases than we have coming out of our cases. Simple physics.

This does not mean we need both intake and exhaust fans .. because intake and exhaust fan in case are basically the same as push / pull fans on cooler or radiator. Push / pull can improve overall airflow only because push / pull increase pressure rating, thus more ability to overcome resistance.

 

[mtcn77]

@The red spirit good stuff, but he took cfm at face value, not at optimal fan efficiency pq value.

Hi, @doyll!
A good fan has to have a good "jet", but not a lot of "wake" which causes turbulence. Wake is very detrimental to a good fan. Too much wake and a fan starts working in static pressure, making just noise and not a lot of air flow. We should look at its pq curve where it is just below its static pressure build up point.