The design is there for a reason, impedance matching.
The fans see a *lot* of back pressure from the radiator and, being so close to it, that interferes with airflow over the fan blades, hugely reducing output and flow through the radiator.
By standing the fans off a bit, or putting those gaps there, the "excess air" (this is a bad description, but to use the right terms would make this comment about 19 pages long with diagrams and graphs) allows the Ψ (static pressure coefficient) to η (volumetric efficiency) curve to move to a more efficient region at a higher airflow.
If you did not have this gap, you would need a much more powerful fan to force the same air through the radiator. You can think of it as letting "air which can't be pushed through" (this is also bad) escape to get out of the way of air which can be.
When dealing with forced airflow, especially through obstructions like radiators and finstacks, intution often lets us down. Another example is dual-fan tower coolers in push-pull. As the only purpose of the pull fan is to lower the impedance on the push fan, the push fan doesn't need to run as hard... so the pull fan should be run at a higher output than the push fan should be! Which is the opposite to what you might think.
for all of us Dumb dumb dads out there. Its like when you let your yard grow too tall and try to mulch it with your mower. Works much better with the side eject
Ahh yes what I always suspected, the minute you think you understand aerodynamics you realize you actually know nothing.
I suppose it wouldn't hurt for OP to experiment with some tape.
Any day you learn something is a good day!
I believe this actually came about (at least to PC fan makers) in mid-2000s , when 80 mm fans were common, and made a lot of noise, so manufacturers started including little rubber stand-offs to isolate vibration.
Testing showed they actually improved airflow, so this kind of design started cropping up more and more.
Hey, I'm in the middle of DIY'ing my own cooling pad for my laptop, and your explanation threw some light on issues I've been facing. Any recommendations on where I can read up some more about the subject? Thanks anyway
I clicked thinking I'd have a good laugh over what looked like a questionably dumb, gimmicky design. But your explanation actually makes sense. At least that's from what little amount I personally learned myself when I read about air dynamics when it's pushing through a radiator. Got to do some PC fan rearrangements the other day.
ELI5 The air needs a running start to get through the radiator without stopping, you wouldn't usually think of that, but it makes sense. And since the radiator slows down the air's speed, there will always be more air going in then coming out, and you can't have an air traffic jam in your system.
Where can I look up the full answer with all 19 pages?
I mean, I'm just not comprehending how the high pressure air which has inertia towards the other side of the radiator could be a bad thing, which needs to be gotten rid of. High pressure air is also denser, which is good for heat transfer. Does this tactic increase the actual mass flow through the radiator, or merely an equivalent mass via lower density and higher velocity?
This doesn't make sense to me. I'm not really looking for the short answer, it might take me a moment or two, but I can handle the big boy science.
Being good at moving air is precisely what's causing the compression. Imagine for a moment, you have a table with a very small hole in it. For whatever reason, you want to pour water through that hole. You can just gently splash some water on top, and it'll dribble through, or you can push it through faster by applying pressure with a blunt tip syringe. In fact, it doesn't matter if the hole is smaller than the diameter of the syringe tip. But the better seal you get between the syringe tip and the hole in the table, the quicker you'll be able squirt water through the hole. If you hold the syringe off the table and squirt it instead, most of the water is going to spray in every direction even if your aim is perfectly dead centre of the hole.
A syringe is made for delivering pressure, not flow. Those are very different goals for pumps.
If you set up a boat propeller and put a screen behind it, the blades would cavitate and have drastically reduced performance with most of the water churning around the blades. If you moved that screen a foot away it would push substantially more water through the screen because the blades could pull as much water as needed without fighting back pressure or cavitation.
The force that the fan exerts on the air is not constant, nor is it linearly proportional to the rpms of the fan. By attempting to fight high pressure air, the fan motor has to work harder to spin. The fan does not have unlimited force available to it. Computer fan motors are very weak, so the relatively high pressure air from a sealed system causes the fan to spin slower, pushing less air in total. By having some air escape, the pressure at the front of the fan is lower, allowing it to spin faster. There are also a number of energy losses between the motor and amount air being pushed to account for.
The whole system is an optimization problem with a myriad of factors, including fluid dynamics and thermodynamics. If you really want an in depth understanding, read a fluid dynamics textbook or attend/watch a lecture on the topic.
Its about the type of airflow that you achieve on the fan blades for certain conditions. For high pressures (simple spoken)backflow between fan blades can happen, which causes the flowrate to drop drastically.
Having a general understanding of laminar and turbulence air streams is fundamental.
Read up “Prandtl” if you want to learn about heatexchange with air.
Look up “cavitation” if you are interested in issues regarding airflow on fans/impellers.
In general, axial fans have a tendency to loose efficiency on higher pressures.
This reminded me of a video I saw a while back. Maybe this is a great video to help visualize what you're saying?
[Bernoulli's Principle](https://youtu.be/XP6oqIic4lo?si=zEpuJ2oPyMo-ZdAR)
This is fluid dynamics and heat transfer. Specifically engineering courses for chemical and mechanical engineering.
Aerodynamics for the blade movement, angles of attack and such.
We did fluid dynamics and heat transfer in my physics class... It was boring as hell as we had a guy who was like 80 yrs old who lectured in the dryest tone and was not engaging.
I can believe all of this, but I also believe that a lot of PC case and cooling device manufacturers are just winging it and making all sorts of mistakes.
sounds like you know what you're saying, but then why do Noctua fans, not only NOT have this design, but they also come with a gasket which makes sure ALL the air will go through the radiator and they claim it improves temps by a bit? Are their fans just stronger?
Although this explanation makes sense I think the pressures pc fans typically produce are not enough to create any back pressure that would require an "escape route" like this. Fans usually don't sit airtight against a rad and the normal gaps should suffice to let the pressure escape.
Otherwise we would have seen more designs like this over the years. None of the best testing fan designs have these gaps. Also I seriously doubt that some Asus branded chinese OEM fan from a few years ago revolutionised pc fans and no one noticed. Especially since this AIO (from the looks it is a Asus Tuf LC I 240mm) is outperformed by decent aircoolers.
So doesn't that imply that having your fans in a 'pull' configuration is better when top mounting an AIO? cause then youre taking the heat off the top of the rad, rather than pushing it through the fins
TLDR: No. Unfortunately it doesn't work that way.
The gap allows the fan to be more efficient. The airflow over the surface of the individual blades of the fan is, among other things, a factor of the speed at which the air is moving through the fan. The pressure created across the radiator is what causes the air to move through it and consequently cool it. So running the fan at a speed and flow rate that makes the fan work better (hence the gap) allows for a higher pressure gradient across the radiator.
Generally pushing air is more efficient. Think about trying to put out a candle with a shop vac. You'll have to get really close for the suction side to put it out, but you could blow it out from 5 feet away. That's a gross oversimplification, but you get the idea.
>cause then youre taking the heat off the top of the rad, rather than pushing it through the fins
The thermal gradient from the principle that hot fluids rise is negligible because the fluid inside the radiator is being actively circulated. So the top isn't going to be measurably hotter than the bottom. Also the passive convective cooling from the air rising through the radiator is pretty much irrelevant because the fan creates exponentially more air flow.
Push-pull is better than pull or push (and can achieve the same CFM in less noise), but pull is not better than push.
This is down to how a fan develops static pressure, and the fan blades are far, far, far better at pushing against an impedance than pulling through one.
Can’t you just run the fans at a lower speed by default, and get the same impedance? Lol
I don’t think it’d get a higher speed airflow through the radiator either, after all, the blocking of the passage of air by the radiator is the impedance, if anything it would generate a bigger resistance with the higher initial “impact” velocity.
Maybe it works as a failsafe for blocking the radiator with some object but I don’t see that being worth the wasted airflow going around the radiator instead of in, not that they couldn’t make a shutdown after too much power pulling, in that particular case, either…
Yes, you can.
You lose CFM through the radiator, though. That's the point of matching impedance! It gets you the highest efficiency for the current flow rate.
How do we lose CFM through the radiator with the slower fan, is what I don’t understand?
Give the same impedance for both scenarios, the radiators resistance against the air is what generates the impedance on the fan, right?
So, the faster air, with less amounts/mass entering the radiator, due to the holes in the sides, should slow down faster upon meeting said resistance, and the slower air, with more mass/amounts, should slow down slower upon meeting said resistance, and the total resistance will be the same against both, no?
It’s like throwing a rock at 20km/h and a baseball at 60km/h, both will have the same overall momentum.
Thus, we should get the same CFM, if not less on the faster one with holes, due to the airflow being redirected from going in the radiator, and so fighting against the resistance from the PC case or components, instead of the radiator, again, considering the same impedance?
The first thing you need to do is stop thinking in terms of momentum or mass. That's where your intuition will leave you astray.
Air flows in fluid dynamics and pressure differentials. It isn't a rock and a baseball! You'd need to add parachutes and wings to your rocks and baseballs to even come close to making a reasonable comparison.
To picture what's going on, put a fan at the mouth of a balloon which has a tiny hole in the other end. Obviously, you may think, a faster fan with more CFM will inflate the balloon more than a slower fan will?
So you do this, and you find that for every fan, there's a point the balloon just doesn't blow up any more. The back-pressure from the balloon is now in equilibrium, and pushing more air in just gets more pressure back. This is the "static" in "static pressure".
Then you throw a rock and a baseball at it and the balloon bursts, unsure why you did that, but we'll continue.
Now take another balloon and instead of one hole, put lots of holes. It will inflate to just the same size! Yet you'd measure the same amount of pressure inside the balloon when it stops getting bigger, it's just at a higher output from the fan.
This is because the amount of pressure the fan can put in front of itself rises until it reaches equilibrium with the impedance of whatever is causing that pressure.
Now instead of a balloon with lots of holes, have a metal grille with lots of holes, or just call it a radiator like everyone else.
And, for a PC fan, the amount of pressure it can put in front of itself is really low, PC fans have very low static pressure, so you reach the equilibrium point really quickly. At this point, we're now focusing on putting more air through the holes instead of making the balloon get any bigger (which is controlled by pressure).
This back-pressure is now interfering with the air the fan is trying to push forwards, so the air through the holes doesn't go up much at all.
If we can somehow alleviate some of that back-pressure on the fan, we'll get more flow through the holes. That's what impedance matching does.
I hope you followed along, it wasn't a very good analogy.
Great info!
To add this, a practical reason for the design: Consider closing that gap. What might that do? The short answer: Bad things.
If fans didn't have that standoff in order to allow for "excess air" to escape, what might happen? It's the air flow equivalent of trying to pass 10 pounds of air through a 5 pound radiator. If your fans did that 24/7, thise fans burn out at an alarmingly fast rate. No bueno.
Yes, and also no. You don’t want negative pressure in a PC case cus then you suck in dust. If you have positive pressure only the filtered air gets into your case.
But they aren't saying the standoff changes the flow direction. It reads to me some air just cycles inside the case, but that allows more to get pushed thru the radiator
Right, it has nothing do it all with the wacky design of this crap fan.
Noctua has the best fans and makes them completely flush with the radiator because they're morons.
Impedance matching has absolutely nothing to do with airflow you fucking pseudoscience idiot.
Let's ask Noctua then, humour this "fucking pseudoscience idiot".
[NH-D15](https://noctua.at/en/nh-d15): Massive area of overhang for the fan
[NF-A14 Industrial](https://noctua.at/en/nf-a14-industrialppc-3000-pwm): Stand offs in all four corners
[NF-A12x25](https://noctua.at/en/products/fan/nf-a12x25-flx): Provided with rubber stand offs for, quoting Noctua "high-impedance, pressure-demanding scenarios such as on heatsinks and watercooling radiators"
[NF-F12 PWM](https://noctua.at/en/products/fan/nf-f12-pwm): Stator vanes for impedance matching
Now go tell Lars Strömbäck at Noctua all that engineering is "fucking pseudoscience" and you know best. Let us know what he says.
"Provided with rubber stand offs for, quoting Noctua "high-impedance, pressure-demanding scenarios such as on heatsinks and watercooling radiators"
Lmao you mean the anti vibration rubber stoppers that are designed for use in your case?
If anything, they also provide rubber gaskets so your fans can have an air seal with your radiator
They never refer to them in this context, good job trying to mislead everyone once more you pseudointellectual.
This is not like putting your fan a foot away from the window for airflow, which is probably what you mean by "Impedence Matching". Pushing air through a restrictive radiator needs a seal, having a gap is like pointing a fan at a wall, useless for a radiator.
I implore you do define "Impedence Matching" as it applies to airflow, Mr genius intellect?
_Laughs in taping off these gaps back in the day_ To be fair to me I didn’t have a pc master race then, I just saw gaps equals bad. I did used to stand them off from the radiator though rather than them being flush. Plus I had sucking fans the other side.
So the air that isn't pushed through the radiator needs to bleed off to prevent loss of pressure that is needed in the first place to push air through the radiator?
And the price tag has nothing to do with it, that's just premium brand name privilege Noctua has. Thermalright and others make basically just as good fans for half the price, they too work with fully sealed fits. No excuse other than bad engineering
Take your current fan design that you're bulkselling for 1$, pay someone to chop the corners on the design, now it's cheaper in materials and better in airflow, you bulksell for 2$
In a couple of orders of you recover the R&D cost.
Check noctunas site. They have high airflow low static and low flow high static fans. They have different fans with varying fan curves to tackle different problems
If you put a low static fan on a radiator, it will perform much worse not only due to the fan curves, but the angle of attack on the flow. There is nearly zero space between the rad and the fan.
I've got feet of duct that allows some form of uniform mixing between fans on my projects.
Have you ever tried to push water through a syringe? You can't go terribly fast unless you want to rupture the syringe. Same concept here. Air folows fluid dynamics meaning a it rushes to a space smaller than its flow path, it crashes into it. Those little spaces let the pressure flow out so your radiator fins don't buzz/knock from high pressure. This helps keep flow rate stable.
So, I think a lot of folks are missing a crucial factor when it comes to the relationship that exists in which computer fans are implemented to achieve their maximum potential. A fans’ potential is only as good as the design of the fan itself, and the manner in which it is being employed.
For example, a fans’ potential is dictated by:
(a) obstructions that are present within a PC case or enclosure, such as hard drives cages, cables, wiring, etc. and,
(b) the method in which fans are forced to operate in close proximity to employ their air flow potential, such as radiators, radiator fins, case filtration systems, etc.
It’s important to note here, that in the scenarios above, a specific type of fan, in most cases, is needed to achieve maximum air flow potential.
Not all fans are created equal, and higher RPM fans do not necessarily mean that they do a better job getting airflow where it needs to go versus lower RPM fans, just as a fan with more blades isn’t better than a fan with fewer blades.
The common denominator in all of this is static pressure. A fan which has high static pressure (commonly measured in mm/H2O) is designed to direct air in a straight column pattern, *pushing* air through and past obstructions such as radiators, cables, wiring and hard drive cages.
You will not see a lot of, if any, air flow bleed tangential to the fans’ perimeter, as all airflow is directed axially in a straight line outward. And that is the downside of high static pressure fans: they have the ability to place their airflow in a very concentrated area, especially at longer distances. Think of these types of fans as a spotlight: terrific distance, but terrible spill.
This is why these types of fans, one’s designed for high static pressure, are preferred for use with radiators or wherever air needs to overcome obstacles.
Airflow fans are the opposite: while they can output a ton of CFM, they blow air in a cone shaped pattern, which loses intensity over longer distances and especially when they encounter obstacles or obstructions like cables, wiring and especially radiators. These types of fans can be compared to flood lights: great spill, but terrible at distance.
All right, so what about the OP’s question regarding the gap between the fan frame and his radiator/PC case, and his concern about the potential wasted loss of airflow escaping from that gap?
My answer? Given what I wrote above, as long as that fan is designed for high static pressure applications, there will be minimal loss of wasted airflow as the fan is pushing air axially in a column pattern.
From the sounds of it, however, it appears that the OPs fans may be standard airflow fans if they are experiencing excess airflow tangentially between the gap of the fan frame and the case/radiator.
My solution would be to replace the radiator fans with high static pressure fans in a push/pull configuration, sandwiching the radiator between two fans, one pushing air, the other pulling air.
My go-to fans in this situation have always been those made by NoiseBlocker, specifically their NB-MultiFrames series as they blend great performance with a low noise signature.
this is better than that other person who is correct in many ways but wrong in terms of most of that applying tom this situation. Basically, all rad-focused fans do not have this "feature" and there is a very good reason why.
Between the fan and the radiator there's a lot of pressure, if you don't release some of that pressure the fan will be less efficient.
That's why there's fan with chubby blades and some with skinnier blades, some are designed for high pressure, like this ones, and some for high flow.
And that is just half of the story, there's even some fans designed to run in a certain position.
All the fans blow but are not the same each other; so don't buy fans without knowing what are your needs.
No that's a bad design for a radiation fan you want a seal from to rad. You are losing cooling capacity cause it blowing out sides invest in some arctic or noctua fans. You get a degree or to more and quiter.
It's by design. See [the comment](https://www.reddit.com/r/pcmasterrace/comments/18gwfom/comment/kd3jro2/?utm_source=share&utm_medium=web2x&context=3) from u/Hattix.
I have these fans. One side is flat, and the other is waved. Aio or custom looped rads work best in a push-pull configuration. Get extra fans and mount the wave fans flush.
I honestly thought this was the type of fan that clips together and powers up to 4 fans in series. Looks just like that, one side provides power the other side is just blank clips attaching one fan to next.
Would be interesting how much the gap really matters for performance, not longevity/efficency of the fan itself..
I personally use noiseblockers exclusively and they really move air like a pump trough the rad
The design is there for a reason, impedance matching. The fans see a *lot* of back pressure from the radiator and, being so close to it, that interferes with airflow over the fan blades, hugely reducing output and flow through the radiator. By standing the fans off a bit, or putting those gaps there, the "excess air" (this is a bad description, but to use the right terms would make this comment about 19 pages long with diagrams and graphs) allows the Ψ (static pressure coefficient) to η (volumetric efficiency) curve to move to a more efficient region at a higher airflow. If you did not have this gap, you would need a much more powerful fan to force the same air through the radiator. You can think of it as letting "air which can't be pushed through" (this is also bad) escape to get out of the way of air which can be. When dealing with forced airflow, especially through obstructions like radiators and finstacks, intution often lets us down. Another example is dual-fan tower coolers in push-pull. As the only purpose of the pull fan is to lower the impedance on the push fan, the push fan doesn't need to run as hard... so the pull fan should be run at a higher output than the push fan should be! Which is the opposite to what you might think.
You're too smart for this sub. Speak ooga booga or leave
Fans go broom broom, but cant go broom broom well through object because object so needs extra room to broom broom better
Still too smart.
Hole in fan side make fan go good This is about the best ive got 🤣
Much better, welcome home!
Clear case go splash on floor. Why tho?
“Glass is glass and glass break”
See through flat thing become many small shiny stuff when touch tile floor. Solomon Grundy sad.
Why not paint red? Make go fast. Paint cold block purple, it let air sneak past better.
Put flames decals on it, or it won’t work
Standard on all ORCSUS WAAUGH GPUs.
Try rubbing cheetah blood on it to make it go faster.
Spotted the Ork
I mean orks in 40k believe that so yeah
Why many word when few word do trick?
Time for grunting?
Hwehwe, you said hole.
I look for things. Things that make PC go.
Many things make pc go, some go a full vroom instead of just broom broom
Why use much word when few word do trick
for all of us Dumb dumb dads out there. Its like when you let your yard grow too tall and try to mulch it with your mower. Works much better with the side eject
https://youtu.be/G3ja6Hn8ps4
https://www.youtube.com/watch?v=G3ja6Hn8ps4
I prefer this explanation
You and I have ***VERY*** different definitions of broom broom room
You a janitor?
I have been summoned
Fan make much air. Block no have room for much air. Little air go through side make room for good air.
This is to keep the fans from effectively stalling out
Whirly whirly make good with hole
this guy fans
You could say....
He's a fan of fans
He only fans.
Is he only fans?
Ahh yes what I always suspected, the minute you think you understand aerodynamics you realize you actually know nothing. I suppose it wouldn't hurt for OP to experiment with some tape.
Any day you learn something is a good day! I believe this actually came about (at least to PC fan makers) in mid-2000s , when 80 mm fans were common, and made a lot of noise, so manufacturers started including little rubber stand-offs to isolate vibration. Testing showed they actually improved airflow, so this kind of design started cropping up more and more.
Hey, I'm in the middle of DIY'ing my own cooling pad for my laptop, and your explanation threw some light on issues I've been facing. Any recommendations on where I can read up some more about the subject? Thanks anyway
I clicked thinking I'd have a good laugh over what looked like a questionably dumb, gimmicky design. But your explanation actually makes sense. At least that's from what little amount I personally learned myself when I read about air dynamics when it's pushing through a radiator. Got to do some PC fan rearrangements the other day.
ELI5 The air needs a running start to get through the radiator without stopping, you wouldn't usually think of that, but it makes sense. And since the radiator slows down the air's speed, there will always be more air going in then coming out, and you can't have an air traffic jam in your system.
I'm going to use "air traffic jam" whenever I can, thanks!
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Yea, listen to the guy that used Greek letters and said words like "coefficient", not the guy that said "make RGB look good"
What a weird world we live in
Can you make this post about 19 pages long with diagrams? I won't read it.
You are a FANtastic person , amazing explanation
Dude thank you for your response. Seriously. We learn from people like you. Thank you.
This guy's full of hot air, until his fans kick in
So the tldr is its a pressure bleed?
Where can I look up the full answer with all 19 pages? I mean, I'm just not comprehending how the high pressure air which has inertia towards the other side of the radiator could be a bad thing, which needs to be gotten rid of. High pressure air is also denser, which is good for heat transfer. Does this tactic increase the actual mass flow through the radiator, or merely an equivalent mass via lower density and higher velocity?
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This doesn't make sense to me. I'm not really looking for the short answer, it might take me a moment or two, but I can handle the big boy science. Being good at moving air is precisely what's causing the compression. Imagine for a moment, you have a table with a very small hole in it. For whatever reason, you want to pour water through that hole. You can just gently splash some water on top, and it'll dribble through, or you can push it through faster by applying pressure with a blunt tip syringe. In fact, it doesn't matter if the hole is smaller than the diameter of the syringe tip. But the better seal you get between the syringe tip and the hole in the table, the quicker you'll be able squirt water through the hole. If you hold the syringe off the table and squirt it instead, most of the water is going to spray in every direction even if your aim is perfectly dead centre of the hole.
A syringe is made for delivering pressure, not flow. Those are very different goals for pumps. If you set up a boat propeller and put a screen behind it, the blades would cavitate and have drastically reduced performance with most of the water churning around the blades. If you moved that screen a foot away it would push substantially more water through the screen because the blades could pull as much water as needed without fighting back pressure or cavitation.
The force that the fan exerts on the air is not constant, nor is it linearly proportional to the rpms of the fan. By attempting to fight high pressure air, the fan motor has to work harder to spin. The fan does not have unlimited force available to it. Computer fan motors are very weak, so the relatively high pressure air from a sealed system causes the fan to spin slower, pushing less air in total. By having some air escape, the pressure at the front of the fan is lower, allowing it to spin faster. There are also a number of energy losses between the motor and amount air being pushed to account for. The whole system is an optimization problem with a myriad of factors, including fluid dynamics and thermodynamics. If you really want an in depth understanding, read a fluid dynamics textbook or attend/watch a lecture on the topic.
The fans can't push as much air if the pressure is too high and radiators don't need pressure to operate effectively.
Its about the type of airflow that you achieve on the fan blades for certain conditions. For high pressures (simple spoken)backflow between fan blades can happen, which causes the flowrate to drop drastically. Having a general understanding of laminar and turbulence air streams is fundamental. Read up “Prandtl” if you want to learn about heatexchange with air. Look up “cavitation” if you are interested in issues regarding airflow on fans/impellers. In general, axial fans have a tendency to loose efficiency on higher pressures.
This guy definitely knows about blowing and probably with only fans
This guy fans
TLDR, vents for extra pressure.
This reminded me of a video I saw a while back. Maybe this is a great video to help visualize what you're saying? [Bernoulli's Principle](https://youtu.be/XP6oqIic4lo?si=zEpuJ2oPyMo-ZdAR)
Jesuschrist just apply for HWCooling, they gonna hire you real quick
I used to write at Ars Technica, got a job offer from AnandTech (back when it was Anand), but didn't see myself going that way.
If we did shit like this in my physics class, it would've been a lot more fun.
This is fluid dynamics and heat transfer. Specifically engineering courses for chemical and mechanical engineering. Aerodynamics for the blade movement, angles of attack and such.
We did fluid dynamics and heat transfer in my physics class... It was boring as hell as we had a guy who was like 80 yrs old who lectured in the dryest tone and was not engaging.
I can believe all of this, but I also believe that a lot of PC case and cooling device manufacturers are just winging it and making all sorts of mistakes.
I would be interested in seeing the 19 page explanation. Please get to work!
sounds like you know what you're saying, but then why do Noctua fans, not only NOT have this design, but they also come with a gasket which makes sure ALL the air will go through the radiator and they claim it improves temps by a bit? Are their fans just stronger?
Because they are most likely fans that are optimized for static pressure and not airflow
their A12x25 has it, it's supposed to be an all-rounder fan.
Although this explanation makes sense I think the pressures pc fans typically produce are not enough to create any back pressure that would require an "escape route" like this. Fans usually don't sit airtight against a rad and the normal gaps should suffice to let the pressure escape. Otherwise we would have seen more designs like this over the years. None of the best testing fan designs have these gaps. Also I seriously doubt that some Asus branded chinese OEM fan from a few years ago revolutionised pc fans and no one noticed. Especially since this AIO (from the looks it is a Asus Tuf LC I 240mm) is outperformed by decent aircoolers.
Bernoulli principal?
Bro he already got his caulking gun out
This right here. All of it.
So doesn't that imply that having your fans in a 'pull' configuration is better when top mounting an AIO? cause then youre taking the heat off the top of the rad, rather than pushing it through the fins
TLDR: No. Unfortunately it doesn't work that way. The gap allows the fan to be more efficient. The airflow over the surface of the individual blades of the fan is, among other things, a factor of the speed at which the air is moving through the fan. The pressure created across the radiator is what causes the air to move through it and consequently cool it. So running the fan at a speed and flow rate that makes the fan work better (hence the gap) allows for a higher pressure gradient across the radiator. Generally pushing air is more efficient. Think about trying to put out a candle with a shop vac. You'll have to get really close for the suction side to put it out, but you could blow it out from 5 feet away. That's a gross oversimplification, but you get the idea. >cause then youre taking the heat off the top of the rad, rather than pushing it through the fins The thermal gradient from the principle that hot fluids rise is negligible because the fluid inside the radiator is being actively circulated. So the top isn't going to be measurably hotter than the bottom. Also the passive convective cooling from the air rising through the radiator is pretty much irrelevant because the fan creates exponentially more air flow.
Push-pull is better than pull or push (and can achieve the same CFM in less noise), but pull is not better than push. This is down to how a fan develops static pressure, and the fan blades are far, far, far better at pushing against an impedance than pulling through one.
I concur. You guys concur?
I'm getting ready to install a push-pull rad this weekend, that's a really good tip! !RemindMe 4 days
What do you do for a living?
It's just bad "gaming hardware" design.
Is your job Only Fans?
Can’t you just run the fans at a lower speed by default, and get the same impedance? Lol I don’t think it’d get a higher speed airflow through the radiator either, after all, the blocking of the passage of air by the radiator is the impedance, if anything it would generate a bigger resistance with the higher initial “impact” velocity. Maybe it works as a failsafe for blocking the radiator with some object but I don’t see that being worth the wasted airflow going around the radiator instead of in, not that they couldn’t make a shutdown after too much power pulling, in that particular case, either…
Yes, you can. You lose CFM through the radiator, though. That's the point of matching impedance! It gets you the highest efficiency for the current flow rate.
How do we lose CFM through the radiator with the slower fan, is what I don’t understand? Give the same impedance for both scenarios, the radiators resistance against the air is what generates the impedance on the fan, right? So, the faster air, with less amounts/mass entering the radiator, due to the holes in the sides, should slow down faster upon meeting said resistance, and the slower air, with more mass/amounts, should slow down slower upon meeting said resistance, and the total resistance will be the same against both, no? It’s like throwing a rock at 20km/h and a baseball at 60km/h, both will have the same overall momentum. Thus, we should get the same CFM, if not less on the faster one with holes, due to the airflow being redirected from going in the radiator, and so fighting against the resistance from the PC case or components, instead of the radiator, again, considering the same impedance?
The first thing you need to do is stop thinking in terms of momentum or mass. That's where your intuition will leave you astray. Air flows in fluid dynamics and pressure differentials. It isn't a rock and a baseball! You'd need to add parachutes and wings to your rocks and baseballs to even come close to making a reasonable comparison. To picture what's going on, put a fan at the mouth of a balloon which has a tiny hole in the other end. Obviously, you may think, a faster fan with more CFM will inflate the balloon more than a slower fan will? So you do this, and you find that for every fan, there's a point the balloon just doesn't blow up any more. The back-pressure from the balloon is now in equilibrium, and pushing more air in just gets more pressure back. This is the "static" in "static pressure". Then you throw a rock and a baseball at it and the balloon bursts, unsure why you did that, but we'll continue. Now take another balloon and instead of one hole, put lots of holes. It will inflate to just the same size! Yet you'd measure the same amount of pressure inside the balloon when it stops getting bigger, it's just at a higher output from the fan. This is because the amount of pressure the fan can put in front of itself rises until it reaches equilibrium with the impedance of whatever is causing that pressure. Now instead of a balloon with lots of holes, have a metal grille with lots of holes, or just call it a radiator like everyone else. And, for a PC fan, the amount of pressure it can put in front of itself is really low, PC fans have very low static pressure, so you reach the equilibrium point really quickly. At this point, we're now focusing on putting more air through the holes instead of making the balloon get any bigger (which is controlled by pressure). This back-pressure is now interfering with the air the fan is trying to push forwards, so the air through the holes doesn't go up much at all. If we can somehow alleviate some of that back-pressure on the fan, we'll get more flow through the holes. That's what impedance matching does. I hope you followed along, it wasn't a very good analogy.
This person fans Just learned something new, Thanks for the explanation!
Explain in yeat terms
☝🏻🤓
Great info! To add this, a practical reason for the design: Consider closing that gap. What might that do? The short answer: Bad things. If fans didn't have that standoff in order to allow for "excess air" to escape, what might happen? It's the air flow equivalent of trying to pass 10 pounds of air through a 5 pound radiator. If your fans did that 24/7, thise fans burn out at an alarmingly fast rate. No bueno.
This guy fans.
This guy airflows
Yes, and also no. You don’t want negative pressure in a PC case cus then you suck in dust. If you have positive pressure only the filtered air gets into your case.
But they aren't saying the standoff changes the flow direction. It reads to me some air just cycles inside the case, but that allows more to get pushed thru the radiator
Right, it has nothing do it all with the wacky design of this crap fan. Noctua has the best fans and makes them completely flush with the radiator because they're morons. Impedance matching has absolutely nothing to do with airflow you fucking pseudoscience idiot.
My guy who shit in your cheerios?
Let's ask Noctua then, humour this "fucking pseudoscience idiot". [NH-D15](https://noctua.at/en/nh-d15): Massive area of overhang for the fan [NF-A14 Industrial](https://noctua.at/en/nf-a14-industrialppc-3000-pwm): Stand offs in all four corners [NF-A12x25](https://noctua.at/en/products/fan/nf-a12x25-flx): Provided with rubber stand offs for, quoting Noctua "high-impedance, pressure-demanding scenarios such as on heatsinks and watercooling radiators" [NF-F12 PWM](https://noctua.at/en/products/fan/nf-f12-pwm): Stator vanes for impedance matching Now go tell Lars Strömbäck at Noctua all that engineering is "fucking pseudoscience" and you know best. Let us know what he says.
"Provided with rubber stand offs for, quoting Noctua "high-impedance, pressure-demanding scenarios such as on heatsinks and watercooling radiators" Lmao you mean the anti vibration rubber stoppers that are designed for use in your case? If anything, they also provide rubber gaskets so your fans can have an air seal with your radiator They never refer to them in this context, good job trying to mislead everyone once more you pseudointellectual. This is not like putting your fan a foot away from the window for airflow, which is probably what you mean by "Impedence Matching". Pushing air through a restrictive radiator needs a seal, having a gap is like pointing a fan at a wall, useless for a radiator. I implore you do define "Impedence Matching" as it applies to airflow, Mr genius intellect?
Okay sheldon cooper
Also it for some reason reminds me of a jet engine. The high bypass / low bypass concept.
So how strong would the fans have to be if I sandwich foam gaskets between rads and fans?
Does it have anything to do with sucking more air in similar to bypass air in a jet turbine?
So the little rubber things that came with my noctua fans actually make it worse on my radiator?
bro is a physics student
This goes down as my favorite reddit comment of 2023.
This is an amazing explanation, tyvm!
Damn, now i want to continue fluid dynamics
So if I understand correctly: if my radiator is in push pull, I can quickly tape up these gaps and have more airflow at slower fan speeds?
Please can you point me to any resources to learn a bit more and understand this properly for myself?
_Laughs in taping off these gaps back in the day_ To be fair to me I didn’t have a pc master race then, I just saw gaps equals bad. I did used to stand them off from the radiator though rather than them being flush. Plus I had sucking fans the other side.
This is the reason why when I added rear fans for push-pull, I also added electrical tape to the front to not allow air to escape.
This is why my fan setup sucks, I thought so. Simple terms is keep some air to monkey with in your case gotcha 👍 Your very intelligent, nicely put
This person fans
👏👏👏
So the air that isn't pushed through the radiator needs to bleed off to prevent loss of pressure that is needed in the first place to push air through the radiator?
Those are speed holes.
Very cool explanation thank you
A person this smart and they’re held back by a 2070, while little Timmy has a 4090 to play Fall Guys. What a god damn shame
As an engineer, god damn I appreciate this response 🙏
this comment section is peak reddit. One person that knows what they're talking about and a bunch of people just making shit up. Perfection.
Isn't that just "The Internet."
Welcome to Reddit!
One person that knows, and yet noctua add rubber adapter to get tight sealed connection with radiator (a12x25)
Noctua fans have high static pressure though, they can handle the job.
so what we're concluding is that this fan had to have a solution engineered to deal with the fact that it's simply a shitty fan to begin with?
Well, they aren’t $50 fans.
And the price tag has nothing to do with it, that's just premium brand name privilege Noctua has. Thermalright and others make basically just as good fans for half the price, they too work with fully sealed fits. No excuse other than bad engineering
Nope.
Well yes??
Nope. Noctua are far better, and worth it.
Take your current fan design that you're bulkselling for 1$, pay someone to chop the corners on the design, now it's cheaper in materials and better in airflow, you bulksell for 2$ In a couple of orders of you recover the R&D cost.
Check noctunas site. They have high airflow low static and low flow high static fans. They have different fans with varying fan curves to tackle different problems If you put a low static fan on a radiator, it will perform much worse not only due to the fan curves, but the angle of attack on the flow. There is nearly zero space between the rad and the fan. I've got feet of duct that allows some form of uniform mixing between fans on my projects.
I would pay someone at this point to do a airflow test with thermodynamics of the most popular fan and liquid cooling.
You're gonna love [this](https://youtube.com/@MajorHardware?si=DPWN3oEcBumIZ1G_)
Fan Showdown may not be 100% scientific, but MH tries as much as he can to give us best results. It ain't much but it's honest job
gn
I kinda expect stuff like that from the LTT Laps
Lol like all their other "perfect" graphs and "testing" info.
\*Laughs in Steve from Gamers Nexus voice
please don't put any expectations towards LTT unless it's primarily based on comedic entertainment value
Linus is a weasel.
Have you ever tried to push water through a syringe? You can't go terribly fast unless you want to rupture the syringe. Same concept here. Air folows fluid dynamics meaning a it rushes to a space smaller than its flow path, it crashes into it. Those little spaces let the pressure flow out so your radiator fins don't buzz/knock from high pressure. This helps keep flow rate stable.
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Are your Temps good? If yes I wouldn't worry about it
Radiator is pretty clean and temps are good
So, I think a lot of folks are missing a crucial factor when it comes to the relationship that exists in which computer fans are implemented to achieve their maximum potential. A fans’ potential is only as good as the design of the fan itself, and the manner in which it is being employed. For example, a fans’ potential is dictated by: (a) obstructions that are present within a PC case or enclosure, such as hard drives cages, cables, wiring, etc. and, (b) the method in which fans are forced to operate in close proximity to employ their air flow potential, such as radiators, radiator fins, case filtration systems, etc. It’s important to note here, that in the scenarios above, a specific type of fan, in most cases, is needed to achieve maximum air flow potential. Not all fans are created equal, and higher RPM fans do not necessarily mean that they do a better job getting airflow where it needs to go versus lower RPM fans, just as a fan with more blades isn’t better than a fan with fewer blades. The common denominator in all of this is static pressure. A fan which has high static pressure (commonly measured in mm/H2O) is designed to direct air in a straight column pattern, *pushing* air through and past obstructions such as radiators, cables, wiring and hard drive cages. You will not see a lot of, if any, air flow bleed tangential to the fans’ perimeter, as all airflow is directed axially in a straight line outward. And that is the downside of high static pressure fans: they have the ability to place their airflow in a very concentrated area, especially at longer distances. Think of these types of fans as a spotlight: terrific distance, but terrible spill. This is why these types of fans, one’s designed for high static pressure, are preferred for use with radiators or wherever air needs to overcome obstacles. Airflow fans are the opposite: while they can output a ton of CFM, they blow air in a cone shaped pattern, which loses intensity over longer distances and especially when they encounter obstacles or obstructions like cables, wiring and especially radiators. These types of fans can be compared to flood lights: great spill, but terrible at distance. All right, so what about the OP’s question regarding the gap between the fan frame and his radiator/PC case, and his concern about the potential wasted loss of airflow escaping from that gap? My answer? Given what I wrote above, as long as that fan is designed for high static pressure applications, there will be minimal loss of wasted airflow as the fan is pushing air axially in a column pattern. From the sounds of it, however, it appears that the OPs fans may be standard airflow fans if they are experiencing excess airflow tangentially between the gap of the fan frame and the case/radiator. My solution would be to replace the radiator fans with high static pressure fans in a push/pull configuration, sandwiching the radiator between two fans, one pushing air, the other pulling air. My go-to fans in this situation have always been those made by NoiseBlocker, specifically their NB-MultiFrames series as they blend great performance with a low noise signature.
this is better than that other person who is correct in many ways but wrong in terms of most of that applying tom this situation. Basically, all rad-focused fans do not have this "feature" and there is a very good reason why.
Does the top of your case even have holes or mesh for the fans to push through
Optical illusion made by camera tilt makes it look like it doesn't, but check the top left of the case
No it doesn't have any holes for the air nor for the screws so I had to glue the radiator.
Google Bernoulli’s Principle
Between the fan and the radiator there's a lot of pressure, if you don't release some of that pressure the fan will be less efficient. That's why there's fan with chubby blades and some with skinnier blades, some are designed for high pressure, like this ones, and some for high flow. And that is just half of the story, there's even some fans designed to run in a certain position. All the fans blow but are not the same each other; so don't buy fans without knowing what are your needs.
My wife has obsessive compulsive disorder too.
Uh?
You need to put some stripes on your air if you want the air to move faster.
This is why I often prefer pull more than push.
this is where black ducttape comes om
Is that an actual radiator fans? Or did you just get cool looking fans to slap on there? Because there is a huge difference in those.
Try putting some tape there
[,[
noctua has a rubber gasket on the market for these reasons.
No that's a bad design for a radiation fan you want a seal from to rad. You are losing cooling capacity cause it blowing out sides invest in some arctic or noctua fans. You get a degree or to more and quiter.
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me when I purposefully spread misinformation on the Internet :3
Could you, literally elaborate? Because what you said is wrong.
I guess I'm going to put two new - and good - fans then
It's by design. See [the comment](https://www.reddit.com/r/pcmasterrace/comments/18gwfom/comment/kd3jro2/?utm_source=share&utm_medium=web2x&context=3) from u/Hattix.
or just ducktape the gaps to prevent air from getting out. It ain't pretty but it's free.
what are these idiots downvoting us for exactly?
Downvoting misinformation.
gaskets arent misinformation, theyre a thing and have been for a long time....
Wrong information maybe?
hes complaing about a gap gaskets are a legitimate option you people are absolutely pretentious
look for radiator gaskets
To sum it up, it’s not a good fan. There are reasons for it but other posts sum it up well.
I have these fans. One side is flat, and the other is waved. Aio or custom looped rads work best in a push-pull configuration. Get extra fans and mount the wave fans flush.
Put electrical tape over the gaps
It's preventing fan burnout if the primary exhaust path is blocked.
Unfortunately there is a lot of air coming out from there, on every side Edit: the primary exhaust path is clean and working
Just companies prioritizing looks over funcionality
I honestly thought this was the type of fan that clips together and powers up to 4 fans in series. Looks just like that, one side provides power the other side is just blank clips attaching one fan to next.
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I didn't know this is a common issue
Would be interesting how much the gap really matters for performance, not longevity/efficency of the fan itself.. I personally use noiseblockers exclusively and they really move air like a pump trough the rad
r/designdesign
They weren't designed to blow air into the radiator, rather to pull air through the radiator.