Fan requirements: CFM or Static Pressure on a rad in a pull config...

[EarthDog]

My setup on my rads are pull due to a lack of room on the other side of the radiator on this test bench. Because of that setup, I was wondering if the need for higher Static Pressure (SP) fans would give way to more CFM since the fan isnt 'pushing' through a radiator, but pulling to get its air. The high SP is on the 'blowing' side after it hits the blades, right?

Please, no guessing. I am doing that already.

 

[Ajay57]

The first question is what are the fans you have now and is the FPI on the Rads low or high? Also are you using the Bios to control the present fans or a fan controller? AJ.


P.S. Congrats on the new Bench unit.

 

[EarthDog]

Oops, yes, more information needed, LOL!

Currently using 3x 120mm Yate Loon High...The rad with fans is MCR320 (high FPI). The other rad doesn't have fans on until I need them (rare), so that I do not care about. The Yate Loons are on a fan controller.

Not looking for a choice in fans, just looking to have the question answered and I will grab the fans I like (cause I can read specs, LOL!).

 

[Ajay57]

You could have a look at the New Corsair fans which have good reviews working on Radiators. Only 1c or 2c difference to using Noctura fans on the same test bed, there is PWM High pressure ones or PWM ones that are low noise as well. Its you choice ED i hope it helps you out! AJ.

1, http://www.corsair.com/us/cpu-cooling-kits/air-series-fans.html

2,

Please take time to look at the video i have posted as it gives you a valued insite to the new fans ED!


EDIT: Sorry these will do the job as i can see!!

 

[Tech Tweaker]

It really shouldn't make much difference if the fan is in the pull position whether it is optimized for high static pressure or high airflow. As long as whatever fan is in use has sufficient airflow, that is.

I know I've seen some minimal difference of 1-3°C with switching from a stock Corsair fan on an H80 to Scythe Gentle Typhoon AP-15.

But yeah, as for a high pressure fan doing better as a pull fan I didn't really see it. The pressure is really only useful if the fan is having to push the air through some sort of obstruction like fins on a heatsink or in a radiator.

 

[JeremyCT]

A high SP fan is a high SP pressure fan. It doesn't matter if it's pulling or pushing, the fan with better static pressure will move air through a restriction better than a fan with the same cfm rating and lower SP regardless of whether the restriction is on the intake or outlet side.

The real problem when shopping, of course, is that there's no standardized method of measuring a fan's static pressure, so the ratings you see on the box are usually pretty worthless when you're trying to compare between brands.

 

[EarthDog]

You could have a look at the New Corsair fans which have good reviews working on Radiators. Only 1c or 2c difference to using Noctura fans on the same test bed, there is PWM High pressure ones or PWM ones that are low noise as well. Its you choice ED i hope it helps you out! AJ.

1, http://www.corsair.com/us/cpu-cooling-kits/air-series-fans.html

2,

Please take time to look at the video i have posted as it gives you a valued insite to the new fans ED!


EDIT: Sorry these will do the job as i can see!!

Yeah, looking for my question to get answered, not a fan selection, but thanks.

But yeah, as for a high pressure fan doing better as a pull fan I didn't really see it. The pressure is really only useful if the fan is having to push the air through some sort of obstruction like fins on a heatsink or in a radiator.

A high SP fan is a high SP pressure fan. It doesn't matter if it's pulling or pushing, the fan with better static pressure will move air through a restriction better than a fan with the same cfm rating and lower SP regardless of whether the restriction is on the intake or outlet side.

The real problem when shopping, of course, is that there's no standardized method of measuring a fan's static pressure, so the ratings you see on the box are usually pretty worthless when you're trying to compare between brands.

Thanks... and here is the problem... Person A says one thing, person B says another...

 

[JeremyCT]

Well, he's ignoring basic fundamental physics and saying "I think so".

I'm not.

 

[EarthDog]

Can you explain in more detail please? I tend to side with his thinking I must admit. The SP comes on the other side of the blades... what happens before that shouldnt matter much, should it? So long as its getting the air, it wouldn't matter? But then, there is a bit of restriction through that rad, but not sure how being on the backside affects what is coming out the other end... perhaps I am just dense.

I'm torn. I honestly see both sides.Thanks in advance for your patience and more thorough explanation... hopefully with some supporting links for me to chew on as well.

 

[Tech Tweaker]

Well, he's ignoring basic fundamental physics and saying "I think so".

I'm not.

I'm not saying I think so. I'm saying I know so.

When I tested this a while back I found that in pull configuration a higher static pressure fan did no better on my test system than a plain high airflow/low pressure fan.

Now, I'm not saying your wrong or lying or something. I'm just saying that in my testing I saw no noticeable difference between the two. With a higher wattage system with a hotter-running CPU I might see more of a difference.

 

[JeremyCT]

Well, you can't escape physics. In order for air to flow, a pressure differential must be created. If you create airflow on one side, it pulls the same amount of air from the other side. Guzinta must be equal to Gozoutta in terms of air volume (cfm).

Correspondingly, you can't have high pressure on one side of the fan without a corresponding low pressure area on the other side of the fan. This is what makes the air move to begin with. Whether that's advantageous in a particular situation or not doesn't change the fact that a high pressure fan that creates high pressure on one side with airflow will create a corresponding lower pressure area on the opposite side as the air is drawn out of that space.

 

[Conumdrum]

Some tidbit from Martin was that with lower speed fans a pull is better. Something about the incoming air goes across the rad fins more evenly for better air dispersal. And push focuses the air more. Don't know if that was on his site or in a post. We have all seen the doughnut dust pattern on rads.

The MCR 320 isn't that high of a FPI, kinda medium.

Found it!

From here, in the MLL Archives:
http://martinsliquidlab.petrastech.com/Radiator-Fan-Orientation-And-Shroud-Testing-Review.html

"While I didn't complete the full series of tests, this was enough for me to see there is some emerging trends going on. The push vs. pull question appears to really depend on the fan power. I believe the gains in the 38mm showing more benefit in push is due to pressure and turbulence. At these stronger speeds, the added pressure compressing the air along with higher turbulence across the radiator in push is providing the best benefit. This appears to change however for the lower speed fan where pull actually does better. I believe at this slower speed pressure and air flow is so slow that it's simply not turbulent enough to show gain in push and the radiator performs better with the more evenly distributed air flow over the radiator that's provided in a pull condition."

 

[JeremyCT]

Yep, I remember that. Actually, if you could PM Martin directly you might get the best answer of all. He has a very good understanding of what makes an effective case/rad fan in practice rather than just in theory.

 

[EarthDog]

Excellent information Conum!

Now, the fans I will choose will, most of the time, be running quite slow/silent. I am also not using 38mm fans, the YL's are 25mm I believe. It honestly seems like I should just keep the YL's I have and save $20+...

 

[JeremyCT]

It honestly seems like I should just keep the YL's I have and save $20+...

Every time I start researching fans I reach the same conclusion.

"Now self, do you want a set of new AP15s for your radiator, or do you want a new GPU block/CPU block/tubing/other toy? You must pick one or the other."

So far, my answer has been consistent and the fancy fans keep losing. I will admit to having the "full set" of YLs. Lows, mediums, and highs. The mediums have proved to be my long term favorites.

 

[EarthDog]

LOL, yeah.. My other problem is I need a block that performs better than the one I have (Swiftech Apogee?) but I need one that just has a mounting plate that isnt screwed on like the Rastorm ones. I bought the raystorm while standing in Microcenter... bad idea. Oh well.

 

[GTXJackBauer]

I get your question Earthdog and Con is the magic man. Great find.

Meanwhile........

Not looking for a choice in fans, just looking to have the question answered and I will grab the fans I like (cause I can read specs, LOL!).

If you do purchase some new fans I stumbled on this - Fan Testing Round 11 and Fan Testing Round 12

 

[EarthDog]

LOL, I was trying to head off Ajay at the pass. I knew where he was going... to offer examples of fans to buy, as he did...which wasn't even my problem/concern/question in the first post. Also, I can read specifications/reivews and the 983479376739457395 threads around the web on which fan should I buy. I appreciate his help, regardless.

 

[Ajay57]

Sorry ED about that, but then again i did understand generally where you where coming from and i do a lot of reading myself and just to prove it, i will post this regards to you. AJ.

1, http://martinsliquidlab.org/

So for next time maybe as you can read reviews its all in here my friend, happy reading!!


And yes this came from a good OCF Member.

 

[Conumdrum]

Some tidbit from Martin was that with lower speed fans a pull is better. Something about the incoming air goes across the rad fins more evenly for better air dispersal. And push focuses the air more. Don't know if that was on his site or in a post. We have all seen the doughnut dust pattern on rads.

The MCR 320 isn't that high of a FPI, kinda medium.

Found it!

From here, in the MLL Archives:
http://martinsliquidlab.petrastech.com/Radiator-Fan-Orientation-And-Shroud-Testing-Review.html

"While I didn't complete the full series of tests, this was enough for me to see there is some emerging trends going on. The push vs. pull question appears to really depend on the fan power. I believe the gains in the 38mm showing more benefit in push is due to pressure and turbulence. At these stronger speeds, the added pressure compressing the air along with higher turbulence across the radiator in push is providing the best benefit. This appears to change however for the lower speed fan where pull actually does better. I believe at this slower speed pressure and air flow is so slow that it's simply not turbulent enough to show gain in push and the radiator performs better with the more evenly distributed air flow over the radiator that's provided in a pull condition."

You mean this tidbit AJ? Old timers remember..........