Static pressure vs airflow - yet another thread on this

[kyufaker]

Dear friends,

I have been tinkering with PC for a little while now and I am still finding myself questioning this topic again and again.

First scenario: push - lets take extreme examples 40cfm 1.8 mm/h2o vs a 90 cfm 08.mm/h2o fan (these are made up)

So what I struggle with is, if the fan is pushing in 90 cfm of air, then surely 90cfm of air comes out on the other side, granted air may slow down here an there, but overall what goes in, goes out. How exactly does a high cfm fan lose out...

I can see a difference where a fan is pushing air through different parts, lets say 80 cfm goes through outer parts of the fan blades and 10 cfm through the middle section, that could mean that some parts are cooled better than others in a rad, but that is just about the only thing i can think of...

Similar to pull i guess...

Completely separate to the above, if I am using pull config, should I go for an SP120 or an AF120? Seemingly air pressure doesnt matter in this case?

Thanks v much, I know its not very coherent but I am at work so needed to type this up v quickly...

Cheers

 

[4Ryan6]

http://www.tomshardware.com/forum/id-2196038/air-cooling-water-cooling-things.html

Static pressure is the fans ability to overcome obstructions, simple as that.

Regarding push or pull, IMO from what I've discovered with my own cooling the best way to achieve a full flow through the radiator, is to use a shroud on the radiator, set up to pull or push air through the radiator.

That way a full unobstructed air flow is pulled or pushed through the entire mass of radiator cooling fins with zero fan motor blockage of the air flow.

The shroud allows a gap between the cooling fan and the radiator, allowing the air pressure to equalize through the cooling fins taking full advantage of what the radiator is designed to do, removing hot spots created by restricted airflow of the fan motor body.

There's at least an inch and a half of air blockage for each fan motor body, even with a push/pull direct fan mounting, so add that blockage up for multiple fans and the radiator airflow restriction adds up, and the cooling efficiency of the radiator goes down.

 

[Godto]

static air is more concentrate in middle ... so if you use on a push config thru a radiator then it the best..
if the fan doesn't have a static rating then it just the air push thru but go wider range.

think of a water hose... it you turn it on said 1/4 turn.... and if you restrict the hose then the same a mount of water do go thru but in a small powerful stream. and static is more like that.

on a pull if you have a non static pressure ... then the air go thru the same speed but they go in wider range and also can be sucking back thru the fan too... you want to push the hot air as far as you can away. but the hot air doesn't go as far then chance they can be sucking back in.

this is how i understand about the static and none static fan,
and why certain thing static fan is so much better for.

 

[4Ryan6]

static air is more concentrate in middle ... so if you use on a push config thru a radiator then it the best..
if the fan doesn't have a static rating then it just the air push thru but go wider range.

think of a water hose... it you turn it on said 1/4 turn.... and if you restrict the hose then the same a mount of water do go thru but in a small powerful stream. and static is more like that.

on a pull if you have a non static pressure ... then the air go thru the same speed but they go in wider range and also can be sucking back thru the fan too... you want to push the hot air as far as you can away. but the hot air doesn't go as far then chance they can be sucking back in.

this is how i understand about the static and none static fan,
and why certain thing static fan is so much better for.

I respectfully disagree!

High static pressure fans can over a distance overcome the fan motor body dead air space, when air pressure equalizes, but not when directly mounted with about a 1/4" ~ 3/8" air gap between the fan and radiator.

When I conducted the "Airflow Inner / Outer Velocity Tunnel exhaust Face Readings:" Tests in the Cooling fan Roundup, I also tested some high static pressure fans that were not listed in the roundup, but they had the same end result characteristics of the traditional fan that slings it's airflow centrifugally outward from the fan face. ( The test result readings were taken at the end of the test tunnel which was 2' out from the actual fan exhaust face)

Creating more outer wall pressure than inner wall pressure, the only fans I tested that could overcome that inner pressure reading weakness, was the Silverstone Air Penetrator designed fans, but it took a 2' distance to achieve that equality.

We obviously do not have a 2' equalization point directly mounted to a radiator.

http://www.tomshardware.com/forum/331629-28-cooling-roundup-2012

High static pressure fans have a steeper blade pitch that pushes air stronger requiring a more powerful fan motor and rpm speed to deal with the blades resistance to air.

They push a high volume of air under constant pressure, but no company as far as I know, has completely overcome the fan motor body dead air space, mounted directly on the radiator.

 

[Godto]

i just use some example hope to draw a pict for easy to understand .. it not perfect ... and yes ... you are correct.

but he was also asking about pull .. will they both be the same since it pull.

I am learning about fan in the last couple of month before I build my comp. want to see what new and what hot.
the last one i build was over 4,5 years. so I'm learning as i go. and the different way OC than the old pentium4.
My last was Q660 some thing like that.. before the I3,I7 stuff. the concept are the same.

 

[4Ryan6]

Using a shroud in a pull configuration will at least allow all the fan or fans working together to create a vacuum pulling air over the full radiator cooling fin face.

Assuming of course the other side of the radiator is unobstructed allowing full air flow through it.

 

[Godto]

the question is ... in pull ... which fan work better ...

static ?
or non static?
or they both the same ?

 

[4Ryan6]

the question is ... in pull ... which fan work better ...

static ?
or non static?
or they both the same ?

Read question 9, in the very first link I posted in this thread that should answer you?

 

[Godto]

it not answer the question me and kyufaker ask ....

if we said only have pull only ... no push ..... that the question.

it pull then the fan doesn't have to be static to be good or viversa or they both the same ????

same speed of fan, same air pressure..... do they matter or as long as they spin fast then they good?

 

[4Ryan6]

Question 9 answered the FPI radiator needs, so are the radiators low FPI or High FPI?

The question you are asking regarding pull is dependent on what the cooling fan is attempting to cool?

You wouldn't use a 33cfm cooling fan on a 16fpi radiator as it needs a high static pressure, high cfm, high speed, cooling fan to be properly cooled whether it is in push or pull.

A low fpi radiator like a 8fpi could be cooled by a 33cfm cooling fan in push or pull, because the radiator is designed to be cooled by a low cfm cooling fan.

Every fin the air is being pulled through restricts and cuts down the airflow whether it is a radiator, or heat sink, because every cooling fin supplies resistance to the fans air flow and disrupts it's airflow pattern.

Even case cooling does the same as the obstacles within the case disrupt the airflow path and creates turbulence, which can be a good thing or a bad thing.

 

[4Ryan6]

So what I struggle with is, if the fan is pushing in 90 cfm of air, then surely 90cfm of air comes out on the other side, granted air may slow down here an there, but overall what goes in, goes out. How exactly does a high cfm fan lose out...

I can see a difference where a fan is pushing air through different parts, lets say 80 cfm goes through outer parts of the fan blades and 10 cfm through the middle section, that could mean that some parts are cooled better than others in a rad, but that is just about the only thing i can think of...

You cannot discount resistance to airflow, like the cooling fins on a radiator or heat sink or the component obstacles within a computer case, some cases with dust screens seriously cut the overall cfm of the cooling fan before it has a chance to cool anything.

So just because a fan pushes 110cfm does not mean you get 110cfm out the other side of the restrictions it pushes or pulls air through, the fan may be 100% capable of pushing or pulling 110cfm of airflow, UNRESTRICTED, but restriction changes that.

Look at the fans performance in the cooling fan roundup regarding restrictions effects on the fans actual output.

http://www.tomshardware.com/forum/331629-28-cooling-roundup-2012

Or the cfm tests that were conducted showing what was left of the airflow after pushing air through a simulated case restricted vs not restricted.