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post #11 of 971
Thread Starter 
How Airflow and Static Pressure Specifications relate to real world use.


Airflow specification is the maximum airflow of a fan with no resistance to the airflow ..
Not a real world use of our fans.
But we use the fan in a case with a grill (restricting airflow) and often a filter (also restricting airflow) and often blowing into a HDD cage (still more restriction to airflow).

End result is that the fan specified airflow is more than twice what is actually flowing .. in fact often even more.


Static pressure rating is the pressure level when air stops flowing .
Again, not a real world use of our fans.

The reality is that if we have 2 fans, one with a higher airflow and lower static pressure rating and the other with lower airflow and higher static pressure rating .. but in almost every case (no pun) the lower airflow / higher static pressure rated fan will flow more air than the higher airflow / lower static pressure rated fan will

Let us look at fan A with 70cfm & 0.8mm H2O rating compared to fan B with 50cfm and 2.0mm H2O rating.

Now let us assume the grill, filter, HDD cage, cables etc. create a pressure level of 0.35mm H2O .. half of fan A's rating .. which drops the cfm by about 60-70% giving us 21 -28cfm of airflow. But for fan B the 0.35mm H2O resistance is dropping the airflow by 20-30% leaving us with 35 - 40cfm of airflow.

Fans A and B with 0.35mm H2O resistance
  • Fan A 70cfm & 0.8mm H2O fan is flowing 21-28cfm.
  • Fan B 50cfm & 2.0mm H2O fan is flowing 35-40cfm.


But what if the grill, filter, HDD cage, cables, etc create 0.8mm H2O? This is the static pressure rating of fan A .. so now it is flowing no air.. But for fan B the 0.8mm H2O is less than have it's static pressure rating and iy will still be flowing about half of it's rating leaving us with about 25cfm airflow.

Fans A and B with 0.8mm H2O resistance
  • Fan A 70cfm & 0.8mm H2O fan is flowing 0 cfm.
  • Fan B 50cfm & 2.0mm H2O fan is flowing 25cfm.

These are estimated resistance and airflow to resistance to give an example. Hopefully it helps you understand how static pressure and airflow relate to each other

In most cases a fan with a real static pressure rating of about 1.5mm H2O will do a good job of moving air.

P/Q Curve
Actual Airflow Versus Peak CFM & Static Pressure:
Testing is done for:
  • Airflow; done in free airflow .. not resistance at all .. fan hanging in open space. All of our fan use has resistance.
  • Noise; done in free airflow .. no resistance means less noise. Again, all our fan use has resistance.
  • Static pressure The amount of pressure it takes to stop fan's airflow. All of our use requires airflow .. so not really applicable to our use. P-Q curve graph is more appropriate.


Here is a P-Q graph and chart of fan performance at 0.5 & 1.0mmH2O to show how far from specs the actual airflow is in use .. like intake through a grill, filter or exhaust through a grill, or on a cooler / radiator. Our fans are working with from 0.1 to 1.0mmH2O .. usually 0.2 - 0.7mmH2O. .. meaning 0.5mmH2O resistance is a quite appropriate for our uses. Also keep in mind this is with fans at full speed. The flow / ability to overcome resistance drops dramatically at fan speed slows down.
Please remember I am not recommending any of the fans. Some are great, some are not. This is only an example of airflow with resistance similar to what we have compared to their published specifications.

Please take note of how many of the fans are flowing no air at all at 0.5mm H2O and how many more are flowing nothing at 0.75mm H2O.
Please take note of how many of the fans are flowing less than 20CFM at these pressure.

Notice how much airflow the other fans are flowing at 0.5 and 0.75mm H2O compared to what they flow with no resistance (0.0mm H2O). I put a line in to show 20 CFM, but if that is all the case is flowing per fan and the CPU cooler has a 60-70cfm rated fan, it will take 3 case fans to just keep up with the CPU cooler .. and most GPU coolers use as much air as the CPU coolers .. meaning 6x case fans each moving 20cfm into the case in order to keep up wiht the component demand.



Also, this data is based on fans running at full speed. It is important to remember that as fan speed decreases, so does it's CFM of airflow .. and also it's static pressure rating. In other words a fan that will flow 65cfm in open air and flows 35cfm at 0.5mm H2O at full speed is lowered to half speed it will flow about halve as much. Add pressure (resistance) and it is much lower still.

http://thermalbench.com/2015/01/30/ekwb-vardar-f2-120-fan/3/

Linear FPM is the air speed. CFM is calculated by using the area of the hole the air is flowing though and the air's speed. For example a 140mm fans is 0.1656 sq feet times 300 FPM (feet per minute) is 49.68CFM


Another example:
  • Scythe GT-15 ratings are 58cfm / 2.03mm H2O
  • Cougar Vortex ratings are 70.5cfm / 2.2mm H2O
  • GT-15 is flowing 7.8-7.9cfm more air at 1.02-1.19mm H2O
  • The area of pressure we use fans in normal applications on radiators, coolers, grills and filters.




Edited from

martinsliquidlab.org
Edited by doyll - 3/27/17 at 2:42pm
post #12 of 971
I have a 2nd Watercooled i7-4770k computer in a Cosair Vengeance C70 chassis, if your familiar with it, if not, it has 2 side intakes, HDD intakes, 1 rear fan, and I have a 280mm RAD on top pushing air out from the top. I'm planning to add 2 more fans on top for a push/pull, and I'm concerned about intake. The other fans are only 120mm, while 140mm x 4 are on the rad.

Should I use the rear fan as an intake, thus making the only outlet through the top radiator?

THanks,

Gregory14
post #13 of 971
Thread Starter 
Quote:
Originally Posted by Gregory14 View Post

I have a 2nd Watercooled i7-4770k computer in a Cosair Vengeance C70 chassis, if your familiar with it, if not, it has 2 side intakes, HDD intakes, 1 rear fan, and I have a 280mm RAD on top pushing air out from the top. I'm planning to add 2 more fans on top for a push/pull, and I'm concerned about intake. The other fans are only 120mm, while 140mm x 4 are on the rad.

Should I use the rear fan as an intake, thus making the only outlet through the top radiator?

Thanks,

Gregory14
Have you read post #5 "Setting up a case for optimum cooling"?
C70 has venting for 2x front, 2x side and 2x bottom fans.
Using the back fan as intake is probably not advisable, but follow the guide in post #5 to find out.

The 2x push /pull can only move a maximum of what one fan is rated in each pair. .. no increase in cfm, but it does improve airflow through restrictions.



TIM (Thermal Interface Material), How Good Should We Go?

Most TIM are within a couple of degrees of each other. Coollaboratory is a couple degrees better, but also harder to apply and get a good seat .. and without a good seat there is little if any improvement.

Honestly, I think getting a good seat .. and even more important is optimizing your case airflow to get the coolest air possible going into cooler intake. Few cases have cooler intake air temp at less than 5c higher than room, and many are 10-20c higher under heavy load. The 2-3c gain with different TIM is negligible if cooler in ingesting 10c warmer air than it should .. making CPU 10c hotter than it needs to be. wink.gif

Tom's Hardware did extensive testing of TIM a few years ago. Here is what they found. Please keep in mind the testing was done in a room with temperatures between 71-73f (21.7-22.8c). That is a +/-0.55c (1.1c total) margin of error before we take any other factors into the results. This means a 1.2c difference in CPU temperatures could be 0.1c or 2.3c with just the differences in room temperature.







Edited by doyll - 2/9/17 at 8:10am
post #14 of 971
yes I did. I just noticed its already plugged into the cpu socket, so I set it to silent mode, 645RPM, I noticed right away temps were lower, most likely due to more positive air pressure in the case than before.

And about the push pull, gonna reconsider it, I havent hit past 60c gaming. I know now I wont get 200% cooling with 2 fans push/pull.

What about Gaskets? I have some spare 140mm ones, where would I sandwich them? Fan-Rad or Rad-top mesh? both? looking to quiet things down.
post #15 of 971
Thread Starter 
Probably between fan and radiator. Will stop air leaking out instead of going through radiator and will increase distance from fan to radiator .. which often lowers noise level. wink.gif


Case Bottom Spacing Effect on Airflow to Bottom Fans
This spacing effect is also often seen with front and top panel/venting too.


Be creative when looking for spacers .. bottle caps, arisol paint can caps, hockey pucks, little brother's building blocks, etc. will all work.


Grill & Filter Effect on Airflow & Noise level



http://www.silverstonetek.com/techtalk_cont.php?area=en&tid=wh_chessis
Scroll down to see how air flows through round wire grill versus punched metal grill.


https://www.pugetsystems.com/labs/articles/Effects-of-Grill-Patterns-on-Fan-Performance-Noise-107/

Here is a drawing of basic grill mesh designs showing what their open area / airflow area is. Notice hexagonal / honeycomb patterns have much more open area for air to flow through.

Edited by doyll - 5/6/17 at 3:16am
post #16 of 971
Thread Starter 
PWM control with PSU power to PWM fan and PWM adapter with 12v power from PSU


PWM Header & Plug Pinout


PWM 'Y' Splitter & with 2nd Fan RPM Monitor


PWM Splitter with PSU Power

Edited by doyll - 4/4/15 at 10:09am
post #17 of 971
Thread Starter 
How to Make Air Ducts


Edited by doyll - 4/30/15 at 3:04am
post #18 of 971
Great thread doyll! Thank you.
how about Phanteks PH-F140HP?
I'm considering this to replace the XT140-

If it's better than XF140.because I like the colors. LOL
post #19 of 971
Thread Starter 
Phillips vs PosiDriv Screws & Screwdrivers Don't confuse them!!







The PH-F140HP is good .. although I have not personally used them, I have used the F140TS, early PHF140HP non-PWM, and PH-F140SP fans. What colors do you need .. err.. want?
Edited by doyll - 2/18/16 at 7:59am
post #20 of 971
LoL.

I need and want a white and blue theme.

Anyways, If they're on par or even better than XF140, I might replace the one on the C1.My case is all black even inside.

Thanks.
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