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Air Flow vs Air Pressure

post #1 of 10
Thread Starter 
Which is better for case cooling a fan with better air flow or air pressure, what is the difference? And also which fan is better for cpu heatsink, and water cooling radiator. Thanks in advance
post #2 of 10
Air pressure is what pushes the air so it will flow when it has resistance.. like grill, filter, HDD cage, etc.

You want good airflow but you need enough power (pressure) to keep it flowing.
post #3 of 10
generally speaking, case fans don't need nearly as much static pressure as rad fans or heatsink fans because there is not much resistance to the airflow.

The exception would be if you are trying to get a significant difference in atmospheric pressure in your case, by having primarily exhaust fans and only one intake fan, for instance. Only reason to do that though is dust control. And then you end up with a dirty filter that needs cleaning weekly.
post #4 of 10
Myself and many others always use fans with decent static pressure.
A simple wire grill restricts 29% of the airflow. That's as much as as many coolers.
http://www.silverstonetek.com/techtalk_cont.php?tid=wh_chessis&area=en

Let's say you have 2 fans;
Fan A is 100cfm / 3mm H2O static pressure. You have 1mm H2O static pressure resistance and it moves 70cfm
Fan B is 100cfm / 1mm H2O static pressure. You have 1mm H2O static pressure resistance and no air moving.
Static pressure = pressure when air stops moving.
Static = still, stopped.
post #5 of 10
Basically covered, but there is actually far more restriction to airflow for case fans than you might think. Hard drive cages, filters, wires, grills... Each one provides a significant amount of restriction, and each one takes away from the airflow.

I don't even bother to look at the CFM of a fan until I am comparing multiple fans with similar amount of static pressure. I aim for an absolute minimum of 2mmH2O, ideally 3mmH2O or more. My radiator fans range from 3.5mmH2O to 6.33mmH2O.
   
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post #6 of 10
Where can I find the static pressure details for a fan? I have been trying to find this out for some time, but most sites only list CFM not static pressure. redface.gif
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post #7 of 10
Thread Starter 
Quote:
Originally Posted by NostraD View Post

Where can I find the static pressure details for a fan? I have been trying to find this out for some time, but most sites only list CFM not static pressure. redface.gif[/quote


its the Air pressure, some do.
post #8 of 10
Thread Starter 
Quote:
Originally Posted by nleksan View Post

Basically covered, but there is actually far more restriction to airflow for case fans than you might think. Hard drive cages, filters, wires, grills... Each one provides a significant amount of restriction, and each one takes away from the airflow.

I don't even bother to look at the CFM of a fan until I am comparing multiple fans with similar amount of static pressure. I aim for an absolute minimum of 2mmH2O, ideally 3mmH2O or more. My radiator fans range from 3.5mmH2O to 6.33mmH2O.


ok thanks, I'm looking at Delta fans and these are the specs
size-120x120x25.4
voltage-12
current-1.45
power-17.40
speed-4000
cfm-150.33
mmh2o-12.43
dB(A)-56.4

i know these fans are really loud, I have a fan controller which gives out no more than 30 watts, how many watts is this fan, It only states power, but doesn't say amperage watts nor anything and if I reduce the wattage does it become more silent? are these fans worth it, and can they be used in the case and cpu heatsink? thank you
post #9 of 10
The 'power' number is watts. The 'current' number is amps. Volts x amps = watts, so 12 x 1.45 = 17.40 watts. This fan is never going to be anything like "silent" unless you slow it down so much that you might as well use something slower to start with. I have a Delta 120mm PWM that tops out around 3500 rpm. It makes a combined whine and hiss on a big air cooler. At 3000 rpm it is tolerable, at 2500 it's still noticeable. A 4000 rpm 120mm is really going to scream.
For higher static pressure at lower RPM try thicker fans. I have some Scythe 120 x 38 mm fans that draw .60 amps, or 7.2 watts. They are not PWM, but DC control only--3 wire with tach. They are rated at 3000 rpm, but do more like 2700 in real life situations. The model is DFS123812H-3000. They move some serious air, and are not quite as loud as the Delta, but they vibrate more. I can feel them through the floor.
Here is a 12 watt 120 x 32 mm PWM model-
http://www.frozencpu.com/products/15476/fan-965/Cooljag_Everflow_120mm_x_32mm_PWM_Fan_R121232BUAF.html?tl=g36c365s941

There's just no way around it, though. The more they move, the louder they'll be. Some do better than others with tricky blade designs. Panaflo style hydraulic bearings aren't as bad as ball bearings for noise. Deltas are notoriously nasty sounding.
Edited by ktony - 6/3/13 at 11:16pm
post #10 of 10
Koolance FAN-12025HBK or FAN -12038HBK, both are 2600rpm with the former being a 120x25mm size and producing1106CFM and 5.4mmH2O, and the latter being 120x38mm and producing 117CFM and 6.33mmH2O.

$8-10/ea, dual ball bearing motors, and excellent performance while still being able to undervolt very well. I have 4 on one channelof my BBitFenix Hydra Pro 30W/ch fan controller and it's still able to push power to more fans. The PCB doesn't even get warm.
   
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LG/Hitachi Slim DVD-R/W Custom MB-Backside VRM-sinks (Copper) 3x NZXT RF-FX140LB 1-2krpm 98.3CFM Case Fans 2x Corsair SP120-PE Case Fans 
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CoolingCoolingCoolingCooling
2x MCP35X + Heatsinks/80x15mm Fan XSPC EX420 Alphacool NeXXos UT60 240 6x Bgears Blasters 140mm 1800rpm Fans 
CoolingCoolingCoolingOS
4x Koolance 120x25mm 2600rpm Fans Comp/Rotary Fittings (BP/XSPC/Monsoon) Primoflex Pro LRT - White (1/2x3/4) Windows 7 Professional 64bit  
MonitorMonitorMonitorMonitor
Dell P2210Hb 21.5" 1920x1080p Viewsonic VA2012WB 20.1" LCD 1680x1050 Dell U3014 Eizo 27" 1440p 10bit RGB-LED Backlit AH-IPS Panel 
MonitorKeyboardPowerCase
55" LG HDTV (their top 2014 model) Ducky Mechanical (Browns) NZXT HALE90 850W + 8 blown-up AX1200/i's NZXT Switch 810 (White) 
MouseMouse PadAudioAudio
R.A.T.3 + MX510 My Desk GRADO RS1i Headphones Grado PS1000 Headphones 
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Bitfenix Hydra Pro Fan Controller 5ch 30W/ch Bitfenix Alchemy Individually-Sleeved Extension... NZXT Individually-Sleeved Front Panel Wires (Bl... Phobya Sleeved 1x3pin-to-4x3pin Fan Splitter 
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Sleeved Wires w Paracord myself (no Heatshrink) Custom Front and Top Panels w HexxMesh *In Prog... Working on Custom Pedestal Prototype 
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Z77 Bench-a-lot
(31 items)
 
CPUMotherboardGraphicsGraphics
i7 3930K @ 4.92Ghz Asus Rampage 4 Extreme EVGA GTX670 FTW 2GB  EVGA GTX780Ti Classified K|ngp|n Edition @ 1483... 
GraphicsRAMHard DriveHard Drive
EVGA GTX780Ti Classified K|ngp|n Edition @ 1483... 16GB G.Skill Ripjaws-Z @ DDR3-2248 9-10-9-26 1T Samsung 830 256GB SSD WD10EZEX 1TB HDD 
Hard DriveHard DriveHard DriveHard Drive
WD10EALX 1TB HDD Seagate Barracuda 7200.14 1TB WD3200AAKS 320GB HDD WD5000HHTZ 10krpm 500GB VelociRaptor 
Optical DriveCoolingCoolingCooling
LG/Hitachi Slim DVD-R/W Custom MB-Backside VRM-sinks (Copper) 3x NZXT RF-FX140LB 1-2krpm 98.3CFM Case Fans 2x Corsair SP120-PE Case Fans 
CoolingCoolingCoolingCooling
Heatkiller GTX680 "Hole Edition" Block + Backplate XSPC Single-Bay Res (Single 5.25 bay) EK Multioption Res X2 - Advanced 150 DD "Fill-Port Res" + Fill-Port Fitting (Red) 
CoolingCoolingCoolingCooling
2x MCP35X + Heatsinks/80x15mm Fan XSPC EX420 Alphacool NeXXos UT60 240 6x Bgears Blasters 140mm 1800rpm Fans 
CoolingCoolingCoolingOS
4x Koolance 120x25mm 2600rpm Fans Comp/Rotary Fittings (BP/XSPC/Monsoon) Primoflex Pro LRT - White (1/2x3/4) Windows 7 Professional 64bit  
MonitorMonitorMonitorMonitor
Dell P2210Hb 21.5" 1920x1080p Viewsonic VA2012WB 20.1" LCD 1680x1050 Dell U3014 Eizo 27" 1440p 10bit RGB-LED Backlit AH-IPS Panel 
MonitorKeyboardPowerCase
55" LG HDTV (their top 2014 model) Ducky Mechanical (Browns) NZXT HALE90 850W + 8 blown-up AX1200/i's NZXT Switch 810 (White) 
MouseMouse PadAudioAudio
R.A.T.3 + MX510 My Desk GRADO RS1i Headphones Grado PS1000 Headphones 
OtherOtherOtherOther
Bitfenix Hydra Pro Fan Controller 5ch 30W/ch Bitfenix Alchemy Individually-Sleeved Extension... NZXT Individually-Sleeved Front Panel Wires (Bl... Phobya Sleeved 1x3pin-to-4x3pin Fan Splitter 
OtherOtherOther
Sleeved Wires w Paracord myself (no Heatshrink) Custom Front and Top Panels w HexxMesh *In Prog... Working on Custom Pedestal Prototype 
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