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Push/Pull across Radiator and Static Pressure

M

maeveth

Weaksauce
Joined
Mar 7, 2007
Messages
71
Im just trying to do some optomization here...

Is Push or Pull better given the same fan? Obviously its all about Static pressure for higher FPI rads but in general which is better?

Related to that which fans of each thickness have the highest static pressure, 25mm, 38mm, ect...

Thanks
 
Pull is better, it creates a low pressure area behind the fan which tends to pull air more uniformly through the rad. Push tends to leave a dead spot at the hub and due to turbulence created by the blades is not as effective. Pull with a shroud or some other device that moves the fan blades 1/2 to 1 inch away from the rad fins is best.

That said the real world difference in temps between the two methods is small and would be difficult to measure accurately. We are talking about a deg or two C at most in typical setups and likely less. The testing has been done but the article is long lost on the junk heap of watercooling sites that are no longer online.

Mounting needs and or aesthetics many times require non-optimal solutions. If it is a major pain to configure the fans to pull, don't worry about it.


You have a slight misunderstanding of static pressure. Fans are typically rated for how much static pressure they can overcome. Since you have no easy way of measuring the static pressure in your system the fan will be working against, saying anything about static pressure in a fan spec is usually bullshit. A PQ curve that can be found on some fan manufacturers web sites is what you want. This is a curve of fan speed (RPM) and CFM vs different values of static pressure (think "back pressure"). As static pressure increases the RPM and CFM fall because the fan has to do more work to overcome the "back pressure". Current draw typically increases as well as static pressure increases. What is useful is that if you have the PQ curves for two fans you can pick values of static pressure and compare the RPM and CFM each fan will deliver at that amount of air flow resistancestatic pressure and see which fan is more powerful (delivers more CFM).



The thicker fans typically have larger more powerful motors and bigger blades so that for a given static pressure to work against these "beefier" fans will push more air than a thinner fan.
 
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