Push V Pull

kitkat9933

kitkat9933

kitkat9933

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Got my W/C setup with Radiator on top of case for CPU.

When I have my fans on the Rad in PULL rather than PUSH i get about 10 degrees lower temps.

Now I am no Physicist, but surely pulling cold air over the radiator and then pushing this warmed up air over the CPU should be worse than pushing all the hot air out of the system.


Does anyone know why PULL is better?
 
It's possible that it stops any air circulating at the top above the rad. Having said that, I wish I saw this before I finished my watercooling setup, both rads are set to push air though.
 
Silenced said:
It's possible that it stops any air circulating at the top above the rad. Having said that, I wish I saw this before I finished my watercooling setup, both rads are set to push air though.
Click to expand...

Yeh that makes sense, I guess cutting of air circulation.

I had a play with push and pull, pull was about 20% cooler. However, I just had to make sure for pull that I put another fan to push air out at the back of the case.
 
10 degrees lower :eek:

One of the potential reasons for one being better than the other may be due to the efficiency of the fans operating in push/pull.

Eg, the static pressure may be significantly higher in pull than in push.

The best analogy I can give is that plane wings only work in one direction as lift is generated by airflow differences due to the shape of the wings. This is similar with fans as the shape of the fans will differ depending on which way it's spinning. One side will possible be greatly more efficient at creating pressure differences than the other.

That's my theory anyway :p
 
I did the tests about 3 times in each setup, for about 20 minutes while running Prime 95.

Max temps in Pull 55 degrees C. Max temps in push were 67.
 
My rads mounted at the outside rear of my case have tried all 3 push/push+pull/ pull, pull is the best option for me basicly no difference in temps but theres less dust gets pulled into the rad.
 
I'm about to swap my radiators for some new ones, i'm going to test which way round is better and see if there is that much difference for me.
 
Is this not the way a car rad works !!
car gets too hot, rad fan kicks in, pulls cold air through the rad from the front of the car.
 
You are correct yes...hmm never thought of that. There must be a reason that every car ever has the rad fan pulling air and not pushing...

Maybe something to do with the fan fins "blocking" or covering up sections of the rad when its not spinning maybe?
 
I think the fan pulls through the radiator on the car as to not block the natural flow of air hitting the car in the first place, having it in front would cause the fan to spin on its own and slow the speed of any incoming air
 
Having the fans pulling could possibly be creating more air turbulence as it's pulling air through the fins, then through the fans due to negative air pressure rather than the fan trying to push the air through.
 
Well, you've got me stumped.

Pulling the air has theoretical disadvantages as any seepage through the side between the fan and the radiator would make the system less efficient. In push air will follow the path of least resistance, ie everything is pushed through the radiator until no more can pass, then it will flow through any gaps.

In pull you have a constraint in front of the fans limit supply of air at source, but in practice, unless you have all your fans blowing from inside a case, out, this will have negligible effect. The same stands true for fans in a blow configuration.

It just doesn't make sense, especially with there being so much difference for your set up!

What fans/rad are you using?
 
Pull keeps air laminar which means the pressure drop is less than if it was turbulent. Push causes the airflow to become turbulent. Whilst turbulent flow is better for taking heat out of the radiator if the static pressure of the fan is not high enough then the resistance to the flow caused by the turbulent air is harder to overcome and the air speed through the radiator decreases too much and you lose the benefit of turbulent flow.
 
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cbr said:
Is this not the way a car rad works !!
car gets too hot, rad fan kicks in, pulls cold air through the rad from the front of the car.
Click to expand...

Also remember that until very recently cars rad fans were driven directly off the engine crank, it would be very difficult to power the fan off the crank if there is a rad in the way. It's just the way it has to be packaged.

Cars are built to totally different designs to PCs (obviously) another reason the fan would be behind the rad is for aesthetic and servicing reasons, the two really can't be compared.

In reality every application of watercooling (and ANY cooling is going to be different) your mileage may vary!

Just more excuses to play with some different testing configs.
 
I remember an artilce said that push v pull was relative to fan speed and rad fpi.
Upto 1500 rpm pull was better.
1500 - 17000 rpm hardly any difference.
1800+ push was better.
Push + shroud / pull + shroud are better than push and pull.
 
very helpful! I was all for pushing but seeing this I am now having a combination :) pull through front, push through top? :) or should I pull through both?

oh confusions?!
 
I'd go with pull simply for the fact that any fans pulling cool air in from the top of the case, also cool components below the rad.

My gentle typhoons pull from the top and "push" any spare air over the motherboard and ram, rather than spew turbulent air randomly below the rad (if it would in push)
 
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