Im talking about CPU coolers.....

I'm having a discussion on this topic on another forum, but i'd like you guys views.

A) should the CPU cooler blow air onto the heatsink

or

B) suck air thru the heatsink and spit it out the top


My opinion is that B is the more effective way

Why? If both fans move air at the same rate, then as far as the cpu's concerned, there is ZERO difference.

Its about fan location. If you have a fan at the top of the case, you'd suck air out the case as heat rises. Blowing air into the top of the case would not remove hot air effeciently.

A fan down low, you'd blow air INTO The case. no point sucking out air at the bottom of the case, you'd just be drawing the rising hot air back across the components.

Best setup is indeed push>pull. One fan blows in the bottom, one fan sucks out at the top.

im talking about the direction of airflow of the CPU cooler, not the case fans

Again depends on setup. If its on top, like most coolers, then it should suck air upwards through the heatsink.

as i said heat rises. You want to draw cool air in from the bottom of it, and out through the top. Anything else goes against common sense if you know the first thing about the laws of physics.

x2 (you shoulda make it a poll gtsman! ) the fan blowing away not only blows hot air away from the heatsink, but draws cool air to it

blow onto the heatsink is more efficient - it's been tested.
the problem then is, what to do with the hot air which now hits the mobo, some designs blow air across the heatsink, to a receiver, then out of the case - this works absolutely the best.

the physics of it:
the maximum amount of 'suck' you can have is 1 atmosphere (total vacuum, approximately 100kPa).
blowing pressure, however, can be increased over 1 million times this - the tyres on the car are usually inflated to 3 or 4 atmospheres pressure, and that's not a lot.

put your hand near the 'suck' side of a cooling fan - feel the air velocity.
put your hand near the 'blow' side of a cooling fan - feels much more blowy due to the focussing of the fan surround, so the air comes out in a stream, meaning more efficient thermal transfer on the blow side.

for CPU fans its blow. hot air rises eh? despite the fact that CPU fans are mounted so they blow air horizontally. different for case fans i guess.

its about where the air goes afterwards thats the problem. my CPU is right next to my passively cooled NB. keeps it a bit warm but meh. works fine.

I dont buy it. You dont feel much suction from a vacuum cleaner either untill you try to block its entire intake path.

Velocity isnt what cools, volume is.
The higher the velocity of air flow in fact, the LESS cooling effect it has, untill the point where friction starts causing heating, not conduction cooling.

A fan "Stream", is merely increasing the flow over a smaller physical volume. Your total cubic feet/min on either side of the fan remains constant.

I don't have an opinion really. Other then to say, that all stock coolers and aftermarket coolers blow onto the heatsink.

edit: This is how i see airflow, obvisouly simplified much, and obviously some people dont have that air flow path thru the PSU or out the top

yer thats pretty much it bondy. i have my intake fan goin over topof my HDD which doesnt bother me. my system ambient temp (read near NB) is around 5 degrees warmer than the room temp. probably most of that is because the sensor is also near the CPU.

velocity does make a difference.

think about it. if u r in ur car when its raining and u r stopped take note of how much water is getting on ur windscreen. then drive ur car forward, notice how there is more water hitting ur windscreen now??

same goes with some magnetic fields and the forces they apply on electrons etc.

because its moving, the velocity is often calculated into how much mass is passing through the heat sink.

velocity is volume.
if the same volume flows onto the heatsink fins, rather than all around them, then more air on the fins = cooler fins.

do you blow your soup cool, or suck it cool?

no you blow, coz if you sucked youd be sucking hot air into your mouth

but yeah, you blow coz its easier, and theres more volume, and more velocity than sucking....

The fan has to obey thermodynamics. For analysis purposes is a steady state closed system. That is whatever mass flows in, flows out.

Volume is not velocity.

Its just more focused on the blowing side of the fan.

Remove the hot air or blow cool air on it!
I pick blow cooler air on it rather than waiting for the air to heat up and remove it.

Gezzz, when you feel hot in summer is it better to stand in front of the fan or behind it?

Depends if you're in direct sunlight when standing in front of it vs. shade standing behind it?

The same principles apply in a computer case, where the hot bits/areas are in relation to the fan.
It all depends on your case layout, mainboard design, graphics card design, other fans, what direction they're facing, etc. etc.

Basically, it can work well either way, test it and find out.

what I was saying.

Easy... Do a test!

Set it to suck - then monitor the temperature if your BIOS allows it. Monitor for several minutes until it reaches it's max temp.

Then set it to blow - then monitor again.

In my set-up, the best for me was to set the front case fan to suck from outside-in, the rear case fan to suck from inside-out, and the CPU fan to blow down.

Well atleast i have the idea now, that there is no definitive way, each case is different.

i think i will end up testing both ways. i havnt got the bios program installed atm, but im about to format the hardrive so will give the full test after that.

I will post the results too

Thanks guys