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question about airflow

T

TuffGuy

Diamond Member
i have a chenbro genie jr, with one 120mm panaflo in front at the bottom, and another 120mm panaflow in the back, right above the cpu.

with my old alpha pal6035 sucking, the front was used as an intake, and the rear as the exhaust since the alpha blew the warm air right into the exhaust stream.

i have recently switched to a taisol cgk760092 with an 80mm fan that blows into the heatsink. so i reversed the airflow. the rear now blows cool air above the heatsink, which then gets blown into the heatsink, and the bottom front exhausts the warm air.

as we all know, warm air rises, so how effective is the setup? should i have left it the way that it was before, with the rear fan as the exhaust?
 
the common setup is suck in the front and blow out the back...i don't personally know anyone who has ever done the opposite...like you said, hot air rises, which makes it really difficult to blow hot air out of the bottom front of the case.

but heck, if you're not having problems, at least you have SOME airflow...so i guess its allright.

i would probably switch it back to the old way if i were you.
 
yeah, but wouldn't the suction from the exhaust fan interfere with the fan blowing into the heatsink? that's my big dilemma...
 
I also wondered about this but never did it. I had planned on just reversing the fan on my Taisol, but it won't allow it. Although I can't complain i have awesome temps, but could they be better?
 
My suspicion is this: the rear 120mm fan will be generating turbulence on its exhaust side, whereas its intake side will have relatively laminar airflow up to the point where the fan blades start chopping it up. I think your CPU fan would have higher airflow into your heatsink if it were on the intake side of your 120mm fan, since the airflow will be less turbulent on that side. That means you'd have to have your 120mm fan exhausting out the rear of the case.

My primary reason for saying that is Bernouli's Principle, which states that the faster a fluid flows (yes, air is a fluid), the lower its pressure will be. If your CPU fan has to try to pull air from the fast-moving exhaust stream of the 120mm fan, it must overcome the pressure differential caused by the fast, concentrated air movement. We know that axial fans don't do very well against pressure gradients. If you still want to use your 120mm rear fan as an intake, you might want to turn Bernouli's Principle to your advantage by flipping your CPU fan to blow upwards into the low-pressure zone being caused by your 120mm rear fan, so that it's working with the pressure gradient rather than against it. The bottom line, of course, is that you are already way ahead of the average cooling setup in either case, with a ventilation setup like that. 🙂

I also assume you aren't bothered by your case pumping 60+ cfm out the front at you. 😉
 
well, just because i had nothing better to do, i changed the direction of the fans. cpu temp increased by 10f. 🙁
 


<< So are you saying your temps are lower when you have the front exhaust and the rear intake? >>


yes. by about ~10F.
 
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