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saturnotaku
05-28-04, 03:46 PM
I'm pretty sure this has been covered before, but I need a reminder. What is the best way to position a fan over a heatsink? Have the airflow go outward away from the heatsink or reverse it and have most of the air get pushed back towards it?

digitalwanderer
05-28-04, 04:04 PM
The air should be blowing towards the heatsink, and don't use a 92mm on a CPU fan as they got a deadzone in the middle.

EDITED BITS: I put "fan" instead of "heatsink", I just had a bit of a mild nightmare when I swapped cases and added a spiffy Zalman...it took a few days to get it working. :rolleyes:

Riptide
05-28-04, 04:05 PM
You want the air going down and towards the heatsink, not away from it. Someone correct me if I'm wrong ofcourse.

jAkUp
05-28-04, 04:17 PM
Towards the heatsink/cpu. A few years ago it didn't matter, but now with increasing temps you want to shove cool air right at that card. Force it through the vents.

SlyBoots
05-28-04, 08:55 PM
Trust me on this :)

If the heatsink comes with a shroud [like some Alphas] they're designed to pull heat off the sink......otherwise you want the fans pushing air through the sink :thumbsup:

Rytr
05-28-04, 10:03 PM
Trust me on this :)

If the heatsink comes with a shroud [like some Alphas] they're designed to pull heat off the sink......otherwise you want the fans pushing air through the sink :thumbsup:

You are correct, even the big 8045's were designed to blow away. However, in testing, I found in some cases the 8045's did better blowing than sucking. Still, if equipped with a shroud you should try both ways to actually see what provides the best cooling.
I have not seen any of the newer HSF's setup to blow away.

|JuiceZ|
05-28-04, 11:10 PM
Its been proven, blowing produces better results than sucking....er that didn't come out right but you get my point :angel2:

Clay
05-28-04, 11:44 PM
This may sound like a weird question (bear with me, the Pacers won tonight so I'm kinda giddy) :p Anyway, I just wondered if there would be any advantage to having a fan on the top of the HS and also a fan on one of the sides so you have both downward and sideways airflow. I would assume that the sideways fan would only be effective if it had a shroud coming in from the outside of the case though. Many 4U rackmount servers have 92mm fans that blow air across the mobo and usually the CPU(s) are right in the direct path of these fans..the CPUs obviously also have a HSF with fan on top...any thoughts?

Oh and Juice, get yur mind outta gutter and don't try and tell me that "sure it's better cause you have more blowing or sucking" :D

saturnotaku
05-29-04, 02:48 AM
I'm changing over to a Thermalright SLK900 so reversing the fan direction will be no big deal. I'm planning on doing some major system cleaning when that gets here - swapping out a power supply, changing the HSF and taking out my motherboard to physically clean my case of dust.

Rytr
05-29-04, 01:02 PM
Case cleaning, ugh! My youngest daughter brings her pc home once a year from school. Once it was candle soot, then it was cat hair...you would not believe!...then again, maybe you would. :D

IMO, the main deficiency in using a fan to cool a heatsink is not so much rpm speed or cfm's but tuberlance created by the fan. Bigger fans are even more notorious for creating this deficiency as has been previously stated. Sometimes, just positioning the fan 1/8" above contact with the heatsink can provide better cooling performance by reducing the tuberlance effect. I have an old AX-7 with an 80mm 39cfm Panaflo which I put rubber spacers between the sink and fan, raising it slightly above the heatsink, provided me with a drop of almost 2C.

Kamel
05-29-04, 02:33 PM
lol, of course blow on to the heatsink... when you don't blow onto the heatsink, it will often make a sortof place of trapped air right over the middle of the heatsink because of turbulence or whatever... this (of course) is horrible for heating, and the further away the airflow from the processor, the less it will be able to carry the temp of the core.

i don't remember where i read all of this at, but it makes plenty of sense. sucking sucks, lol.

saturnotaku
05-29-04, 02:53 PM
I figured as much, I'll be attaching a high-output Vantec fan to the heatsink. I'll also be attaching it to a rheobus so the noise will be less irritating. Thanks to all who've replied. :)

Case cleaning, ugh! My youngest daughter brings her pc home once a year from school. Once it was candle soot, then it was cat hair...you would not believe!...then again, maybe you would.

IMO, the main deficiency in using a fan to cool a heatsink is not so much rpm speed or cfm's but tuberlance created by the fan. Bigger fans are even more notorious for creating this deficiency as has been previously stated. Sometimes, just positioning the fan 1/8" above contact with the heatsink can provide better cooling performance by reducing the tuberlance effect. I have an old AX-7 with an 80mm 39cfm Panaflo which I put rubber spacers between the sink and fan, raising it slightly above the heatsink, provided me with a drop of almost 2C.

I'm mostly cleaning out the dust that my can of compressed air can't remove. I'm going to take out the motherboard and the drive cages and clean them inside and out. There won't be any cat hair or soot as 1) we don't have any pets and 2) there's no fireplace or smoking. Shouldn't be too bad.

As far as the rubber spacers go, I'll definitely look into that. I can probably pick some up at Home Depot or something. Thanks for the tip.

u46gb
06-07-04, 04:47 AM
how do you know which way the fan is blowing and how do you change it if it's sucking anyway?

saturnotaku
06-07-04, 07:39 AM
how do you know which way the fan is blowing and how do you change it if it's sucking anyway?

Most fans have arrows on the sides to indicate the blade rotation and airflow direction. And to change the airflow as it applies to the heatsink, remove the fan, flip it over and re-attach it - pretty simple really.

Sazar
06-07-04, 09:19 AM
Its been proven, blowing produces better results than sucking....er that didn't come out right but you get my point :angel2:

nice to know you've tried both :angel: