Which way should hte air be flowing o nmy HSF?

PCMonkey

Weaksauce
Joined
Nov 10, 2002
Messages
102
Ok the title pretty much asks the question. For a while now i've been having the air blow into the HS so that it was fresh cooler air from the room because i have my case side open because my HDD overheats because it has hardly any room to breathe. My cpu temps have been fine but i recently looked inside my case and notice that the HS was packed with dust. The thing with my CPU fan is that it is a Tornado and has the fins that change the direction of air flow to blow at a 90 degree angle onto the HS. I was wondering if it would be better to flip the fan over so it is sucking air through the HS and away from the CPU because inoticed on some cases there is a hole on the side of the case so htat hte hot CPU hair can be exhausted. This would prevent dust from collecting in the HS as much, but is it safe to have the spinning fan blades on the HS side when the fan was clearly desgined to have the air being pushed onto the CPU. Also any sugestions on a case that has a lot of room a lot of fan locations and is a decent price? I know the Xaser III is a good case, but kinda pricey. Any near Xaser quality cases that are cheaper?
 

PCMonkey

Weaksauce
Joined
Nov 10, 2002
Messages
102
Despite the logic in that reply, i'd rather have a more in-depth response...please.
 

Spare-Flair

Supreme [H]ardness
Joined
Apr 4, 2003
Messages
7,471
Blowing is the only way it was designed for. I don't have the links right now but if you look at airflow diagrams, the direction of airflow when the fan is flipped caused the air to be sucked in through the sides of the fan, and not directly below it.

You can test it yourself. Put your hand on either side of the Tornado or any other fan. When it's blowing onto your hand, you can feel it quite aways away and you know that the air is blowing down onto the heatsink and reaching the center/bottom with a lot of force and also is being forced out the sides. When it's sucking, you can't feel any air until your hand is up close to it, almost to finger cutting distance, to near the sides. It hardly feels like there is any airflow.

If you do want to suck, it can work and can be better but you need to build a fan/air shroud that surrounds the heatsink so that air is pulled in from the the bottom of the heatsink. If the fan is sucking, air will only touch the tips of the heatsink and skip most of the sink. A shroud allows air to come through the bottom and the resulting vacuum causes the air to flow into the rest of the heatsink.

Then the fan can pull air off the heatsink and then the hot air can get sucked out the rear exhaust or if you're more [H]ard, you can duct it right out the back.

My setup has the fan sucking but mine is far from conventional or orthodox.

120mm Fan Shroud:
stop.jpg

sbot.jpg


Case shroud that keeps the air in the upper corner to be sucked out by rear fans and PSU:
inside.jpg

fans.jpg
 

RancidWAnnaRIot

EspantaPajaros
Joined
Feb 19, 2004
Messages
11,039
I don't know.. i mean wouldn't the engineers and stuff that designed the HSF have tried it out?? when you buy the HSF it comes with the fan oriented so air is blown into the Heatsink. I figured this would be the best way.. i would guess it's best to leave it like that.. that's how the engineers did it.. i think they know what they are doing..
 

Spare-Flair

Supreme [H]ardness
Joined
Apr 4, 2003
Messages
7,471
RancidWAnnaRIot said:
I don't know.. i mean wouldn't the engineers and stuff that designed the HSF have tried it out?? when you buy the HSF it comes with the fan oriented so air is blown into the Heatsink. I figured this would be the best way.. i would guess it's best to leave it like that.. that's how the engineers did it.. i think they know what they are doing..

Sigh, read my post.
And as for Alpha's stance:
"According to our tests, the induction type showed better results the the expulsion type. This is because we used an intake cover to draw air through the lower part of the heat sink for more heat dissipation from the lower part of the fins. However, if some other heat source is located near the heat sink, heated air would come into the heat sink and affect the thermal performance, so the choice must be made depending on the environment."

And quoting Geoff on another board:
"the difference is that when you push something (eg air) you give it momentum and it heads in the direction you push it (in this case towards the heatsink). If you're trying to suck something in, you're basically creating a lack of the substance (eg air) and it will be replaced from all directions. What tends to happen with fans is that a fair bit of air actually curls around the lip of the fan rather than coming straight in like a crazed hornet from a couple of feet away.
So you get more flow at the base of your heatsink if the fan is pushing air towards the heatsink. If you want to suck air off the heatsink, you need to shroud it so that air can only enter near the base, or you're wasting your time. This needs more careful design so that you maximise airflow as well, and also if the fan fails you've got this big shroud around your heatsink... That's why pushing air down is a more failsafe and easier approach."

Also, a great Lost Circuits article:
http://www.lostcircuits.com/advice/cooling/2.html
heatsink1.gif

Model 1: hot air is blown over the heatsink and constantly recyled

heatsink2.gif

Model 2: Hot air is extracted completely from the case by suction through a sealed duct
As you can see, there is a duct, otherwise the air would all come in from the sides of the top of the heatsink, thus only cooling the tips of the fins.

One more thing to note, the current configurations of all cases have a rear exhaust fan on the panel right beside CPU HSF. Because of this, the PSU and the rear fans AND the CPU HSF are all sucking from the same area if you have a blowing HSF. This is a major low-pressure area and it may cause a deficiency of air supply for your HSF to use. That's another reason why I flipped my HSF.
 

RancidWAnnaRIot

EspantaPajaros
Joined
Feb 19, 2004
Messages
11,039
I would say it's still best to leave it how it was designed..... but, if you really want to know just try it.. it sholdn't be hard to do...
 

PCMonkey

Weaksauce
Joined
Nov 10, 2002
Messages
102
Anothing i've been worried about is that since my RAM is right bside my CPU, the hot air that is being blow out the base of the HS is pushed into my RAM. Is this much of any issue and could it cause my system to lose performance?
 
Top