View Poll Results: Should a CPU Fan be intake or exhuast?

mpcrsc562 · 23 Mar 2010

O.k., some aoutomobile radiator fans may suck...

Anyway, look at it like this: what is usually right under the cpu heatsink / fan? A very hot video card. If the cpu fan is exhausting air away from the heatsink, the first batch of air being sucked across the heatsink is the hot air from the videocard--which will NOT aid in cooling the cpu.

CommonTater · 23 Mar 2010

seekermeister said:

While I think that I agree with most of what you have said, your definition of the Bernouli effect leaves something to be desired. This is the effect of either a gas or liquid that is forced through a restricted aperture, causing it to speed up. When it speeds up, the pressure is reduced, This is what occurs in a carburetor, where the throat creates a restriction, which causes the air to speed up and lose pressure, which in turn causes fuel to be pulled from the jets by the lower air pressure.

Actually, it doesn't require an aperture as such, because the same effect occurs over the wing of an airplane, where the upper surface of the wing is curved in a fashion that requires to air to travel at a greater speed than the air below, creating a low pressure above the wing, producing lift and keeping the aircraft aloft.

Yes carbouration is another demonstration of Bernouli's effect as is the wing of an airplane... However, carbouration occures as an inlet to a closed system created by the valve action of an engine's moving piston and is thus not totally analogous to the operation of a fan.

In our example the casing of the fan with the blades spinning in the smallest part of the aperature is what causes the increase in velocity, and the reduction in pressure on one side of the blades. However it is also what causes the increase in pressure on the other... Just like the curvature of a wing causes an increase in pressure underneath the wing... This is not a closed system... one side can (and does) affect the other.

I may be a tad off on the science --it's been 15 years since I designed cooling systems of any account-- but the palm test explains it very well... It is what the heatsink "feels".

CommonTater · 23 Mar 2010

mpcrsc562 said:

O.k., some aoutomobile radiator fans may suck...

Anyway, look at it like this: what is usually right under the cpu heatsink / fan? A very hot video card. If the cpu fan is exhausting air away from the heatsink, the first batch of air being sucked across the heatsink is the hot air from the videocard--which will NOT aid in cooling the cpu.

Actually it's much simpler than that... In very basic terms; to get the most cooling effect, you want to force the coolest availible air into the hottest part of the equipment.

YTBOY83 · 23 Mar 2010

The HS want to stay cool as well so it can absorb more heat, if the heat was exhausted there would not be as much coolness.

mpcrsc562 · 23 Mar 2010

CommonTater said:

mpcrsc562 said:

O.k., some aoutomobile radiator fans may suck...

Anyway, look at it like this: what is usually right under the cpu heatsink / fan? A very hot video card. If the cpu fan is exhausting air away from the heatsink, the first batch of air being sucked across the heatsink is the hot air from the videocard--which will NOT aid in cooling the cpu.

Actually it's much simpler than that... In very basic terms; to get the most cooling effect, you want to force the coolest availible air into the hottest part of the equipment.

Right. Which was what I was attempting to illustrate--heat from a videocard being sucked through a heatsink will not aid in cooling.

Product FRED · 23 Mar 2010

mpcrsc562 said:

O.k., some aoutomobile radiator fans may suck...

Anyway, look at it like this: what is usually right under the cpu heatsink / fan? A very hot video card. If the cpu fan is exhausting air away from the heatsink, the first batch of air being sucked across the heatsink is the hot air from the videocard--which will NOT aid in cooling the cpu.

You're removing the heat from the card. That's why the air is hot after passing over it. That is the point of cooling the card. Laws of Heat transfer?

win7clutz · 23 Mar 2010

Desktop computers typically use one or more fans for heat management. Almost all desktop power supplies have at least one fan to exhaust air from the case. Most manufacturers recommend bringing cool, fresh air in at the bottom front of the case, and exhausting warm air from the top rear.

This is absolutely correct as you're trying to remove hot air from inside the case ( a large volume) that's being create by multiple components. The same concept does not apply to a single device in the machine. Have you ever seen a North bridge or South bridge cooler that doesn't blow down directly on the chip. This would make you believe not only are Intel and AMD wrong, but that all board and video manufacturers are equally ignorant..

Do you see how the sucking motion draws the hot air out and creates a lower pressure zone to draw in cool air?[/QUOTE]

mpcrsc562 · 23 Mar 2010

Product FRED said:

mpcrsc562 said:

O.k., some aoutomobile radiator fans may suck...

Anyway, look at it like this: what is usually right under the cpu heatsink / fan? A very hot video card. If the cpu fan is exhausting air away from the heatsink, the first batch of air being sucked across the heatsink is the hot air from the videocard--which will NOT aid in cooling the cpu.

You're removing the heat from the card. That's why the air is hot after passing over it. That is the point of cooling the card. Heat transfer?

Right... The heat is transferred from the card to the surrounding air. The heated air rises and is blown across the hsf. At least with a fan blowing on the heatsink, the cool air from the front of the case would be blown into the hsf.

Product FRED · 23 Mar 2010

mpcrsc562 said:

Product FRED said:

mpcrsc562 said:

O.k., some aoutomobile radiator fans may suck...

Anyway, look at it like this: what is usually right under the cpu heatsink / fan? A very hot video card. If the cpu fan is exhausting air away from the heatsink, the first batch of air being sucked across the heatsink is the hot air from the videocard--which will NOT aid in cooling the cpu.

You're removing the heat from the card. That's why the air is hot after passing over it. That is the point of cooling the card. Heat transfer?

Right... The heat is transferred from the card to the surrounding air. The heated air rises and is blown across the hsf. At least with a fan blowing on the heatsink, the cool air from the front of the case would be blown into the hsf.

There is no cool air already inside the case. It's all warm. Suction draws in air from the outside. It may not be as powerful as blowing, but it's definitely cooler. And the heatsink aborbs most of the heat anyways, so the cold air is effect on both.

CommonTater · 23 Mar 2010

Product FRED said:

Right, but what I'm saying is that the hot air will leave more concentrated, and cool air will come in more concentrated. By using exhaust, you're making it easier for the air to travel to the rear and top exhaust fans. Why would you scatter it?

To dispurse the heat over the widest possible area allowing it to mix with cooler air causing less temperature increase.