Should a person have more intake fans or more exhaust fans and why.

[Deagle]

I was wondering if I were to build a comp and when I set up the fans, should I have more front intake or more back exhaust? Why?
Thanx:)

[Rick]

Blow Cool Air IN

BUT You still need to Get the heat Out of the case

In fact you need them setup so they move the air correctly also
Removing the heat from all areas of the case

[Deagle]

But then I remember Budfred said that I should have more exhaust than intake?:confused: Plus if I have more intake then where will the hot air go? I know that I must set them up so that the air will go from front to back. Also I heard from a friend that I should use air condition, but how do I get the air condition inside there?
Thanx:)

[Budfred]

This is another one of those arguments that ultimately get answered with "yes". Some people advocate more exhaust, some advocate more intake. Either way the most important thing is the air flow through the case.

I don't know what your friend meant by air conditioning. There are water cooling systems and other elaborate cooling systems. There are also cowls that go over the CPU fan to channel the air more effectively. Probably the most important thing you could add would be some filter material at the intake fans to reduce the amount of dust that comes into the case.

[Jiggy]

This old link (http://www.pcguide.com/vb/showthread.php?s=&threadid=20301) mite give you more info.

[Steve]

I take a simplistic approach. Put in as many fans as there are places to put them. I haven't heard of problems with to many fans but I have heard of problems with to few.

Fans are dirt cheap. Buy quite fans and load the box up. :)

[Sylvander]

What you want is a flow of [cool] air through the case, in one way and out another.
Whether you push it in or push it out is practically irrelevant.
As is generally how many are pushing and how many pulling.
The total work expended in creating a rate of flow is shared by all the fans; each makes a contribution.
What is more important is the flow path taken through the case.

If there was only one inlet and one outlet and they were side by side, then the flow would short circuit from the inlet to the outlet and there would be no flow through the body of the case and over the components.
The air inside the case would remain unmoved or stagnant while a rapid flow took place at one little corner of the case.
So you need the inlet as far from the outlet as possible and positioned to produce a good flow path.
In at bottom front, out at top rear would be good because natural convection [hot air rising] would work with, not against the fans.

Now imagine only one exhaust fan in one panel [the top and facing up would be good unless other considerations rule it out] and lots of leaks or intake holes all over the case except that panel.
[Difficult if you want to filter dust from the incoming air.]
Air could not short circuit because the panel has no intake holes. The air is forced to come from the furthest reaches of the case, travelling over the components [being heated and naturally rising] to reach the fan then being forced out to the surroundings [straight up would be ideal].
You really want that air to jet as far away from the case as possible, because otherwise it’s going to tend to flow back to the intake holes and back into the case. [Not if it is hot air being thrown upwards.]

[pave_spectre]

I personally go with the theory that :

exhaust fans = intake fans.

Theoretically this should produce a nice smooth flow of air through the case without causing too much turbulence which i understand to be detrimental to good cooling.( This only works if the fans rated airflows are all roughly the same of course).

[Sylvander]

Imagine your car had broken down and you were trying to move it.

You could harness one great workhorse to the front and pull it along.
Or you could use two weak people pushing from behind and two strong people pulling at the front.
Whether you push or pull is just a detail.
How strong each individual is who is helping is also a detail.
You could use ten weak people or four strong.
The important thing is the total POWER available to do the moving.
The speed the car moves at depends on the actual total rate of work done by all in helping move the car.

It's the same with the fan[s].
If you had one great strong fan moving air from the inside to the outside, the atmosphere [due to the fact that "Nature abhors a vacuum"] would instantly work [given the opportunity] to fill, through all available apertures, the attempted creation of a void .
The atmosphere [because of the air pressure] has the potential to do work [just like a mass in a gravity field has the potential to do work] and it does work at a certain rate [power] in pushing air into the case.
[Now I'm getting technical and perhaps causing confusion.]
The fan has to do work to move the air out and the atmosphere does work to move the air in.
If there is very little resistance to flow, the power required is small.
Resistance to flow increases rapidly as velocity [and the resulting friction] increases; so the power expended increases dramatically.

I would think that the heat transfer rate [due to "forced convection"] would be increased if the flow was turbulent rather than "laminar".
This is because the cold air is in more intimate contact with the components. The chaotic buffeting brings the air into DIRECT contact rather than flowing sedately past at a distance with the air near the components moving slowly over them.
[I'm gonna get technical again.]
The "Velocity Gradient" in turbulent flow is MUCH greater than in laminar flow.
In laminar flow the air velocity at the component surface is zero and increases very gradually to the velocity of the moving air in the body of the case.
[They use laminar flow from ceiling to floor in operating theatres to prevent the movement of germs from one region of the patient to another. All contaminated air is taken safely away.]
In turbulent flow there is only a VERY THIN layer of slow air near the component surface and there is a metaphorical "raging hurricane" only a millimetre or two away. Expended heat only has to travel that millimetre [by conduction] to be whisked away [by the much more efficient "forced Convection"].

[Deagle]

Woh, I have no idea what you just said:confused: But about the nature abhors a vacuum thingy, I think you means that fresh air from outside will rush in trying to replace the hot air that's being push out. Right?
Then it should be more exhaust than intake right?
Thanx:D

[Sylvander]

EXACTLY RIGHT.

Imagine you tried to make a hole in the sea by baling it out.
As soon as you removed a bucketful the ocean would rush in to fill the hole.
[Nature Hates a Vacuum]
Now the question is whether the ocean pushed the water in, or whether the empty hole PULLED the water in.
The answer is that the ocean pushed the water in.
When you make the hole you create an imbalance of forces.
[Previously they were in balance, in a state of “equilibrium”, the water was moving at constant velocity or at rest.]
The water pressure acting over an area produces a force acting on one side only.
There is no counteracting force on the hole side.
It is the absence of this force that allows the surrounding water to PUSH water in to fill the hole.
The water [no longer in equilibrium] accelerates into the hole to restore the balance of forces and therefore equilibrium.
Nothing does any pulling.

It’s similar with air in the case.
If you force some air out [by whatever means], that creates a [fairly small] reduction in pressure.
The pressure imbalance accelerates air in to fill the partial void and restore uniformity of air pressure.
You could do this continuously.
The surrounding ocean of air [12 miles deep and we live at the bottom of that ocean of air] exerts a pressure of 14.7 pounds per square inch at the bottom. It is capable of exerting a MAXIMUM level of force equal to 14.7 pounds times the number of square inches over which that pressure is exerted.
This maximum can be EXTREMELY FORCEFUL.
In our case though, the pressure differences and forces are small and the power required to move the air is low.

[sleddog]

It doesn't really matter if you push or pull. Just get it [the air flow or the car!] moving.

You can't really have "more" exhaust than intake, nor can you have more intake than exhaust. At least not to any significant degree.

If you add more exhaust fans then your air intake also increases -- air is drawn in through ventilation slots and every crack and cranny.

If you add more intake fans then your exhaust increases the same way.

To maintain a good airflow there must be a balanced capacity for airflow in and out.

If you add a whacking great exhaust fan rated at, say, 500 cfm to your case, in all likelihood it will not move 500 cfm of air. Why? Because the tiny slots and crevices in the case are insufficient to support an equal amount of inflow. You might get, say, 100 cfm of inflow, and consequently the exhaust fan will push out 100 cfm of air.

If you add a 500 cfm exhaust fan and a 500 cfm intake fan, you will probably then get 500cfm of air moving through each fan (and through the case).

Ever open the windows on a warm day? If you want a breeze through the house it's best to open two windows on opposite sides of the house. Opening one window is much less effective. When the second window is opened, the air flow through the house increases signifacantly.

If you're working in a room with the window open and someone opens the outside door, all your papers suddenly blow off the desk. Same principle. The wind outdoors didn't get any stronger -- the capacity for airflow through the room was increased.

[Sylvander]

I was going to say I agree with EVERYTHING you said, but perhaps it’s only 99.9%

The bit I’d like to examine is:
“If you add a 500 cfm exhaust fan and a 500 cfm intake fan, you will probably then get 500 cfm of air moving through each fan (and through the case).”

I know more about pumps so I’ll use that example to begin with.
The rated flow output of a pump is normally shown on a graph.
The flow rate varies depending on the back-pressure it is working against.

In other words: there is a pressure increase between the pump inlet and outlet.
This would normally make the fluid [something that flows (like air or water)] rush backwards through the pump but the power supplied and the action of the pump forces the flow and maintains the pressure increase.
The water then flows by various routes back to the pump inlet.
The pressure gradually decreases [due to frictional resistance] as it flows along its route back to the inlet.
[It’s the same with blood in the body, but the heart is a reciprocal pump and the tubes are elastic and stretch with each beat.]

So the flow rate varies with pressure difference and the maximum flow rate is decided by the power of the pump and its characteristics.
Increase the flow resistance and the back-pressure increases and the flow decreases and vice versa.

Now if you put two pumps in series:
The back-pressure they can work against is additive.
The first pump increases the pressure from inlet to outlet then the second pump takes that increased pressure and boosts it further.
[Like your two fans, one blowing in, the other blowing out. (This assumes that the case is well sealed.)]
In a similar way, fans working in series can work against higher resistance.
You could, of course, bolt one fan directly to the other to put them in series.
But in practice you don’t have high resistance.
What you really want is high flow rate at low resistance.
Therefore you should really work fans in parallel or have one, big, powerful high flow rate fan.
Fans working in parallel should almost certainly be identical.
They would all be working against the same back-pressure and their flow rates would add together to give a total rate of flow.

The statement you made that I quoted is not quite right because:
If you studied the performance graphs for the fans under the following conditions:
1. You have only one fan working at the peak of its performance curve and there is a certain back-pressure [x] and flow rate [500 cfm] at this point.
2. Now you add a second identical fan in series but the total back-pressure is x and the back-pressure for each fan is only half x which takes you to a different point further along on the performance curve.
This point has a different flow rate much greater than 500 cfm but less than 1000 cfm I would guess.
[They don’t work quite so nicely as batteries in parallel but it’s rather similar.]

[pave_spectre]

To semi-amusingly paraphrase all of the above - Put all the fans you want on and then see if anything explodes.

[Whyzman]

If you add a whacking great exhaust fan rated at, say, 500 cfm to your case, in all likelihood it will not move 500 cfm of air. Why? Because the tiny slots and crevices in the case are insufficient to support an equal amount of inflow.If inaudible to humans though, the whistling effect ought to at least have a very interesing effect on any animals within a couple blocks.

You'll know you've an imbalance when the dogs start howling... :D