Intake or exhaust for these fans?

[Guest]

I know the best way is to just test it and compare the temperatures but I want to hear your thoughts before I do it. I have a bit of an unusual airflow situation since my Corsair 600C case has an inverted layout and I'm wondering if the bottom fans should be exhaust or intake.

 

Right now I have two intake at the front with 3 exhaust (technically 4 with the top PSU).

 

If I flipped the bottom ones it would likely cause high positive pressure being 4 intake and 1 (2 with the PSU) exhaust, but I'm not sure.

[archiso]

2 minutes ago, RiktigaRonny said:

I know the best way is to just test it and compare the temperatures but I want to hear your thoughts before I do it. I have a bit of an unusual airflow situation since my Corsair 600C case has an inverted layout and I'm wondering if the bottom fans should be exhaust or intake.

 

Right now I have two intake at the front with 3 exhaust (technically 4 with the top PSU).

 

If I flipped the bottom ones it would likely cause high positive pressure being 4 intake and 1 (2 with the PSU) exhaust, but I'm not sure.

the bottom fans should be intake as long as there is some type of filter like mesh at the bottom.

[Rauten]

Intake.

Keep in mind hot air naturally wants to go up, so if you set it as exhaust you're going to be pushing it down and then it's going to want to come back in the same way. It wouldn't be terrible but certainly inefficient.

[Dedayog]

It's much easier to intake with small gap than exhaust into one.  Plus with how heat moves, bottom fans are usually intake.

[TVwazhere]

5 hours ago, RiktigaRonny said:

If I flipped the bottom ones it would likely cause high positive pressure being 4 intake and 1 (2 with the PSU) exhaust, but I'm not sure.

You can easily counter this by reducing fan intake speeds; this gives you the benefit of keeping similar airflow from less fans spinning faster, but at a lower noise level. 

5 hours ago, Rauten said:

Keep in mind hot air naturally wants to go up, so if you set it as exhaust you're going to be pushing it down and then it's going to want to come back in the same way. It wouldn't be terrible but certainly inefficient.

Natural heat convection is overwhelmingly negated by mechanically forced air. 

 

https://www.pugetsystems.com/labs/articles/Vertical-vs-Horizontal-Case-Cooling-89/page3

Quote

Our conclusion is that the forces of convection in a computer are simply not strong enough to overcome even the turbulence and airflow eddies caused by the fans. The lack of any temperature variances when we tested with the air-cooler supports this theory, as air-coolers contribute more airflow and turbulence to the core of the system than a closed-loop liquid cooler (which only has a fan at the edge of the system).

Quote

Our very own company President Jon Bach was so intrigued by these results that he dusted off his college textbooks to try to come up with a mathematical reason for our results. This is his take on the physics involved:

Let's do a thought experiment to see what we would expect in terms of the bouyancy of hot air inside a chassis, and how that relates to the air pushed by a typical 120mm fan. We'll use an average room temperature of 20C (68F).  In our thermal testing, under load with maximum temperatures, we saw chassis panels around 40C average.  Let's round it up to 50C so we're sure to give convection the biggest advantage possible.  Heck, let's double the average air temperature difference measured, and use 60C.

Density of air at 20C: 1.2041 kg/m^3
Density of air at 60C:  1.067 kg/m^3
Bouyancy of 60C air in 20C air:  0.1371 kg/m^3

A P183 chassis is 0.04 cubic meters in internal volume.  Therefore, if you fill an Antec P183 chassis with 60C air, and surrounding air is 20C, the air inside the P183 would have a bouyancy equivalent to the weight of 5.484 grams.  That's about the weight of two pennies. How does that translate into air pressure across a top 120mm fan?  The column of air coming into play has an air volume of 0.00576 m^3, creating a bouyancy of .79 grams over the fan's area of 144 cm^2.  That translates to 0.0054861 grams/cm^2, or 0.54861 mmH20 (the standard unit of measurement for fan static pressure).

That's about half the pressure put out by our Antec TriCool fans on their lowest setting.  That means that even one of the lowest pressure, quietest fans that we sell, would *double* the pressure necessary to overcome the air pressure caused by convection, in the hottest scenario we can imagine.  And this was after doubling the average air temperature increases we actually measured.  When using a 40C average air temperature, an Antec TriCool fan on low setting has 4x the pressure necessary to overcome convection.  Given the results of this thought experiment, the results of our emperical testing are making a lot more sense.  Convection, while a strong concept in thought, simply does not generate the results necessary to play a discernible role in a typical chassis.

 

[Mick Naughty]

Id have them all intake if they can be filtered. And run the aio as exhaust. And remove any filtering it may have on the front.