Question Case Pressure (For Fun/Curiosity)

[SyCoREAPER]

Just out of curiosity I calculated the presure on my case to see if roughly it was positive or negative.

What I came out with was:

Out: 446.5 m^3 /h

In: 420.6 m^3 /h

Which comes to negative 25.9 m^3 /h.

HOWEVER, how do I estimate the loss of flow from fans going through an AIO rad? I'm guessing by the time I deduct the resistance from the rad I am about equal.



I know SOMEONE will say you're overthinking it or you'll be fine. I know, I'm doing this out of curiosity sake.

 

[Colif]

So AIO is exhaust I assume? it probably is about even

I worry more for health of AIO being cooked by a 4090 from below, how hot does CPU get?

 

[SyCoREAPER]

So AIO is exhaust I assume? it probably is about even

I worry more for health of AIO being cooked by a 4090 from below, how hot does CPU get?

Correct. It's at the top as an exhaust.

CPU (i7-13700K) under heavy gaming maxes around 76c, some rare times 80c but again these are maxes read by HWInfo, averages are mid 70's. Time Spy Stess Test temps were even lower.

Corsair iCUE crapapp reports the fluids are in the 30s IIRC?

GPU stays pretty cool. Think the max I've seen it reach is 42c.

Id say there is pretty good airflow though as temps have been to date very cool. AIO has 3 Noctua A12x25, front intake are 3 Noctua A14 and rear exhaust is a other Noctua A14. Case fans run at full speed (sound doesn't bother me, barely any there to begin with), so there is constant fresh air

 

[Colif]

I don't need to calculate mine to know its positive
2 x 120mm Corsair ML120 fans on AIO as intakes on front.
2 x 140mm Noctua Chromax Black Swap fans as intakes in roof.
1 x 140mm Noctua Chromax Black Swap fan as exhaust on rear.
All that air into a Fractal Design Meshify S2.

Air is now finding new ways to get out. I just get some strange noises.
Probably need to slow fans in the roof more.

 

[Karadjgne]

The issue I see is in the fact you assume certain parameters, but leave out others.

As is the assumption the case is a sealed unit and subject only to what the fans can provide. You've most likely discounted/ignored the pressure differentials caused by airgaps at the pci slots, surrounding the fans, between the rad and case, around the side panels etc.

With even the slightest negative pressure case, you'll have @ 14.7psi pushing in every single crevice or crack or gap, if slightly positive you'll have @ 14.7psi + case pressure pushing out of those same cracks.

Also discounted/ignored changing conditions under loads. A case is never at a static pressure, either negative or positive, even a slight change in ratio of fan speeds (seperate headers under seperate controls) will change the pressure inside the case, can even go from a negative to positive differential, or vice versa.

That goes also for temperature gradients. A cold case will be at a different pressure to a warm case, given even identical conditions otherwise.

Math is absolute, except where variables are concerned, so only applies to a single instance. So ppl can say it's positive or negative, based on fan setups and general identity, just like you can say it's warm or cold outside, but specific numbers are beyond calculation unless actually measured in comparison or every single possible variable is either taken out of the equation or accounted for.

That would mean sealing up the case perfectly, knowing expansion/contraction rates of air at specific temps according to specific static pressure and cfm, knowing the exact amount of vacuum applied to the exhaust fan in comparison to the amount of cfm and static pressure applied to the intakes etc etc...

Basically calculating case pressure would be akin to trying to calculate the temp outside, based on sun position, time of day, time of year, current weather and barometric readings etc. Easier just to stick a meter inside and measure the pressure and compare it to ambient pressure.

 

[Colif]

This program is really good - https://github.com/Rem0o/FanControl.Releases
it solved my weird noises, turns out I had to slow rear fan down a bit to stop them. I don't need high speed exhaust with the amount of air coming into PC now.
It only took me a few days of playing with fans before I looked at a software solution