Heat calculation for CPU/GPU AIO Intake

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2018/05/03 19:07:46 (permalink)
Just some facts
1. At ambient 20 °C, air density is 1.2041 kg/m³, air heat compacity is 1005 J/kg.°C
2. The airflow of a 140mm Noctua NF-A14 is 140.2 m³/h, the airflow of a 120mm Noctua NF-F12 is 93.4 m³/h
3. The power draw of a 5.2GHz overclocked 8700K at full load with Prime95 AVX0 is 225W
4. The power draw of a 2.0GHz overclocked 1080Ti at full load with 3DMark Ultra is 350W
For CPU AIO intake alone, how much heat will rise if the CPU is doing a Prime95 test?  Let's say the heat of CPU is dissipated by a 280mm AIO cooler.
And the calculation is 225J/s ÷ ( 1005 J/kg.°C × 1.2041kg/m³ x 140.2 m³/3600s x2) = 2.387°C
The result is 2.4°C more heat dumped into your case when you are doing Prime 95 with an overclocked 225W 8700K CPU.
And the motherboard components such as VRM would be 2.4°C hotter, though the VRM tolerance is above 100C. And for a good motherboard such as Asus Apex, the VRM is well under 80°C during Prime 95.
For 1 GPU AIO with a 120mm intake, the heat generation will be
350J/s ÷ ( 1005 J/kg.°C × 1.2041kg/m³ x 93.4 m³/3600s ) = 11.148°C
So it will be 11.2°C hotter for the motherboard under full load with max power draw
And for multi GPUs AIO intake setup, the heat generation will still be 
N x 350J/s ÷ ( 1005 J/kg.°C × 1.2041kg/m³ x 93.4 m³/3600s x N ) = 11.148°C
No matter how many GPUs set as intake, the heat rise will be the same 11.2°C.
So, if you make the CPU plus GPUs AIO intake setup, the overall VRM temperature would be roughly 14°C hotter under stability test such as Realbench (actually 8°C), and this is not a daily usage.
But if you set the N GPUs and CPU AIO as an outtake setup, they need as much as 2X140mm and NX120mm equal airflow to reach the same cooling effect. To this point, not many cases are able to mount enough fans so the CPU and GPU will be a daily hotter compared to the intake setup. 
I have been using intake setup for 6 months to do many torture tests and hit some benchmarks, plus 3 months of mining, the system is stable without a problem and I didn't shut it down for 6 months, motherboard VRM is well under 70°C. Btw, the exhaust fan is running at 100%, and other intake fans spin at least 80% regardless, so yeah, it is not a quiet setup.

post edited by SilentMarket - 2018/05/03 19:31:44

Attached Image(s)

CPU - Intel 8700K - 5.1GHz core, 5.0GHz cache, 1.37v
GPU - EVGA FTW3 1080Ti SLI - 2.0GHz core, 12GHz memory
Motherboard - Asus Maximus X Hero
Memory - Corsair Dominator 4x16GB - 3000MHz default XMP 15-17-17-35
PSU - EVGA 1600T2
Fire Strike 36838 Extreme 25250 Ultra 14464

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    Re: Heat calculation for CPU/GPU AIO Intake 2018/05/15 11:29:36 (permalink)
    interesting post
    Moving to Overclocking, Cooling and Benchmarking

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