The cooling is (usually) the noisiest component in the computers.
Is it possible to cool completely passively? Yes. It is, but usually is not done, because large heatsinks are required (assuming that not ultra low power CPU is used).
What about passive that switches to active- it is done pretty frequently. Almost all laptops switch to passive if the load is low.
What about mini PCs and desktops- there are some mini PCs that are fanless, but they get hot. Some don’t throttle, but are hot. For desktops- it is rare to see such PCs.
Because of necesity (actually desire to test my skills and get something quiet) the tivilin (live parameters link) home lab server is semipassively cooled.
Some pictures:
So the idea on the above pictures is to use 2 easily found heatpipe coolers and one large solid heatsink for GPU to create enough surface for passive cooling. The fans are Arctic TC series. I prefer the TC14, because it does not spin at all when the temperature is low and increases the speed from really low speed (less than 200 rpm) to 1500 RPM. The TC12 spins constantly at low sped (probably 400rpm, which is still really quie). The TC14 were sold out when I decided to add the second fan, otherwise TC14 was the preferred choice.
The normall PWM fans spin all the time at at least 30%, even when the fill rate is less than 10%, so they are good quiet option also.
This can be done also using standard heatpipes and CPU bracket for the heatpipes, but they were not available in the neighbouring store and eatpipe bending is not the easiest thing to do without tools. Aditionally heatsink on the heatpipe cold end has to be added and this was also not available in the nearest PC store.
Although the CPU is cooled properly, the M.2 SSD (currently removed) does not get enough airflow and gets hot. Will use a SSD with proper heatsink and probably remove the side fan.
Anyway this PC is in the closet above the washing machine so I do not care much if it is noisy, but it was initially intended to be used as 24/7 HTPC and was used as such for quite a while.
This is 4 years old experiment that I was reminded by Facebook 🙂