1

It sucks in air from inside the case but how does the heated air get out of the PSU? There's holes at the back but we all know that hot air doesn't travel sideways unless forced. Also in my case the PSU sits atop the CPU heatsink so the air drawn inside the PSU might already be quite warm. Isn't this inefficient?

My setup looks like this minus the fan at the front of the case:

enter image description here

7
  • 3
    How exactly is it inefficient? Cool air enters, warm air raisesm, then leaves the case. – Ramhound Jun 16 '15 at 10:43
  • Read carfully. I don't have a fan in the front of the case (which isn't the point really). What I mean is that there's no fan that blows hot air out of the PSU... – H3R3T1K Jun 16 '15 at 10:50
  • 2
    yea the PSU itself pulls a lot of heat through and out, i always thought it was nice to have the psu fan be dual purpose. Newer designs can have the psu on the bottom in 2 different configurations, pulling cold to itself from outside the case, or pulling the warmer case air through and out. I do not see it as any more inneficient as the cpu and or gpus having to have thier heat double removed, first from the sinks, then out of the case. There are ducting designs that solved that too. It just isnt as nice to the PSU as it could be, but works fine. – Psycogeek Jun 16 '15 at 10:52
  • You said you have an exhaust fan though.. PSU has an exhaust fan also. – Ramhound Jun 16 '15 at 10:54
  • If you have a fanless psu, the case airflow and fans and all should be arranged to push air through the psu, like it would on many designs, or things like the capcitors would suffer unnessisarily. – Psycogeek Jun 16 '15 at 10:56
1

It sucks in air from inside the case but how does the heated air get out of the PSU?

As air is pulled into the PSU by its fan, the air pressure within the PSU will increase. This pressure increase will cause air to be expelled through any PSU opening where there is lower air pressure on the other side. So most of this air would exit through the backside of the PSU into open space outside the PC case.

However if you inspect the PSU thoroughly, you should also find openings that face into the PC case. (These openings exist to ensure proper air circulation within the PSU so that deadzones and hotspots are minimized.) So if the PC case is not pressurized (by case fans that pull air in) to a level greater than within the PSU, some of the air heated by the PSU will be recycled back into the case instead of being expelled outside.

Due to this recycling of heated air, I avoid using PSUs with 12cm fans. (FWIW I also think cooling in a PC has been marginal since day one of the IBM PC.)

but we all know that hot air doesn't travel sideways unless forced.

A pressure differnential (the outside of the PSU enclosure needs to be at a lower pressure than inside) is supposed to provide this force.

Also in my case the PSU sits atop the CPU heatsink so the air drawn inside the PSU might already be quite warm. Isn't this inefficient?

(That not the proper use of "sits atop", which implies contact.)
Inefficient is not the perfect word if you're concerned about this preheated air entering the PSU. It's not an ideal cooling method.
There's an additional concern of the proximity of these fans. Both the PSU fan and the rear-case fan are facing the same intake air space and trying to draw the same air. Since the air flow is primarily between the CPU-heatsink fan and the rear-case fan, the PSU fan seems to have poor intake flow.

1
  • Thanks for clearing this up. English is not my first language and as a result my questions may seem vague from time to time... – H3R3T1K Jun 27 '15 at 8:00
2

If your PSU has an inlet fan pulling air into it from in the case as your comment suggests, then that fan will by definition be pushing air out of the PSU as well.

You cannot push a volume of gas (air) into an area and expect it to just stay there, it will raise the pressure slightly, then that pressure increase will push outwards and the air will then flow out of the area through any open vents such as the back of your PSU.

Quite simply if you push or pull air into an open area then it will flow through that area and out via any path available. Just because that path is sideways is irrelevant, you have increased the pressure inside the unit by using a fan and the best path available to equalize the pressure is via the outlet. Your PSU is not a sealed unit so it has an airflow through it.

Without this mechanism then air pressure would continue to build up in the area and, as fusion is pretty hard to achieve with oxygen and nitrogen, you would first end up with some kind of electron degenerate matter. If you continue pushing air in then you may well achieve fusion, but by that point I would expect your computer to have achieved several million degrees Celsius and probably melted.

1
  • "Without this mechanism then air pressure would continue to build up in the area" -- Not "area" but volume. But the statement is false because the fan is not capable of maintaining air flow as pressure increases. These fans have performance graphs that chart the actual "cfm" under varying conditions other than ideal (i.e. open space). – sawdust Jun 16 '15 at 18:23

Not the answer you're looking for? Browse other questions tagged or ask your own question.