Friday, July 3, 2009

New Layout and Airflow

Have been out and looked at fans. It seems that there is not much choice but to go for standard axial fan...
The other centrifugal fans are typically large and chunky, and not that silent. Laptop centrifugal fans are expensive, and I still dont really know how to incorporate a flat fan into a layout.

Anyway - after much fiddling around, I have come up with the following...



Looking from the back of the motherboard. The power supply has shifted to the other side of the motherboard now - which should make it easier for the routing of the power cables, and has the effect of placing all of the rear connectors into the center of the box.

For the power supply, I plan to take the existing top off the 1U power supply (the part of the case that I have already butchered according to the initial design :-), and encase it in a larger metal box - previously the 1U was 40mm high, 100mm wide. The new enclosure will be around 60mm high, 100mm wide. I will then use 60mm fans to push the air through to keep it cool. Putting the compact power supply into the more open box area should allow greater airflow - but will it provide cooling to the bits that need cooling? - I think (hope) so. Using the bigger fans should prove quieter (wishful thinking).
However - to push the air through, and to also pull the air into the case, I believe that I will have to put TWO of these 60mm fans in 'series'.
One fan will push a certain amount of air at a certain pressure - if you put two fans in 'series', you will still get the same amount of air flowing, but at double the pressure. And given that they need to push as well as suck the air in, maybe this is needed.

For fresh air comming into the box, I will put a slot duct across the top of the back of the box. In the middle, this air will feed directly to the fan sitting over the CPU - good situation. In fact, the CPU fan can actually help suck the air in.

One negative with this air flow, is that there is no airflow underneath the motherboard, which is where the DVD and hard-disk will be positioned. Maybe need to rethink this - at least maybe the hard-disk position could relatively easily be shifted.

As a first step, I made up some cardboard mock-ups of things...
A ~15mm high duct should fit nicely in over the rear panel connectors.


Some initial playing showed that the Scythe thin fan mod provided some reasonable suction, pulling air in through this duct. Using the standard Intel fan however didnt have much pull for the air. Without the shroud around the fan, too much air gets pushed out sideways...



The distance between the Scythe fan and the eventual top of the case impacts the air flow... around 1cm seems good, less than that seemed to reduce the airflow, and the suck of the air through the duct.

With the power supply and duct in place, comes out something like this...



The opened up power supply sits now in a larger enclosure, allowing greater airflow. Not sure if hot air exiting and cool air entering will get mixed up ??

From the other angle...



There are two 6o mm fans which would push the air through the power supply (not pushed up to the power supply in the photo - need to handle the wiring...)

So the next steps are to start constructing and bending the metal bits...
Note that I have some other ideas for the back face of the box - maybe simplify the construction method, more suited to simple tin-snip construction.
 

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