This is my first instructable,so if something is vague or wrong let me know.
In this instructable I create a CPU fan duct for an Intel Cpu fan (I3,I4,I4),although it could be applied to other 80mm fans.
I wanted for a long time to create a duct, but I am not really good at measuring and cutting things to proper size.
So no measuring is required.
Step 1: Materials
What you will need:
A 1.5 litre soda bottle.I used one of a 'popular' cola brand.Any bottle will do as long as it is approximately 80mm in diameter(and plastic...).
A ruler or other similar straight object, and a razor from a utility knife(as sharp as possible).
You will probably need a clamp, weights or more than two hands for a few steps.
You will need to have your case open and disconnected from power outlets.
Also your case should have an opening directly above your cpu for the duct to bring fresh air.
If not then you can find many other tutorials for creating fan holes.
Step 2: Preparation and Installation
Take the ruler and the razor and stick them with tape like in the picture.The razor should not move or it may come loose when we do the cutting.
After emptying the bottle of its content cut at the end of the neck(at the widest end of it).You don't need the neck part.
Disconnect the fan cable from the motherboard connector and uncoil it from the cpu fan.
Push the bottle in the fan.It should just fit.The fan cable should be left inside the bottle and should not be caught between the bottle and the heatsink.
Once the bottle is in place, place the ruler-razor contraption on the edges of the case and get the razors edge to touch the bottle.Then use the clamp,weights or extra pair of hands to hold the ruler in place.
Now start rotating the bottle.The razor edge should start scratching the bottle.After a few turns get the razors edge even closer to the center as to deepen the scratch.Repeat and after a few iterations you should have a clean cut,that should be perfect fit in height for your case.
You can either use the piece you just cut, or you can repeat the same procedure with the left over bottle.If you continue the next piece you will cut will have a smooth cut on both sides.
Step 3: Done
Now you have your duct.If everything was done correctly you will have a fan duct that perfectly fits your case.
If you made a mistake,just try again with a new bottle.
Step 4: Evaluation
So after the comment of mikeasaurus i decided to see what improvement i get from the duct.
As i currently have no disks i used a live cd(usb) Linux distro.I created a script that consists of the following 3 phases:
In phase one the system is idle and we sample the CPU temperatures once every 2 seconds for 2 minutes.
Phase two spawns 8 threads of yes(its a command that prints y continuously,thus wasting cycles).I know it is not the best bench marking tool but it raises the temperature of the CPU.Again this runs for 2 minutes and samples every 2 seconds.
The third phase is similar to the first.The system is idle and we check the temperature of the CPU.
In the following diagrams you see the temperatures.You can notice the 3 phases.
You can see that runs with the duct have approximately 4-5 degrees lower temperatures.
I assume that since my case has no hard disks or power hungry graphics cards the air inside the case wont be extremely hotter that the out side air.In a beefy system where the case will be hotter it should show greater improvement.