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Idea came to mind..

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Jun 29, 2001
Reality, USA
This has probably been done before, but I've never seen an article on it or read a post about it. If you tried it and it worked well, let me know.

I have been thinking about some type of ducting system. Anyway, I have some generic case fans right now and I am thinking about upgrading to Panaflo's or some other high cfm / low noise solution. Then I thought, wow, if I gutted my old generic fan, I can screw the outside frame on the new fans and that would make a perfect duct!

You could use 2 gutted fans, and screw one on the inside and one on the outside of the "actual working fan" and that should create some pretty good air flow while spacing the fan away from the case and also shooting the cold air deeper into your case. The principle could also improve exhaust fans I think.

Any comments? Has anyone done this?
ducting isn't new but this is the first I have heard of using this method. Try it out and tell what happens!
oh yeah, I should have clarified... I know ducting is nothing new. Just the method I described might be new....

If you look at most 80 x 25mm case fans, they are very streamlined on the inside once you remove the guts. Screwing them together should be a fairly air tight, low resistance air tube.
You have to keep in mind that, while alot of the fans out there have a streamlined duct already, not all of them are straight. Most have a curve to them from in => to out, peaking at the center by the blades. Looks like a fan in the middle of a torus, aka, donut. Stacking such fans would induce eddie currents and the whatnot since the path isn't perfectly streamlined between them. I know there are fans out there that have a flat surface on the inside, though, I dont think those are the high quality type. Interesting twist to the idea, just have to be careful about the details. :)
Kingslayer (Jul 15, 2001 05:52 p.m.):
Well if the fans with the flat insides are low quality, can you think of a better purpose for them other than to be gutted and used as ducting?

Monitor fans? TV/VCR/HiFi/Amp fans?
Maybe you can cut off the curved blades and glue on flat plastic paddles to convert them to centrifugal fans (fits in drive bays)?
When I was working on the Hoot Chute, I took a couple of aluminum housed Rotron Sprites that were bad and gutted them. Yes they were tapered housings, but I screwed them together and used them.
They worked great as a duct, despite not having smooth, flat inner surfaces. I'd say go for it, but leave the case fan on the surface and put both housings on the exhause side. You would ultimately benefit from using a piece of square PVC gutter downspout, with nice smooth sides. as a duct. The square form mates nicely to square fan housings. They also make them in painted aluminum and painted steel. One 10 ft. length of downspout will last you a lifetime of experimenting.

I'm currently trying this idea with one modification.

Instead of gutting one of the fans, I left both fans fully operational. That's right, I basically stacked two 80mm fans on top of each other - Screwed one right onto the other.

The location for this combo is on the side panel of my case blowing very near my cpu HSF. Initial impression shows that it has dropped my cpu idle temp by 2c. This is probably due mostly to the fact that the air flow is closer to the HSF. I've basically created an 80mm x 50mm air duct with 2 fans. I haven't tested full load temps yet, but I suspect they will drop by about 2c also. I'll keep you updated.

I'm not even sure if the 2 fans are the same CFM rating. Needless to say, this could shorten the life of the fan motors because they will probably create some resistance for each other. Anyway, by the time they die, I will probably looking to upgrade anyway.

The 80 x 50mm prototype is about 1.5 to 2.0 inches away from the cpu HSF now I would guess.