Useful info for dual 120mm fan radiators
 

You have to register to read (??) but this was I thought a very useful post on the OCAU forums:

http://forums.overclockers.com.au/sh...threadid=61410

Basically the guy (Cathar) has added a baffle on his shroud to separate the two 120mm fans. He finds lower water temperature as a result. Worth a look if you have such a core. Not too much work to modify a shroud like that either.

Nice read, Thanks man :)

ok...but why? less turbulance with the airflow from both fans?

Actually, it's pretty simple...

(btw, I have to laugh at the "20% improvement" figure, it should have simply read 1.5C improvement)

The fans we use are not designed to be used in tandem, like that. There is a gap between the fan blades, and the fan housing. Normally it's not a concern when used as a single fan, unless there's a lot of resistance (look at it this way: why can't you inflate a balloon with a fan?).

In tandem, fans are setup to create additional air flow, but the result is also a higher pressure at the fan outlet, which leaks right back out the prop/housing.

By isolating the fans, this pressure loss is minimized.

A fix would be to use what I refer to as turbo fans, where the fan blades are encased in a ring, which sits deep in the fan housing. These are also known as ducted fans.

It would not be wise to try to mod a fan, as the accumulated dust can bring one to a grinding halt. It's far better to just get the right fan.

Personally, I'm not going to use a regular fan on my rig, I'd rather use the cross-flow type, because they are more compact (for the same power), more powerfull, and quieter than the fan types. I don't understand how ya'll don't use these, they're just perfect for a radiator.

Well for starters, where can you get some of these "cross-flow" and ducted fans? :)

http://www.mpja.com/allpict.asp?dept=48

last item.

40cfm, 44dba, 17" x 2.5" x 2.5"

those are very uncompetitive figures ;) 2.5" is basically 60mm, you could fit 7x 60mm fans in this area.

Papst make a 14.7cfm 60mm fan, it makes 19dba. 7 x 14.7cfm is 103cfm, for much much less than 44dba.

Please explan why the cross flow fan is so good, I'm missing it. Papst's catalogue says they are good for high flow, low back pressure, which probably isn't the thing we want in a fan.

Papst also make a 172mm fan that goes from 53cfm at 18db to 353cfm at 65dba, the rate is controllable through a small potentiometer, or through a thermistor. Wouldn't this be the perfect radiator fan?

Glad you asked.

cross-flow fans are much harder to find, but they are very often used in AC units, so they should be easily available that way.

Those fans can easily reach 100 cfm, with less than 30 DB noise. Regardless, since they have to have a housing to cover them, whatever noise they make could easily be isolated.

Mounted on top of a rad that sits at the bottom of a case, they can suck air in from the front, where you can put your air filter.

I have found 2 types of crossflow fans: one with straight fins, and another with curved or angled fins. the later performs better, but will not run nearly as efficiently in reverse.

An alternative would be a squirrel cage (same principle) fan. These are very common as fans for car interiors. Again, because they have to be encased (a little fiberglass work?), whatever noise they make can easily be isolated.

Papst makes some of these, but there are many other manufacturers of these "tangential" or "cross-flow" fans. They are available in a wide variety of sizes, and I've seen 24" drums on the web. The one you found would be a little big, no?

The papst I mentioned at 18dba - 65dba is just a normal 172mm axial fan. Download their 10mb .pdf catalogue. Even on 56k it's definately worth it.

*cough* Here's what I have in my possession... It's just a tad bigger than the chevette heatercore... Pushes a decent amount of air, deals well with backpressure and is pretty quiet...

DataSheet

Pic from datasheet

-ymboc

My point exactly...

As far as I'm concerned, the more air that flows through a rad, the better. The only problem is noise.

Using a regular bladed fan can be noisy at high RPM, but a cross-flow (or blower) HAS TO be encased so regardless of the noise it makes, it is a better choice.

I will setup my heater core lying flat at the bottom of my case (cut open at the bottom), setup 1 or 2 x-flow fans, sucking air from the front of the case, where the air filters will sit, conveniently located for regular maintenance. Dust in a rad is bad, very bad...

Very easy to setup, requiring little or no ducting, gives a number of options, like a clear acrylic housing with colored LEDs (for the mod freaks), or internal padding to collect even more dust.

It's just a smart choice.

real simple question here


clearly running two of the same fan types (both lets say 40 cfm) can have problems.

so why is this getting more complicated then simply having a stronger fan being used as the "Pull" fan in a push/pull setup.


40CFM ||Rad|| 20CFM


this way you're sort of running only a "Pull" fan but you are just giving it a little 'boost'

(I can't believe that I have to explain this!)

That setup will limit you because you're trying to suck more cfm than the other side is providing. You'd be better off with the 40cfm fan by itself.

Ya'll need to understand a few things about these push-pull setups:
1-the resulting cfm will be just about the same (very slightly better).
2-the only reason for doing this is to compensate for the air flow resistance through the rad.
3-the alternative to this is a single bigger/faster fan, at the cost of noise.

That's why I mention x-flow fans, because regardless of the noise, they will be encased, making the noise a non-issue.

So if you want a quiet 100+ cfm, you can easily achieve that with an x-flow.

could use a blower fan in an enclosure

Good point. A blower fan, commonly used in cars, could pull air in from the side of the case, and blow it down into the rad.

I've looked into x-flow (aka tangential) fans versus blowers (aka squirrel cage), and the blower is far easier to get. Like I said above, it's an automotive part, so even a scrap yard would have them. I pulled mine off of my old '85 Nissan 240sx when I scrapped it. I didn't rip out the housing though, but I can easily make one out of fiberglass, or plexi, if I feel like it. Not sure about the fit though... It'd be nice if the motor was mounted inside the cage (another mod?).

I had tried this concept once on a BIX ducted to ambient and it did give me a small gain with moderate noise increase. I didn't have two 86CFM 120mm fans at the time so I used an 86CFM puller and a 69CFM pusher. Of course my combination was only a 20% reduction while your example is a 50% reduction. I got a .5C reduction in water temp and a loaded CPU temp reduction of .8.

why type of RES was that? it was might-T-fine

i'm also considering using a duct to bring the air conditioning from the central air in my house right into my case/rad