Crazy idea.... 2 fans for one CPU heatsink. What do you think???

[alexruiz]

I am thinking about ideas to get a quiet/cool PC. I just realized that if we could have more airflow moving through the heatsink we could have beter cooling (I mean moving, not just being blown at)

I want also quiet, and we know that usually quiet doesn't match with cool. I got this crazy idea:

If we use 2 fan with one heatsink, we could (in theory at least) get twice the airflow. Now, to make it more effective, they should be blowing air from different angles to maximize the air flow going into the heatsink.

Also, most of the heatsink have the fins (when mounted) in a vertical array. That means, there are "tunnels" in the heatsink that go from top to bottom.

Now, what if I think "from bottom to top". Hot air tends to go up, so if I blow the air form the bottom, I can help it to go higher. Obviously, the fins array have a lot to do here, as if they were in an horizontal way, we would be blowing the air to the sides.

My idea would be to use the normal fan in the heatsink, plus another one perpendicular to the regular fan. The perpendicular fan would be located in the part of the heatsink that is closer to the bottom of the case, the fan would face the heatsink directly to blow air. If that works, then you have the normal fan blowing aire, plus the perpendicular fan blowing air toeards the top of the case, thus moving the air faster. Do you think it could work???

I am going to try it next week.

 

[whitelight]

it has been done before, but i wouldn't expect a drastic change in temps.

 

[McPhreak]

Originally posted by: whitelight
it has been done before, but i wouldn't expect a drastic change in temps.

Yeah, I've seen it done before on some OC website as well. Like a lot of fan adapters, the theory is great, but in reality I don't think it works really well.

 

[Gene396]

Good idea, but theory does not always pan out. You can move more and more air across a HS, but there comes a point at which the effecency of the HS to move heat from CPU to surface of HS begins to dememinish. At this point noise begins to become a large factor. Use of copper and design of HS does effect the amount of heat that can be transfered. In other words at some point; if you want more cooling you will have to use another method rather than air cooling.

 

[2Cool]

Thing is, with one fan on each side, one pushing and one drawing air, you aren't doubling the airflow. You may slightly increase it by lessening the pressure inside the fin area, but in reality if your pusher fan moves 30cfm (number used just for reference), and your puller moves 30cfm, you don't move 60cfm. You move 30cfm into the heatsink, and the same time you move the same 30cfm out of the heatsink. So each fan moves 30cfm... unfortunately its the same air, not 2 separate 30 cubic foot chunks. So pressure is lessened, airflow is slightly closer to the actual optimal free air flow rating of the fan, but it isnt twice as good.

 

[Ilmater]

Well, it's not a bad theory, but make sure you think about how heat is transfered. Heat is transfered from the HS to the air through contact. Thus, just like a watercooling setup, you want to have as much "turbulence" as possible with whatever is pulling heat away. Now, while heat sinks have become really good at pulling heat away from the base and into the fins where they can be more easily dispersed, the reality is that most of the heat stays in the base. If you have a fan blowing air parallel to the base, you'll get very little turbulence - and thus very little heat transfer. There is not enough gain from extra air/metal contact in the fins to justify the loss from the base.

Let me use an example. Swiftech heatsinks (the best on the market IMHO) are extremely good at getting rid of heat in those helicoil things because of two factors: 1) they have an immense amount of surface area, which means that there are more chances to pull heat away, and 2) the "coils" themselves create the aforementioned turbulence, thus pulling the heat away. However, they don't create too much turbulence. If the air flow was too restricted, the hot air wouldn't be able to get out fast enough to let the cool air take mroe heat away. This and all heatsinks are designed with the top fan in mind. Thus, you would actually hurt their performance a little when you do that. However, you're right, shoving tons of air through will help some. but, if you took two relatively low CFM fans, placed them in your configuration, and then put a big bad "screaming" Delta Black Label on the top, you'd see better performance from the Delta.

Another example would be Zalman. Their quiet HSFs work by not just having fins, but by spreading them out so that air hits them more directly. If your idea were applied to one of them, the same thing would happen. The perpendicular fan would blow through the fins, taking little - if any - extra heat with them. Again, I'm not saying that you wouldn't increase performance some, but after factoring in time, money, and noise, you'll see that it isn't worth it.

Oh, btw, if noise is an issue, the new way the air moves might hit something just right and make a really annoying noise. Maybe not, just a thought.

 

[GiZzO]

This might give you some ideas. Heres how i put two quiet fans on 1 sink. As you can see the fans get better coverage on the center of the sink (the hottest part). Some of the fan may be hanging off the edge push the hotter air away from the sink. It works pretty good on both sinks i've played with this on was pretty significant, difference with 1 quiet fan from almost too hot, too usable with two fans on a 1.4 Tbird.

Taisol CGK 760 Dually
Same idea on a Thermalright CB-6L


GiZzO's Fan Database Page

 

[Ilmater]

Now THAT could work. Does it? You didn't say if you got any performance benefits. Surely it is quieter than one loud fan, but I'm curious as to how much performance you can get.

 

[Chu]

>> If we use 2 fan with one heatsink, we could (in theory at least) get twice the airflow.

This theory is wrong. You don't get NEARLY twice the airflow with 2x fans in most cases, and in some cases, you will get less then a single fan. There are three ways of doing this . . .

#1: Two fans on top of each other.

This does not work. If the fans are 'out of synch' you get less airflow because of turbalance. If the fans are in synch you get the same airflow, with twice the noise.

#2: Two fans blowing in.

You might get more airflow. You will not get much more though, because of static pressure and turbalance. Is this worth the tradeoff? Try different angles, and see what happens. You might get lucky

#3: One fan in, one fan out (think wind tunnel).

The catch is you need to have it set up in a way that the negative static pressure created by the out fan is actuially being fufilled by the in fan. This is *NOT* easy outside of enclosed spaces for obvious reasons. The best way to do this is probably to actuially create a wind tunnel. Use your imagination, would make an interesting mod. Of note though, you are *NOT* getting 2x the air with this setup. It gets you closer to the theoritical maximun throughput of your fan(s), which might be significant depending on the design of the heatsink.

-Chu