CPU Cooling Push Push, Thermodynamics & Heat Transfer

Do you guys ever try push / push. Some people say they "fight" each other but that doesn't ring true to me. If the mass flowrate increases, the temps will be lower (in Q=mc delta t, if m increases, delta t decreases). The air will blow out the sides of the cooler and flow in thru the front and back. This might create some compensating factors (such as portions of the heat exchanger not receiving airflow) but those exist in the dead spot of the fan in Push or Push Pull anyway. The only other thing that would make me think push pull could be more efficient and effective than push push (or pull pull) is if the fluid resistance of the smaller sides is far below that of the front and back. I would think this would only become a factor with extremely high cfm thru the cooler.

So I guess my question is:

Has anyone actually tested this? Writing it off before trying it is kind of silly. Those compensating factors might be more of an impact, but without using computational fluid dynamics software (like what I use at work), testing is the only real way to know.

I think that especially at lower RPMs the push push would excel. So for those looking to do hyper efficient and quiet computing it might work well.


Also, in a cooler where the open area of the sides and the front are the same (a square if looking down on the cooler) I think push push would excel further as the compensating factor of higher fluid resistance (with the smaller sides) would be gone.

You could also place a cooler on the front and side (so they make an "L" shape around the heat exchanger) which should eliminate the dead spots in the center of the fan (if you look at a fan, there is not any flow thru the center where the fan motor and rotor rest and no fins lie). If you could duct the exhaust from the cooler out of the case (or duct the fan exhaust in a pull pull which might be easier) then your inlets would be lower, your delta would be lower, and your cpu temp should be lower for any given load and fan speed.

I know I'm talking a lot of thermodynamics and heat transfer / fluid flow, but most of those concepts scale absolutely (I just wonder if the degree to which effectiveness increases are measurable). I would love to know if someone has given these ideas a try and would love to help coach them thru what I am thinking. I am planning to build a rig in the future and I want to totally geek out on it, but right now I'm saving for a down payment on a condo so it's somewhere on the horizon.

FYI I am thinking about the asus p8p67, i5-2500k, coolermax 212 plus, using the case from my Gateway LX6810-01, 8 gb of ripjaws, a corsair builder 650w psu and some type of hd 6870 with my existing raid 150 vraptors and and 600 gb storage drive and using a ducting system to create hot aisle / cold aisle in my case.

PS. I still think it might be more effective to install one fan with more area for the prime mover and a higher speed than using two.

Yes of course, a flowpath must exist.

I agree- if you are going to use 2 fans, you really need to do a push/pull setup...otherwise you are simply crippling the performance of using 2 fans to begin with.

There are a couple of things here I would like to emphasize-

Agree.

I realize this is a forum and meant for discussion, but let's try to keep all the 'what if's' to a minimum...try and see...give us your results. (I wish I could get people that keep starting the 'I want to put my PC inside of a refrigerator/freezer- think of the great temps! What do you think??' threads...most of us already know the answer- it's been tested before and is posted in many stickies...otherwise, give it a shot for yourself. (another gripe...people not reading stickies...)

Agree.

Incorrect or questionable information being posted where users might stumble across it and simply try it out. I am a firm believer that you are responsible for anything you decide to do with your rig, but let's try to minimize questionable information as much as possible until there are some firm results to either support or oppose it.

I plan to try it. I feel like you guys are lecturing me. If someone has tried it before, why would I not want to benefit from their experience.

What misinformation am I spreading? If by misinformation, you mean things written in textbooks, then you got me good.

To 4Ryan6's points, the crappy airflow in the case that would result is something that worries me. I was thinking if I tried this I would use shrouds to route the hot exhaust. And it is a good point that the coolers are designed to operate in a certain way and one would like to think that way was most optimal. But my counter to that is that these are mass produced items, and looking at the metal on the 212 +, its hard to imagine that they really did anything herculian to make flow direction as important (such as vanes, dimples, channels etc) although I will be able to examine it more closely when I pick it up from the cleaners tomorrow morning. Features like that are expensive to produce and I doubt I will get them with a 20 dollar cooler. In that same vein, I am sure most coolers will have their own peculiarities, so this might be a solution for some and awful for others, or it might be something that works at low rpm but is terrible at high rpm. That's why I thought I would share the device I plan to use. The face of the cooler has an area of 18444 sq mm, and the sides have an area of 8109. So less than half. It should be interesting.


I plan to test the crap out of my theory at some point. I am ordering a PSU today, and I have my coolers and paste already. I have a board picked out (but I'm waiting to order from Newegg until I see if an ebay auction pans out). And the first chance I get near a MicroCenter I'll get my processor.

I am really anxious to see how well I can manage temps with low fan speeds. Does anyone know of or have any experience with fan speed control apps other than the bios management or the automatic fan speed control?

My experience with VFD software is on a much greater scale (10000 sq ft data halls) but I think dead spots wouldn't be a huge issue as the turbulence inside the cooler will create little mini cyclones. Although at the same time, those types of effects are undesirable, so I am really torn with what I think will happen. I have definitely been surprised before by the degree to which funky airflow (and how much air temperature differentials can move) can positively and negatively impact cooler effectiveness (but as a rule, effective removal of hot air from the environment ALWAYS kicks butt).

Also, does anyone have experience undervolting with Asus P8P67 boards?