Hey duuuude.... Let me place me whole head in there one more time and laugh again.... only this time harder

HA HA HA HA HA HA HA HA HA HA HA HA HA HA HA HA HA HA

Yes, but what exactly is the result of those gaps? Wouldn't it also allow air to escape? If it doesn't, why does it affect resistance so much?

Here's the afterthought to my last post that went MIA due to unforeseen consequences:


I would also be interested in learning more about how a short stack impedes flow less than a long one, as asked by Olaf. SPCR has an article on the properties of fans, but not so much one on heatsinks - the information is sort of scattered, and I could not find it in the Recommended or the Mugen 2 article.

If I were to hazard a guess, I would think that as "excess" pressure is vented from the slits, there is less back pressure building up to resist the movement of the airflow, provided that the fan creates sufficient force to push the air along. This got me thinking of muzzle brakes you see on guns, using the force of redirected gas to compensate for recoil, although the intent is probably different here, but it reminded me of "to every action there is always an equal and opposite reaction."

Trying to research this with no technical training was somewhat difficult, so my thoughts are speculation.

I disagree.

My hazard of a guess is that those gaps cost some fin area. But in return they provide less impedance. The impedance is what encourages the cool air to circulate elsewhere.

In my short search while killing time I didn't come across any good reading on impedance, so I guessed based on what I knew. And impedance is a vague area for me at best, as I haven't seen it explained well so far.

The descriptions "short" and "long" fin stack are a bit confusing to me. I trust you mean a "thick" stack like the Thermalright HR02 vs a "thin" stack like the Prolima Armageddon:


Thermalright HR02 Macho


Prolima Armageddon

No theories regarding airflow & heatsinks; I can only tell you what I've observed over the years -- ie, empirical experience:

With a large, thick fin stack that has tight spacing between fins, there is very little airflow on the opposite of the stack even with a powerful, high speed fan. But you can feel a lot of airflow coming through from the sides of the stack (ie, perpendicular to the fan), as well as around the periphery of the fan where it meets the fin stack. This does mean lots of black pressure. It also means that airflow across the fins drops dramatically the farther you go from the fan. Hence, these types of heatsinks can work very well with a dual push-pull fan setup, especially with higher pressure/speed fans, which increases pressure so airflow reaches all of the large cooling surface area of the tightly arrayed fins.

Take a big, thick fin stack with widely spaced fins like the HR02 or Ninja, and there is much more airflow that comes through on the side of the fin stack opposite a single fan, and much less airflow around the perimeter of the fan/stack interface -- ie, less back pressure, more air flowing through the entire surface of all the fins. These designs benefit much less from a dual-fan push-pull setup.

This applies to large, thin fin stacks like the Armageddon. Ditto the unique 5 fins stack array of the Mugen (I don't recall any other HS using this design.) The high impedance that a single fin stack of the same size and spacing as the Mugen would present is reduced just enough by those 4 gaps between the 5 stacks so that it does not require a high pressure/speed fan to get airflow across most of its fins. But I do think the Mugen has higher impedance than say the Ninja or HR02; iirc, it benefited quite a bit from a second fan.

What do you think of the idea of placing paper around the sides of a CPU cooler?

I trust you mean so that the air cannot flow out the sides of the fin stack? It would force more of the airflow through the center, but this depends a lot on the details. If the fin stack was especially dense w/ narrow spacing, that might just create more back pressure.

Yes that what I mean.

Do you mean that this might be a worthwhile experiment if you have wide fin spacing, or some trick to otherwise keep impedance down such as the Mugen and the Prolimatech Megahalens use?

It's worthwhile if you want to know what happens -- regardless of the type of tower HS you have.

Seems like it would be very very interesting to
(a) block the sides and top of a Mugen (a tight 1.89 mm fin spacing, but with multiple channels to help airflow)
(b) block the sides and top of a Prolimatech Megahalens (2.00 mm fin spacing, but with a channel to help airflow)
(c) block the sides and top of a HR-02 Macho (a generous 3.12 mm fin spacing and deep enough to benefit from the help)
(d) block the sides and top of a Scythe Ninja 3 (a still healthy 2.64 mm spacing and deep enough to benefit from the help)

Though it is unclear whether doubling up on fans helps deep coolers more than skinny coolers. Maybe:
http://www.silentpcreview.com/article1279-page6.html

Alright, thanks for the clarification Mike. I'd say that experience is worth its weight in gold, as practical applications are, as they say, "where it's at". I used "long" and "short" as I was thinking about the "length" the air has to travel to reach the opposite side of the fins. I realise this also somewhat translates into how tall the stack might be (oops!).

After trying to read up on impedance more, it seems the word is often used in such a general meaning or context that it's no wonder it's stayed vague.

Yeah, glad someone else spotted this. Outliers require that you've used the same method to collect all the data. If you collect 1/3 of your data with controls and accurate equipment, and then 2/3 with a potato, it does not follow that the potato data is right.

... Very interesting analysis of CPU cooler theory & practice. Thanks to you all for writing that!

A simple question for those who could have had this Dark Rock 2 Tower Heatsink in their hands: is it possible to turn the provided fan from "push" to "pull"?

I mean, can I install the provided fan from initial position "push-air" (the default position: see here
http://www.silentpcreview.com/article1277-page1.html
the last picture in the page "The Dark Rock 2", I can read "be quiet" in the centre of the fan, this is "push" position, where fan pushes air towards the cooler)

to "pull position" where I could not read "be quiet" in the centre of the fan (fan pulls air from the cooler)?

Please forgive me for my explanation, due to my bad English.

Thanks for your answers.

My question is because I'd like to test this cooler in both positions of the provided fan.

Hey guys,

I had been looking around for a air based CPU cooler that both performed well and looked good, and had settled on one of the Be Quiet! coolers until reading this review. Is their any chance you guys could revisit the brand and have a look at the Dark Rock Pro 2? I sifted through something like 20 different reviews on it and the only negative things they had to say about it really was it was expensive and a bit of a pain to install. I like the reviews SPCR does and would be interested to see your take on this revision.

In case you can't wait for another review, there is always the Donate for Reviews subforum: http://www.silentpcreview.com/forums/viewforum.php?f=32.