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A brief explanation on CPU coolers

By Julio Franco ยท 13 replies
Aug 17, 2016
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  1. Recently I was looking to double check the accuracy of a CPU cooler from Noctua, mainly for my own curiosity as well as part of our ongoing process to ensure we are only selling high quality parts to Puget customers. Right above is the Noctua NH-U12S. It did very well through our testing, and was added to our product line. When we qualify a new product to be a fit for our product line, everyone is emailed all of the details about the product and given a chance to offer opinions or concerns as part of the process. I had some concerns based on a combination of the pictures of the product and the manufacturers' specifications not quite lining up in my mind.

    Editor’s Note:
    Guest author Richard Falk works for Puget Systems, a boutique builder of gaming and workstation PCs. This article was originally published on the Puget blog.

    Before I get into it, if you do not know much about CPU coolers, I want to give you a quick run down of how the air coolers work.

    Heatsinks use either copper, aluminum, or a combination of the two in order to move heat from the base of the cooler through heatpipes to the heatsink. A fan then blows air through the heatsink to move the heat into the air, and then out of the system, effectively keeping the CPU within safe operating temperatures.

    A liquid cooling system essentially applies the same idea but replaces the copper heatpipes with tubes filled with a thermally conductive liquid that is pumped to a radiator. Copper is a very good thermal conductor, aluminum is about half as good, and air is absolutely pathetic. I will explain the differences in further detail in the next section.

    How does a CPU cooler work exactly?

    Thermal conductivity (how well materials transfer heat) is measured in watts per meter Kelvin. I know that sounds like gibberish, but we do not need to understand the science so much as to pull the nice even numbers scientists have worked hard to get so we can have a real number we can look at to gauge the differences between materials. These numbers here are not absolute, as different purities of materials have different properties, so you will see all sorts of numbers if you do some research on the topic. But for comparative purposes, lets use these numbers I have found.

    • Copper's thermal conductivity is 385 W/m*K
    • Aluminum's is about 205 W/m*k
    • Arctic silver MX-2 thermal paste (we use this on most systems) 5.6 W/m*K
    • Air's thermal conductivity (measured at 0c) is about 0.024 W/m*K

    This is the same reason why the sun takes many hours to heat up the air in the morning, but it takes only a few minutes to heat up a piece of metal (if you have morning frost you will notice this).

    So the way a CPU air cooler works is pretty simple!

    A CPU cooler consists of its heatsink, heatpipes, and base. In addition there is the heatplate on the CPU and the thermal paste in between the CPU and the CPU cooler.

    A base (usually copper, but aluminum on lower cost units) connects directly to the heatplate on the top of a CPU. The heat then gets transferred from the CPU heatplate through the thermal paste, which is used to ensure any gaps between the CPU heatplate and the CPU cooler base are filled. The base then connects to heatpipes in the CPU cooler. The base and heatpipes typically contain copper, as copper's thermal conductivity is very high.

    The heatpipes have a solid shell, a porous inside, and a hollow center that contains a liquid/gas. As heat gets transferred from the base of the cooler to the heatpipe, it heats up the liquid to the point of evaporation which turns it into gas. Once in gas form, it moves through the center of the pipe until it gets cool enough to condense back to a liquid. Once it is liquid again it flows through the porous material until it gets back to the base of the heatsink to get hot enough to evaporate again.

    The heatsink contains a large array of fins, typically made from aluminum. The heatpipe will deliver heat into the fins, which are spread out thinly so that the airflow through them can dissipate heat easily. Since they're designed to cover a large area, they don't need the high level of thermal conductivity that the heatpipes and base need.

    Now, going back to why I wrote this - the manufacturer specifications said the materials were a copper base and heat pipes with aluminum cooling fins. Copper is the color of a penny and aluminum is the color you see on the Noctua cooler up above.

    Because they stated that it was copper pipes and a copper base which you would expect on a really high end cooler to have, I was confused when in the pictures of the product, it looked like aluminum. I was skeptical of the manufacturers statement that it was zinc covered copper. So I went and got a heatsink and (with my boss's permission) started to use a filing tool to file off the metal to prove if that was an accurate statement. After removing the coating of zinc, I discovered that indeed, the base and heatpipes were made of copper. Not only were my fears resolved, but Noctua was proven by fire once again to have a solid product. But I was able to have fun with it! Here are some pictures to prove I can break things too!

    Here you can see the heatsink which has a copper heatpipe, and the copper base which were exposed after filing off the zinc coating. Zinc does not have as good of thermal conductivity as copper or aluminum, but being as it is such a small amount of it (a very thin layer like paint) It does not really affect the cooling ability of the unit. It was likely done as Zinc is resistant to corrosion and copper as we know can corrode.

    After reading this, you probably think I like to break some of our new products, but that is not the case at all. And to make you feel better about me breaking perfectly nice things, after I was done attacking this cooler, I sanded down and cleaned the unit and we will actually use it internally for a specific use. After reading this article, I hope you have a better understanding of how CPU coolers work and also learned a little bit about how we test new products.

    Also Read: The Best CPU Coolers

    Permalink to story.

  2. Uncle Al

    Uncle Al TS Evangelist Posts: 5,267   +3,682

    It's got excellent reviews from the users on Amazon and another site so it might be worthy of an investment. I'm still on the fence but just about ready to jump
  3. Icysoul

    Icysoul TS Enthusiast Posts: 39   +13

    It's also worth mentioning that one should match or exceed the maximum TDP of the CPU with the maximum thermal dissipation of the cooler. For example, the FX-9590 needs the elder brother of this cooler, namely the NH-D15 or a similar beast...
    Last edited: Aug 17, 2016
  4. hellokitty[hk]

    hellokitty[hk] Hello, nice to meet you! Posts: 3,415   +145

    That is NOT why the sun heats up metal but not air LOL.
  5. robb213

    robb213 TS Evangelist Posts: 345   +113

    Zinc...I would've assumed nickel but close enough.

    And that's where people start getting concerned over PCB morphing over time. Although I can't blame them for their concern with that much awkward weight. Still usually nothing to worry over though.
  6. erickmendes

    erickmendes TS Evangelist Posts: 567   +246

    Noctua wouldn't make such a mistake.
  7. Tinderbox

    Tinderbox TS Rookie

    Great cooler but man, the brown is an ugly color.
    Raoul Duke likes this.
  8. Surely there must have been a better way to verify the composition? Archimede's Principle, perhaps?
  9. Greg S

    Greg S TS Evangelist Posts: 1,607   +443

    Q = mc*(Tf - Ti) read as Q = mc delta t.

    This is the basics of thermodynamics, where Q = the heat energy in joules, m = mass, c = specific heat constant for the material, temperature final minus temperature initial. This lets you figure out what the equilibrium temperature will be between two different temperature materials when they come in contact in an ideal situation.
  10. Chesterfried

    Chesterfried TS Enthusiast Posts: 39   +12

    I've been using it's smaller brother (NH-U9S) for over a year now in my HTPC and it has been great. Fantastic build quality, quiet and dropped the thermals down about 20-25% compared to the stock cooler on my i7-3770k. If you like to push your system, I definitely recommend after market cooling.
  11. I like coolers with absurdly more heat dissipation than I require just so the damn fans run quietly
  12. Adhmuz

    Adhmuz TechSpot Paladin Posts: 1,914   +699

    What the heck did I just read??? Was that supposed to be informative or show us how little the people over at Puget actually know about the hardware they use, in this case the coolers they use. Given I always thought Noctua used Nickle to plate all their heatsinks and not Zinc and in fact after a quick bit of research it turns out they do in fact use Nickle to plate their Copper and not Zinc nor does it look like Aluminum for that matter but I digress. I had no doubt in my mind it was copper under the plating for the base and heat pipes something I personally discovered when lapping one years ago. Just feel how heavy one of those things are, had it been nothing but aluminum it would be much lighter. Also industry standard for heat pipes is Copper and not Aluminum, if a $25 tower style cooler has non plated Copper heat pipes do you really expect a premium priced unit to cheap out of this? Perhaps the title should have been "Heatsink Technology for Dummies" or in this case, presented by one...
  13. Bubbajim

    Bubbajim TechSpot Staff Posts: 656   +633

    They're going to need even better coolers now, they just got buuuuurned.
  14. My Skylake I7-6700 is cooled by a Noctua NH-U9S. http://noctua.at/en/nh-u9s - and I'm totally awestruck by it's performance. Never have I had a more compact cooler so silent, able to keep my CPU below 48 degrees, even after 3 hours of continous 100% CPU usage on all cores (1080p encoding). I can't hear the damned thing, according to hwmonitor it's trundling along at 750-800 rpm, crammed into a Fractal Design Core 500 mITX case with less than optimal airflow. Don't know what kind of witchcraft those boys ans girls at Noctua uses, but by gaw they can make coolers that rocks...cools...and is awesomely (is that a word) funkin' quiet...

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