Thermal Conductance 101 with Dr. Fylladitakis

Simplified, thermal conductance is the ability of a material or arrangement to conduct heat. Thermal conductance is inversely related to the absolute thermal resistance, meaning that a lower absolute thermal resistance will improve thermal conductance. In our particular case study, that arrangement is the CPU/Cooler setup. When studying arrangements, the absolute thermal resistance of the entire arrangement is the sum of the thermal resistance that each individual part has. Anything that lowers the absolute thermal resistance of the CPU/Cooler arrangement will result to better thermal conductance, i.e. lower operating temperatures. Vice versa, if the absolute thermal resistance of the arrangement increases, the thermal conductance will be lowered.

The figure above displays a simplified CPU/Cooler arrangement. At the bottom layer we have our CPU die(s), the middle layer is the CPU’s copper lid and, finally, the top layer is the CPU cooler. With such a setup, we have three individual thermal resistances: R1) the CPU’s die (heat conduction from the CPU die to the CPU lid), R2) the CPU’s lid (heat conduction from the CPU’s lid to the cooler), and R3) the cooler’s absolute thermal resistance. These three resistances sum up to make the total absolute thermal resistance of the CPU/Cooler arrangement. Simplified and assuming one-dimensional conduction, each absolute thermal resistance depends on three things: a) the length of the material in parallel to the heat flow (i.e. its thickness), b) the thermal conductivity of the material, and c) the cross-sectional contact area.

The cooler’s absolute thermal resistance obviously depends on the cooler itself (size, materials, design, air flow, etc.). However, no matter how good a cooler is, the absolute thermal resistance of the entire arrangement can still be poor if any other thermal resistance is too high. For example, it is known amongst enthusiasts that some of Intel’s previous processor generations had poor thermal performance that was unjustified given their very low power requirements. That was because the CPU’s lid was making poor contact with the CPU’s die(s), greatly decreasing the thermal flow between the die and the lid. Hardcore enthusiasts were “delidding” their processors in order to fix this issue.

Introduction AMD Threadripper Processors & Cooler Compatibility
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  • FreckledTrout - Wednesday, March 14, 2018 - link

    'Cus it's all about that base, 'bout that base, no TIM.. Reply
  • mr_tawan - Wednesday, March 14, 2018 - link

    Can you please give me some more mid. Reply
  • Holliday75 - Friday, March 16, 2018 - link

    <15hz or nuttin. Reply
  • Yurius - Wednesday, March 14, 2018 - link

    Thnx for review, but IMHO final words and conclusion is bad. Max allowed temp for 1950x is 68 degrees (https://www.amd.com/en/products/cpu/amd-ryzen-thre... but measured delta in best case is 59 degrees! Yes, throttling temp is about 85C, but who knows how long TR will operate with temp higher then recommended. Reply
  • E.Fyll - Wednesday, March 14, 2018 - link

    Hello Yurius. That was my bad - it is not the delta over ambient but the temperature reported by the motherboard's sensor. I had forgotten to edit the graph's subtitle. So it's 59°C real, about 9°C below the throttling point. Reply
  • Yurius - Wednesday, March 14, 2018 - link

    Wow, that's big different, thnx for update. Nevertheless it's to close even in stock on top rate cooler and there is huge problem with VRM on X399 boards, so I think AMD recommendations make sense and fullcover that fits CPU and VRM is a great idea. Reply
  • colonelclaw - Wednesday, March 14, 2018 - link

    That Noctua Threadripper cooler is a minor masterpiece of engineering. About 5 seconds after opening the box it came in, I had already forgotten about it's cost. Hell - even the box it comes in is beautifully made - a sure sign that you're dealing with a company that cares. Reply
  • FreckledTrout - Wednesday, March 14, 2018 - link

    I have a NH-D15 on my Ryzen and felt the same way when it came in. The Noctua coolers are just well made. Reply
  • tamalero - Wednesday, March 14, 2018 - link

    Agree, not only that.. they also have the signed paper of the CEO thanking you for the purchase.

    Probably one of the best coolers I've bought, right there with the famous 212EVO from CoolerMaster.
    Reply
  • Dr. Swag - Wednesday, March 14, 2018 - link

    Just out of curiosity, but what's your PhD in, Dr. Fylladitakis? Reply

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