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I've been asking myself this question for probably more than 10 years now... What's the point of heat pipes? For example on a CPU cooler.
It just seems super unreasonable to me that 4,6,8 or I don't know how many heat pipes would be more efficient at transferring the heat to the aluminum fins than simply using a solid copper block. Or why not just leave it and mount the fins closer to the CPU? I mean you could still use a little bit of copper, but not these two or more inches long heat pipes..

It really seems like a marketing thing to me tbh. I mean Intel's stock coolers do just fine without any heat pipes. (Considering how small they are and that there are not a lot of fins.)

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  • Is there a real issue you are trying to deal with here?
    – CharlieRB
    Sep 9, 2015 at 16:41
  • Solid copper block is not very good for dissipating heat to the air. Its one thing to soak up the heat into the heatsink, it another to remove it from the heasink into the air and out of the enclosure.
    – Moab
    Sep 9, 2015 at 16:53
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    @Ramhound what's the point of only quoting half of my sentence, you are changing the meaning of it. You're answer has nothing to do with my question. You should read the whole sentence again.
    – Forivin
    Sep 9, 2015 at 17:08
  • @CharlieRB Depends on how you'd define "issue". I'm just looking for an answer to this question.
    – Forivin
    Sep 9, 2015 at 17:09
  • @Moab I'm pretty sure the fins are component that is meant to dissipate the heat to the air. Pipes would do a terrible job at this compared to thin fins to which the fan is usually mounted.
    – Forivin
    Sep 9, 2015 at 17:09

2 Answers 2

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A Heat "Sink" as its commonly, but perhaps incorrectly called, has two jobs:

  1. evacuate heat directly from the CPU die as quickly as possibly
  2. to allow evacuated heat to dissapate without reintroducing the heat into the system you are attempting to cool.

This second part is why I don't like the term "sink". it implies that you can keep pouring heat "down the drain", without ever filling the sink.

Traditionally the metal "fins" of a heat spreader provided maximum surface area in contact with the surrounding air, so that heat would move from the fins to the air and be blown out by the system exhaust fan as quickly as possible. If the fins were not able to get rid of their own heat fast enough, a fan could be attached to the spreader to increase the amount of air that comes into contact with the spreader surface per time interval, presumably increasing the transfer of heat from the fin to the air.

Some of the key concepts are:

  1. Heat (energy) will always move from the highest energy conductor to the lowest energy conductor available. When you put an ice cube in a glass of water, the heat moves from the water into the ice cube, thus reducing the heat in the water.
  2. You can never cool an object by moving its heat to an object that is already hotter than it is. This generally means that you can never cool a CPU to less than room temp without refrigerant.
  3. Materials with a lower specific heat will both heat faster and cool faster than materials with a high specific heat.

So in a traditional scenario, the heat spreader has a lower specific heat than the CPU die, so the heat flows into it quickly. The low specific heat also allows the heat to exchange into air, but the rate varies based on the amount of heat produced with any given time interval.

The flaw in this approach, is, what happens when the CPU is producing so much heat/second that the heat spreader cannot evacuate it fast enough, causing the spreader to heat up to the point where heat will no longer flow into it (or will only take heat so slowly, in too little quantity) such that the CPU's heat doesn't go anywhere.

Thats where it becomes important to seperate the concerns of immediate evacuation of heat from the die, and more gradual evacuation of the heat from the heat spreader. if we can keep taking heat from the CPU quickly, then it really doesn't matter to us much how quickly the fins disappate it into air.

Heat pipes are specifically designed to evacuate heat from the CPU as quickly as possible, and move it further away from the die than was traditional, which makes the whole system more effective when the CPU is running hot, and might have swamped a traditional spreader.

The material heat pipes are composed of (as well as the material in direct contact with the CPU die) must have a very low specific heat and conductive resistance to be effective. The mass of conductive material has an impact on this equation, such that the more pipes of lower mass individually will perform better than fewer pipes that are aggregately of the same mass. So, from that perspective, all else being equal (and it rarely is), the more pipes the greater the capacity to evacuate in any given time interval.

So, that was way more answer than you wanted, and represents only a minimal knowledge of thermodynamics, but hopefully its of some use to you.

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  • Well, but wouldn't it be more efficient to just leave the heat pipes and mount the fins closer to the CPU and make half of an inch of the fins of copper or something like that? .
    – Forivin
    Sep 9, 2015 at 18:45
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    well, in theory, that would be bad practice because that will cause a heat build up closer to the cpu die, and reintroduce heat into the CPU when the spreader starts to heat up, so we are once again bottlenecked by the rate at which the spreader can evacuate to the air. That said, there are plenty of heat pipe designs where the fins go all the way down to the base of the unit, so yes it is done. The key takeaway though is that the pipes move heat faster than fins evacuate it. And for my cpu coolers, I already insist on copper from top to bottom already. Sep 9, 2015 at 18:51
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The heat pipes are basically pipes, to carry heat, (no duh) to the fins on your heat sink. The Heat sink increases surface area, and improves cooling and your fan, further aids the cooling. The most common type of heat pipe is copper, and usually attached to aluminum fins. Copper conducts heat better than aluminum.

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