Heat pipe – 250x faster heat transfer than copper | Hacker News Reader

Heat pipe – 250x faster heat transfer than copper

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49 pointspunnerud34 comments

> Modern CPU heat pipes are typically made of copper and use water as the working fluid.

So there's water inside my laptop?

Water is the original coolant. Abundant, decent performance, cheap, non-toxic.

Not only decent performance but the highest head capacity of all liquids, and it’s boiling point can be easily adjusted by lowering pressure if required.

Ammonia tends to outperform water, but it's toxic. I believe it was used in some of the first refrigeration applications (and I think Einstein had a patent related to one).

I came across potassium nitrate + water being used for making things cold - https://cordis.europa.eu/article/id/36036-making-things-cold... . Wonder if that could be used too?

Absorption refrigerator: https://en.wikipedia.org/wiki/Absorption_refrigerator

Einstein refrigerator: https://en.wikipedia.org/wiki/Einstein_refrigerator

The principle is still used in some refrigerating devices (typically hotel mini fridges and similar small units for RV's) as there is no need of a compressor (i.e. the device is completely silent) and also in some HVAC machines.

We aren’t talking about regurgitation but rather about heat transfer.

Ammonia has lower heat capacity than water, and it’s nasty.

>Ammonia has lower heat capacity

You’re probably confusing gaseous ammonia, but the GGP said “of all liquids.” Liquid ammonia has a higher heat capacity than liquid water. Refrigeration is just an engineering application of the heat capacity of a working fluid (and I’ll let you guys why some of the earliest heat pumps used ammonia)

>it’s nasty

I clearly stated toxicity as an obvious downside.

But also corrosive.

unless distilled

Ah distilled water is terrible for metal pipes. It’ll leach out metal ions from the pipes.

And steam!

I want a steam generator on my cpu now, whistle and all

If it has heat pipes/vapor chambers then yeah, it's like the chips are heating elements for a little low temperature, low pressure boiler.

Interestingly, heat pipes in a computer can corrode and leak the coolant (largely escapes as water vapor). Once it's gone, the heat pipes are basically junk. I've seen this a few times, wondering why the thermal performance was so abysmal (think 90-100 degrees celsius with low loads). It was only after completely replacing the heat sink or whatever assembly contains it that temperatures would be normal again.

Corrosion requires a constant source of fresh oxidant. The water trapped inside a heat pipe cannot corrode anything.

The tiny amount of free oxygen that was ever trapped inside gets consumed essentially immediatly and amounts to a relative handful of atoms on the inner surface.

If a heat pipe ever corroded and leaked, it was manufactured with a leak to begin with, or was corroded from the outside.

I never said the coolant corroded the heat pipe.

Your CPU pins rusting is a bigger concern then.

I never said it was a risk or concern or anything else in that direction. I was just pointing it out because I thought it was interesting. There was a time I didn't realize there was coolant in these heat pipes that could escape. Until encountering one where it had dissipated and, after some consternation and googling, realizing what must have happened to cause such terrible thermal cooling performance. Even if it does happen, heat pipes are among the cheapest components to replace (also the easiest).

Does everybody just want to argue over nothing now?

Maybe I'll rephrase.

Is the CPU pins rusting a bigger concern, compared to if the heap pipe busts ? Thats not an argument, it is a question.

I wonder if the obsolescence of such heat pipes corrode just outside of the warranty period...

Honestly, I think that's extremely unlikely. In the time I worked as a PC tech I think I saw this only twice and they were very old devices (like 8-10 years old).

Sometimes they use ammonia instead!

I was quite surprised to see the complexity of inner heatpipes https://www.powerelectronictips.com/wp-content/uploads/2020/...

I can't work out if that was sarcasm or not, but isn't that just corrosive buildup?

No, that’s the wick. It lets the condensed water move by capillary action.

ah thanks for the context

I recall stumbling upon this while trying to answer the question "can you tell if there's a risk of fire on one end of the extension cord by measuring temperature on the other?"

Turns out that no - at least not for any extension cord of practical length and design.

Copper is a great heat conductor, but not nearly as effective as a dedicated heat pipe. You'd have to run it along the length of the cord to get a temperature reading above noise.

We once did math on finding overheating FETs with an on-PCB temperature sensor. We came to the same conclusion as you.

Our supplier advertised a sensor, which we found eventually on the other end of the PCB. The reaction time would have been five or ten minutes if at all, essentially the whole device would burn down and eventually it would take the sensor with it.

Turns out, the sensor would had to sit directly opposite the FET on the PCB, and there had to be a plugged via going straight through for sufficient thermal coupling. A lot of the physics boils down to simple aspect ratio, and normal vias are really thin.

(The real solution would have been putting the sensor on an FPC, and to glue onto the transistor. The real real solution was to make sure the part didn't blow up in the first place, which was much easier to do.)

Also, making custom heat pipes from China is really quick and inexpensive. We trial-ed some for one of our projects, all we had to do was send the CAD drawings, and they did the rest. The thing is that they didn't have to make tooling for samples-level of quantity, and thus it was very inexpensive to make for trying things out. The company we used is called Soodeco Metalworks, but we changed our design to have no cooling as it wasn't required, thus we never went mass production for it.

The Action Lab did a very informative and interesting video on Heat Pipes: https://www.youtube.com/watch?v=OR8u__Hcb3k

I had seen those things inside laptops, but always assumed it was just ordinary copper rod.

If it's water, how does it turn into vapor below 100 C? Is there some pressure magic in the heat pipe?

Yes. The air is partially removed before sealing, resulting in the heat pipe interior having a lower pressure than ambient air pressure.

Ah, thank you!

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