Heatpipe

Prelude

Heat pipe, what is that? besides being a potential nickname for penis, it is a technology used as a more effective heat sink.

The theory of operation is rather simple and explained in length on Wikipedia, but the 101 version is this:

As we all know from physics, changing state of matter require more energy than just heating / cooling 1 degree C in the same state. This is the reason why heat pipes works so well.

Please note, that no heat / energy by magic disappears, it is just relocated. In this case, it is just moved away from the source to a remote and usually bigger place to dissipate to the surroundings.

Practical application

One obvious place to use this technology, besides your fridge, is the cooling of laptop CPU's.

The size and layout of a laptop means the CPU is located in a tight place and room for a fan on top of the CPU is a luxury that we just cannot afford, thus heat pipes on a flat heat sink is ideal, move the heat horizontal and quick out to the side and let a fan, placed at the same horizontal level as the motherboard/CPU, deal with the heat in the heat sink by means of lovely fresh cold air from just outside the nimble fan-grill on the side of the laptop.

You know the place, the place where you placed your once cold Coca Cola and never your coffee.

When shit and not heat hits the fan

In the old days, when PC's ran hot, it was just from clogging up with dust in the heat sink and/or fan or a faulty fan, but heat pipes pose a new problem:

They can leak....

This is what happened to my Thinkpad T42, CPU was running hot, in fact it would reach 90 C when CPU load was 100% for more than 5 min, causing a shutdown.

Several things was tried. Cleaning the heat sink, applying new thermal compound (twice), nothing helped.

I took the chance and got a cheep and brand new heat sink for the T42 off eBay.

Measurements

What would this wiki be without measurements?

Setup: The laptop with a fresh Debian 7.3 with GNOME 3.4.2 desktop. Fraqtive + X-sensors installed

Test method: 100% CPU Load until stable temperatures are seen, loading done with generating fractals in Fraqtive, pretty loading in more than one way. Temperature + fan-speed monitored with X-sensors. First 100% load, then let it sit in idle until temperature stops dropping.

Old heat sink:

100% load = 86 C, 4273 RPM. - note that test was terminated before Linux reboots at 90 C, it will go pass 90 C.

Idle = 40 C, 3579 RPM.

New heat sink:

100% load = 70 C, 3573 RPM, stable readout and nice fractal.

Idle = 37 C, 2965 RPM. - from time to time, the CPU fan switch off fully.

Conclusion

It is somewhat interesting, that the idle temperatures are almost identical, with a bit higher fan-speed, perhaps this show a lower limit for the liquid in the heat pipes. During load there is no doubt the heat pipes are working and they were indeed faulty in the old heat sink, 20 C / 29% lower temperature with lower fan speed, impressive.

I have yet to find a way to tell if a heat pipe is dead, the gas/liquid cant be heard or measured, but perhaps low idle temperatures and high load temperatures are indeed the indicator.