NaK (Sodium Potassium) | Danamics LM10 - Liquid metal put to the test

Danamics LM10 - Liquid metal put to the test - NaK (Sodium Potassium)

Cooling - Published on Thursday, 04 December 2008 01:00 Written by Andreas Galistel

I included NaK in the table on the previous page (and below for convenience) to show you that it is has properties similar to those of other metals. As mentioned on the previous page, NaK is an eutectic mix consisting of approximately 78% potassium and 22% sodium. Eutectic means that the mixture of the two metals has been optimized to achieve a melting point as low as possible, often lower than each of the two components by themselves. In the case of NaK the melting point is -12.6 °C (it boils at 785°C but we sincerely hope that you have never registered such temperatures with your CPU).

NaK sounds like a rather reactive compound you might say, and you would be right. It is actually extremely reactive. However, it is located inside hermetically sealed tubing and if a hole would appear the metal would coagulate and plug the hole instantly. We seriously discourage anyone from trying to open up the tubing. NaK reacts violently with water, even the moist in the air is sufficient to cause a minor reaction. Fortunately we don’t have free water inside our PCs and you will never hear a story of how a PC got damaged when the pipes of an LM10 started leaking. Unfortunately this means that the cooler will not be available in the USA, but only inside the European Union.

Substance	Heat capacity (J/g)	Thermal conductivity (W·m−1·K−1)
Water (liquid)	4.184	0.58
Air (gas)	1.012	0.024
Aluminum (solid)	0.897	237
Copper (solid)	0.385	401
Hydrogen (gas)	14.30	0.168
NaK (liquid)	0.982	23

As mentioned above, NaK has properties similar to those of the solid metals in the table. It has slightly better heat capacity, but also worse thermal conductivity. With a stationary cooler you want to be able to move the heat from the core up to fins, or mass of the cooler, as fast as possible. Since NaK is actively pumped around it is that it can absorb the heat quickly, but also emit it when it reaches the fins. When the heat reaches the upper portion of the cooler the heat is transferred off the cooler into the air, often with the assistance of a fan to increase volume of air coming in direct contact with the fins of the cooler. Heatpipes have been proved to be very efficient for moving the heat quickly from the base to the fins/mass and it does it through rather basic physics with passive movement of heat through phase changes.

If you want to skip the fan on the CPU cooler you need a great contact surface and high thermal conductivity. The heat has to transfer off the core up to the mass of the cooler and there emit into the air that gets hotter and hotter. Unfortunately air has very poor thermal conductivity so you can't rely on it to move the heat anywhere really, but have to do the best of a poor situation and use a great contact surface. When the air heats up, the cooler will get warmer, which means the heatpipes will get warmer and efficiency will decrease.

Liquid metal might just be the a better way of doing this it since it will deliver consistent performance even when the temperature surrounding the cooler rises.

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