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Danamics LM10 - Liquid metal put to the test - Sida 2:

First of all, there are many metals, metalloids and alloys that conduct heat much better than for example water, which is a fairly common type of cooling among enthusiasts.  Also, far from all metals need to be heated to high temperatures to become liquid. Mercury for example becomes liquid at -39 °C. Mercury is not suitable for these kinds of applications though, mainly since it is regarded as highly toxic. Danamics has chosen to use an eutectic mix of sodium and potassium known as NaK. NaK is used for cooling reactors already and is an acknowledged metal for this kind of application.

As with all kinds of cooling there are numerous variables to consider. Thermal conductivity and heat capacity of the materials are usually considered the two most important. The latter is referred to as specific heat capacity, or just ‘specific heat’ in physical and chemical terms. Among laymen it is simply referred to as heat capacity. Specific heat capacity is the amount of energy required to raise the temperature of a unit quantity by one degree. We will use the term ‘heat capacity’ to keep things simple even though it may not be the most scientifically correct.

Thermal conductivity is a materials ability to conduct heat, usually measured in Watts per meter and Kelvin. Both air and water have poor thermal conductivity, while water has good heat capacity. This is partly why water cooling works so well for computer cooling. It may not always lower your temperatures that much compared to good air cooling, but the amount of heat that can be absorbed by the water is so massive that it will give you more headroom and even allow you to overclock your gear and still stay in about the same temperature range.

With water cooling you need keep the liquid moving since the heat transfers poorly through medium. As long as you have a good flow it will compensate for the lower conductivity. In theory you can actually use a medium that has both poor capacity and poor conductivity if the flow rate is sufficient and the contact surface between the medium and the heat exchanger is great enough. Another great thing about water is that is dirt cheap and easily accessible, while the kit can often be upgraded when needed. Danamics is not trying to compete against the modular enthusiast kits though, but mainly the entry level all-in-one water coolers.

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
2

The table shows it with utmost clarity. Metal have a vastly superior thermal conductivity, while water has higher heat capacity. For example, it takes about four times as much energy to raise the temperature of water one degree as it does with an equal amount of aluminum. However, aluminum is about 400 times better at transferring the heat through the medium. You can also see that it takes a lot less energy to raise the temperature of copper than aluminum, but it on the other hand it conducts heat better. It all comes down to how you use them.

With high thermal conductivity you don’t have to have high heat capacity if you can remove the heat fast enough. With a large contact surface, like the fin and heatpipe design used by most high-end CPU coolers of today you can get away with low airflow since the heat is transferred quickly from the base up to the colder fins where the heat is emitted into the air. LM10 takes this one step further by actively pumping the liquid metal through the pipes actively moving the heat from the base up to the fins. This has the advantage that the performance of the cooler is more or less consistent no matter how hot the cooler gets, while heatpipes in general will perform worse the hotter they get.

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