Scientists from Korean Institute of Science and Technology (KIST) developed a groundbreaking cooling system for powerful electronic chips and datacenters. They created a thermomagnetic mixer, running on the heat from processors and thus enhancing the cooling process without a single watt of additional energy.
The concept is to try to make the waste heat to perform useful function. Even modern cooling systems, where the electronic devices are completely submerged into a dielectric fluid, remain energy-intense: pumps, fans or condensers are needed to efficiently remove heat from them. But Korean researchers proposed a completely passive mechanism turning the heat of the chip directly into mechanic motion speeding up the heat exchange close to the hottest surface.
Gadolinium, the metal with unusual magnetic properties, became the key element of the arrangement. Under relatively low temperatures it is a ferromagnetic material, i.e., it becomes magnetized and is drawn to a magnet. However, when heated above a certain threshold, the so-called Curie change point, gadolinium is converted into a paramagnetic state – it stops maintaining its own magnetization and practically is not drawn to a magnet. For gadolinium, this conversion takes place under about 40 °C, which coincides with the operation modes of modern processors.
In the pilot system, the gadolinium plate was fixed on elastic brass panels by the heated chip, and a permanent magnet was placed above it. Cold gadolinium is drawn to the magnet and is close to the surface of the chip. In the process of heating, it loses its magnetic properties, the attraction gets weaker, and the elasticity of the panels pushes the plate down. This motion draws colder liquid to the chip and destroys the thermal boundary layer. In the process of cooling, gadolinium is magnetized again, the magnet attracts it up again – and the cycle is repeated. Eventually, the chip itself “shakes” the mechanical element, which constantly renews the cooling liquid at its surface.
The team performed extensive calculations and a series of experiments tailoring the geometry of the equipment – the length of the panels and the distance to the magnet. The configuration with the panels about 50 mm long and 3 mm gap turned out the optimal. In this mode, the system demonstrated steady oscillations and maxim efficiency of mixing the liquid.
During the lab tests, the thermomagnetic mixer increased the convective heat transfer rate up by 81% vs the natural convection in the standard immersion tank.
The practical check was performed on a real graphic processor – NVIDIA GTX 1050 Ti video card with 75 W thermal envelope. In the acceleration mode given circa 1,700 MHz frequency, the temperature of the processor decreased approximately by 10 °C. This resulted in minimizing the leakage currents and reducing additional energy consumption approximately by 0.3 W, which means 20-30 % decrease maintaining the previous calculating capacity.
It is crucial that the equipment does not need external power supply. All the mechanical work is thermally induced, while as in standard systems the heat is just dissipated.
Now the researchers plan the scaling of the technology for more powerful chips. As is known, modern server accelerators operate at the level of hundreds of watts and even circa 1 KW per crystal.
