Pushing the Limits of Air Cooling with Novel Two-Phase Prototypes for High Power Microprocessors

Due to the higher power dissipation of moderns integrated circuits, such as central processing units (CPU) and graphics processing units (GPU), traditional thermal management solutions face significant challenges. We have conducted a thermal performance study of two novel two-phase thermosyphon prototypes with an air-cooled condenser to increase the thermal dissipation power of air-cooling for microprocessor cooling applications. Experimental tests were performed to quantify the heat dissipation capacity of a two-phase thermosyphon design, by comparing the two prototypes against state-of-the-art commercial air-cooled heatsinks in the 2U and 4U form factors. The prototypes were mounted on a heater assembly for the thermal performance tests. Different attachment interfaces were tested, corresponding to the popular LGA-4189 and LGA-2011 CPU sockets. In the 4U prototype, the thermal resistance (TR) between the heater and ambient air of the thermosyphon was the same as for the commercial 4U heatsink up to 300 W, but the commercial heatsink reached the dry out of its heat pipes for higher power levels, while the 4U prototype maintained a low TR value of $(\mathbf{0}.\mathbf{11}\pm \mathbf{0}.\mathbf{004}){{}^{\circ}\mathbf{C}}/\mathbf{W}$ up to $(\mathbf{500}\pm \mathbf{7})$ W. The TR of the 2U prototype was lower than the TR of the commercial 2U heatsink at all tested power levels, and the thermosyphon prototype achieved a heat flux of $(\mathbf{78}\pm \mathbf{1}.\mathbf{1})\mathbf{W}/\mathbf{cm}^{\mathbf{2}}$ on the heater, thus providing an air-cooled solution up to 500 W per socket. With these performance gains, the thermosyphon prototypes could have important applications, such as allowing the inlet air temperature of a data center server rack to be increased by 10°C at a power of 300 W per socket while maintaining the same junction temperature as a system using a commercial heatsink with the colder inlet air.