Electro-kinetic microchannel cooling system for servers

While servers have always required careful thermal design, three compounding trends are making system design unusually demanding with next generation: a) higher power in individual chips, b) higher local heat flux in chip hotspots, and c) the goal of integrating more chips with less separation on a 1U rack system. Pumped liquid cooling is a promising alternative because it allows the heat sink volume at the chip backside to be reduced, and also provides flexibility in locating the heat sink remotely. Further, heat can be collected from multiple chips and fed to the remote heat sink conveniently located in the system for optimum performance. However, this approach requires innovation and optimization through analysis and testing to achieve the necessary performance and reliability. We present here a new closed loop liquid cooling system for server cooling capable of handling dual processor power with local hotspots up to 500 W/cm2 and total heat loads up to 120 W per chip. The cooling system features a microchannel heat exchanger for high heat flux removal capability, an electrokinetic pump for delivering fluid with the required flow rate, and a counter flow liquid-air heat exchanger. The microchannel heat exchanger cools CPU hotspots efficiently, and the solid-state electrokinetic pump is silent and compact. A solid state pump results in high reliability through the lack of moving parts. This manuscript presents data for a closed-loop cooling system, as well as simulations extrapolating performance at various server configurations, power levels and geometries.