Girish Upadhya

Electro-kinetic microchannel cooling system for desktop computers

The requirements for thermal management in high performance desktop computers are rapidly outpacing the capabilities of the best commercially available active and passive air cooling solutions. The problem lies in three compounding trends: a) higher average chip power density, b) higher peak power densities in chip hotspots, and c) more stringent system boundary conditions. Pumped liquid cooling system is a promising alternative to address these thermal management challenges. We present here an electro-kinetic microchannel cooling system for desktop computers that can handle average power density greater than 150 W/cm/sup 2/ and hotspots with peak power densities on the order of 500 W/cm/sup 2/ and above. The cooling system features a microchannel heat exchanger for high heat flux removal capability, an electrokinetic pump for delivering fluid at the required flow rate and pressure drop, and a liquid-air heat exchanger. The microchannel heat exchanger is well suited for hotspot cooling on microprocessors, and the solid-state electro-kinetic pump is silent, compact, and promises high reliability through its lack of moving parts. This manuscript describes simulations and experiments on a system prototype, which, when fully integrated, fits well within the boundary conditions required for high performance desktop computers.

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.

Closed-loop cooling technologies for microprocessors

Recent trends for next generation microprocessors clearly point to significant increase in power consumption, heat density, and to corresponding challenges in thermal management. In desktop systems, the trend is to minimize system enclosure size while maximizing performance, which in turn leads to high power densities. The thermal management technologies used today consist of advanced heat sink designs and heat pipe designs with forced air cooling. However, these techniques are approaching fundamental limits for high heat flux, and there is a growing need for development of more efficient and scalable cooling systems. To this end, a new closed loop liquid cooling system has been developed to handle heat fluxes greater than 500 W/sq cm. The cooling system comprises a micro channel heat exchanger for high heat flux removal, an electro-kinetic pump for delivering fluid with required flow rate and pressure, and a counterflow heat rejector to dissipate heat to the ambient. The thermal performance of such a system was analyzed with ICEPAK. Experimental work was carried out to validate the modeling results and evaluate performance for a high end computer system cooling application.