Closed Loop Liquid Cooling for High Performance Computer Systems

The power dissipation levels in high performance personal computers continue to increase rapidly while the silicon die temperature requirements remain unchanged or have been lowered. Advanced air cooling solutions for the major heat sources such as CPU and GPU modules use heat pipes and high flow rate fans to manage the heat load at the expense of significant increases in the sound power emitted by the computer system. Closed loop liquid cooling systems offer an excellent means to efficiently meet the combined challenges of high heat loads, low thermal resistance, and low noise while easily managing die level heat fluxes in excess of 500 W/cm². This paper describes the design and attributes of an advanced liquid cooling system that can cool single or multiple heat sources within the computer system. The cooling system described use copper cold plates with meso scale channels to pick up heat from CPU and GPU type heat sources and highly efficient liquid-to-air heat exchangers with flat copper tubes and plain fins to transfer the heat to air by forced convection. A water based coolant is used for high thermal performance and additives are used to provide burst protection to the cooling system at temperatures down to −40 °C and corrosion protection to critical components. A highly reliable compact pump is used to circulate the fluid in a closed loop. The overall system is integrated using assembly methods and materials that enable very low fluid permeation for long life.