Hideo Kubo

Thermal Design and Packaging of a Prototype Refrigeration Cooling System for CMOS-Based MCMs

Thermal design and packaging strategy of a prototype dual-loop vapor compression refrigeration cooling system, developed as a pilot model for thermal management of high performance CMOS based MCMs, is introduced in this paper. The cooling system was comprised of two separated refrigeration units providing low temperature cooling via a dual-path cooling module (evaporator) mounted on a CPU-MCM package. Cooling capacity for each refrigeration unit was controlled ranging from 250W to 2500W with a refrigerant evaporating temperature at −25 degree centigrade. The CPU-MCM mounted with the refrigeration cooling module was packaged on a system board assembly, together with other electronic devices. The assembly was accommodated into a dew-point control box where two dewpoint control units were operating in a redundancy to remove moisture and keep a dew temperature inside the box below −30 degree centigrade for completely preventing from condensation. Cooling redundancy was provided by both the refrigeration units and dual-path cooling module. The cooling module was redundant in that two sets of refrigerant passages were staggered within a thin copper plate, where each set was connected to a separated refrigeration unit. Apart from the robust system and steady operation, the configuration and operation mode also provided the cooling system a high power efficiency and much shortened starting time. Numerical simulations were also performed for investigating airflow and thermal characteristics, in a system board level inside the dew-point control box. Detailed predictions of airflow and temperature distributions were significantly helpful for improving and verifying practical system designs.Copyright

Liquid immersion cooling technology with natural convection in data center

We proposed a liquid immersion cooling technology with natural convection for high power server boards used in data centers with high cooling-efficiency. The cooling performance was evaluated by CFD simulation and actual experiments. As the refrigerants, several non-conductive, thermally and chemically stable fluids were applied, including silicone oil, soybean oil, and perfluorocarbon structured liquids. The CPU temperature in the refrigerant monotonically decreases with the Rayleigh numbers of the refrigerant. The smoother refrigerant is better for cooling the high power CPU. The changes in any CPU task and any slot-removal give limited cooling effects to other slots and other CPUs. These are quite useful features for stable operation of servers in data center. As a result, this proposed technology with natural convection exhibits promising potential for low energy and space-saving board cooling which demonstrates a Power Usage Efficiency (PUE) below 1.04.