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Experiments and Modeling of a Cabinet Level Two-Phase Thermosyphon Based Thermal Management System for Rack Mounted Servers
Keywords: Microchannel, Thermsyphon, Server Rack
Although air cooling is the dominant mode for cooling electronic cabinets in Data Centers, there is heightened interest in evaluating hybrid air-liquid and liquid only cooling strategies because of the scale up in thermal capacity and efficiency gained by adopting liquid as the primary coolant in the cabinet. The volumetric density of servers and cabinets and the attendant device level heat fluxes can both be greatly increased by adopting liquid as the primary coolant. Furthermore, liquid cooling systems have higher thermodynamic efficiencies because of the elimination of the mixing losses that are prevalent in air cooling systems. Single phase pumped water systems have been extensively studied at the cold plate, server, rack, and room levels and have been shown to be highly efficient and useable up to component heat fluxes of order 100 W/cm2. Two phase coolant based systems offer even greater capacity for heat removal due to the latent heat of evaporation of the primary coolant. The present study is devoted to a preliminary assessment of a novel pumpless liquid based system for use in cooling rack mounted servers. By allowing for highly controlled convective boiling to occur in the server cold plates, the efflux from the servers has high vapor content. After cooling in an air cooled condenser outside of the rack, the coolant is returned to the cold plates as a saturated liquid. Because of the density imbalance between the rising vapor efflux stream and the descending liquid return stream, the loop operates as a pumpless, buoyancy driven thermosyphon. In this presentation we show results of a system level model that was used to evaluate the key design issues in designing and operating such a system. Experimental measurements were made in servers mounted in a conventional rack and compared to the model. Results of the study indicate that the system will easily handle conventional thermal loads in a cabinet and can be made to operate in a stable, reliable mode with careful attention to mitigating two-phase instabilities both at the cold plate and at the manifold level.
Benjamin Zuk, Graduate Research Assistant
Villanova University
Villanova, PA

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