This paper advances the state-of-the-art in novel passive two-phase systems for more efficient cooling of datacenters and central offices compared to the traditional air-based cooling solutions (e.g. hot-aisle/cold-aisle containment cooling systems). The passive two-phase technology uses numerous server-level thermosyphons, one for each CPU and/or hardware accelerator to dissipate the heat generated by these critical components. The main goal of this study is to experimentally investigate the thermal performance of a server-level thermosyphon for cooling compact servers. The experimental apparatus, built at Nokia Bell Labs, is used to characterize heat transfer performance of a single 7-cm high liquid-cooled thermosyphon that fits within a 2U server. The heat source is represented by a pseudo-chip, composed of six parallel cartridge heaters installed in a copper block, able of dissipating a total power of 400 W over a footprint area of 3.5 x 3.5 cm2 (heat fluxes up to 33 W/cm2). Steady-state experiments were carried out at various heat loads and secondary side inlet conditions (coolant temperatures and mass flow rates) using a range of low GWP working fluids. Test results demonstrate higher thermal performance and energy saving compared to traditional air-cooled heat sinks. In addition, thermosyphon cooling systems can significantly improve operation in terms of lowering electrical usage (passive gravity flow), allowing for higher server density (since no outsized heat spreader is required), increased processing speed (higher cooling rates) and reliability (no electrically driven fans or pumps within the thermosyphon).

Operational Maps and Thermal Performance Analysis of a Thermosyphon Cooling System for Compact Servers

Paper Proceedings: https://asmedigitalcollection.asme.org/InterPACK/InterPACK2021/volume/85505

ASME 2021 International Electronic Packaging Technical Conference and Exhibition (InterPACK2021)

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