The present study is focused on the experimental characterization of two-phase heat transfer performance and pressure drops within an ultra-compact heat exchanger (UCHE) suitable for electronics cooling applications. In this specific work, the UCHE prototype is anticipated to be a critical component for realizing a new passive two-phase cooling technology for high-power server racks as it is more compact and lighter weight than a typical brazed plate heat exchanger (PHE). This technology makes use of two separate thermosyphon loops, one at the server-level and the other at the rack-level, to passively cool an entire rack. The UCHE is envisioned to play a critical role in transferring heat from the server-level and rack-level thermosyphon loops. In particular, a smaller form factor UCHE is used to transfer heat from the server-level thermosyphon cooling loop to the rack-level thermosyphon cooling loop, while a larger form factor UCHE is used to reject the total heat from the server rack into the room-level cooling loop. The UCHE is composed of a double-side-copper finned plate enclosed in a stainless steel enclosure. The geometry of the fins and channels on both sides are optimized to enhance the heat transfer performance and flow stability and to minimize the pressure drops. These features make the UCHE the ideal component for thermosyphon cooling system, where low pressure drops are required to achieve a high passive flow circulation rate and thus achieve high critical heat fluxes. The UCHE’s thermal-hydraulic performance is first evaluated in a pumped-loop system (EPFL-LTCM), where experiments include many configurations, such as refrigerant-to-water both in single-phase flow, two-phase refrigerant (condensation)-to-single-phase water and adiabatic two-phase flow. Then, the UCHE is installed and tested as the condenser of a thermosyphon loop that rejects heat to a pumped refrigerant system (Nokia Bell Labs), in which both sides operate with refrigerants in phase change (condensation-to-boiling). Experimental results demonstrate high thermal performance with an overall heat transfer coefficient of about 34 kW/m^2^/K based on the footprint area on 10 x 10 cm^2^, which is much larger than that of conventional small pressing depth PHE and even higher than those provided by the best enhanced tubes with internal ribs. A scaling analysis is also presented to characterize the form factors of the server-level and rack-level UCHEs based on the targeted heat dissipations.


Ultra-Compact Microscale Heat Exchanger for Advanced Thermal Management in Datacenters

Division / Sponsors: 
Electronic & Photonic Packaging Division (EPPD)

Paper Proceedings: https://asmedigitalcollection.asme.org/InterPACK/InterPACK2020/volume/84041

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