Experimental Characterization of a Compact Thermosyphon Cooling System Operating with R1234ze(E) and R1233zd(E) Low-GWP Refrigerants

Abstract

The proposed work is built upon the research findings published at ITHERM 2020 and 2021 in which a novel thermal management solution has been introduced for next generation computing and telecom hardware platforms. The increasing demand towards achieving greater functionality and massive device connectivity is calling for new hardware and server architectures, including new materials and packaging techniques, which will require more efficient thermal management solutions to realize economic scaling compared to existing air-based, liquid cold plate and immersion cooling systems. The envisioned compact thermosyphon-based cooling system that passively dissipate the heat generated by the hardware components (e.g. central processing units, memory units, accelerators, etc.) via latent heat operates with numerous server-level, and has the flexibility to be interfaced with new or existing cooling infrastructures for broad market adoption. The present study mainly focuses on the thermal performance characterization of a compact thermosyphon cooling system, introduced in previous ITHERM publications, where the existing database has been expanded with new operating conditions, using R1234ze(E) and R1233zd(E) as the low-GWP working fluids. Experiments have been carried out in steady-state mode, analyzing the effect of base heat flux, filling ratio, secondary side water mass flow rate and inlet temperature on the system performance. Dedicated experiments with contact pressure variations have also been performed to characterize the contribution of thermal interface material on the total thermal resistance of the cooling system. Our results demonstrate that better thermal performance can be achieved using R1234ze(E) in place of R1233zd(E) with a reduction up to 40% in total thermal resistance, however the improvement in cooling capability needs to be accommodated by higher operating pressures.