Thermal Performance of Common Cold Plate for Pumped Single- and Two-Phase Direct Liquid Cooling for Next Generation High Power Server Processors

Abstract The rapid expansion of Generative AI and ML applications has led to a surge in demand for advanced accelerators. These next-generation accelerators require high power, with some reaching nearly 1kW and continuing to rise. Consequently, server power envelopes have expanded to 10kW and beyond, while rack-level power for AI applications is approaching 100kW. The high TDP (Thermal Design Power) and heat flux of these processors, combined with power-dense servers and racks, necessitate cooling technologies with superior thermal performance. As IT power consumption escalates, most data centers are transitioning to liquid cooling solutions that align with corporate sustainability objectives. This paper assesses the thermal performance of single and two-phase pumped direct liquid cooling technologies. It explores a unified cold plate construction approach, a COMMON cold plate, enabling both technologies to address cooling challenges faced by data center operators and to expedite the Time to Market (TTM) for server manufacturers’ cooling solutions. The paper outlines the design methodology, laboratory testing procedures, and thermal performance of a common cold plate design suitable for both single and two-phase pumped direct liquid cooling technologies. For single-phase liquid cooling, Propylene Glycol-25 (PG25) is the chosen fluid medium, while a medium-pressure refrigerant with a lower Global Warming Potential (GWP) is considered for two-phase cooling. Three types of Thermal Test Vehicles (TTVs) were utilized under uniform and non-uniform heat load conditions, with power levels up to and beyond 1kW and high heat fluxes up to 300W/cm∧2. Additionally this paper emphasizes the significance of characterizing non-uniform heat flux in thermal solutions by varying the heat flux at high heat flux locations. Understanding how to cool these high heat flux hotspots are crucial for the development of thermal solutions, as the heat fluxes of new generation accelerators are significantly higher than those of traditional processors. In conclusion, the paper highlights the need for further ecosystem development for various cooling loop components to enhance the adoption of two-phase liquid cooling solutions.