Server-Level Test System for Direct-To-Chip Two-Phase Cooling of Data Centers Using a Low Global Warming Potential Fluid

Cooling of data centers is becoming increasingly challenging with the surging power density, and direct-to-chip two-phase cooling is a promising solution with high cooling capacity and efficiency. Due to the difficulty in accurately modeling two-phase heat transfer under complex configurations, experimental investigations of direct-to-chip two-phase cooling under practical conditions are needed. In this work, we developed a server-level thermohydraulic experimental test system to characterize the performance of this novel and promising cooling solution. The system is a fluid circulation loop consisting of a test server sled, a refrigerant reservoir, a condenser, and a liquid pump. Refrigerant R1233zd(E) is used in this work, which has a low global warming potential of 1. The test server sled has two mounted thermal test vehicles (TTVs) with a maximum power rating of 1000 W each, which are used to simulate two Intel Sapphire Rapids CPUs. Two microchannel cold plates are attached onto the two TTVs to provide cooling by vaporizing the liquid refrigerant flowing inside. Case temperatures, fluid temperatures and pressures, pressure drops across multiple components in the loop, and liquid flow rate are measured using sensors implemented in the cooling loop. Preliminary tests demonstrated sable and efficient cooling of CPU power up to 1000 W with case-to-fluid thermal resistance below 0.02 K/W. At these power levels, we also showed that the flow rates between two parallel cold plates are balanced when the heat is applied nonuniformly. Our work establishes a server-level test system capable of characterizing various working parameters and system configurations, providing valuable insights into both the fundamental understanding and the practical realization of the two-phase direct-to-chip cooling solution for data centers.