System-Level Thermal Analysis of Two-Phase Direct-to-Chip Cooling for Data Centers with Chilled Facility Water

Abstract The increasing power densities of processors and server racks necessitate advanced thermal management solutions for data centers. Pumped two-phase (2P) direct-to-chip (DTC) cooling leverages boiling of a dielectric refrigerant and offers high efficiency, reliability, and scalability. However, a comprehensive framework to analyze thermal contributions in 2P DTC systems is lacking due to fundamental differences between the heat transfer characteristics of 2P and single-phase (1P) DTC cooling. In this work, a systematic thermal analysis is conducted for 2P DTC systems coupled with chilled facility water (FW). The end-to-end temperature difference between processor case and FW inlet is adopted as the system performance metric. Refrigerant temperatures at the cold plate outlet and condenser inlet are introduced as intermediate nodes to break down the end-to-end temperature difference into three contributions from cold plate, vapor line pressure drop, and condenser. Using this framework, system-level comparisons between representative 1P and 2P DTC systems are performed. A correlation-based microchannel model is used to analyze cold plate performance with PG25 in 1P mode and R515B in 2P mode. The two systems exhibit comparable performance at a processor heat flux of 100 W/cm2. Under the representative conditions considered, the 2P system enables a 5 °C higher FW inlet temperature at 200 W/cm2, suggesting potential for reduced facility-side cooling energy consumption. This work establishes a quantitative framework for analyzing 2P DTC systems and supports their large-scale adoption in data centers.