Numerical study on free cooling and mass distribution in a pump-driven two-phase cooling loop for data centers

Generally, the integrated cooling system in data centers consists of a vapor compression (VC) loop and a pump-driven two-phase cooling (PDTPC) loop. The PDTPC loop, utilizing free cooling without compressor operation, is a promising energy-saving technology for data center cooling. However, research on the factors influencing the upper limit of free cooling temperature and refrigerant mass distribution in the PDTPC loop remains limited. This study developed a steady-state numerical model to investigate the effects of pipe pressure drop and vapor quality on these parameters. Results show that reducing the pressure drop between the evaporators and condenser significantly increases the upper limit of free cooling temperature. Additionally, reducing the pressure drop between the condenser and reservoir substantially decreases the refrigerant mass in the condenser. Operating at high vapor quality is beneficial to increase the upper limit of free cooling temperature and reduce refrigerant mass in the pipes, evaporators, and condenser. A reservoir is essential to manage changes in refrigerant mass distribution. This work provides theoretical guidance for extending the annual utilization of free cooling and reducing refrigerant charge in the practical application of the PDTPC loop in data centers, thereby improving energy efficiency and reducing overall costs.