Experimental and numerical investigation of thermo fluid 2026 International

This study presents a combined experimental and numerical investigation of the thermo-fluid behavior and thermal performance of a two-phase closed thermosiphon (TPCT) under subatmospheric conditions, targeting data center cooling applications. The TPCT is constructed from a copper tube with a 20 mm inner diameter and a total height of 500 mm, with water as the working fluid. The filling ratio (𝐹 𝑅) is varied from 50% to 150%, and the input power (𝑄in) from 100 W to 500 W, representing the operating range of high-performance AI and HPC CPUs. Numerical simulations are performed in STAR-CCM+ using the Volume of Fluid (VOF) method coupled with the Lee phase-change model. Experimental validation confirms the fidelity of the numerical model, with maximum absolute relative errors remaining below 2.74%. Five distinct flow patterns are identified across the investigated parameter space. Both permanent and intermittent liquid-trapping phenomena are observed and characterized with respect to their influence on flow structure and thermal performance. The spatiotemporal evolution of the local heat transfer coefficient (𝐻𝑇 𝐶 ) along the inner wall is analyzed. Thermal performance metrics are evaluated across all investigated conditions, confirming the significant role of sensible heat transfer.