An experimental study on a novel two-phase loop thermosyphon applicable for cooling in 2U servers

This study focuses on cooling design for 2U servers by proposing a novel two-phase loop thermosyphon. The proposed thermal module is capable of dissipating up to 830 W of generated heat, exceeding the performance of previously published loop thermosyphon solutions for 2U servers. In order to optimize its performance, key parameters influencing thermal resistance are experimentally investigated, including filling ratio (FR), heat load, and frontal air velocity. The heat load varies from 120 W to 850 W, while the frontal air velocity ranges from 1.98 m⋅s⁻¹ to 4.88 m⋅s⁻¹. Additionally, different filling ratios (35–60 %) were tested, with 40 % identified as the optimal value for achieving the best thermal performance. The proposed module provides a cooling solution for high-power and high-heat-flux applications, demonstrating the capability to handle a power and heat flux up to 830 W and 92 W∙cm⁻², respectively. The minimum thermal resistance of 0.081 °C∙W⁻¹ was achieved when the separated loop thermosyphon (SLTS) was filled to 40 %. Based on the second law analysis, it was also found that this best filling ratio results in the least entropy generation. Previously, the merit number was proposed as a key criterion for selecting working fluids in the design of separated loop thermosyphons. However, this study demonstrates that the Merit number alone is insufficient. Another critical parameter, the density ratio (defined as the ratio of vapor density to liquid density), is identified as an essential factor, with higher density ratio values being preferable for improved performance.