Experimental Study on the Heat Transfer Performance of Dielectric Fluids in a Two‐Phase Closed Thermosyphon

This study experimentally evaluated the thermal performance of two‐phase closed thermosyphons (TPCTs) using dielectric fluids. Experimental results showed that HFE‐7100 and HFE‐7200 exhibit maximum allowable powers that are up to 78.2% and 80% lower than that of DI water. These results were obtained under the condition of FR of 0.25. At this condition, the confinement numbers for DI water, HFE‐7100, and HFE‐7200 were 0.247, 0.087, and 0.090. However, dielectric fluids demonstrated more stable operation by preventing the geyser boiling phenomenon. Particularly, HFE‐7100 exhibited the lowest thermal resistance below 130 W heat inputs. These findings are expected to provide a valuable foundation for developing high‐efficiency cooling technologies for high‐power electronics and energy systems.