Experimental study on a pump-driven CO2 two-phase thermosyphon loop

In order to better understanding the internal operating principles of liquid pump-driven two-phase thermosyphon loop (LPTPTL) and promote the application of environmentally friendly working fluids, a LPTPTL using CO₂ as the working fluid was studied through experiment. Both the operating mechanisms and performance of the CO₂ LPTPTL was investigated. It was found that the impact of the pump on the two-phase thermosyphon loop (TPTL) varies significantly across different operation stages. During the oscillatory operation stage, activating the liquid pump eliminated the geyser boiling in the loop and made the TPTL to transition from oscillatory to stable operation. During the normal operation stage, the pump power had little effect on the total thermal resistance of the TPTL. While the system’s EER (Energy Efficiency Ratio) significantly decreased with the increasing pump power. During the overload operation stage, activating the liquid pump helped alleviate overheating or subcooling in the loop. With the pump power increasing from 3.0 W to 18.8 W, the heat transfer limit of the TPTL increased from 1800 W to 3300 W, while the system’s EER decreased from 600 to 176. This study proves the feasibility of CO₂ LPTPTL, and provides theoretical guidance for its real application.