In terms of environmental conservation

it is very meaningful to use CO2 as working fluid in the two-phase thermosyphon loop (TPTL) to replace R22. According to the experimental results in some research

the flow boiling or condensation heat transfer coefficient of CO2 is much higher than that of the conventional refrigerants

which means CO2 has the potential in improving the heat transfer performance of the TPTL system. Considering the high heat transfer coefficient of the refrigerant

the convective thermal resistance of the air/water outside is the main restriction of the performance. Thus

the improvement of the heat transfer performance by using CO2 may be limited. The present study compares the heat transfer performance of CO2 and R22 TPTL through experiment. Combined with some heat transfer model

each part of the thermal resistance is analyzed. The result shows that the total thermal resistance of CO2 TPTL is 22%-25% lower than that of R22 TPTL due to the reduction of the boiling and condensation thermal resistance.