Two-phase thermosyphon heat exchangers are widely used in different industry fields. The fluid flow characteristic is very important for the design of thermosyphon. However

the existing two-phase models are not accurate enough for the simulation of two-phase thermosyphon loop .Therefore it is important to make an assessment of existing two-phase momentum models corresponding to thermosyphon loop features. The mathematical model of two-phase thermosyphon loop

which include 4 homogenous pressure drop models

24 separated-phase momentum combination models (4 separated-phase frictional pressure drop models multiply 6 representative void fraction correlations)

has been developed in the paper. The predicted results from different models are compared with the experimental results of two-phase thermosyphon with refrigerants H2O

R113 and R600a. The comparison results show that the combination of Lorkhart-Martinelli frictional pressure drop model and Tom void fraction model is better than other models. Finally

the flow features of two-phase thermosyphon loop have been simulated. It is shown that for a specific loop

the mass flux increases and then decreases slowly with the increase of heat flux. A reasonable explanation is given to the phenomenon.