Taking a two-phase closed thermosyphon with one side vertical surface heated in the evaporator which is used for cooling power semiconductors as an object,we developed a comprehensive model with including the interfacial shear stress, pool boiling and other complex flow and heat transfer phenomena for the thermosyphon. Also,the steady-state performance is described. The prediction for the steady-state operation is given for the specified boundary conditions. Some limits of heat transfer and main factors whi...