A one-dimensional, steady-state analytical model was developed to predict the CCFL in GATPTs, which treats the shear stress at the liquid-vapor interface as the sum of two terms : (a) adiabatic shear stress; and (b) dynamic shear stress. The latter accounts for the effect of evaporation/condensation at the liquid-vapor interface. The model predictions were in good agreement (within +/-10%) with the data of other investigators for water and methanol. The results showed that neglecting the dynamic shear stress at intermediate and high liquid film flows underestimates the film Reynolds number at CCFL by more than 20%. The model was used to develop operation maps for R-113, acetone, methanol, heptane, water and Dowtherm-A working fluids, which give the film Reynolds number at the CCFL (or maximum power throughput) as a function of the vapor temperature in the range from 250 to 700 K. The effects of the thermosyphon inner diameter and length of the evaporator section on the film Reynolds number at CCFL were also investigated.