Based on the double-film and boundary-layer theories

a mathematical model of the gas- and liquid-film thicknesses and the heat transfer coefficient of a drop tube were established

which considers the vapor-liquid interfacial thermal resistance. The distributions of the gas- and liquid-film thicknesses and heat transfer coefficient along the tube wall under different initial parameters and curvatures were obtained by simulation. The results indicate that the heat transfer coefficient is decreased (by approximately 30%) and the liquid-film thickness is increased (by approximately 7%) with the increase in the mixing gas pressure (when the pressure is from 81 325 to 121 325 Pa). With the increase in the non-condensable gas mass content (when the non-condensable gas-mass content is from 0.1% to 10%)

the film thickness is decreased (by approximately 52%)

the mass content of the non-condensable gas in the gas film is increased (by approximately 58%)

and the heat transfer resistance of the gas film is increased (by approximately 61%). For an equivalent drop-tube diameter with the other conditions remaining unchanged

the larger the curvature is

the easier the separation of the liquid film is

and the larger the heat transfer coefficient is.