Numerical study of the cross vapor stream effect on falling film hydrodynamics over a horizontal tube

Abstract

Falling film technology has been widely applied in various industrial processes, but vapor shearing effects cause significant problems. The mechanism by which vapor affects the hydrodynamics of a falling film has not yet been fully understood, particularly for cross vapor streams. In this paper, a three-dimensional model is developed to investigate the hydrodynamics of a falling film on a horizontal tube with a cross vapor stream. The results indicate that (1) there are valley and peak zones during the spreading of the liquid film; (2) the effect of cross vapor flow on the hydrodynamics of the falling film depends on the film flow rate, the cross vapor velocity, and the position on the tube; (3) with increasing vapor velocity, the peripheral film thickness increases on both the upwind and downwind sides for values of z* (the dimensionless axial coordinate) from 0 to 0.1, while decreasing on the upwind side but increasing on the downwind side for values of z* from 0.2 to 0.5; and (4) under the action of the cross vapor stream, liquid film offset occurs, characterized by the formation of new stagnation and detachment zones on the downwind side of the tube.