Numerical simulation of falling film flow of aqueous lithium bromide solution over hydrophilic horizontal round tube

In order to study the effect of wettability on falling film configuration over horizontal round tube, a two-dimensional two-phase flow model was developed based on the finite element method (FEM) to simulate the falling film configuration of aqueous lithium bromide over hydrophilic horizontal round tube with different wettabilities (static contact angle from 0° to 60°). The transient behaviors of film flow process and the distributions of steady film thickness and velocity along horizontal tube were analyzed in detail. The results show that when the static contact angle increases or the wall wettability decreases, the time spent on film spreading prolongs and the accumulation quantity of the liquid at the forefront of the film increases. The film thickness first decreases and then increases along the circumferential tube surface in the steady-state, while the velocity of the film first increases and then decreases along the circumferential tube surface, the film with the minimum thickness or the maximum velocity appears around circumferential angle of 120°. According to the comparison results between the simulation and the experimental data of the film thickness on a horizontal round tube, a modified correlation based on Nusselt theoretical formula is suggested. © 2016, Editorial Department of Journal of Southeast University. All right reserved.