Three-Dimensional Flow Behavior of a Falling Film on Horizontal Tubes: A Comparative Study on Smooth and Finned Tubes

In this work, the two-phase flow behavior of a falling film on horizontal smooth and finned tube systems was investigated and compared using a three-dimensional computational fluid dynamics model based on the volume of fluid method. The model was established to capture the microscopic gas-liquid interface of the falling film for smooth and finned tubes. The three-dimensional flow behavior of the falling film, including the liquid film spreading, the film thickness, the velocity distribution, and the effect of Reynolds number (Re) on the film distribution, was investigated systematically. The results show that the liquid film spreads on the smooth tube rapidly and forms a film thickness distribution of "crest-stable-crest", while the axial spreading of the liquid film is significantly restricted and hindered by the fins on the finned tubes. The falling films of the smooth tube and the finned tube present a staggered column flow and an in-line column flow, respectively. Besides, the axial liquid film spreading on the smooth tube is more sensitive to the Re compared with the finned tubes. The finned tube with a lower fin density achieves better axial spreading, and the finned tube is completely covered by the liquid film at Re = 521 with an optimized liquid column spacing.