Numerical investigation of liquid film flow characteristics in column mode under counter-current airflow conditions

Results are reported of a three-dimensional numerical simulation of gas-liquid counter-current flow outside two horizontal tubes with airflow velocities ranging from 0 to 3 m/s. The findings reveal that the fluctuations in the liquid film thickness increase with the circumferential angle. In the impingement and wake regions, the film thickness exhibits a distinctive "W" pattern along the axial direction, while in the development and developed regions, it displays a "stable-peak-stable" profile. At a film Reynolds number of 187, an airflow velocity of 3 m/s triggers a transition in the falling film from a stable column mode to a droplet-column mode. Additionally, a significant increase in film thickness is observed outside the first tube within circumferential angles of 75 degrees to 135 degrees with increasing airflow velocity. Outside the second tube, film thickness increases with airflow velocity once the circumferential angle exceeds 90 degrees. The average film thickness grows with the Reynolds number, but decreases with increasing tube spacing, with the reduction in film thickness becoming progressively smaller.