Falling film fluctuation and thickness distribution on mini-grooved surfaces with cross-airflow

The falling film process is characterized by a simple structure, low energy consumption, and high heat and mass transfer efficiency, making it widely adopted in industrial applications. Groove structures represent a common means of enhancing heat and mass transfer. This study established an experimental system for vertical falling film flow with cross airflow. Using a high-speed camera and a white-light confocal displacement sensor, observations and measurements are conducted on the flow patterns and film thickness distribution of liquid films on surfaces featuring horizontal and vertical grooves with depths ranging from 0.5 to 1.1 mm. The effects of liquid film Reynolds number (221–803) and airflow velocity (0–4 m/s) on liquid film flow are analyzed. The results demonstrate that larger horizontal grooves accelerate the generation, collision, and coalescence of surface waves on the liquid film. Conversely, larger vertical grooves enhance flow stability by reducing surface wave formation. Both groove structures increased the mean liquid film thickness, with the effect being more pronounced for horizontal grooves than for vertical ones. The maximum increase in mean liquid film thickness reached 5.05 times for the H3 surface. For both horizontal and vertical grooves, the strengthening effect intensified as the groove dimensions increased. Empirical correlations predicting liquid film thickness for horizontal and vertical grooved surfaces under quiescent airflow conditions are obtained. These findings offer valuable guidance for the application of mini-groove structures in various falling film devices.