Droplet Dynamics of Thin Water Films Flowing on Flexible Fibers in a Stagnant Gas Environment.

Fiber-supported liquid-film structures are promising for improving direct-contact condensation in low-temperature humid flue-gas waste-heat recovery, but the flow behavior of low-viscosity water films on fiber surfaces remains insufficiently understood. A single-fiber visualization platform integrating high-speed imaging technology was constructed to capture the formation and migration processes of deionized water droplets. Image-based measurements were used to determine how liquid flow rate (23-31 mL/min), nozzle diameter (1.55-1.95 mm), fiber diameter (0.2-0.4 mm), and fiber material regulate droplet size, volume, cross-sectional area, generation frequency, and the spacing between droplets. Within the tested flow rate range, a larger liquid flow rate promoted earlier rupture of the water film, resulting in smaller droplets and a higher generation frequency. Conversely, increasing the nozzle diameter from 1.55 to 1.95 mm increased the amount of buildup before droplet detachment, leading to a maximum increase in droplet volume of 90.7% and a maximum increase in droplet cross-sectional area of 48.1%. Comparisons among fiber materials showed that materials with smaller apparent contact angles and relatively smooth surfaces tended to produce smaller droplets and more compact droplet distributions. The results provide experimental evidence for optimizing water-film distribution in fiber-based direct-contact condensers.