Methodology for Droplet Measurement in Gas-Liquid Flow Using High-Speed Photography

This paper presents a detailed methodology for droplet size measurement in gas-liquid flow. The approach involves a rotating lateral visualization system to capture moving droplets in two-phase flows. This setup methodology includes determining optimal camera settings and the object plane's position. A high shutter speed of 1/300000 s and a framerate of 1000 fps is selected, along with a relatively large aperture to balance image brightness. A 2X teleconverter is integrated into the system to enhance magnification, enabling reliable detection of droplets down to ~ 16.7 μm. Considering the droplet volume distributions, the object plane was positioned 3 mm from the pipe wall to balance image quality with the influence of the wall boundary layer. Calibration processes for the depth-of-field (DOF) and the calibration factor for image-processing are carefully performed. Sample sizes range from 5,000 to 80,000 droplets, ensuring statistical robustness of the reported distributions. The methodology was validated by applying it to a representative flow condition, in which the measured droplet distributions were consistent with expected transport mechanisms in gas-liquid flows. The results demonstrate an increase in the droplet population as the measurement location approaches the pipe bottom. Moreover, droplet mean volume is larger at lower heights within the pipe, as further validated by the observed volume distributions across varying heights. These trends are attributed to droplet transportation mechanisms, such as turbulent diffusion and ballistics, as well as the stronger gravity effect on larger droplets.