Simultaneous measurement of diameter and velocity of liquid droplets in annular-mist flow using shadowgraph technique

This study aimed at measurement of diameter and velocity of liquid droplets in a vertical upward annular two-phase flow by an image-processing based on shadowgraph. A viewing section for taking liquid droplet image in a test pipe was located over a liquid film extraction section made of porous material. After removing the liquid film through the extraction section, only droplets flowed up the viewing section. Shadowgraph images of droplets in the viewing section were taken by a video camera synchronized with double pulsed-Nd:YAG-laser and the diameters and velocities of the liquid droplets were measured by an image-processing of the captured images. An experiment to confirm the effectiveness of the present measuring technique was conducted for annular two-phase flow flowing up a vertical pipe with 10 mm-ID at predetermined superficial liquid and gas velocities of 20.4 and 0.488 ms^-1, respectively. It was confirmed that the measured diameters and velocities of liquid droplets respectively tended to increase and decrease towards the wall. Formation of the slip between droplets and gas flow was also observed. (author)