Novel interferometric measurement of size and velocity distributions of spherical particles in fluid flows

The present investigation describes a novel measurement technique used to d etermine both velocity and diameter of transparent spherical particles, mai nly droplets and gas bubbles. We have developed a special receiving optical system that acquires the interferential image without any losses due to th e overlapping of neighbouring fringes. The system enhances the spatial reso lution by compressing the circular image with fringes into a linear image w hile maintaining the information of the fringe spacing, which is related to the particle diameter. The compression simplifies and ensures the detectio n of the interferograms in the digitized image. The image provides both the location and the size of particles simultaneously. The velocities of indiv idual particles are obtained by capturing sequential images of interferogra ms with double-pulsed illumination. The technique was examined with the mea surement of monodisperse droplets and estimated with a resultant error of l ess than 3% for arithmetic mean diameter.