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

The present investigation describes a novel measurement technique used to determine both velocity and diameter of transparent spherical particles, mainly droplets and gas bubbles. We have developed a special receiving optical system that acquires the interferential image without any losses due to the overlapping of neighbouring fringes. The system enhances the spatial resolution by compressing the circular image with fringes into a linear image while maintaining the information of the fringe spacing, which is related to the particle diameter. The compression simplifies and ensures the detection of the interferograms in the digitized image. The image provides both the location and the size of particles simultaneously. The velocities of individual particles are obtained by capturing sequential images of interferograms with double-pulsed illumination. The technique was examined with the measurement of monodisperse droplets and estimated with a resultant error of less than 3% for arithmetic mean diameter.