Measurement of bubble and droplet diameters by the Doppler anemometry

Interaction of a probing laser beam with a liquid droplet is analyzed theoretically. It is shown that the amplitude of the Doppler signal obtained from a moving droplet depends on its position with respect to the beam waist. The possibility of determining the radii of droplets and bubbles moving in the flow from the spatial positions of the extreme points of the Doppler signal amplitude is justified theoretically and experimentally. The radius of glass spheres is measured (1.75 and 5 mm). The relative error of measurements is 1.1 and 8%. The radius of bubbles upfloating in a viscous liquid is measured. It is shown that the proposed method based on the Doppler anemometry offers prospects in studying two-phase flows.