Simultaneous Measurements of Drop Size and Velocity in Large-Scale Sprinkler Flows Using Particle Tracking and Laser-Induced Fluorescence

This paper reports an experimental technique that is developed for instantaneous planar measurement of droplet size and velocity for dilute sprays in general and sprinkler sprays in particular. This particle tracking technique relies on photographic measurements of two-color fluorescence or fluorescence and Mie scattering from droplets to determine their size and velocity. Measurements were made in a plane that passes through the vertical axis of symmetry of an axis-symmetric sprinkler spray. Drop velocities and drop sizes down to 200 µm were measured from the digitized double-exposed photographs of sprinkler sprays. The directional ambiguity was resolved by color differentiation. A combination of fluorescence and Mie scattering was investigated for a 250 mm 350 mm measurement area, while two-color fluorescence was investigated for 460 mm 540 mm measurement area. Dye selection and concentrations were determined by testing the fluorescence output of various water tracer dyes. Collection optics and laser powers were varied to optimize the color differentiation and maximize the resolution for drop size measurements.