Spatially resolved droplet size measurements

This paper encompasses initial tests of a droplet sizing technique, providing spatially and temporally resolved measurements within a liquid spray from an air assist nozzle. The method utilizes laser interferometry. The primary size measurement is based on the visibility function; it is validated by the peak intensity of the scattered light. As the system is based on the Doppler effect, a single component of the drop velocity is extracted concurrent with the size information. The measurement volume size is controlled by off-axis light collection. Beam splitting is accomplished by a rotating diffraction grating, allowing the signal to be frequency shifted. Measurements are compared directly to those of a standard diffraction based sizing system (i.e., Malvern). Shadow photography is also used to visually validate the laser based measurements. Correspondence between the diffraction and interferometric results is very good. The differences that do exist are believed to be related to the limited dynamic sizing range of the interferometric system.