Spatially Resolved Droplet Size Measurements

Abstract

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 upon the signal visibility; it is validated by the peak intensity of the scattered light. As the system is based on the Doppler effect, a single component of velocity is extracted concurrent with the size information. The size of the measurement volume is controlled with off-axis light collection. Beam splitting is accomplished with 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). The diffraction information is processed via Rosin-Rammler (2 parameter) and Model Independent (15 parameter) distribution algorithms. Correspondence between diffraction and interferometric results is satisfactory for the Model Independent algorithm. Differences observed using the Rosin-Rammler distribution are attributed to an inadequate representation of the spray by the two parameter model.