Complete particle field characterization with optical diagnostics

A discussion of the practical aspects of particle sizing using light scatter detection is presented. The primary focus is on single particle counter methods for performing in situ size and velocity measurements. One objective of the presentation is to provide information on the applicability and limitations of these methods when measurements in practical environments are required. The problem of dealing with irregularly shaped particles is considered. Light scattered by such particles is not easily analyzed except in the near-forward direction. Examples of the scattered intensity as compared to that of spheres are presented. A method for performing an optical deconvolution to resolve the trajectory problem when using Gaussian beams is described. The method uses confocal beams along with a simple algebraic solution to determine the particle path through the beam. The phase Doppler method for obtaining the size and velocity of spherical particles is discussed and several examples of data obtained with this method are presented. This method allows the complete characterization of the particle field by providing measurements of the size and velocity, number density, volume flux, and temporal statistics. The time-of-arrival information of the particles can be used to analyze such phenomena as the formation of particle clusters in turbulent flows.