Drop size distribution in sprays by image processing

Abstract

An automatic analysis system has been developed and used to analyze photographs obtained by high-speed microphotography, the final aim being to derive spatial resolved size distributions of drops in sprays. The problem of determining whether photographic images of particles are in focus or not is solved by obtaining a calibration of geometric parameters of particle images as functions both of the particle position in the camera's field of view and of the particle diameter. On the basis of the results of this calibration on the particular photographic system being used, the drops are automatically rejected or sized and counted. This is done through a procedure based on the geometrical characterization of drop images at different ranges of gray levels. The main body of such a procedure is constituted by an algorithm of original design (connected components detection algorithm) which allows for the simultaneous detection of the boundaries of drop images at different gray levels and generates a hierarchical structure among them. Size distributions obtained by means of the procedure described in the paper offer significant reduction in experimental time as well as improvement in experimental accuracy, in relation to manual sizing and counting techniques.