Volumetric characterization of dispersed two-phase flows by digital image analysis

A digital-based image analysis system has been developed for the experiment al determination of size, spatial distribution and two components of veloci ty for particles suspended in any clear fluid flow. A volumetric measuremen t directly provides number density and consequently particle flow. A peculi arity of the developed system is its suitability for relatively large parti cles (some mm in diameter), which can hardly be measured with other systems . Double exposed particle images, in the same frame, provide the starting p oint for image processing. The system includes a procedure for the classifi cation of the particles in the image, the separation of the partially overl apped particles and the selection of those that are found in the control vo lume. These parameters serve as a basis for the velocity determination thro ugh a particle-tracking algorithm (PTV), which is based on iteratively esti mating the match probability as a measure of the Likelihood of pairing. The depth of the control volume is obtained with a new technique, based on the loss of focus of the particles in the image, combined by diffuse illuminat ion, provided by twin short pulse argon spark discharge lamps. The system h as been extensively checked using calibrated micro-balls and sprays that si mulate rain.