Detection of particles and estimation of size distribution in process fluids

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Title: Detection of particles and estimation of size distribution in process fluids
Author: Li, Bo
Abstract: Process fluids may be degraded by large concentrations of suspended particles, formations of gel slugs, or the infiltration of air bubbles. The scattering of ultrasound is dependent upon the relation of the wavelength and the scatterers' dimensions. Relatively large objects are easily detected because of their strong scattering in the short wavelength limit (SWL), but small ones may be missed because of their weak scattering in the long wave length limit (LWL). When the object dimension is comparable with the wavelength of ultrasound (intermediate region), the approximations of both the SWL and the LWL do not apply. The work described in this thesis has experimentally investigated the scattering characteristics of particles in the intermediate region in order to estimate the size distribu tion of particles in some industrial fluids. A log normal particle size distribution which has a mean close to the ultrasound wavelength is selected and three kinds of industrial fluids are used in the experimentation. These lab-made fluids have various particle concentra tions so that the possible ranges of real conditions could be covered. A circulating fluid system is employed to simulate an industrial process. The ultrasonic images of particles in fluids are produced by an acoustic imager and are processed by an image processing sys tem. Different signal gains are used in the imager to test the effects of signal compensation on images. In ultrasonic video images, echoes of independent particles are recognized, adjoining or overlapping echoes are segmented by morphological operations, and each echo area of particle is individually measured. Also, particle size distributions are found and an exponential regression approach is proposed. The frame processing rate could be considered real-time processing because it is less than a second. The results demonstrate that moving scatterers detected by ultrasound can be recognized in real time by the system and their sizes can be individually determined as well as their statistical distribution in each trial period. Finally, rules have been found to estimate the original distribution of particles from derived system parameter and observed data.
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Date: 1992-10-05

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