Ultrasonic techniques for dispersed phase characterization

Ultrasonic techniques have been used for monitoring variations in particle size and measurement of particle size distribution in suspensions. The inherent ability of ultrasonic wave to propagate in dense and opaque suspensions makes it a desirable method for characterization of dispersed phase operations in the industry. Changes in measured parameters of the ultrasonic pulse due to the presence of particles (spherical glass beads) were studied in Liquid-Solid and Gas-Liquid-Solid systems. Acoustic velocity measurements were used in Gas-Liquid-Solid systems to detect variations in particle size. Particles settling and sedimentation in Liquid-Solid systems were investigated using simultaneous measurement of acoustic velocity and attenuation. The attenuation spectrum was measured in suspensions of varying concentrations of large particles to study the effect of polydispersity for developing a particle size distribution determination technique applicable in these systems.;The ability of ultrasonic attenuation spectroscopy to determine particle size distribution has been extended to dense suspensions of particles with size comparable to the wavelength of the ultrasonic pulse. This was achieved by accounting for the effect of detector size and shift in the frequency spectrum under dense conditions in the theoretical model and deconvolution algorithm, respectively. The proposed modifications enable the application of this technique in various industrial processes requiring in-situ and real-time measurement of particle size distribution such as crystallization and mineral processing.;Keywords. Ultrasonic Techniques, Acoustic Velocity, Attenuation Spectrum, Two and Three Phase Suspensions, Size Monitoring, Particle Size Distribution Determination;Interaction of the ultrasonic pulse with gas phase caused significant fluctuations in the measured acoustic velocity in Gas-Liquid-Solid systems. The nature of these fluctuations was investigated and a technique was developed to obtain acoustic velocity measurements free from the gas phase effect. This technique can be used for scale-up studies in these reactors and has potential application in process monitoring. Ultrasonic measurements during settling in dense Liquid-Solid slurries captured the effect of particle segregation, dense layer formation and transition from suspension to settled bed. The measurements also detected bed compaction and effect of polydispersity and settling height on settled bed porosity. These measurements are useful for monitoring various processes requiring minimization (e.g. hydraulic conveying, fluidized beds), maximization (e.g. thickeners) or controlled settling of particles (e.g. hydrosizing, separation).