Ultrasonic wave propagation in concentrated slurries – The modelling problem

Abstract

The suspended particle size distribution in slurries can, in principle, be estimated from measured ultrasonic wave attenuation across a frequency band in the 10s of MHz range. The procedure requires a computational model of wave propagation which incorporates scattering phenomena. These models fail at high particle concentrations due to hydrodynamic effects which they do not incorporate. This work seeks an effective viscosity and density for the medium surrounding the particles, which would enable the scattering model predictions to match experimental data for high solids loading. It is found that the required viscosity model has unphysical characteristics leading to the conclusion that a simple effective medium modification to the ECAH/LB is not possible. The paper confirms the successful results which can be obtained using core-shell scattering models, for smaller particles than had previously been studied, and outlines modifications to these which would permit rapid computation of sufficient stability to support fast particle sizing procedures.

Experimental verification of nanofluid shear-wave reconversion in ultrasonic fields

“…However, when particles are close together, at high concentrations, or high number density, the thermal and shear modes scattered by one particle may have significant amplitude when they reach the surface of a neighbouring particle. [15][16][17] They can then be re-scattered by that particle, and contribute to the scattered compressional wave. This kind of mode-conversion is also generated partially as a result of the difference in acoustic impedance between the scatterer and the surrounding medium.…”

Inline Measurement of Particle Concentrations in Multicomponent Suspensions using Ultrasonic Sensor and Least Squares Support Vector Machines

“…The variations of component concentrations have effects on the physical properties of multicomponent mixtures, including density, viscosity and bulk modulus [ 9 ]. So the ultrasonic waves (amplitude and shape) transmitted through the multicomponent mixtures will also change along with the component concentrations, and, in turn, it is possible to measure the component concentrations through analyzing the ultrasonic signals.…”

Thermo-elastic multiple scattering in random dispersions of spherical scatterers

“…However, existing scattering models have been demonstrated to be limited in the range of concentration and particle size to which they can be applied; high concentrations or small particles cause inaccuracies in the models. [9][10][11][12][13][14] For an aqueous suspension the maximum concentration for traditional models is around 15%v/v for 1 micron diameter particles at 5 MHz.…”

“…Experimental data in both suspensions and emulsions have demonstrated that the standard multiple scattering model does not correctly predict the attenuation spectrum for small particles, low frequencies, and at high concentrations. [9][10][11][12][13][14] The neglect of the multi-mode scattering contribution is believed to be the reason, and thus causes a significant constraint on the use of ultrasonics as a process analytical technology.…”