Acoustic Probe for Solid-Gas-Liquid Suspension Page: 3 of 375
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3. Executive Summary
The main objective of the project during the first period of funding is to develop an
acoustic probe for monitoring particle size and volume fraction in slurries in the absence and
presence of gas bubbles. The goals are to commission and verify the probe components and
system operation, develop theory for the forward and inverse problems for acoustic wave
propagation through a three phase medium, and experimentally verify the theoretical analysis.
The acoustic probe will permit measurement of solid content in gas-liquid-solid waste slurries in
tanks and pipelines across the Department of Energy complex. Particularly, in the second
funding period, a prototype probe will be fabricated, commissioned and tested to demonstrate the
capability to accurately measure slurries of one to five weight percent solids.
Our research work has established a solid theoretical foundation for predicting
attenuation and phase speed of acoustic waves propagating through solid-liquid suspensions,
both in the presence as well as absence of gas bubbles. The theory is based on ensemble
averaging of the equations of motion in the solid and liquid phases to obtain expressions for the
"effective properties" of the slurry mixture in terms of coefficients which appear in the equations
of motion for the solid particle. The attenuation theory accounts for losses due to viscous
dissipation, nonadiabatic thermal effects, and incoherent scattering, and as a result can cover a
wide range of frequencies and particle sizes. The theory also applies to polydispersed
suspensions of spherical particles. The theory agrees with results obtained by previous
investigations who examined limiting cases of thermal attenuation at small volume fraction
(Allegra and Hawley, 1972) and viscous attenuation at large frequencies (Sangani, Zhang and
Prosperetti, 1991). The comprehensive theory developed allows us to interrogate a relatively
large range of particle sizes and physical properties. The attenuations predicted from theory are
in generally good agreement with experimental data obtained by Pulse/FFT data acquisition
methods for solid-liquid slurries of soda-lime glass particles of 14.9 microns and 65 microns
mean radius and polystyene particles of 79 microns mean radius at concentrations ranging from 5
to 50 percent solids by volume in water. The primary attenuation mechanisms for the former
system are due to viscous and scattering losses, whereas, for the latter system, thermal and
scattering losses dominate. Good comparisons are also obtained for 0.11 micron radius
polystyrene particles in water from 5 to 50 percent solids by volume (Allegra and Hawley, 1992)
where attenuation is dominated by thermal affects.
Another goal of the project was to devise a technique to remove the noise introduced by
the presence of a small amount of gas bubbles in the suspension to infer the properties of the
solid-liquid suspension. Experiments and analyses were made for the solid-gas-liquid slurries of
soda lime glass particles of 14.9 micron mean radius at 5 and 10 percent by volume in water with
gas bubbles from 25 to 150 micron radius at low volume fractions. The primary conclusion is
that the noise is significant at low frequencies near the bubble resonance frequencies and the
noise is minimal at high frequencies. We show it is possible to estimate the effects of bubbles
and eliminate the slight noise produced by bubbles at higher frequencies to yield the volume
fraction of the particles.
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Tavlarides, L.L. & Sangani, Ashok. Acoustic Probe for Solid-Gas-Liquid Suspension, report, September 14, 2003; United States. (https://digital.library.unt.edu/ark:/67531/metadc780899/m1/3/: accessed April 22, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.