Acoustic probe for the characterization of solid-gas-liquid slurries

The development of nuclear weapons technology during the Cold War Era has left a legacy of large quantities of radioactive waste which are stored throughout the US Department of Energy (US DOE) Nuclear Weapons Complex. During the proposed remediation stages of processing, it will be necessary to characterize and monitor these waste slurries by remote methods. Acoustic probes have shown promise because of their non-intrusive nature and ability to penetrate optically opaque slurries. A forward theory for the acoustic response in both dilute and concentrated solid liquid slurries is developed. It 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 attenuations predicted from the theory are in generally good agreement with the experimental data obtained by Toneburst and Pulse/FFT data acquisition methods for solid-liquid slurries of soda-lime glass particles of 14.9 μm and 65 μm mean radius and polystyrene particles of 79 gm radius at concentrations ranging from 5% to 50% solids by volume. The forward theory is readily extended to systems containing more than one dispersed phase, such as particles and gas bubbles, and the theory predictions are observed to be in good agreement with preliminary attenuation data obtained in solid-gas-liquid slurries of soda-lime glass particles of 14.9 gm mean radius at 5% and 10% by volume and gas bubbles ranging from approximately 25 μm to 150 μm radius at volume fractions on the order of 10-5. An inverse theory is also developed to determine the concentration and solids volume fraction distribution in a solid-liquid slurry given its experimentally obtained acoustic response. A Tikhonov scheme is employed to regularize the ill-posed integro-differential equations and solve them as a linear programming problem. Solution of the inverse problem is found to be successful in several cases, but the results are observed to be sensitive to the choice of frequency range, the physical properties of the particles, and the nature of the particle volume fraction distribution