Acoustic Characterization of Concentrated Suspensions and Emulsions. 2. Experimental Validation

Abstract

In the first part of this work, a core−shell extension of the isolated-particle framework of Epstein, Carhart, Allegra, and Hawley (ECAH theory) has been developed for the simulation of sound attenuation in concentrated emulsions and suspensions. In the present paper, the model predictions are validated by comparison with a systematic set of experimental data. The systems under consideration include silica/water, poly(tetrafluoroethylene) (PTFE)/water, and corn oil/water at a range of particle sizes, particle volume fractions, and frequencies. These data cover a wide variety of situations where energy dissipation is dominated by viscoinertial losses, thermal losses, or combinations thereof, thus providing a significant test for the reliability and generality of the model. Moreover, the potential of the model as a basis for the estimation of particle sizes from acoustic data is investigated.

Ultrasonic wave propagation in concentrated slurries – The modelling problem

“…The model has been shown to successfully simulate attenuation in high concentrations of small particles, and we confirm these results for silica in water suspensions of considerably smaller particle diameter than those considered by Hipp [9]. The model, or indeed its predecessor by Anson and Chivers [10], has a number of disadvantages in the context of particle sizing in that both are computationally intensive and can be prone to numerical instability.…”

“…One solution to the shear-wave (and indeed thermal-wave) scattering problem is the core-shell model developed by Hipp [8][9], whose model is almost identical to that of Anson and Chivers [10]. Anson and Chivers solved the problem of scattering by a particle with an actual shell of material (encapsulated particle) around it, by constructing a modification of the ECAH model but with two surfaces on which boundary conditions are applied.…”

“…In terms of wave propagation, there will be two sets of boundary conditions -one at the surface of the particle and one at the surface of the surrounding sphere, Figure 2. Full details of the models can be found in the original papers [8][9][10]. Hipp [9] later demonstrated that this model could successfully predict attenuation in silica suspensions at high concentrations.…”

“…It therefore makes sense to consider whether or not there exists some effective medium properties for viscosity and other parameters that would represent the hydrodynamic environment surrounding any given particle and account for the shear wave influences on neighbouring particles. The advantage here would be that a simple effective viscosity and density model would be used in combination with the simpler ECAH/LB model, and that this would not require additional boundary conditions resulting from the use of a shell (Hipp [8][9]), but would nevertheless incorporate those higher order effects which are significant at high concentrations.…”

“…One approach to the problem is that of Hipp et al [8][9], who developed a core-shell model to account for the effective properties of the suspension as whole. The model has been shown to successfully simulate attenuation in high concentrations of small particles, and we confirm these results for silica in water suspensions of considerably smaller particle diameter than those considered by Hipp [9].…”