Sound propagation in concentrated emulsions: comparison of coupled phase model and core-shell model.

The predictions of two models of sound propagation in concentrated emulsions are compared with experimental measurements of ultrasonic velocity and attenuation in emulsions with volume fractions up to 0.7. The core-shell model includes irreversible heat transfer, viscoinertial forces, and multiple scattering [McClements et al., J. Acoust. Soc. Am. 105, 915-918 (1999)]. This model accounts for the effect of thermal interactions between neighboring particles by introducing an effective medium, and is valid for all volume fractions. The coupled phase model includes irreversible heat transfer and viscoinertial forces, and also is valid for all volume fractions, since it is derived from volume-averaged balance equations [J. M. Evans and K. Attenborough, J. Acoust. Soc. Am. 102, 278-282 (1997)]. This model has a significantly simpler formulation than the core-shell model and does not require the assumption of an effective medium. The coupled phase model is shown to be a good approximation to the core-shell model when the acoustic radius is small. Despite the fact that it does not include thermal interactions, the coupled phase model is shown to give at least as good agreement as the core-shell model with the experimental data, for all volume fractions, as long as the acoustic radius is less than 0.01.