Hemant P. Pendse
Dept. of Chem. Eng., 5737 Jenness Hall, Univ. of Maine, Orono, ME 04469-5737
The unified coupled phase continuum (UCPC) approach is utilized to analyze sound propagation through colloidal dispersions consisting of solid particles or liquid droplets suspended in a fluid. Attention is focused on the case of submicron particles at moderate to high (5% to 50%) volume fractions under ultrasonic frequencies. The governing equations involve equations of state, continuity, momentum, and energy for the discontinuous and continuous phases, respectively. The viscous (thermal) coupling between the two phases is accounted through matching terms in the equations of momentum (energy) formulated separately for each phase. Expressions for the viscous and thermal coupling coefficients explicitly account for the effects of particle size, shape factor, orientation, as well as concentration and the sound frequency. Theoretical predictions of sound speed and attenuation coefficient spectra are compared with several available experimental measurements on a variety of colloids including aqueous suspensions of polystyrene latex, TiO[sub 2] or kaolin pigment, as well as a toluene in water emulsion and an oleic acid in nitrogen aerosol. The UCPC approach can successfully predict the attenuation spectra of concentrated colloids covering a wide range of relative magnitudes of viscous versus thermal contributions. Its applications for particle size and shape characterization will be discussed.