Hemant P. Pendse
Dept. of Chem. Eng., 5737 Jenness Hall, Univ. of Maine, Orono, ME 04469-5737
Acoustic wave propagation in concentrated suspensions is analyzed using a modified coupled-phase modeling approach. The particle, size, shape, and orientation are taken into account for estimation of viscous drag coefficient of spheroid particles over wide ranges of frequency and particle concentration. The study deals with frequency-dependent and concentration-dependent ultrasound attenuation coefficient of clay suspensions, with particular attention to the effect of particle size and shape distributions. For clay suspensions, the major loss of acoustic energy results from the viscous dissipation arising from the relative particle--fluid motion. Predicted results of sound-speed and attenuation coefficient based on consideration of particle shape factors agree well with the measurements available in literature for frequencies of 0.10--5.0 MHz and solid concentrations up to 40 vol%. Experimental results of attenuation spectra of plate-shaped kaolin clay slurries with solid concentrations of 0.6 to 16.9 vol% over 3 to 60 MHz are obtained using a newly developed AcoustoPhor System 8000. These attenuation spectra are interpreted in terms of realistic particle size and shape distributions. The effects of nonsphericity become dominant as particle concentrations and operating frequencies are increased. Realistic size-dependent shape factors are shown to explain the measured spectra.