Noise emission of suspended particles in an agitated environment

The mechanism of noise generation during the agitation of a suspension was investigated. Glass beads with known diameters and of known number were suspended in a paraffin-type organic liquid. The low frequency and the high frequency noises emitted during the agitation of the suspension were measured, characterized and correlated with the number and size of the beads. Low frequency noise signals contained mechanical and hydraulic noises that interfered with the monitoring of the noise signature of suspended particles. In contrast, high frequency noise signals exhibited characteristic changes relative to the size and number of suspended particles. An increase in the size or in the number of beads increased the event rate, energy rate, oscillation rate, relative energy and frequency power spectra. The fundamental frequencies of vibration were estimated. The order of magnitude of the calculated frequencies of vibration arising from bead-wall and bead-bead impacts was in good agreement with that of the measured frequencies. It is concluded that the high frequency noises emitted during the agitation of a suspension containing model particles are mainly generated by bead-wall and bead-bead collisions. An empirical relation between the noise relative energy and the diameter and number of the beads is also derived.