Measurements of the modal decay rates of a gas/particle suspension confined in a cylindrical tube: Relationship to particle concentration

A novel method to measure the particle concentration in a gaseous suspension has been investigated. The measured impulse response across a section of cylindrical tube containing the suspension has been processed to determine the decay rates of radial modes in the tube. These decay rates are sensitive to the attenuation coefficient of the suspension, and hence to the particle concentration. The decay rates observed with and without suspended particles have been used to establish an empirical relationship between the particle concentration and the model decay rates. The frequency range used was 1.5–15 kHz, and the particle volume concentration has been varied between 0.7–10 ppm. The mean diameter of the particles was 6 μm. [Work supported by the S.E.R.C.]