(78g) Application of Helmholz Resonance to Determination of Bulk Density and Fill Fraction of Dry Particulate Solids

Helmholz resonance is the term for resonance occurring in a cavity linked to the surrounding atmosphere via a constricted neck or necks. The resonant frequency is principally determined by the volume of the cavity and the dimensions of the neck(s). An object placed inside a resonator reduces its effective volume, and it follows that for a well defined system, the volume of the object can be estimated from the change in the resonant frequency.

Such a system is thus potentially useful for characterizing bulk volumes of particulate solids, and hence the degree of fill in a container or bin, though we anticipate constraints with large bins, dictated by the low resonant frequencies of large volumes.

Experiments have been carried out with one, two and three liter resonators using a variety of particulate materials including glass ballotini, sand and plastic pellets. Degree of fill is calculated and compared with values estimated from direct measurements of material mass and loose-poured bulk density measured off-line. Fill ratios were also calculated from optical assessment of the material in situ. Estimates of bulk density made using direct measurement of mass and the volume inferred from resonance measurements are also compared with the loose-poured values.