Characteristics of acoustic standing waves in packed-bed columns

Abstract

The acoustic characteristics of a column are described when filled with different random packings of various shapes, sizes and void fractions. An experimental setup was developed to study the acoustic field in a packed-bed column. Eight different packings were used to fill the column and for each packing the acoustic pressure amplitude and phase were measured along the length of the packed bed. The speed of sound and the attenuation coefficient were determined using a nonlinear regression technique. The speed of sound inside the column decreased when the column was filled with packings. The natural frequencies increased as the void fraction of a particular packing decreased. It is shown that the attenuation coefficient depends on a nondimensional frequency defined as ωd²/v, where v is the kinematic viscosity, ω is the angular frequency and d is the effective diameter of the packing.