Primary axial acoustic force

Date: 2015-10-07; view: 580.

Almost immediately following the application of an acoustic field, particles experience a time-averaged primary axial acoustic force, F_ac (F_PARF), which is generated by the interaction between particles and the primary wave field. The primary axial radiation force drives dispersed particles toward the velocity antinodes of the resonance field. The magnitude of the force depends on the difference in compressibility and density between the particle and the medium. The primary acoustic force was derived by Yosioka and Kawasima [4] and given below.

(1)

The acoustic energy density, E_ac, is a measure of the energy residing in a wave field. V₀ is the volume of one particle, k = 2π/λ is the wave number of the acoustic radiation, λ is the sound wavelength, x is the axial distance from a pressure node, and k is the unit vector in the axial direction. The response of any solid suspended in a fluid, to a resonant acoustic field, depends on the acoustic contrast factor, G. For any solid particle of size r λ suspended in a fluid, the acoustic contrast factor is given by:

(2)

where, β_f and β_p are the compressibility of the fluid and particle respectively, and ρ_f and ρ_p are the densities of the fluid and particle respectively.