Precise measurements of particle entrainment in a standing-wave acoustic field between 20 and 3500 Hz

An experimental study is presented to investigate entrainment coefficients of aerosol particles in a sonic wave. The experimental results are contrasted with a well-established analytical expressions for the entrainment coefficient derived from the Brandt-Freund-Hiedemann (BFH) equation. The measurements are carried out in a standing-wave field with an extremely homogeneous and well-determined acoustic velocity field. A CCD-camera with a microscope lens attachment is used to visualize the displacement amplitude of 7.9 µm glass beads in the frequency range from 20 Hz to 3.5 kHz. The particle entrainment coefficients obtained with this visualization method are in good agreement with the theoretical predictions of the BFH equation and with earlier experimental data by Gucker and Doyle. While this prior study revealed some apparent experimental limitations, the present data is derived with an accurate and repeatable measurement technique. The large number of measurements in the current study helps to draw a detailed representation of the acoustic entrainment coefficient.