Investigation on Optimal Ultrasonic Frequency for Effective Particle Aggregation in Suspension

An analytical investigation is conducted to obtain optimal ultrasonic frequency for effective particle aggregation in suspension. In this investigation, we are discussed the proper mode of action of ultrasound to produce the ultrasonic standing wave field, due to the fact that the aggregation of particles in suspension occurs in the ultrasonic standing wave field. The mechanism of ultrasonic aggregation is also investigated qualitatively. Equation for calculating optimal ultrasonic frequency is derived based on the consideration of the forces acting on the particle in ultrasonic standing wave. According to current results, the optimal ultrasonic frequency is proportional to −3/2 power of the particle size. According to the experimental results, when the size of the particles to aggregate is micrometer, the effective ultrasonic frequency becomes the MHz band. The order calculations using this relationship are in good agreement with the experimental results that the effective frequency of ultrasonic cohesion is in the MHz range. In addition, a comparison with previous studies is also carried out to validate the relationship. According to previous study, the most effective frequency for pulverized coal recovery is 100kHz, among 80kHz, 100 kHz and 120 kHz. The theoretical calculations of this using the relations we derived are 101.806 kHz, which is in close agreement with Wang's results. This equation can be used effectively in several fields such as mineral dressing, particle control and separation of blood cells.