Investigation of particle agglomeration under angular harmonic and non-harmonic ultrasonic acoustic fields

The paper presents numerical and experimental results on ultrasonic agglomeration of solid particles. A piezoelectric acoustic pressure source was driven by sinusoidal and square-shaped electrical signals, which ensured generation of harmonic and non-harmonic acoustic fields. These fields were applied to an airflow containing fine and ultrafine particles at different angles. The numerical investigations showed that a piezoelectric acoustic pressure source operating at 25.82 kHz, when excited by different signal types, generated acoustic fields with distinct patterns and intensities. Varying the angular position of the source relative to the airflow enhanced the interaction of the acoustic fields with particles, thereby improving the agglomeration process. The results of numerical and experimental investigations have shown that the excitation of piezoelectric acoustic pressure source by of non-harmonic signal ensures higher sound pressure levels compare to harmonic fields. Therefore, generation of non-harmonic acoustic fields ensures improvement of sound pressure levels as well as agglomeration process. Finally, results of experimental investigations of agglomeration process have shown that inclination of acoustic pressure source driven by non-harmonic signal against the air flow ensures more effective agglomeration process and ensures decrement of the finest particles up to 66 %.