Coupling effect of gas jet and acoustic wave on inhalable particle agglomeration

Inhalable particle pollutants from industrial processes have a typical size of less than 2.5 μm and have recently gained much attention because they are considered as a serious public health concern. These particles can penetrate deeply into the lungs and are difficult to remove by conventional separation devices. A turbulent gas jet was introduced into the acoustic agglomeration chamber to form the coupling external field. This work studied the effect of operation parameters on the agglomeration behavior of inhalable particles, such as frequency (280–3500 Hz), sound pressure level (100–130 dB), jet velocity (14–28 m/s) and injection angles (40–140°). Scanning electron micrographs of aerosols, with and without external fields, demonstrated that the inhalable particles were removed by the formation of large aggregates. The mass median diameter of the particles increased from 2.47 μm to 6.48 μm after exposure to the coupling external fields, i.e. sound frequency 1416 Hz, sound pressure level 128 dB, jet velocity 25.5 m/s and injection angle 90°. The inhalable particles had maximum agglomeration efficiency at 1416 Hz at an SPL of 128 dB. Increasing the sound pressure level from 100 dB to 128 dB improved the removal efficiency. High gas velocity of 28.3 m/s favors the collision of inhalable particles in a turbulent flow. However, increasing gas velocity initially enhanced and subsequently decreased the removal efficiency in the coupling external field. The maximum efficiency occurred at 22.5 m/s jet velocity. Vertically injected turbulent gas jet was the best method to improve removal efficiency. The application of an external field resulted in higher removal efficiency for particles smaller than 1 μm and larger than 5 μm, but relative lower removal value for mid-sized particles (1–5 μm).