Agglomeration of oil droplets assisted by low-frequency sonic pretreatment

The metalworking process in industrial buildings produces small droplets of oil. The efficient purification of small oil droplets can protect the built environment and human health. Purifier performance is generally related to particle size, and increasing the particle size by pretreatment significantly improves purification efficiency. Acoustic agglomeration is a widely recognized technique for increasing dust particle size. In this study, the agglomeration efficiency (decrease in the number concentration) of oil droplets with a particle size of <5 μm under a sound wave was investigated. The operating parameters studied included sound wave frequency (1000–4000 Hz), waveform (sine, square, and triangular waves), sound pressure level (130–145 dB), and oil droplet residence time (2.5–4 s). The results show that the agglomeration efficiency peaks with frequency and increases linearly with the sound pressure level, first increasing sharply and then leveling off with residence time. The following were the optimum parameters:1800 Hz sine wave, 145 dB, and residence time of 3 s. Under these operating conditions, the agglomeration efficiency is 9.9%. The enhancement of acoustic agglomeration on purification by a wire mesh filter was verified, and it was shown that the purification efficiency of a wire mesh filter for 0.3–5 μm oil droplets increased by over 20%.