Acoustically generated turbulence and its effect on acoustic agglomeration

Abstract

Acoustic agglomeration (AA) is an intermediate treatment of aerosols containing submicron- and micron-sized particles so that conventional cleaning devices such as electrostatic precipitators, bag houses, and scrubbers can remove these fine particles more efficiently. The high-intensity acoustic field in the AA causes local velocity fluctuations to move the particles relative to one another, collide, adhere, and grow. This paper addresses the question of whether such highly intense acoustic fields (approximately 160 dB) will cause random velocity fluctuations of such a magnitude that this acoustic ‘‘turbulence’’ significantly affects AA. The experimental study results show that only the acoustic velocity fluctuations at the excitation frequency dominate the local velocity and therefore the particle motions. Although some acoustically generated random motion is noted with increasing acoustic intensity above 160-dB sound pressure level, the energy in turbulent fluctuations is about three orders of magnitude lower than the energy in acoustic frequency and harmonics. The paper concludes that acoustically induced turbulence does not play a significant role in AA.

Application of acoustic agglomeration to enhance air filtration efficiency in air-conditioning and mechanical ventilation (ACMV) systems

“…At high acoustic intensities (above 160 dB), acoustically induced turbulence is also generated and promotes particle collisions [ 18 – 20 , 82 , 83 ]. There are in general two mechanisms associated with turbulence agglomeration.…”

“…The effect of turbulence on acoustic agglomeration is less conclusive. Some have reported little improvement in particle agglomeration in the presence of turbulence [ 20 ], while others have observed dominating effects on the overall acoustic agglomeration rate [ 18 , 82 ].…”

“…Acoustic agglomeration is the process in which acoustic waves are used to manipulate the motion of airborne particles [ 16 – 20 ] and in the process, promote collisions that lead to the formation of agglomerates (clustering of particles). The newly-formed clusters continue to agglomerate with others and results in a cascading growth of particles.…”

Direct Simulation Monte Carlo Method for Acoustic Agglomeration under Standing Wave Condition

“…The particle interactions due to the mutual radiation pressure effect and the acoustic wake effect have been observed in both experiments and model simulations (Hoffmann and Koopmann, 1996;Hoffmann and Koopmann, 1997;González et al, 2001;González et al, 2002;González et al, 2003). Generally, the acoustic turbulence occurs at an acoustic intensity higher than 160 dB (Chou et al, 1982;Tiwary et al, 1984;Chen et al, 2008). Therefore, for an acoustic intensity less than 160 dB, the acoustic particle interactions are mainly caused by the orthokinetic interaction, the mutual radiation pressure effect and the acoustic wake effect.…”

“…Experiments have been carried out in the past decades to determine the factors affecting the agglomeration behavior of PM 2.5 under the acoustic field (Volk et al, 1976;Rajendran et al, 1979;Tiwary et al, 1984;Hoffmann et al, 1993;Kashkoush and Busnaina, 1993;Sharifi et al, 1994;Capéran et al, 1995;Manoucheri and Ezekoye, 1996;Gallego-Juárez et al, 1999;Spengler and Jekel, 2000;De Sarabia et al, 2003;Komarov et al, 2004;Liu et al, 2009;Liu et al, 2011;Wang et al, 2011;Yan et al, 2015). The experimental results indicated that the removal efficiency using acoustic agglomeration depends on the acoustic frequency and intensity, particle size and concentration, and residence time.…”