Investigation of orthokinetic collision and acoustic wake effect for acoustic agglomeration of flyash aerosols

Acoustic agglomeration using acoustic waves to agglomerate small particles suspended in the gas medium has potential applications in the fine particle control. In this dissertation, a new concept of "effective agglomeration length", which measures the maximum particle separation distance for possible particle collisions in horizontal direction, is proposed as a measure of combining and calculating the effects: the orthokinetic collision and acoustic wake on the acoustic agglomeration of a polydisperse aerosol with particle gravity and particle collision efficiency taken into account. Parametric analyses with particle size or size ratio, sound frequency and sound pressure level (SPL) are conducted for the case of a horizontal sound wave field. The theoretical results indicate that the orthokinetic collision dominates at low frequencies for the moderate particle size ratios while the acoustic wake effect is more significant at higher frequencies. It is confirmed that there is there is an optimum frequency for the orthokinetic collision but shifts downward with increases of sound power. Calculations of "effective agglomeration length" also show that the orthokinetic collision is not effective for treatment of sub-micron particles due to a low particle collision efficiency.; Agglomeration experiments are conducted with flyash particles in standing wave fields at frequencies from 200 Hz to 2000 Hz and SPLs from 136 dB to 164 dB. The particle mass distributions are measured with a cascade impactor. The results show that the orthokinetic collision is dominant at the frequencies below 600 Hz to 800 Hz with an optimum frequency around 305 Hz while the acoustic wake effect is dominant at the higher frequencies. It also shows that low frequencies have a high-energy efficiency. Accumulation of flyash particles at the velocity nodes is observed at SPLs of 152 dB and above.