Previously, a new concept of effective agglomeration length, which measures the maximum particle separation distance for effective collisions, was proposed (J. Aerosol Sc., Vol. 37, 540–553, 2006) for acoustic agglomeration of polydisperse aerosols. Two mechanisms are taken into account, orthokinetic collision and acoustic wake in a horizontal acoustic wave. Predictions of the model indicate that orthokinetic collision dominates at low frequencies for intermediate particle size ratios while the acoustic wake effect is more significant at higher frequencies for all particle sizes. Experimental results of acoustic agglomeration of flyash in two resonators, one a constant cross-sectional resonator and the second a variable cross-sectional resonator, are reported. The effects of frequency and sound pressure level (SPL) on acoustic agglomeration are measured. The experimental results are compared with predictions from the effective agglomeration length model. It is confirmed that for orthokinetic agglomeration an optimum frequency exists. However, the optimum frequency is found to be a function of SPL. Resonator design has an effect on the maximum achievable SPL and the power consumption of the device.
A new concept of effective agglomeration length, which measures the maximum particle separation distance for effective collisions, is proposed for acoustic agglomeration of polydisperse aerosols with respect to the separate and combined effects of orthokinetic collision and acoustic wake in a horizontal acoustic wave. Particle gravity is found to be significant for the acoustic wake effect while the particle collision efficiency is important for the orthokinetic collision. Results indicate that orthokinetic collision dominates at low frequencies for intermediate size ratios while the acoustic wake effect is more significant at higher frequencies for all particles. The optimum frequency for orthokinetic collision is confirmed but shifts downward with the increase of sound power. For the acoustic wake effect, the agglomeration increases monotonically with sound frequency. Results also show that the orthokinetic collision is not effective for agglomeration of sub-micron particles because of low particle collision efficiency.
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