The effects of frequency and sound pressure level on acoustic agglomeration of flyash

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.