AEROSOL AGGLOMERATION AND DEPOSITION IN HIGH-INTENSITY ACOUSTIC FIELDS

An experimental investigation of acoustically induced turbulence and shock-waves in both standing-wave and traveling-wave tubes is performed under both stationary and flowing conditions. Acoustic intensity (I) and frequency (f) effects are studied using a constant-temperature anemometer and a fast Fourier transfer data processor. Sampled data are conditioned and processed to estimate the characteristics of turbulence. It is found that, regardless of the spatial locations in a standing-wave tube, turbulence appears at sound pressure level larger than 160 dB. Furthermore, at slightly higher level ((TURN) 162 dB) shock waves occur within a narrow band ((+OR-) 20 Hz) around the resonance frequencies. In a traveling-wave tube, turbulent bursts are noticed around I = 158 dB, and the shock waves appear at approximately I = 160 dB over the range of all frequencies. In both cases, the turbulent spectrum (F) and the wave number (K) are found to satisfy a power law F (PROPORTIONAL) K('(alpha)) with (alpha) (TURNEQ) -1.7 to -2.1. The rms turbulent velocity u(,*) is found experimentally to have an I(' 1/2) dependence, yet is relatively insensitive to variation of f. Throughout the whole measuring range of f and I, the rate of energy dissipation ((epsilon)) is estimated to be 10('6) - 10('7) cm('2)/sec('3). It is also found that the superimposed air flow through the test tube reduces the turbulent intensity.; The acoustic agglomeration kernels in various regimes are evaluated for parameters, such as: aerosol concentration, median diameter, geometric standard deviation, acoustic intensity, frequency, ambient temperature and pressure. Based on the estimation of (epsilon) and the Kolmogorov micro-scales of time ((tau)) and length ((eta)), the acoustic agglomeration rate is determined. In addition, a numerical computation is performed to provide a comparison of the relative importance of the agglomeration mechanisms at different I and particulate emission mass-loadings (M).; An experimental study is reported for the wall deposition of monodisperse polystyrene latex particles with diameters ranging from 0.5 to 5.7 (mu)m in an acoustically induced turbulent flow. Using an optical particle counter, together with a multi-channel analyzer, a set of measurements are conducted in which both acoustic intensity and frequency are independently varied in the range of I = 161-168 dB and f = 500-1600 Hz under the traveling-wave condition. In order to justify the theoretical prediction, the particle eddy diffusivity is evaluated according to the theoretical consideration of the decay of turbulence in the boundary layer. Furthermore, the advective contribution due to the turbulent velocity gradient is also included in the description of the mass transfer of aerosol particles. Based on the assumption of perfect sticking conditions (no particle rebound and/or reentrainment) theory and experiment are in fairly good agreement.; Experiments have also been performed to verify the validity of the acoustic agglomeration theory in high-intensity acoustic fields. Using a laboratory-scale transmissometer for the continuous light-opacity measurements, separate experimental runs have been directed to investigate the effects of I, f and M. In the operating range of I = 160-164 dB, f = 500-2200 Hz and M = 10-30 gm/m('3), the experimental data show a fairly good agreement with the theoretical results. It is also revealed that, under the same operating conditions, the standing-wave operation is more effective than the traveling-wave operation.