Numerical Simulation of Acoustic Agglomeration Using the Multi-Monte Carlo Method

Particle pollution has been recognized as a significant form of environmental pollution. More specifically, the inhalation of very small (ultrafine) airborne particulate matter that is emitted from the burning of fossil fuels poses one of the most serious threats to human health. High-efficiency retention of these particles is one of the most challenging environmental problems, since conventional techniques such as electrostatic precipitators, bag filters, or cyclones have low collection efficiency in the respirable range (0.1 μm–1.0 μm). Acoustically induced agglomeration of ultrafine particles is a promising technique to increase the size of small particles before they enter a conventional filter. During this process, high-intensity acoustic fields are applied to the flue gas stream, inducing interactions among suspended particles that give rise to collisions and agglomeration. The preconditioned aerosol can then be filtered within conventional filters with higher collection efficiency. The present work reports the results of a numerical investigation of the effect of ultrasound preconditioning on the particle size distribution as a function of parameters related to the ultrasound system design, such as the sound frequency and intensity, and the initial distribution characteristics. Particle agglomeration is modeled via the solution of the population balance equation with the Multi-Monte Carlo method. Results show that acoustic agglomeration can shift the particle size distribution toward larger diameters and reduce the number concentration of particles, thus leading to increased capture efficiency of conventional filters.