Filtration of particulate suspensions in acoustically driven porous media

Retention of suspended solids within a porous medium subjected to resonant ultrasonic fields was studied experimentally. In laboratory tests, 325 mesh polystyrene particles were collected with high (typically > 80%) single-pass efficiency using a polyester foam mesh with pores more than two orders of magnitude larger than the particles retained. Deactivation of the acoustic field allows the retained particles to be flushed from the porous medium. The effects on filtration efficiency of processing variables (suspension flow rate, solids concentration in the feed, intensity of the acoustic field, and frequency of the acoustic field) are reported. A simplified analysis of particle trajectories toward cylindrical collectors in response to acoustic and hydrodynamic forces provides insight into the fundamental physical phenomena that govern the acoustically enhanced filtration process.

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