Enhancing the performance of fibrous filters by means of acoustic waves

The influence of low-frequency acoustic waves on the operating time of fibrous filters was investigated experimentally. It was found that the application of acoustic waves can dramatically extend the operating time of fibrous filters. The experiments indicate that at frequencies of 50–1000 Hz and sound pressure levels of 110–130 dB the operating time of fibrous filters increases 2–10 times, as compared to filtration without acoustics. The effect is more pronounced at lower frequencies and higher sound intensities. A simple theoretical model shows that, because of secondary acoustic streaming, the aerosol particles moving toward the filter surface are deflected toward the deposited particles, resulting in increased voids and a more porous structure of the filter cake, which in turn leads to a lower pressure drop across the filter. This conjecture is supported by pictures of the filter cake surface.