Some studies of ultrasound assisted filtration rates

Some recent experimental results of ultrasonically assisted pressure filtration rates through sintered brass and woven stainless steel filters are presented. The liquids studied are clean motor oil (Velocite Mobil No. 6) and slurries formed by adding aluminium powder or hollow glass spheres to the motor oil. Relations between the parameters: pressure drop across the filter, ultrasonic field intensity and the ratio of particle to pore diameter are investigated. Previous explanations on the mechanisms leading to observed flow rate increase by ultrasonic irradiation, given by various authors, are critically evaluated in the light of new observations. These include the critical frequency theory, the influence of cavitation and microstreaming and the influence of turbulence. Some essential relations between parameters influencing the flow rate which still need a systematic investigation are emphasized. It is concluded that the use of ultrasound in pulsed mode operation may be the way out of the present stagnation in the field.