Investigation On Ultrasound-Enhanced Plate Membrane Microfiltration Of Fine TiO₂Suspension

The paper mainly investigated the ultrasound-enhanced plate membranemicrofiltration process. The acoustic intensity distribution in ultrasonic generatorwas calculated and then was measured. The α-Al₂O₃ceramic membrane waschosen for the following experiments by comparing the membrane stability. Theoptimization diameter for ultrasound-enhanced plate membrane microfiltrationprocess was selected. And the relationship between acoustic intensity andultrasonic enhancement effect was discussed.Based on the acoustic theory, the relative acoustic intensity of ultrasonicequipment in horizontal and vertical direction was calculated. And theexperimental acoustic intensity distribution and attenuation in ultrasonic generatorwas measured by ultrasonic power measuring meter. The results showed that theacoustic intensity distribution in three-dimensional space of ultrasonic generatorwas non-uniform. And the experimental acoustic intensity value matched with thetheoretical value to some extent, which indicated that the theoretical acousticintensity value could be used to verify the experimental value.The evolution of the property of plate membrane exposed to ultrasonicirradiation was followed by the calculation of the membrane flux factor F and therejection rate R. As for the α-Al₂O₃ceramic membrane, when the acousticintensity was1.04W cm^-2, the ultrasonic frequency was45kHz, and theirradiation duration was60min, F was1.34and R was0.92. The α-Al₂O₃ceramicmembrane was chosen for the following experiments due to its high resistant underultrasonic irradiation.The effect of operation factors on the cross-flow microfiltration of fine TiO₂suspension system with ceramic plate membrane was investigated. Theoptimization diameter was selected that the feed concentration was1.0g·L^-1, thecross-flow velocity was0.5m·s^-1, the trans-membrane pressure was0.04MPa, themembrane pore size was200nm, the nominal ultrasonic power was200W and theultrasonic frequency was45kHz, ultrasonic irradiation showed high enhancementeffect and the ultrasonic enhancement factor （E） was1.34while the ratio ofremoved cake layer （B） was0.44. Based on the above optimization diameter, the influence of the acousticintensity distribution on membrane filtration was studied. The results showed thatthe acoustic intensity was positively correlated with B and E. When the averageacoustic intensity on membrane surface was about0.5W cm^-2, B was higher than0.23, and E was about1.2, and when the average acoustic intensity on membranesurface was about0.6W·cm^-2, B was bigger than0.4, and E was about1.3. Whilethe average acoustic intensity on membrane surface was about0.01W·cm^-2,ultrasound irradiation showed no enhancement effect. In order to effectiveutilization of the acoustic energy, the optimized location found forultrasonic-enhanced membrane microfiltration module was as follows: theultrasonic irradiation direction was the same as the direction of permeation flux;membrane module was placed on top of the transducer and in the near field of theultrasonic field.