Theoretical And Experimental Researches On Multiple Standing Waves Acoustic Field Effects On Migrating Particulates

Air pollution is caused mainly due to particulates suspended in air, which threat the natural environment and human health. Traditional particle processing mainly aim at larger size particles; for particulates, processing technology is still in its gradual exploration research stage. In the research on the processing of particulates by means of sound waves, especially standing wave sound field has good maneuverability to the migration behavior of particulates and can aggregate or separate them. In this work, a multiple standing waves particle separation device was designed and constructed based on the concept of acoustic particulates processing. The acoustic characteristic of the device was explored, and the effectiveness of the device to particulates separation was also experimental verified.The key to acoustic particulates processing technology lies in that the sound field has a certain intensity gradient and structure distribution. The major parts of the experimental apparatus were Helmholtz sound sources (HSSs) and planar echo cavity (PEC). Signal generator produced an AC signal, and was be amplified by power amplifier initially before entering the HSS. The signal was converted to high intensity of acoustic signal by HSS. and then the acoustic signal directly radiated to the PEC. The same multiple acoustic waves recombined and made a superposition to form multiple standing waves composite acoustic field. The acoustic field took an effect on the migration of particulates suspended, and prompted mass of particulates to accumulate and disperse, therefore realized the separation of particulates finally. The physical models of HSS and PEC were established through the analysis of the multiple standing waves particle separation device, and the acoustic characteristics and the effect on migrating particulates of the device were also analyzed.Experimental results show that:The interaction between loudspeaker and Helmholtz resonator will influence the HSS equivalent electric/acoustic impedance, and affect the source voltage, output pressure and electro-acoustic conversion efficiency of the HSS; the resonances of loudspeaker membrane and Helmholtz resonator can enhance the acoustic signal emission. Under certain conditions, the resonance of Helmholtz resonator will increase the electro-acoustic converting efficiency of HSS. Contrast to the general loudspeaker, the HSS with resistance of 6.5 Ω obtains an electro-acoustic converting efficiency up to 113%.The acoustic signal at frequency of 1.805 kHz can realize the resonance of HSS and PEC. Located at PEC wall center,16 symmetric HSSs will prompt cavity to generate obvious resonance characteristics, and the intensity distribution in composite acoustic field of the PEC performs a characteristic in accordance with the circular division. The acoustic characteristic of the composite acoustic field is stable within the resonant frequency band, and it can realize a lot of tobacco smoke particles to aggregate and separate.The experiment also compared the influences on PEC frequency resonance and the migration and separation effect on a large number of tobacco combustion particles under different number of HSSs. Experiments show that the multiple standing waves particle separation device makes a good effect on particulates migration.