Study On Ultrasonic Atomization Nozzle

Respiratory dusts in coal mine are the most fundamental cause of worker’suffering from pneumoconiosis in pits. At present, spray-on process is applied to dealing with the dust in coal mine, but its effect on the respirable dust is limited.The main reason is the spray droplet size is too large, and previous studies showed that the smaller the droplet diameter is, the more effective the trapping of respirable dust will be. Ultrasonic atomization is a new dust removal technology. The droplet diameter generated by ultrasonic atomizing nozzle can be as tiny as ten microns, which can effectively improve the deposition efficiency of respirable dust.This paper analyses the sounding principle and atomization mechanism of the ultrasonic atomizing nozzle. It is concluded that the ultrasonic frequency,sound pressure and nozzle exit airflow velocity are the main factors affecting the ultrasonic atomization; the nozzle resonance cavity has a great effect on the ultrasonic frequency and sound pressure.The frequency of ultrasonic atomizing nozzle under different air pressures is measured; and the working range of the nozzle air pressure(0.25-0.6Mpa) is worked out by the frequency variation law in the experiment. Meanwhile, the experience formula of ultrasonic atomizing nozzle is tested and verified. Theimpact on the sound pressure from the key variables, including air pressure,cavity diameter(d), length(L) and distance from Nozzle to resonant cavity(s),is analyzed through FLUENT. The result shows that the sound pressure increases with the increase of air pressure, and the design ranges of the three structural parameters of the resonant cavity are as follows, d=1.5-2.5mm,L=1.0-2.0mm, s=3-4mm, which provides reference for the design of the nozzle cavity in the future.A simulated research on the flow field of gas-liquid two-phase ultrasonic atomizing nozzle is conducted with the tool FLUENT, the impacts of working parameters and structure parameters on the air rate of nozzle exit are analyzed.Research shows that the air velocity of nozzle outlet increases as the air pressure increases, but decreases with the increasing of water pressure. On the basis of the above rules, the optimal working air pressure of ultrasonic atomizing nozzle is 0.5MPa, and the matched water pressure is 0.3-0.4MPa. Liquid phase inlet angle θ has a little impact on the air velocity of nozzle outlet. The air velocity of nozzle outlet increases with the increase of liquid entrance aperture(D), which gives the design range of D, 1.0-1.2mm.The atomization characteristics of the ultrasonic nozzle are experimentally addressed. The results show that as the air pressure increases, SMD will first decrease dramatically and the atomization angle increase rapidly; and then if the air pressure continues to increase, there will be no clear change of both the SMD and atomization angle. As the water pressure increases, SMD will dramaticallyincrease. At the same time, the optimal working air pressure and water pressure are verified by the experimental results. And the experimental results show that the uniformity of fog field is the best in the axial distance range of 0-150 cm when the air pressure is 0.5MPa and the water pressure is 0.4MPa.