Research On Dynamics Of Cavitation Self-excited Pulsed Nozzle

The treatment of industrial wastewater is a major issue that scientists all over the world have conducted in-depth study. The technology of cavitation impinging stream has the advantages of simple operation, wide application scope, clean and no secondary pollution in the treatment of industrial wastewater. In this paper, based on the cavitation impinging stream processing of industrial wastewater as the background, the cavitation self-excited pulsed nozzle is studied as the technology core part. The research adopted the organ resonant cavity and Helmholtz resonator in series, and the numerical simulation method was applied to guide the design of the cavitation self-excited pulsed nozzle for cavitation impinging stream device.This paper first theoretically analyzed the mechanism of formation of the cavitation and its effect, as well as the generation principle of the self-excited oscillation pulsed jet and feedback conditions required to produce the disturbance wave; then the paper analyzed the principle of the cavitation self-excited pulsed nozzle and main factors influencing the effect of self-excited oscillation pulse; and then a series of structure of organ resonant cavity and Helmholtz resonator were designed, the optimal structure was selected in series by using numerical simulation method, numerical simulation was carried out on a series of cavitation self-excited pulsed nozzle, the internal flow field and cavitation of the nozzle under different inlet pressure were studied, and its optimal working conditions were determined; finally, the optimal structure of cavitation self-excited pulsed nozzle was obtained by adjusting the structure of the transition section of the nozzle.By numerical simulation, it is found that the cavitation self-excited pulsed nozzle of the organ resonant cavity and Helmholtz resonator in series can improve the nozzle exit velocity more than a single one does. For a specific structure of the nozzle, only when the fluid pressure meets certain pressure range condition, it produce self-excited oscillation, and the speed have been amplified twice. And for a specific structure of the nozzle, there is a starting pressure to produce cavitation, only when the pressure is higher than or equal to the starting pressure, it produces cavitation jet. For this design of a series of cavitation self-excited pulsed nozzle, working pressure range is 0.4 to 2.7 MPa, taking into account the energy saving factors, 2 MPa is selected as the suitable working pressure of the cavitation self-excited pulsed nozzle. By changing the length of the transition nozzle for optimization, the nozzle of the 2mm length is determined to be the best structure.