Design Of A New Cavitation Reactor And Study On Flow Field And Degradation Characteristics

Increasingly complex industrial and agricultural wastewater causes a great threat to ecological environment and human health.Hydrodynamic cavitation,as a new water treatment technology,has attracted wide attention due to its low cost,ability to treat a variety of obstinate organic pollutants without secondary pollution.Cavitation bubbles will produce extreme environment of high temperature and pressure locally when they collapse,and chemical reaction will take place to produce hydroxyl radicals with extremely strong oxidation,which is the basic mechanism of applying cavitation to water treatment.Based on the mechanism of hydrodynamic cavitation degrading organic wastewater,the optimum design scheme of the cavitation reactor is given in this paper,and a new Venturi tube with throat part flow component is put forward.The numerical simulation,water test and degradation test of typical pollutants are carried out for this type of cavitation reactor.The unsteady characteristics and degradation characteristics of the cavitation flow field are analyzed in depth,and some guidance suggestions are given for the optimum design of the cavitation reactor.In terms of optimization design,from the point of view of energy conversion,taking the size of cavitation volume as the optimization criterion,the steady RANS method is used to simulate the cavitation flow field,and the cavitation reactor with different divergence angles(β)and different throat characteristic parameters(γ)are simulated and analyzed under different inlet pressures under different conditions.The optimization results are determined: γ= 0.67,β= 10 ° and inlet pressure of inflow 0.6MPa.In the research of unsteady characteristics of cavitation flow field,large eddy simulation(LES)method is used to carry out numerical research of transient flow field and experimental study of clear water medium.LES was used to further study the spatio-temporal evolution of the new Venturi cavitation flow field.It was found that the cavitation flow field has quasi-periodic characteristics and the cloud cavitation shedding mechanism was analyzed.High-speed photography of flow field,wall pressure fluctuation measurement and collapse noise measurement were carried out.The flow structure and frequency characteristics of cavitation flow field are analyzed by proper orthogonal decomposition(POD)and dynamic mode decomposition(DMD).Cavitation shedding and collapse have a great influence on pressure fluctuation of flow field.The intensity of cavitation collapse can be indirectly judged by means of the average sound pressure level of noise.The frequency domain characteristics of the collapse noise show that cavitation collapse significantly increases the high frequency component.In terms of cavitation degradation,the degradation experiments are carried out with Rhodamine B,Ofloxacin and disinfection by-products as treatment objects.First,the degradation test of a certain concentration of rhodamine B was carried out under several operating conditions,and the maximum degradation rate was 16.7% after 40 min cyclic degradation of the system.The optimum operating conditions of the new cavitation reactor are determined as inlet pressure0.4MPa and outlet pressure 0.05 MPa.Then,Ofloxacin as degraded pollutant was compared with the previous test results,and the number of passes was proposed as an objective index to evaluate the degradability of the cavitation reactor.By calculation,the new Venturi tube is 4 times more degradable than the porous plate.The treatment effect under acid condition is better than that under neutral condition.Finally,the degradation test of disinfection by-products was carried out with this type of cavitation reactor.to verify the degradation effect of mixed pollutants and to illustrate the potential of hydrodynamic cavitation technology to treat such pollutants.The influence of flow characteristics on degrading efficiency was revealed through clear water and degrading experiments.Cavitation number,intensity of cavitation collapse and periodic frequency of flow field all affect the productivity of ·OH,but they are mutually restricted and cannot reach the optimum value at the same time.The degrading efficiency of cavitation reactor is the result of the combination of the above flow characteristics.