Experimental Study On Enhancive Effect Of Hydrodynamic Cavitation

Hydrodynamic cavitation is a new method of energy use due to its ability to enhance chemical processes. It generates extremely high temperature and pressure during the violent collapse of cavities, which destroys the molecular bond of water and forms free radicals. The strong oxidbillity of free radicals are responsible for enhancing chemical processes. And the high velocity of jet, shock wave, high intensity of turbulence generated by cavitation causes enhancing physical processes.In order to research the mechanism and effect of hydrodynamic cavitational enhancement, find the basic rule which affected it. The work has been carried out as following.First, an effective equipment of hydrodynamic cavitition is built. Second, we find a new method to capture the free radicals, which is used to measure the amount of hydroxyl. And its correlation with the intensity of cavitation has been studied aims at analyzing the effect of various factors on the yield of hydroxyl, achieving the optimum hydrodynamic cavitation conditions. Then, hydrodynamic cavitation is used to the degradation of organic wastewaters containing rhodamine B, and sterilization of biologic wastewaters containing enterobacter aerogenes. Finally, numerical simulation based on computer fluid dynamic (CFD) has been made for verifying the effect of hydrodynamic cavitation theoretically.From the results obtained in the study, the following conclusions can be made:The methylene blue and spectrophotometer method can capture the free radicals generated successfully. This is an effective way to measuring the free radicals quantitatively in cavitation, moreover it is easy to fulfill.The intensity of cavitation increases with reduction in the cavitation number. But the different mechanism of various enhancive processes (chemical and physical processes) results in different effect by cavitation number.The effect of operating parameters, such as inlet pressure, temperature and time on cavitation indicate that optimum operating conditions exist at the cavitation enhancive effect is maximum.It is important to optimize the structure of hydrodynamic cavitation reactor for achieving a desired effect. A reasonable geometric parameter can promote the enhancive effect for a fixed hydrodynamic condition.Ventilating appropriate gas to cavitating flow can increase cavitational intensity and hence promote the enhancive effect of hydrodynamic cavitation. It works reversely while the gas rate is large enough.Results of numerical simulation for venturi cavitation reactor show that the vapour volume fraction and turbulent kinetic energy in cavitational area are much higher than in the rest area. The vapour volume fraction and turbulent kinetic energy are quite high in the reactor's optimum geometric parameters condition.