Experimental and numerical study of cavitating flow with suction in a mixing reactor for water treatment

Hydrodynamic cavitation technology, as well as its collaborative technologies, have been widely studied in advanced oxidation processes (AOPs) for the engineering application of water treatments. Cavitation evolution process, which could be greatly changed by the injection (or suction) in cavitating flow, might significantly affect the efficiency of water treatment. However, few interests have been focused on the flow and mixing pattern of cavitating flow with injection. In this study, the interactions (including flow and mixing pattern) between cavitating flow and oxygen active species were investigated in a hydrodynamic cavitation mixing reactor. A visible experimental set-up was designed to capture the cavitation flow and mixing phenomena in this reactor. Besides, three-dimensional numerical simulations were conducted to gain further insight into the distribution of oxygen active species (OASs) in the reactor using commercial CFD code. Experimental results show that the change of cavitation structure might be related with the OASs suction. Numerical simulations demonstrated that vortices due to cavitation collapse caused the OASs mixing with the cavitating flow. Moreover, the lower the pressure ratio, the lower value of weighted coefficient variation of OASs volume fraction at outlet, resulted in better mixing quality. The findings of this work could offer theoretical supports for using hydrodynamic cavitation technologies over a wide range of applications in water pollution control.