Hydrodynamic Cavitation And Numerical Simulation With CFD

Cavitation is the phenomenon that microbubbles (or called gas nucleus) suddenly grow due to local lower pressure in the liquid and then collapse. Based on the cavitation generation,the cavitation is classified into four types, including acoustic cavitation, optic cavitation, particle cavitation and hydrodynamic cavitation. Hydrodynamic cavitation can occur in the sudden change of piping diameter, hydraulic machinery and so on. The process intensification can be accomplished by energy release in an instant of bubbles collapse.To investigate the mechanism of hydrodynamic cavitation and the fundamentals of its intensificaion law, the detailed studies has been made. The experimental equipments of hydrodynamic cavitation were built. The CFD software FULENT was used to simulate the flow fields of cavitation based on computer fluid dynamics. The hydroxyl radical induced by hydrodynamic cavitation was measured with methylene blue as the catcher. Three types of equipments of hydrodynamic cavitation including orifice plate, composite equipment of orifice plate and cantilever reed, rotating cavitation equipment were studied to obtain the optimum hydrodynamic cavitation condititions.From the studies, the conclusions can be drawn. (1) In FLUENT, the hydrodynamic cavitation with orifice plate was simulated with the standard k ?? model and the cavitation bubble dynamics model. The results showed that the increase of inlet pressure could enhance cavitation effect when outlet pressure was invarible. The strength of cavitation also increased with the increase of diameter and amount of orifices, and it decreased with the increase of liquid density and liquid viscosity. When the initial gas fraction increased, the strength of cavitation increased first but then droped.(2) The relationship between the amount of hydroxl radicals induced in hydrodynamic cavitation and the strength of hydrodynamic cavitation was quantitatively established. And methylene blue was used as the catcher for hydroxyl radicals and an ultraviolet-visible spectrophotometer was used to measure the amount of induced hydroxyl radicals.(3) The strength of hydodynamic cavitation of orifice plate increased with the increase of the inlet pressure. And decreased with the increase of the diameter and amount of orifices. When the liquid rate was invarible, the strength of cavitation increased with the ratio of total perimeter of holes to the total area of the holes.(4) The strength of cavitation of composite equipment of orifice plate and cantilever reed increased with reduction in the cavitation number. When the inlet pressure increased, the strength of cavitation also increased. Compared with single- hole orifice plate, the strength of cavitation of composite equipment increased obviously, which may reach 26.7% most greatly. When the distance of reed to orifice plate and the free reed length decreased, the amount of hydroxyl radical increased, the strength of cavitation also increased.(5) The strength of cavitation of rotating cavitation equipment increased firstly, and then decreased with the increase of the liquid rate . The results showed that optimum flow existed to reach the maximum strength of cavitation.