Study of hydrodynamic cavitation in static appliances for industrial application

Cavitation identifies the appearance of vapor cavities inside an initially homogeneous liquid medium. Bubbles formation and growth are due to a sharp decrease of local pressure below the saturation pressure of the state. Once the fluid flow returns to the higher-pressure state, the bubbles collapse releasing a large amount of thermal and pressure energy. Due to the high energy released, different potential processes to exploit it have been considered. The theoretical possibility of using cavitation for wastewater treatment is highlighted in the literature. Researchers have recognized in Hydrodynamic cavitation a promising technology, suitable for this purpose. One of the more promising geometries adopted is the so-called “Venturi” tubes. Unfortunately, until now no standard procedures for the design of this type of cavitation reactor have ever been established. THe idea is to define a procedure for the design of the cavitating device (Venturi tube) and develop an optimized geometry for it, working on the main geometrical parameters to obtain a configuration granting consistent cavitation and high efficiency. The focus of this research has been the evaluation of which are the most important parameters defining the performances of a Venturi tube and the development of a stable and efficient cavitation field. In particular, cavitation seems to be favored by: wall geometry, turbulence, unsteady natural flow, roughness, and vibratory motion. The design of a Venturi tube is characterized by a higher number of degrees of freedom with respect to the orifice case, for example, as its geometry is defined by more than one parameter. It's crucial to understand the effect of the singles. In particular high influence is given to: ratio of the perimeter of the throat to its open area, pressure recovery rate, Slit Height to Length Ratio. To simplify the design process, a correlation involving the two adimensional parameters characterizing the cavitation process was considered: cavitation number and resistance number . This relationship, obtained for the single geometry allows to simplify a lot the optimization, giving analytical relationships involving parameters otherwise only obtained by CFD simulations. We are so moving in the direction of finding some specific 1D equations to optimize the geometry.