Eulerian–Lagrangian modeling of phase transition for application to cavitation-driven chemical processes

Hydrodynamic cavitation (HC) is a promising technology for several applications, like disinfection, sludge treatment, biodiesel production, degradation of organic emerging pollutants as pharmaceutical, and dye degradation. Due to local saturation conditions, cavitating liquid exhibit generation, growth, and subsequent collapse of vapour- filled cavities. The cavities’ collapse brings very high pressure and temperature; this last aspect is essential in some chemical processes because it induces the decomposition of water molecules into species with a high oxidation poten- tial, which can react with organic substances. Properly exploiting this process requires a highly accurate prediction of pressure peak values. To this purpose, we implemented a multi-phase Eulerian-Lagrangian code to solve the fluid-dynamic problem, coupled with the Rayleigh- Plesset equation, to capture the evolution of bubbles with the required accuracy. The algorithm was validated against experimental data acquired with optical techniques for different cavitation-shedding mechanisms. Then, we used the developed tool to investigate the decolouration of organic substances from a cavitation Venturi tube operating at different pressure. We compared the obtained results with the experimental observation to assess the reliability of the developed code as a predictive tool for cavitation and the possibility of using the code itself to assess scale-up criteria for possible industrial applications.