Numerical Investigation into the Chemistry Induced by Hydrodynamic Cavitation

Abstract

The chemical effects induced by acoustic cavitation (popularly known as sonochemical effects) in aqueous medium are well-known and are attributed to the production of various radicals during bubble collapse. Under the influence of pressure variation due to acoustic wave, the bubble expands with the evaporation of water at the gas−liquid interface. This water vapor condenses at the gas−liquid interface during compression. At the final moments of bubble collapse, the dynamics of bubble motion is far more rapid than the diffusion dynamics of water vapor. Therefore, not all the water vapor that has entered the bubble during expansion escapes during compression. The entrapped water molecules are subjected to extremely high temperature and pressure reached during bubble collapse and undergo cleavage to produce various radicals. These radicals are then mixed with the bulk, where they induce various chemical reactions. Similar chemical effects have also been demonstrated by hydrodynamic cavitation, produced because of bubble oscillation and collapse driven by pressure variation in liquid flow. In this work, we try to give a numerical explanation to the sonochemical effects induced by hydrodynamic cavitation. Using a simplified ordinary differential equation (ODE) model for the dynamics of argon bubbles (released because of pressure reduction in the flow) with associated heat and mass transfer, we show that the phenomena of water vapor entrapment and cleavage due to extremes of temperature and pressure at bubble collapse also occur in hydrodynamic cavitation. We also try to investigate the effect of several operating parameters on the extent of water vapor entrapment, the extreme conditions of pressure and temperature generated in the bubble during collapse, and the production of radicals.