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.

Physical mechanism of sono‐Fenton process

“…We refer the reader to our earlier article for a review of these studies. 31 We have used the diffusion limited ordinary differential equation (ODE) model using boundary layer approximation proposed by Toegel et al for our analysis, 32 which is based on the comprehensive PDE model of Storey and Szeri, 22 who showed that vapor entrapment in the cavitation bubble, leading to formation of radicals is essentially a diffusion limited process. Large amount of evaporation occurs at the bubble interface during the expansion phase of bubble motion, and vapor molecules enter and diffuse toward the bubble core.…”

“…Although calculating the composition of the bubble at the time of collapse, we assume that thermodynamic equilibrium is attained. 31 The equilibrium mole fraction of the various species in the bubble at the conditions of temperature and pressure at first the compression of the …”

The Enhancement of H2O2/UV AOPs for the Removal of Selected Organic Pollutants from Drinking Water with Hydrodynamic Cavitation

“…It has to be noted that the hydrodynamic phenomena caused by HC are modelled by the complex hydraulic models and is the subject of numerous past and current research. [33][34][35] The description herein is provided solely for the readers to conceive the matter in an easier way. At the throat of the constriction the calculated v was approx.…”

Mechanistic analysis of ultrasound assisted enzymatic desulfurization of liquid fuels using horseradish peroxidase

“…Transport of solvent vapor in the bubble during radial motion, and its entrapment in the bubble at the moment of transient collapse leads to formation of radicals through thermal dissociation of the vapor molecules. Greater details on this model can be found in our previous papers (Krishnan et al, 2006;Sivasankar et al, 2007), as well as in the original papers (Toegel et al, 2000;Toegel and Lohse, 2003). For the convenience of the readers, essential equations and thermodynamic data of this model have been given in Tables S.1 and S.2 in the supplementary material.…”