Flow regime maps and optimization thereby of hydrodynamic cavitation reactors

Abstract

Hydrodynamic cavitation reactors are known to intensify diverse physical and chemical processes. In this article, flow regime maps have been proposed that give an overview of the operation of hydrodynamic cavitation reactor for different combinations of design and process parameters. These maps are based on simulations of cavitating flow using mathematical model that couples continuum mixture model with diffusion limited model. Specific flow regimes have been identified depending on the energetics of the collapse of cavitation bubble as sonophysical, sonochemical, and stable oscillatory (no physical or chemical effect). The radial motion of the bubble in the cavitating flow is governed by the mean and turbulent pressure gradients, which in turn, are decided by the design parameters. An analysis of variations in the pressure gradients in the cavitating flow with design parameters has been given. The flow regime maps form a useful tool for identification of most optimum set of design parameters for hydrodynamic cavitation reactor for a physical or chemical process. © 2012 American Institute of Chemical Engineers AIChE J, 58: 3858–3866, 2012

Solvent degradation studies using hydrodynamic cavitation

“…This behavior can be attributed to choked cavitation-increase in inlet pressure is expected to give rise to choke cavitation as formation of large number of cavities at inlet pressure beyond optimum value result into cavities coalescence and formation of larger vaporous bubbles that get carried away with the flowing liquid without collapsing [ [11], [30][31][32]]. The trend observed for the cavitation number in orifice is similar to vortex diode; the cavitation number decreases with increase in pressure drop indicating higher cavitation events at lower Cv similar to that reported in literature [33,34]. In orifice, above Dp of 5 bar, the cavitation number was found constant indicating choked cavitation.…”

Chemical effect of hydrodynamic cavitation: Simulation and experimental comparison

“…The integration of SBD ODE system gives the spatial prediction of the main variables downstream the constriction as represented in the sketch of mathematical algorithm (see Figure ). This way of showing numerical results is widely used in the literature as first rough way to understand the cavitation intensity . The variations of bubble radius and temperature are shown in Figure , for a bubble of initial radius R 0 = 20 μm and three values of inlet pressure p in = 0.2, 0.4, 0.6 MPa.…”

“…The core of the algorithm is the simulation of the reactive cavitating bubble, by considering the five ordinary differential equations (ODEs) summarized in Table . This approach is in continuity with other research articles and assumes the diffusion limited model with a boundary layer approximation introduced by Storey and Szeri and Toegel et al A similar approach, which couples momentum and continuity equation, is described in a recent work that reports different maps of cavitation regimes obtained by varying the operating parameters.…”

“…The integration domain [0 ≤ x ≤ L ] is the length of a cavitating device: a convergent–divergent nozzle, symmetric to the x axis, with a cross section A . The model also includes the estimation of turbulent fluctuation velocity downstream of the orifice, following the approach first proposed by Moholkar and Pandit and recently developed by Kumar et al It allows the calculation of the local velocity by adding the turbulent term to the mean flow contribution, u, derivable from the continuity equation.…”

“…Numerical studies, focused on the dynamics of a reactive‐collapsing bubble, give the necessary physical insight for an extensive technology development: prediction of collapse pressure, temperature peaks, and concentration of chemical species. Two seminal papers published in 2000 18,19 proposed that bubble dynamics are limited by diffusion and paved the way for several studies on HC applications . A short historical review is given in the work by Sharma et al…”