Engineering Design of Hydrodynamic Cavitation Reactors

Analysis on the Basis of Bubble Dynamics The bubble behavior and hence the pressure pulse generated at the collapse of the cavity in the case of hydrodynamic cavitation depends upon the operating conditions as well as the geometry of the mechanical constriction that results in the generation of cavitating conditions downstream of the orifice. Thus, as a first step towards the design of hydrodynamic-cavitation reactors, it is important to understand the relationship between the cavity behavior and the operating parameters and possibly quantify the intensity of cavitation and then the net cavitational effects as a direct function 

The bubble-dynamics equations are very similar to acoustic cavitation the only difference being the fact that the surrounding fluctuating pressure field is driven by hydrodynamic conditions existing downstream of the constriction, whereas in the case of acoustic cavitation, it is dependent on the frequency and intensity of the ultrasonic irradiation (sinusoidal variation). There are two approaches used for the estimation of the local pressure at any location downstream of the constriction (the typical pressure recovery profiles are shown in Fig. 8.2.6). 

Without turbulence In such a case, the local pressure at any downstream position can be estimated as  

Pf is the final recovered pressure, which depends on the pressure loss arising due to the presence of the constriction. The typical radius history obtained for such a case is exactly similar to stable cavitation, as discussed earlier (Fig. 8.2.2). Such low magnitude pressure pulses are unlikely to bring about the physical/chemical effects observed in the case of hydrodynamic-cavitation reactors (Save et al., 1997, Suslick et al., 1997, Vichare et al., 2000b) and hence this approach is not suitable and the predictions cannot be relied upon. 

The instantaneous turbulent velocity at a certain position was calculated by assuming a sinusoidal velocity variation in the instantaneous local velocity (V ) with a frequency of the velocity perturbation (similar to the case of acoustic cavitation) and is given by  

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