Modeling hydrodynamic cavitation in venturi: influence of venturi configuration on inception and extent of cavitation

Hydrodynamic cavitation (HC) is useful for intensifying a wide variety of industrial applications including biofuel production, emulsion preparation and wastewater treatment. Venturi is one of the most widely used devices for hydrodynamic cavitation. Despite the wide spread use, the role and interactions among various design and operating parameters on generated cavitation is not yet adequately understood. This paper presents results of computational investigation into the cavitation characteristics of different venturi designs over range of operating conditions. Influence of the key geometric parameters like length of venturi throat and diffuser angle on the inception and extent of cavitation is discussed quantitatively. Formulation and numerical solution of multiphase computational fluid dynamics (CFD) models are presented. Appropriate turbulence model and cavitation model are selected and solved using commercial CFD code. Care was taken to eliminate influence of numerical parameters like mesh density, discretisation scheme and convergence criteria. The computational model was validated by comparing simulated results with three published data sets. The simulated results in terms of velocity and pressure gradients, vapour volume fractions and turbulence quantities etc. are critically analysed and discussed. Diffuser angle was found to have a significant influence on cavitation inception and evolution. The length of the venturi throat has relatively less impact on cavitation inception and evolution compared to the diffuser angle. The models and simulated flow field were used to simulate detailed time-pressure histories for individual vapour cavities, including turbulent fluctuations. This in turn can be used to simulate cavity collapse and overall performance of hydrodynamic cavitation device as a reactor. The presented results offer useful guidance to the designer of hydrodynamic cavitation devices, identifying key operating and design parameters that can be manipulated to achieve the desired level of cavitational activity. The presented approach and results also offer a useful means to compare and to evaluate different designs of cavitation devices and operating parameters.