Vortex based hydrodynamic cavitation reactors offer various advantages like early inception, less erosion and higher cavitational yield. No systematic modelling efforts have been reported to interpret the cavitation performance of these vortex based devices for cavitation. It is essential to develop a modelling framework for describing performance of cavitation reactors. We have addressed this need in the present work. A comprehensive modelling framework comprising three layers: per-pass performance models (overall process), computational fluid dynamics models (flow on reactor scale) and cavity dynamics models (cavity scale) is developed. The approach and computational models were evaluated using the experimental data on treatment of acetone-contaminated water. The presented models were successful in describing the experimental data using initial cavity size as an adjustable parameter. Efforts were made to quantify optimum operating conditions and scale-up. The developed approach, models and results will provide useful design guidelines for pollutant degradation using vortex based cavitation reactors. It will also provide a sound and useful basis for comprehensive multiscale modelling of hydrodynamic cavitation reactors.

The interest in cavitating flow reactors has intensified over recent years, and a significant amount of research effort has been focussed on demonstrating the potential applications of hydrodynamic cavitation. The knowledge base on the design of devices to optimise cavitation yield, performance and industrial scalability remains lacking however. It is essential to develop a sound understanding of the key hydrodynamic characteristics of cavitation devices to address these knowledge gaps. This work presents a comprehensive experimental and numerical investigation into the hydrodynamic behaviour of cavitating devices which feature linear and swirling flows. Two of the most commonly utilized cavitation device geometries are studied, namely orifice and Venturi, with and without swirl. These devices are compared to a high swirl flow device (vortex diode). A series of experimental configurations were designed with the aid of multiphase, unsteady computational fluid dynamics simulations, so as to achieve matching power input in terms of flow rate versus pressure drop across all 5 device configurations, allowing their cavitation characteristics to be directly compared on a consistent basis. High speed flow visualisation and detailed numerical predictions are presented which clearly describe the influence that key parameters such as swirl ratio and Reynolds number have on the nature of the observed cavitating flow structures. Cavitation inception conditions are described for each device, with Venturi and vortex devices shown to generate incipient cavitation at lower pressure ratios than orifice devices. Cavitation numbers are computed, which indicate that values of unity are obtained at inception across the range of devices provided that appropriate characteristic velocities are defined. Swirl is identified as an important parameter in cavitation device design, with the swirling flow device designs shown to successfully move the cavitating region away from solid surfaces towards the device axis. Importantly, this is achieved without an energy consumption penalty; the results describe how swirl can be utilized to design devices which minimise or eliminate the risk of surface erosion.

Hydrodynamic cavitation (HC) may be harnessed to intensify a range of industrial processes, and orifice devices are one of the most widely used for HC. Despite the wide spread use, the influence of various design and operating parameters on generated cavitation is not yet adequately understood. This paper presents results of computational investigation into cavitation in different orifice designs over a range of operating conditions. Key geometric parameters like orifice thickness, hole inlet sharpness and wall angle on the cavitation behaviour is discussed quantitatively. Formulation and numerical solution of multiphase computational fluid dynamics (CFD) models are presented. The simulated results in terms of velocity and pressure gradients, vapour volume fractions and turbulence quantities etc. are critically analysed and discussed. Orifice thickness was found to significantly influence cavitation behaviour, with the pressure ratio required to initiate cavitation found to vary by a factor of 10 for orifice thickness to diameter (l/d) ratios in the range of 0-5. Inlet radius similarly has a pronounced effect on cavitational activity. The results offer useful guidance to the designer of HC devices, identifying key parameters that can be manipulated to achieve the desired level of cavitational activity at optimised hydrodynamic efficiencies. The models can be 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 HC device. The presented approach and results offer a useful means to compare and evaluate different cavitation device designs and operating parameters.

This paper details the numerical analysis of different vaned and vaneless radial inflow turbine stators. Selected results are presented from a test program carried out to determine performance differences between the radial turbines with vaned stators and vaneless volutes under the same operating conditions. A commercial computational fluid dynamics code was used to develop numerical models of each of the turbine configurations, which were validated using the experimental results. From the numerical models, areas of loss generation in the different stators were identified and compared, and the stator losses were quantified. Predictions showed the vaneless turbine stators to incur lower losses than the corresponding vaned stator at matching operating conditions, in line with the trends in measured performance. Flow conditions at rotor inlet were studied and validated with internal static pressure measurements so as to judge the levels of circumferential nonuniformity for each stator design. In each case, the vaneless volutes were found to deliver a higher level of uniformity in the rotor inlet pressure field.

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