110th Anniversary: Comparison of Cavitation Devices Based on Linear and Swirling Flows: Hydrodynamic Characteristics

The interest in cavitating flow reactors has intensified recently, and a significant amount of research effort has been focused on demonstrating the potential applications of hydrodynamic cavitation. However, the knowledge base on the design of devices to optimize cavitation yield, performance, and industrial scalability remains lacking. 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 behavior of cavitating devices that 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 (CFD) simulations, to achieve matching power input, in terms of flow rate versus pressure drop across all five device configurations, allowing their cavitation characteristics to be directly compared on a consistent basis. High-speed flow visualization and detailed numerical predictions are presented that 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 toward the device axis. Importantly, this is achieved without an energy consumption penalty; the results describe how swirl can be utilized to design devices that minimize or eliminate the risk of surface erosion.