Numerical investigation of effect of geometric parameters on performance of rotational hydrodynamic cavitation reactor

Effect of protrusion structure on the performance of an advanced hydrodynamic cavitation reactor: An entropy-based analysis

Hydrodynamic cavitation (HC) has emerged as a promising technique for process intensification. Recently developed advanced rotational hydrodynamic cavitation reactors (ARHCRs) have attracted significant attention from both academia and industry due to their notable economic advantages, high processing capacity, and continuous operation in specific applications. However, existing evaluation and optimization criteria for these reactors primarily rely on external parameters, often overlooking the complex micro-scale properties and energy dissipation of internal flow within the cavitation generation unit (CGU) of ARHCRs. To address this, a "simplified flow field" computational flow dynamics (CFD) approach combined with entropy production theory was employed to assess the impact of protrusion installation upstream of the CGU on ARHCR performance. The cavitation volume and total entropy generation were analyzed for protrusions of various shapes, circumferential offset angles (γ), radial positions (r), and side lengths (s). The findings revealed that energy dissipation in ARHCRs is predominantly localized in regions of flow separation and vortex formation within the CGU. Furthermore, an evaluation of multiple design factors identified that a triangular protrusion with a γ of 3.75°, r of 122.5 mm, and s of 1 mm achieved optimal performance. Comparative analysis of the flow field and vortex structures between the triangular protrusion and the baseline model demonstrated that the protrusion modifies downstream vortex dynamics, stabilizes the clearance flow field, and reduces entropy production. Additionally, these flow field modifications expand the low-pressure region, thereby enhancing cavitation performance. In this study, the employed entropy production theory identified the spatial distribution of energy loss and the dominant energy dissipation pathways within the ARHCR, thereby revealing the underlying energy loss mechanism associated with vortex formation and flow separation. These insights contribute to a deeper understanding of energy efficiency in ARHCRs and offer a foundation for optimizing reactor design to minimize energy consumption and enhance process intensification.

Investigation on the cavitation characteristic of a novel cylindrical rotational hydrodynamic cavitation reactor

Hydrodynamic cavitation reactors are of great promise for the applications of chemical process intensification and water treatment. In this work, a novel cylindrical rotational hydrodynamic cavitation reactor (CRHCR) with rectangular grooves and oblique tooth protrusions on the rotor surface was studied. The three-dimensional characterization of cavitation within the CRHCR was observed from the front and left views by the high-speed camera experiments. Interestingly, a new phenomenon of simultaneous formation of the attached cavitation and shear cavitation was found in the CRHCR. The synergistic effect of attached cavitation and shear cavitation contributes to the enhancement of the cavitation performance of CRHCR. In addition, the evolution of attached cavitation is explored. It is found that attached cavitation forms a trapezoidal-shaped cavitation cloud in the groove, which undergoes three various stages: incipient, development, and collapse. Finally, the pulsation frequency and cavitation intensity of shear cavitation in the chamber were investigated. The results show that the cavitation pulsation frequency is the same at the same rotational speed in the chamber near diverse oblique teeth. As the rotational speed increases, the cavitation pulsation frequency increases linearly. These findings in this paper are of great benefit to understanding the mechanism of the cavitation effect of CRHCR.

Numerical simulation of cavitation-vortex interaction mechanism in an advanced rotational hydrodynamic cavitation reactor

Hydrodynamic cavitation (HC), a promising technology for enhancing processes, has shown distinct effectiveness and versatility in various chemical and environmental applications. The recently developed advanced rotational hydrodynamic cavitation reactors (ARHCRs), employing cavitation generation units (CGUs) to induce cavitation, have demonstrated greater suitability for industrial-scale applications than conventional devices. However, the intricate interplay between vortex and cavitation, along with its spatial-temporal evolution in the complex flow field of ARHCRs, remains inadequately elucidated. This study investigated the interaction mechanism between cavitation and vortex in a representative interaction-type ARHCR for the first time using the "simplified flow field strategy" and the Q-criterion. The findings reveal that the flow instability caused by CGUs leads to intricate helical and vortex flows, subsequently giving rise to both sheet and vortex cavitation. Subsequently, utilizing the Q-criterion, the vortex structures are identified to be concentrated inside and at CGU edges with evolution process of mergence and separation. These vortex structures directly influence the shape and dimensions of cavities, establishing a complex interaction with cavitation. Lastly, the vorticity transport equation analysis uncovered that the stretching and dilatation terms dominate the vorticity transport process. Simultaneously, the baroclinic term focuses on the vapor-liquid interface, characterized by significant alterations in density and pressure gradients. These findings contribute to a better comprehension of the cavitation-vortex interaction in ARHCRs.