Explore the vast range of titles available.

The article deals with the modeling of high-energy cavitation processes, such as shock waves, cavitation erosion, bubble glow (sonoluminescence), etc., in a high-intensity acoustic field. It is shown that the well-known model based on the Keller–Miksis and Bjerknes equations does not correspond to a number of experimental data obtained in the study of a “single” cavitation bubble pulsating motionlessly in the antinode of a standing wave and an “ordinary” bubble moving in a cavitation cloud. To eliminate these inconsistencies, a new system of equations is proposed, which additionally takes into account the nonequilibrium processes of vapor evaporation and condensation and the imperfection of the vapor–gas mixture in the bubble, as well as the translational motion of the bubble. It is shown that with rapid compression of the bubble, the vapor inside it does not have time to condense and strongly damps this compression. The resulting equation explains the strong dependence of the intensity of “single” bubble glow on the temperature of the liquid. Contradictions in the description of the translational motion of bubbles associated with the application of the Bjerknes equation are eliminated. It is shown that a translationally moving bubble is compressed much weaker than a stationary one, since in the compression phase the energy of the radial motion of the bubble flows into the energy of translational motion. This allows us to explain the reason for the difference in the mechanisms of light emission from bubbles of different types. A “single” bubble emits light at maximal compression due to heating of the vapor–gas mixture up to 5000–10 000 K. Bubbles in a cavitation cloud move progressively, and their glow, in the absence of strong compression, is caused by micro-discharges in the vapor–gas phase during deformation of the bubble surfaces.

An analysis of literature sources in the field of the use of cavitation technologies has shown that the effects of cavitation are used in a wide range of industrial technologies. This paper presents the main results of work on the cavitation treatment of various liquid compositions, multicomponent media in recent decades. The presented review allows us to conclude that the use of cavitation technologies in various fields of engineering and technology is relevant for solving important practical problems and, as a result, the need for their comprehensive study.

The phenomena of cavitation and cavitation erosion affect hydraulic machines, increasing their maintenance costs. Both these phenomena and also the methods of preventing the destruction of materials are presented. The compressive stress in the surface layer created from the implosion of cavitation bubbles depends on the aggressiveness of the cavitation, which in turn depends on the test device and test conditions, and also affects the erosion rate. Comparing the erosion rates of different materials tested using different tests devices, the correlation with material hardness was confirmed. However, no one simple correlation was obtained but rather several were achieved. This indicates that in addition to hardness, cavitation erosion resistance is also affected by other properties, such as ductility, fatigue strength and fracture toughness. Various methods such as plasma nitriding, shot peening, deep rolling and coating deposition used to increase resistance to cavitation erosion by increasing the hardness of the material surface are presented. It is shown that the improvement depends on the substrate, coating material and test conditions, but even using the same materials and test conditions large differences in the improvement can be sometimes gained. Moreover, sometimes a slight change in the manufacturing conditions of the protective layer or coating component can even contribute to a deterioration in resistance compared with the untreated material. Plasma nitriding can improve resistance by even 20 times, but in most cases, the improvement was about two-fold. Shot peening or friction stir processing can improve erosion resistance up to five times. However, such treatment introduces compressive stresses into the surface layer, which reduces corrosion resistance. Testing in a 3.5% NaCl solution showed a deterioration of resistance. Other effective treatments were laser treatment (an improvement from 1.15 times to about 7 times), the deposition of PVD coatings (an improvement of up to 40 times) and HVOF coatings or HVAF coatings (an improvement of up to 6.5 times). It is shown that the ratio of the coating hardness to the hardness of the substrate is also very important, and for a value greater than the threshold value, the improvement in resistance decreases. A thick, hard and brittle coating or alloyed layer may impair the resistance compared to the untreated substrate material.

The modelling of internal and external flow phenomena of high pressure injection systems has developed significantly in the last few decades. The challenge currently however, is to model these areas of flow together accounting for different multi-phase phenomena that require a wide range of resolutions. More specifically, the highly turbulent nature of internal nozzle cavitation requires a high grid and temporal resolution, whereas the external nozzle atomisation processes exists over a comparatively much larger space with lower time and space resolution needed. The research described in this thesis is focused on coupling the internal nozzle and external processes using a single Eulerian Volume Of Fluid (VOF) multiphase model. First, investigations into the dynamics of internal nozzle cavitation is presented, through simulation of two phase nozzle flows without spray formation demonstrating sensitivities to discretization techniques and boundary conditions. Then, the simulation of internal nozzle cavitation with spray formation using a single model was achieved by the construction of a three phase VOF model with cavitation which is described. A non-condensable gaseous phase is considered alongside the liquid and vapours phases, the liquid interface is sharp with a diffusive interface between gaseous phases. Comparisons were made with both experimental data and previous numerical investigations. Finally, a new solver with the introduction of the Eulerian-Lagrangian Spray Atomization (ELSA) framework with the Interface Capturing Method (ICM) for surface density to the system to describe the liquid structures below the Sub-Grid Scale (SGS) is presented. Thus quantities such as droplet Sauter Mean Diameter (SMD) and droplet spray angle at these scales can be extracted, with comparisons made with experimental data. The coupling of the ELSA-ICM model with the three phase cavitating model allows for processes of the entire spray formation to be resolved. More specifically, for the first time, the evolving surfaces of the entire injection process, from internal nozzle cavitation to spray atomisation, can thus be tracked throughout even at the SGS. This allows for a direct insight into the interaction between the cavitation and atomisation processes.

The lifespan and structural integrity of various high temperature low stress applications are limited by creep damage. For most metals and alloys, cavitation damage is understood to be the dominant damage mechanism. Currently, there is no reliable and precise method for industries to model creep deformation and predict rupture time. The situation is even more challenging due to the strong stress level dependency of the minimum creep strain rate and creep lifetime. This research focuses on developing a cavitation-based method for predicting creep rupture time using early-stage creep data. For accuracy, cavitation data obtained using x-ray synchrotron tomography are chosen for the study. Two methods of calibrating damage criteria based on the cavitated area and volume fractions have been reported. From the calibrated damage criteria, relationships between creep exposure time and cavitation damage are developed to enable a time-based extrapolation method for predicting rupture time. This approach offers traceability as quantifiable physical changes in the material (cavity nucleation and growth rates) are calibrated. The cavitated volume fraction method offered better accuracy (87%) in assessing the level of damage in the material. The cavitated area fraction method produced 82% accuracy and was developed for comparison with current practices. The impact of cavity coalescence on the total number of cavities was illustrated, a result that suggests that evaluating damage via number of cavities per unit area can be erroneous. Furthermore, the research clearly identified the need of excluding measurements taken at the point of final rupture in creep lifetime modelling. This thesis contributes to the specific knowledge of modelling creep cavitation and rupture. It also offers a theoretical foundation and support for a time-based extrapolation approach of predicting creep lifetime. In addition, the cavitation modelling approach used in this study is expected to find application in other failure modes like fatigue.

With growing consumer demand for natural products, greener extraction techniques are found to be potential alternatives especially for pharmaceutical, nutraceutical, and cosmetic manufacturing industries. Cavitation-based technology has drawn immense attention as a greener extraction method, following its rapid and effective extraction of numerous natural products compared to conventional techniques. The advantages of cavitation-based extraction (CE) are to eliminate the application of toxic solvents, reduction of extraction time and to achieve better extraction yield, as well as purity. The cavitational phenomena enhance the extraction efficiency via increased mass transfer rate between the substrate and solvent, following the cell wall rupture, due to the intense implosion of bubbles. This review includes a detailed overview of the ultrasound-assisted extraction (UAE), negative pressure cavitation (NPC) extraction, hydrodynamic cavitation extraction (HCE) and combined extractions techniques which have been implemented for the extraction of high-value-added compounds. A list of essential parameters necessary for the maximum possible extraction yield has been discussed. The optimization of parameters, such as ultrasonic power density, frequency, inlet pressure of HC, extraction temperature and the reactor configuration denote their significance for better efficiency. Furthermore, the advantages and drawbacks associated with extraction and future research directions have also been pointed out.

The cavitation development process in regulating valve under different inlet pressures is investigated experimentally and numerically in our paper. The influence of inlet pressure P in on cavitation location, shape, area and intensity is studied in axial and radial directions, and the axial and radial pressure distributions are also analyzed. The cavitation is generally annular in shape radially and irregular polygon in shape axially. Cavitation bubbles occur at the throat entrance when the inlet pressure increases. The bubbles then accumulate, and a bubble ring is formed. The cavitation development process under different inlet pressures is separated into three stages, no-cavitation, initial cavitation and steady-cavitation stages. During the no-cavitation stage, no bubbles exist. During the initial cavitation stage, bubbles occur and the area and intensity of cavitation increase in the radial and axial directions with increasing inlet pressure. During the steady-cavitation stage, the calculation area and intensity of bubble rings reach their maximum values and then remain stable. The cavitation bubbles extend downstream, and the area of cavitation ring and cavitation intensity increase with increasing inlet pressure. A slit exists between the upper and lower parts of bubbles in the cavitation process, both parts touch each other forming a whole.

Abstract Even though the list of references associated with this review is rather extensive, in no way does it exhaust the vast literature dedicated to the study of cavitation. The intent was to summarize (i) advances in analytical and numerical modelling, (ii) draw attention to the thermodynamic aspects of cavitation, and (iii) do so while reflecting on physical or experimental observations.

The phenomena of cavitation and cavitation corrosion exist widely in the fields of hydraulic machinery, ship propulsion, water conservancy, and hydropower etc., which often bring negative impacts, but their research is significant for energy-saving technology. This paper discusses the importance of pump cavitation and cavitation from numerical simulation and experimental measurement. Numerical simulations reveal that cavitation in centrifugal pumps begins at the impeller inlet vanes, and the extent of the cavitation bubbles increases and expands along the flow path. When serious, the vane outlet flow velocity increases, causing a vortex, affecting the normal work of the pump, reducing the operating efficiency, and increasing the energy consumption. Reducing cavitation through optimised design can improve efficiency, reduce energy consumption, and help save energy. In terms of experimental research, the method, process, and results of the cavitation test are introduced. Cavitation wear causes changes in equipment characteristic curves and loss of quality, resulting in reduced efficiency, shorter life, and increased energy consumption. The study of the cavitation mechanism, the development of cavitation-resistant materials, and the optimisation of design can extend equipment life and reduce energy consumption. Finally, this paper proposes the development direction of cavitation research, including in-depth investigation of the micro-mechanisms, development of more accurate simulation and measurement techniques, and optimisation of design and material selection in combination with energy-saving requirements to reduce cavitation and improve the energy-saving performance of equipment.