Cavitation Zone Research Articles

Hydrodynamic Cavitation as a Method of Removing Surfactants from Real Carwash Wastewater.

The present work aimed to evaluate whether the use of an innovative method such as hydrodynamic cavitation (HC) is suitable for the simultaneous removal of surfactants of different chemical natures (non-ionic, anionic and cationic) from actual car wash wastewater at different numbers of passes through the cavitation zone and different inlet pressures. An additional novelty was the use of multi-criteria decision support, which enabled the selection of optimal HC conditions that maximized the removal of each group of surfactants and chemical oxygen demand (COD) with minimal energy input. For the optimal HC variants, Fourier transform infrared spectroscopy (FT-IR/ATR) as well as investigations of surface tension, zeta potential, specific conductivity, system viscosity and particle size were carried out. The highest reduction of non-ionic surfactants was found at 5 bar inlet pressure and reached 35.5% after 120 min. The most favourable inlet pressure for the removal of anionic surfactants was 3 bar and the removal efficiency was 77.2% after 120 min, whereas the most favourable inlet pressure for cationic surfactant removal was 3 bar, with the highest removal of 20% after 120 min. The obtained results clearly demonstrate that HC may constitute an effective, fast and cost-efficient method for removing surfactants from real industrial wastewater.

On the mechanism of growth of lactose crystals from supersaturated solutions

The substantiation of the existence of cavitation zones on the edges of a growing lactose crystal and its driving role in the crystal growth process is presented. It is shown that the most favorable conditions for the conversion of dissolved lactose into its crystalline form are created around the edges of the crystal in the phase transition zones. The size of the phase transition zone of the crystallizing substance is calculated and compared with the available data on the size of crystalline nuclei. The values of the radius of cavitation zones were obtained, which amounted to: nanometers (for a crystal with a size of 60.5 microns, at a temperature of 30°C and supersaturation of 0.55) and nanometers (for a crystal with a size of 84 microns, at a temperature of 50°C and supersaturation of 1.88). A mathematical model of the growth rate of lactose crystals in a supersaturated solution is proposed. The possibility of studying the mechanisms of crystallization and determining the growth rate of lactose crystals is substantiated, based on the theory of dynamic interaction of bodies and liquids by A. Y. Milovich.

Numerical analysis of hydrophobic surface effects on cavitation inception and evolution in high-speed centrifugal pumps for thermal energy storage and transfer systems

This study explores the influence of wettability surfaces on cavitation inception and evolution in high-speed centrifugal pumps used for thermal energy storage and transfer systems through numerical simulations. The simulations were conducted using the Kunz mass transfer model implemented in Fluent, combined with the Eulerian multiphase flow approach and the shear stress transport k–ω turbulence model. The cavitation dynamics were analyzed across contact angles ranging from superhydrophilic to superhydrophobic conditions. The results demonstrate that superhydrophobic surfaces delay cavitation onset compared to hydrophilic ones, reducing the critical cavitation coefficient by at least 28%. At flow rates of 1.11 Q0 and 0.89 Q0, cavitation numbers show distinct trends, with superhydrophobic surfaces enhancing cavitation stability and reducing the frequency of cavitation shedding. The reentrant jet dynamics are also affected, with increased hydrophobicity weakening the jets and stabilizing cavitation zones. This research aims to advance the understanding of using surface wettability to manage cavitation in high-speed centrifugal pumps, thereby improving the performance and reliability of thermal energy storage and transfer systems.

New insights into coarse particle lifting performance of a hydraulic ejector with an ultra-large area ratio

Hydraulic ejectors with ultra-large area ratios (HE-ULAR) have potential applications as particle lifting equipment in fluidized coal mining. This study analyzed the effects of area and pressure ratios on the coarse particle lifting performance of HE-ULAR. The cavitation, valid, and failure zones for coarse particle lifting were mapped out. The results show that the pressure gradient force acting on each particle is approximately 2.02–3.70 times greater than the drag force, indicating that the pressure gradient force is the more significant interaction force for particle migration under the influence of HE-ULAR compared to the drag force. Additionally, insufficient energy transfer between the energetic fluid and particles in the valid zone of HE-ULAR reduces the fluid energy density and particle lifting concentration at low pressure ratio conditions. The HE-ULAR exhibits optimal particle performance at the operating conditions with an area ratio of 12.51 and a pressure ratio of 0.0735. Finally, a series of prediction formulas for fluidized coal mining parameters were established based on the optimal operating condition of the HE-ULAR. These results will guide the application of the HE-ULAR in a fluidized mining system.

Spatiotemporal Evolution of Gas in Transmission Fluid under Acoustic Cavitation Conditions

The presence of gas in transmission fluid can disrupt the flow continuity, induce cavitation, and affect the transmission characteristics of the system. In this work, a gas void fraction model of gas–liquid two-phase flow in a transmission tube is established by taking ISO 4113 test oil, air, and vapor to accurately predict the occurrence, development, and end process of the cavitation zone as well as the transient change in gas void fraction. This model is based on the conservative homogeneous flow model, considering the temperature change caused by transmission fluid compression, and cavitation effects including air cavitation, vapor cavitation, and pseudo-cavitation. In this model, the pressure term is connected by the state equation of the gas–liquid mixture and can be applied to the closed hydrodynamic equations. The results show that in the pseudo-cavitation zone, the air void fraction decreases rapidly with pressure increasing, while in the transition zone from pseudo-cavitation to air cavitation, the air void fraction grows extremely faster and then increases slowly with decreasing pressure. However, in the vapor cavitation zone, the vapor void fraction rises slowly, grows rapidly, and then decreases, which is consistent with the explanation that rarefaction waves induce cavitation and compression waves reduce cavitation.

Investigation of Cavitation Flow and Entropy Production Characteristics in a Dual-Rotor Turbine Flowmeter

Flow meters are extensively utilized in fields such as chemical engineering, petroleum, and aerospace, and are an indispensable component of modern industry. This paper examines the metrological properties of a dual-rotor turbine flow meter within its measurable flow range through experimental approaches and investigates the cavitation flow dynamics within the flow meter using numerical methods. First, the flow characteristics curve of the dual-rotor turbine flow meter was established experimentally, and the accuracy of numerical simulation results was validated. Secondly, the transient characteristics of the cavitation cavity were revealed using the Z-G-B cavitation model and dynamic mesh technology. Finally, entropy production theory was applied to investigate the energy losses caused by cavitation, analyzing the contributions of different types of energy losses during the cavitation process. Flow calibration experiments and numerical simulations reveal an increase in the meter coefficient of the dual-rotor turbine flow meter in high-flow cavitation zones, indicating that the displayed flow rate is slightly higher during cavitation compared to non-cavitating flows. Transient cavitation flow undergoes three stages: attachment, development, and collapse. At 323 K, the volume fractions of upstream and downstream cavities increase by 38.9% and 48.3%, respectively, with the cavitation cycle duration being 1.21 times that at 298 K. At 343 K, these increases are 75.3% and 239.2%, with the cycle duration being 2.63 times that at 298 K. Among the various sources of loss, the contribution from losses due to pulsating velocity gradients is the most significant, with maximum proportions of 81.95%, 85.1%, and 87.11% at 298 K, 323 K, and 343 K, respectively.

Dual frequency ultrasonic liquid phase exfoliation method for the production of few layer graphene in green solvents

In this work, we implement a dual frequency (24 kHz and 1174 kHz) ultrasonic assisted liquid phase exfoliation (ULPE) technique in deionized water (DIW) and other eco-friendly solvents, to produce a variety of high-quality few-layer graphene (FLG) solutions under controlled ultrasonication conditions. The resulting FLG dispersions of variable sizes (∼0.2–1.5 μm2) confirmed by characterisation techniques comprising UV–Vis spectroscopy, Raman spectroscopy and high-resolution transmission electron microscopy (HR-TEM). For the first time we demonstrate that high yield of FLG flakes with minimal defects, stable for 6 + months in a solution (stability ∼ 70 %), can be obtained in less than 1-hour of treatment in either water/ethanol (DIW:EtOH) or water/isopropyl alcohol (DIW:IPA) eco-friendly mixtures.We also scrutinized the underlying mechanisms of cavitation using high-speed imaging synchronized with acoustic pressure measurements. The addition of ethanol or IPA to deionized water is proposed to play a central role in exfoliation as it regulates the extend of the cavitation zone, the intensity of the ultrasonic field and, thus, the cavitation effectiveness. Our study revealed that lateral sizes of the obtained FLG depend on the choice of exfoliating media and the diameter of a sonotrode used. This variability offers flexibility in producing FLG of different sizes, applicable in a wide spectrum of size-specific applications.

Rapid Failure of Lubricated Contacts with Grease Under ZEV Condition

Abstract In response to the rapid failure of grease lubrication under low surface speed with zero entraining velocity (ZEV), a common occurrence in ball screws or retainerless rolling element bearings, detailed observations were conducted through optical interferometric experiments. It was observed that despite a constant surface speed and load, the motion remained transient due to the transition between outlet cavitation and inlet starvation. The reciprocating motion of the cavitation zone rapidly depleted the contact area, leading to severe surface peeling. However, as the surface speed increased, this phenomenon was alleviated and eventually disappeared. To enhance lubrication performance, bilateral grooves were created using laser technology, proving to be advantageous for grease lubrication life under low surface speed conditions. Despite the occurrence of rapid surface failure, grease lubrication demonstrated clear benefits over oil lubrication when operating at low surface speeds.

High-speed photography and particle image velocimetry of cavitation in a Venturi tube

This article details the construction of an experimental visualization platform for observing cavitation. The platform uses high-speed photography and particle image velocimetry (PIV) techniques to conduct experimental research into the flow pattern and vortex field of cavitation in Venturi tubes. Dynamic mode decomposition is employed to extract the energy distribution characteristics of the cavitation flow field. Cavitation occurs at an exit-to-inlet pressure ratio of 0.595, and the length of the cavitation zone increases as this ratio decreases. When the pressure ratio reaches 0.280, the flow rate remains almost constant and the flow becomes chocked. The cavitation shape evolves periodically in the chocking flow, and the cavitation zone can be divided into three parts: an initiation and development area, a fusion area, and a collapse area. The fusion area exhibits periodic changes in the form of contraction, expansion, and re-contraction. Near the wall, the collapse area exhibits complex boundary conditions, with re-entrant jet causing bubble aggregation, rolling, and shedding. PIV and energy extraction reveal that vortices primarily appear near the wall, where they undergo a periodic process of fragmentation and fusion. The strength of the vortices exhibits a small–large–small pattern that is related to the cloud aggregation, rolling, and shedding caused by the re-entrant jet.

A method of spraying based on hydrodynamic and ultrasonic influence on the sprayed liquid

The article is devoted to the development of a sprayer based on the method of simultaneous hydrodynamic and ultrasonic influence on the flow of sprayed liquid. The proposed spraying method makes it possible to increase spraying productivity while reducing the size of aerosol droplets. By establishing optimal conditions, with a nozzle diameter of 0.7 mm, an ultrasonic tool diameter of 8 mm and an excess pressure of the sprayed liquid of 0.7 MPa, the atomizer provides a productivity of 9 ml/s and forms an aerosol with droplet sizes D32 = 40 μm. This is primarily due to the establishment of the optimal operating mode and conditions in the cavitation zone, which make it possible to ensure the highest quantitative concentration of cavitation bubbles.

Damage characteristics of ribbed cylinder in motion under near-field underwater explosion

The damage characteristics of a ribbed cylinder in the torpedo compartment shell is explored. An arbitrary Lagrange–Euler method is used to establish the fluid–structure interaction model for analyzing the ribbed cylinder’s response under near-field underwater explosion while in motion. The influence of detonation direction and standoff distance on the dynamic response of the moving ribbed cylinder is considered. The investigation reveals that the cylinder’s motion causes an uneven distribution of bubble load and secondary load, stemming from cavitation zone collapse, on the shell. This imbalance leads to a notable deflection difference between the shell’s front and rear sections, with maximum deformation concentration at the rear. In addition, in comparison to the lateral condition, static state analysis shows reduced average deflection and increased maximum deflection when the explosion point is above or below the shell, while in the sailing state, both average and maximum deflections increase. Notably, when the charge radius is between 6 and 15 times, the average damage rate in the sailing state consistently remains lower than that in the stationary state, while the maximum damage rate is higher at a specific burst distance.

Numerical investigation on design parameters of orifice plate for positioning of workpiece in cavitation zone for cavitation machining

ABSTRACT The recent development of non-traditional machining techniques, such as cavitation machining (CM), has been gaining traction amongst researchers due to its sustainable nature. The present research focuses on the use of computational fluid dynamics (CFD) model to predict the location of workpiece in the fluid domain and bubble distribution during CM process. For efficient CM, the correct positioning of a workpiece in cavitation zone is essential, as the implosion of the cavity bubble leads to formation of micro-jet and shock waves for a few milli-to-microseconds generating high temperature and pressure on workpiece. The aim is to harness cavitation phenomena in material processing, particularly by using orifice plates as a common tool to induce hydrodynamic cavitation. To generalise the investigation, the flow simulation through orifice plate with different aspect ratios (l/d) are carried out. For the bubble distribution and their diameters, the Lagrangian discrete phase model (DPM) is used in the downstream side of the flow domain. Using this information, bubble dynamics have also been investigated using the Keller–Miksis (KM) model to compute the implosion time and intensity in the zone. The presented exploration determines the orifice dimensions to optimize implosion intensity, ensuring precise workpiece placement in real-time CM.

Investigation of influence of geometry of jet orifice of throttling device on formation of cavitation

Throttling devices are used in hydraulic systems both as regulating valves and to provide protective functions, which determines the relevance of developing such a design that will ensure their cavitation-free operation. The aim of the study is to investigate cavitation phenomena in single-stage throttling devices with different geometry of the jet orifices in order to identify the geometric shape capable of minimizing cavitation. The paper presents a study of the effect of different geometric shapes of the orifices of single-stage throttling devices on cavitation formation in the low-pressure areas. In addition, the objective of the study is to investigate the influence of physical quantities (velocity and pressure) on cavitation formation and to carry out a comparative analysis by means of which the influence of the correlation between the geometrical shape of the orifice of the jets, the velocity of the working medium and the pressure in the area of the orifice of the jets on the formation of cavitation zones in the areas of reduced pressure is clearly demonstrated. The computational experiment was conducted using Ansys CFX software and was based on the Rayleigh-Plesset mathematical model of cavitation. The study investigated the possibility of cavitation phenomena in single-stage throttling devices, and identified the geometric shape of the jet orifice that promotes cavitation-free operation of the single-stage throttling device. Thus, the results of the study show that the jet with a conical orifice minimizes the volume fraction of vapor, arising during cavitation processes, in single-stage throttling devices. The conducted research has practical significance and can increase the service life of single-stage throttling devices by minimizing the formation of cavitation zones in areas of low pressure.

Experimental and numerical simulation investigation of cavitation phenomenon during bubble pulsation process

The current research on the cavitation phenomenon in the underwater explosion process is focused on the shock wave phase. In this study, it was found that there was also significant cavitation during bubble pulsation. Underwater explosion experiments were carried out at the bottom of a sheet using 2.5 g of TNT, which also showed that: (a) Cavitation lasts for the same duration as the bubble contraction time, (b) A cavitation closure pressure, the peak of which is greater than the bubble pulsation pressure, is produced by the closing of the cavitation zone. A tensile cut-off model was introduced to simulate the cavitation phenomenon during bubble pulsation, and the formation mechanism was investigated. The numerical simulation results show that: (a) The cavitation phenomenon is visible when the sheet above the explosive and the explosion distance are between 0.93 and 1.17 times the radius of the largest bubble, or between 0.69 and 1.85 times the maximum radius of the bubble when the sheet below the explosive, (b) The cavitation region and cavitation closure pressure increase and decrease with increasing explosion distance, peaking at a value close to one times the theoretical maximum bubble radius, and (c) The cavitation zone shrinks and the cavitation closing pressure drops as sheet thickness increases.

Characterization of the acoustic cavitation in ionic liquids in a horn-type ultrasound reactor

Most ultrasound-based processes root in empirical approaches. Because nearly all advances have been conducted in aqueous systems, there exists a paucity of information on sonoprocessing in other solvents, particularly ionic liquids (ILs). In this work, we modelled an ultrasonic horn-type sonoreactor and investigated the effects of ultrasound power, sonotrode immersion depth, and solvent’s thermodynamic properties on acoustic cavitation in nine imidazolium-based and three pyrrolidinium-based ILs. The model accounts for bubbles, acoustic impedance mismatch at interfaces, and treats the ILs as incompressible, Newtonian, and saturated with argon. Following a statistical analysis of the simulation results, we determined that viscosity and ultrasound input power are the most significant variables affecting the intensity of the acoustic pressure field (P), the volume of cavitation zones (V), and the magnitude of the maximum acoustic streaming surface velocity (u). V and u increase with the increase of ultrasound input power and the decrease in viscosity, whereas the magnitude of negative P decreases as ultrasound power and viscosity increase. Probe immersion depth positively correlates with V, but its impact on P and u is insignificant. 1-alkyl-3-methylimidazolium-based ILs yielded the largest V and the fastest acoustic jets – 0.77 cm3 and 24.4 m s−1 for 1-ethyl-3-methylimidazolium chloride at 60 W. 1-methyl-3-(3-sulfopropyl)-imidazolium-based ILs generated the smallest V and lowest u – 0.17 cm3 and 1.7 m s−1 for 1-methyl-3-(3-sulfopropyl)-imidazolium p-toluene sulfonate at 20 W. Sonochemiluminescence experiments validated the model.

Electrical Discharge in a Cavitating Liquid under an Ultrasound Field.

A theoretical model for an electrical discharge in a cavitating liquid is developed and compared with experiments for the optimization of the water treatment device. The calculations based on solution of the Noltingk─Neppiras equation support the hypothesis that the electric field promotes the formation of vapor microchannels inside a liquid gap between the electrodes, where at a low gas pressure Paschen's conditions of rupture and abnormal glow discharge maintenance in those microchannels are fulfilled. Theoretical analysis of the cavitation processes and the discharge formation processes is in qualitative agreement with the experimental data obtained in this work in a water treatment device using a hydrodynamic emitter. The following graphic illustrates the experimental setup: (1) feeding tank, (2) hydrodynamic emitter, (3) zone of cavitation inside the plasma reactor, (4) high-frequency generator of electric impulses, and (5) outlet.

Characterization of cavitation zone in cavitating venturi flows: Challenges and road ahead

Dynamic features of a cavitating venturi have been a topic of investigation for the past few decades. This review presents state-of-the-art of experimental and numerical studies in cavitating venturi to address the challenges in understanding flow behavior and developing reliable numerical models. Many experimental studies have shown that two strongly coupled mechanisms, namely, Re-entrant Jet and the bubbly shock influence the cavitation zone behavior. We provide pointers from the past and recent studies to the influence of geometry and operating conditions, introducing changes in cavity oscillation. From an operational viewpoint, the modeling studies need to predict four crucial parameters related to its steady and dynamic operation: choked mass flow rate, operating pressure ratio range, cavitation length, and frequency of cavity oscillations. In this paper, we discuss the possible ways to properly configure a one-dimensional (1D) model, which can be a handy tool for extracting the key integral parameters. Realistic predictions require direct numerical simulations, which is not always an economically viable option. Recent three-dimensional (3D) simulations with compressible formulations for flow field and a cavitation model coupled with large eddy simulations to handle turbulence have achieved some success in predictions. Many simplified approaches have been popular. In this paper, we systematically bring out the predictability limits of popularly used mixture models coupled with cavitation and turbulence in more commonly studied two-dimensional (2D) and fewer three-dimensional geometries. Two-fluid models could provide answers, but further studies are required to mitigate the modeling challenges and to enable realistic predictions of the steady and dynamic features of this elegant flow control device for a chosen application.

Numerical study on the hydrodynamic lubrication performance improvement of bio-inspired peregrine falcon wing-shaped microtexture

Bio-inspired surface microtexture has been adopted in mechanical systems for its advanced lubrication performance. In this study, we discerned the aerodynamic characteristics of different parts of the peregrine falcon’s wing, summarized the influence of its distinctive shape on the fluid flow, and, based on simplified geometries and the bionic concept, designed a novel wing-shaped microtexture to enhance lubrication performance in friction pairs. Its shape was simplified by the following parameters: area ratio Sp, dimensionless depth h*, and orientation angle α. Using a multiphase flow model, we investigated the effect of the above geometrical parameters on the lubrication performance of the wing-shaped microtexture by numerical simulation. The corresponding geometrical parameters of the wing-shaped microtexture to achieve optimum lubrication performance were: Sp = 30%/h*=1.75/α = 0°. The wing-shaped microtexture’s friction coefficient(COF) corresponded to a reduction of 18.8% and 20.7%, respectively, compared to the triangle and rectangular microtexture, which had the best lubrication performance for existing applications. The results showed that the wing-shaped microtexture enhanced the lubrication performance for three reasons: 1. The biomimetic leading edge created more negative pressure and cavitation zones; 2. The interference between positive and negative pressure zones was effectively mitigated; 3. The sharp design of the biomimetic trailing edge and tail wing concentrated the positive pressure zone while increasing its area. Two double-layer composite wing-shaped microtextures were further introduced to maximize friction reduction. The impact of inner-outer layer area ratio Sp* and inner-outer depth ratio h* on the lubrication performance was investigated. Their simulation results revealed that the optimal geometric parameters for the composite microtextures were Sp*=6.3%/hp*=3.0 and Sp*=12.7%/hp*=2.0, respectively. The configurations led to additional COF reductions of 7.6% and 10.56% compared to the single-layer wing-shaped microtexture. These insights offer valuable guidance for reducing friction and wear in mechanical systems.

A parameter map of cavitation from impacts between solids immersed in water

Cavitation when two solids immersed in water collide has been studied theoretically and experimentally. A dimensionless parameter map showing a threshold line that delimits with good agreement the cavitation and non-cavitation zones was constructed. The threshold line was set by a cavitation number established with a lubrication model. Experiments were conducted using a device with a solid steel sphere colliding with a solid aluminum plane for different impact velocities and water column heights. When the impact forces are in the order of 100 to 1000 N, only cavitation generated by the rapid separation of solids in the liquid (CSSL) is observed; however, this type of cavitation along with cavitation due to tensile waves (TWC) are perceived for collision forces greater than 1000 N. In some events in which both types of cavitation (TWC-CSSL regime) appear, light emission also takes place. The kinematic coefficient of restitution and impact speed can be used to determine the cavitation onset, the transition from CSSL to TWC-CSSL regimes and the collision events in which photon production occurs. The obtained map will provide key information to develop potential applications as cavitation machining and surface treatment.

Possibilities and limits of modeling cavitation in high-pressure homogenizers – a validation study

High-pressure homogenizers are widely used in industrial processes to produce emulsions with small droplet sizes. During the process, cavitation occurs under industrial process conditions. In order to investigate the flow conditions inside a homogenizer geometry, CFD simulations are commonly used, since it is not possible to evaluate local flow conditions experimentally. However, these studies have, so far, investigated flow under non-cavitating conditions, which do not adequately reflect industrial process conditions. This study investigates the extent to which the two cavitation models, the Schnerr-Sauer model and the Zwart-Gerber-Belamri model, can represent cavitation in the gap of the homogenizing geometry using RANS simulation. Simulations are validated with experimental cavitation visualization data. Results show that the Schnerr-Sauer model (with appropriately set modeling constants) is able to accurately predict the operating conditions responsible for cavitation inception in the valve, as well as the length and width of the cavitation zone.