Cavitation Behavior Research Articles

Dual-Mode 1-D Linear Ultrasound Array for Image-Guided Drug Delivery Enhancement Without Ultrasound Contrast Agents.

Pulsed high-intensity focused ultrasound (pHIFU) uses nonlinearly distorted millisecond-long ultrasound pulses of moderate intensity to induce inertial cavitation in tissue without administration of contrast agents. The resulting mechanical disruption permeabilizes the tissue and enhances the diffusion of systemically administered drugs. This is especially beneficial for tissues with poor perfusion such as pancreatic tumors. Here, we characterize the performance of a dual-mode ultrasound array designed for image-guided pHIFU therapies in producing inertial cavitation and ultrasound imaging. The 64-element linear array (1.071 MHz, an aperture of 14.8×51.2 mm, and a pitch of 0.8 mm) with an elevational focal length of 50 mm was driven by the Verasonics V-1 ultrasound system with extended burst option. The attainable focal pressures and electronic steering range in linear and nonlinear operating regimes (relevant to pHIFU treatments) were characterized through hydrophone measurements, acoustic holography, and numerical simulations. The steering range at ±10% from the nominal focal pressure was found to be ±6 mm axially and ±11 mm azimuthally. Focal waveforms with shock fronts of up to 45 MPa and peak negative pressures up to 9 MPa were achieved at focusing distances of 38-75 mm from the array. Cavitation behaviors induced by isolated 1-ms pHIFU pulses in optically transparent agarose gel phantoms were observed by high-speed photography across a range of excitation amplitudes and focal distances. For all focusing configurations, the appearance of sparse, stationary cavitation bubbles occurred at the same P- threshold of 2 MPa. As the output level increased, a qualitative change in cavitation behavior occurred, to pairs and sets of proliferating bubbles. The pressure P- at which this transition was observed corresponded to substantial nonlinear distortion and shock formation in the focal region and was thus dependent on the focal distance of the beam ranging within 3-4 MPa for azimuthal F -numbers of 0.74-1.5. The array was capable of B-mode imaging at 1.5 MHz of centimeter-sized targets in phantoms and in vivo pig tissues at depths of 3-7 cm, relevant to pHIFU applications in abdominal targets.

Effect of laser surface melting on microstructure evolution and cavitation behavior of nickel aluminum bronze

The laser surface melting was employed on the nickel aluminum bronze to augment the cavitation performance. To investigate the effect of laser treatment, the microstructure was characterized by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. And the cavitation behavior was tested on an ultrasonic vibratory machine. The results show that the optimal process parameter with laser power of 3 kW and scanning speed of 10 mm/s contributes to the increased corrosion resistance and reduced cavitation mass loss, compared with the cast sample, respectively. The enhancement of the cavitation resistance is dominated by the synergistic mechanism of grain refinement strengthening, dislocation strengthening, and precipitate strengthening, with the homogeneous structure eliminating selective corrosion.

Cavitation behavior study of the aging heat treated aluminum alloy 7075

Aluminium-based alloy type 7075 is known for its good ductility, high mechanical strength, toughness and high fatigue strength, which is why it is mainly used in the construction of dynamically stressed parts in the structure of airplanes, vehicles and ships. Although it has these qualities, at present its behavior has not been studied at the hydrodynamic stresses that allow it to be used in parts that work in cavitation conditions, such as pump rotors and boat propeller blades. Therefore, the research in this paper highlights the behavior of laminated semi-finished structures and obtained by heat treatment of artificial aging at 180°C, with a maintenance time of one hour. Of the 7075 alloy at the demands generated by the vibrating cavity, created by the standard vibrating device with piezoceramic crystals (frequency of 20 kHz, amplitude of 50 µm and electrical power of 500 W). Analysis based on the curves MDE (t) and MDER (t), of the specific parameters of cavitation erosion MDEmax and MDERs as well as of the macro and microscopic images of the eroded structures of cavitation show that, compared to the delivered state (semi-finished), by the heat treatment applied the microstructure does not change cavitation

Microfluidic ultrasonic cavitation enables versatile and scalable synthesis of monodisperse nanoparticles for biomedical application

Controllable and scalable synthesis of biomedical organic nanoparticles (NPs) with tailored properties is critical for their clinical translation. However, the existing microfluidics-based synthesis is challenged by clogging and limited throughput, while the traditional ultrasound-assisted synthesis suffers from inhomogeneous cavitation activity, leading to wide particle size distribution. Herein, a series of biomedical organic NPs were successfully synthesized in a controlled, clog-free and scalable manner via a versatile microfluidic ultrasonic cavitation (MUC) approach. First, the effects of microchannel dimension and operating conditions on ultrasonic cavitation behavior and mixing performance was systematically studied. Cavitation pattern maps were developed for different operating conditions. By adjusting microchannel dimension and operating parameters, rapid mixing on a millisecond scale can be accomplished across an extensive range of conditions, including flow rates between 4 and 24 mL/min and flow rate ratios from 5:1 to 1:1. Then, the MUC approach was utilized to synthesize polymeric NPs, lipopolymeric NPs and lipid NPs encapsulating mRNA (mRNA-LNP). Compared to traditional microfluidics and ultrasound-based methods, NPs synthesized by MUC approach showed smaller sizes and more uniform distributions. The ability of MUC approach for clog-free and scalable production was demonstrated by the continuous synthesis of lipopolymeric NPs at a throughput of 1.6 g/h with desired properties. The successful synthesis of soft and fragile mRNA-LNPs has been accomplished by tailoring the cavitation pattern of MUC approach. The resultant mRNA-LNPs showed a mRNA encapsulation rate as high as 98.3%, over 99% transfection efficiency of cell with 0.5 μg dosage, and robust luciferase expression with 10 μg dosage at the injection site of BALB/c mice 24 h after injection.

Numerical Investigation of the Cavitation Characteristics in Venturi Tubes: The Role of Converging and Diverging Sections

Cavitation is a typical physical process that has shown to be highly valuable in the wastewater treatment field. This study aims to investigate the effects of the converging and diverging sections of a Venturi tube on the cavitation flow field. Multiphase flows in tubes are presented using the mixture model and the standard k-ε model. And the Schnerr and Sauer cavitation model is employed to simulate the vapor–liquid phase transition process. Both grid independence and the numerical method’s feasibility were validated before the research. The results showed that the influence of the divergence section length on Venturi cavitation characteristics depends on the provided pressure conditions. As the pressure increases, shorter divergence sections result in more significant cavitation effects. The length of the convergence section displays various cavitation behaviors under different pressure situations. A small contraction section length can achieve better cavitation effects in high-pressure applications, whereas the opposite is true in low-pressure cases. Within the scope of this study, it was observed that the Venturi tube with a divergent section of 14 Lt and a convergent one of 2.4 Lt provided enhanced cavitation performance when subjected to inlet pressures ranging from 0.8 to 1.2 MPa. Our findings indicate that the selection of converging and diverging section lengths in Venturi tubes should consider the corresponding operational pressure conditions, which provides valuable guidance and engineering significance in the research and development of Venturi cavitation devices in hydraulic engineering.

Experimental Study of the Cavitation Effects on Hydrodynamic Behavior of a Circular Cylinder at Different Cavitation Regimes

In this work, we experimentally investigated the cavitation effects on the hydrodynamic behavior of a circular cylinder at different cavitating flows. We analyzed the cavitation dynamics behind the circular cylinder using a high-speed camera and also measured the associated hydrodynamic forces on the circular cylinder using a load cell. We studied the cavitation dynamics around the cylinder at various types of the cavitating regimes such as cloud cavitation, partial cavitation and cavitation inception. In addition, we analyzed the cavitation dynamics at three different Reynolds numbers: 1 × 105, 1.25 × 105 and 1.5 × 105. The results showed that the hydrodynamics force on the circular cylinder can be increased with the formation of the cavitation behind the cylinder compared with the cylinder at cavitation inception regime. The three-dimensional flow caused complex cavitation behavior behind the cylinder and a strong interaction between vortex structures and cavity shedding mechanism. In addition, the results revealed that the effects of the Reynolds number on the cavitation dynamics and amplitude of the shedding frequency is significant. However the effects of the cavitation number on the enhancement of the amplitude of the shedding frequency in the cavitating flow with a constant velocity is slightly higher than the effects of Reynolds number on the enhancement of the amplitude of the shedding frequency at a constant cavitation number.

Nanoemulsification of soybean oil using ultrasonic microreactor: Process optimization, scale-up and numbering-up in series

Ultrasonically-induced nanoemulsions have been widely investigated for the development of functional food, cosmetics, and pharmaceuticals due to ideal droplet sizes (DS), low polydispersity index (PDI), and superior physical stability. However, a series of frequently-used ultrasonic set-ups mainly suffered from a low ultrasonic energy efficiency caused by the large acoustic impedance and energy consumption, subordinately confronted with a low throughput, complicated fabrication with complex structure and weak ultrasonic cavitation. Herein, we employed a typical ultrasonic microreactor (USMR) that ensured the high-efficient energy input and generated intense cavitation behavior for efficient breakage of droplets and continuous production of unified oil-in-water (O/W) nanoemulsions in a single cycle and without any pre-emulsification treatment. The emulsification was optimized by tuning the formula indexes, technological parameters, and numerical analysis using Response Surface Methodology (RSM), followed by a comparison with the emulsification by a traditional ultrasonic probe. The USMR exhibited superior emulsification efficiency and easy scale-up with remarkable uniformity by series mode. In addition, concurrent and uniform nanoemulsions with high throughput could also be achieved by a larger USMR with high ultrasonic power. Based on RSM analysis, uniform DS and PDI of 96.4 nm and 0.195 were observed under the optimal conditions, respectively, well consistent with the predicted values. Impressively, the optimal nanoemulsions have a uniform spherical morphology and exhibited superior stability, which held well in 45 days at 4℃ and 25℃. The results in the present work may provide a typical paradigm for the preparation of functional nanomaterials based on the novel and efficient emulsification tools.

Thermodynamic effect on attached cavitation and cavitation-turbulence interaction around a hydrofoil

This paper aims to numerically investigate the thermodynamic effect on attached cavitation and cavitation-vortex interaction around a NACA0015 hydrofoil. Based on the isothermal cavitation model, the compressibility and thermodynamic effect are considered by adding the state equation and modifying the evaporation and condensation source term in the mass transport equation. The thermodynamic effect on the hydrodynamic performance and the cavity volume fluctuations, the temporal evolution of the unsteady cavitation, the temporal evolution of vortex structures in the hydrofoil wake, and the cavitation-vortex interaction are presented. The main features of the unsteady quasi-periodic cavitation behavior are illustrated for the isothermal and non-isothermal conditions. The new omega vortex identification method depicts the influence of the thermodynamic effect on the shedding structure around the wake of a hydrofoil. Furthermore, the cavitation-vortex interaction is examined to show the relationship.

Numerical investigation on the hydrodynamic performance with special emphasis on the cavitation intensity detection in a Venturi cavitator

Venturi is one of the structures that have been frequently adopted for the generation of hydrodynamic cavitation, which is now a promising technology and method in wastewater treatment. Despite the wide spread application, insight into the characteristics of cavity dynamics and cavitation intensity to optimize cavitation performance remains lacking. This paper presents computational investigation of the cavitation performance with emphasis on cavitation intensity prediction inside a Venturi cavitator, through a robust modeling approach. Particularly, a new physical model as the criterion to account for the evaluation of cavitation intensity was developed. The predictions gave satisfactory agreement with published data for acoustic bubble dynamics, and experimental results for typical cavitation characteristics of the Venturi. Further investigations analyzed the size oscillations, collapse pressure and collapse temperature of bubbles, as well as the cavitation intensity during its dynamic behavior of the hydrodynamic cavitation in this cavitator. The results showed that the bubbles originally generated near the wall of the Venturi had the strongest oscillations for cavity dynamics. The normalized average bubble collapse pressure was consistent with the distributions of the cavitation intensity within the whole flow domain. Besides, the rear part of the attached cavity at the stage of developing cavitation showed the strongest intensity of cavitation, while the chocking cavitation had no advantage for this issue. This research provides an available and useful criterion to effectively compare and evaluate the bubble dynamics and cavitation intensity in the multiphase flow of cavitational reactors.

Instability measurement of cavitation conditions in a spool valve through the definition of a cavitation instability index

Cavitation phenomenon is commonly known as a cause of deterioration of hydraulic components and a source of noise. In a proportional spool control valve for fluid power applications, the reduction of the cross section area at small openings can lead to the growth of gas bubbles inside the fluid phase. This phenomenon modifies the operating efficiency of the valve and can damage the material over time. The oil flow has been visualised through an experimental activity by using a 2-way 2-position spool valve with a plexiglass case and analysed by a CMOS type camera, with a high sampling rate. The recorded images focus the interaction between gas and liquid phases and highlights how the shape of cavitation bubbles is modified when the surface stress increases. In the present work, the interaction between liquid and gas phase has been studied by applying a non-linear method on the numerical matrices, derived from the acquired images. A cavitation instability index has been proposed, which is able to describe the cavitation behaviour and to define the instability of the equilibrium between the two phases. The trend of this index gives information about the two phase flow conditions, in order to reduce the cavitation phenomenon.

Numerical investigation of compressible cryogenic cavitating flows by a modified mass transport model

The objectives of this study are to propose exact numerical methods for the compressible cryogenic cavitating flows and investigate the cavitation behaviors and vortex structures. A numerical modeling framework including large eddy simulations, vapor–liquid equations of state, and a modified mass transport model is presented in this paper. The modified transport model is proposed based on the convective heat transfer in which the convective heat transfer coefficient is associated with the material properties and local temperature. To validate the applicability of the modified model, the liquid nitrogen cavitating flows in the inertial and thermal modes (σ ≈ 0.50, Tthroat = 77.24 K and Tthroat = 85.23 K) are simulated, respectively. Meanwhile, the influence of thermodynamic effects on compressibility is investigated. The numerical method is further utilized to visualize the detailed cavity and vortex structures in different cavitating flow patterns (Tthroat ≈ 77 K, σ = 0.58, 0.39, 0.18). The results show that the predicted cavity structures with the modified mass transport model agree better with the corresponding experimental data. For the thermal mode, since the significant thermal effects restrain the development of cavity, the area of the low sound speed region is smaller than that of the inertial model. The value of the minimum sound speed is larger, so that the Mach number in the cavitation region is reduced. Therefore, the compressibility of the liquid nitrogen cavitation in the thermal mode is weaker. For different cavitating flow patterns, the core region of attached cavities near the throat remains stable during an evolutionary cycle. Compared to the attached cavity region, since some hairpin vortices break into many small-scale discrete vortices, the multi-scale effect of vortex distribution is more remarkable in the shedding cavity region.

Effect of Tip Rake Distribution on the Hydrodynamic Performance of Non-Planar Kappel Propeller

Taking advantage of end-plate effects to enhance propeller efficiency is engaging. This paper applied a 4-order B-spline curve to design the rake distribution of Kappel propellers using five types of Kappel propellers that each possesses different tip rakes, and one type has no constructed end-plate. The RANS method coupled with the γ transition model was utilized to analyze the open-water performance of the six propellers, considering cavitating flow. It was found that the tip rake is conducive to the thrust capacity of the Kappel propellers, mostly improving the propulsion efficiency by 2.5% at a designed advance speed with the appropriate tip rake. The increase in the tip rake will magnify the low-pressure value and area on the suction side blade surface, together with the phenomenon of the stretching tip vortex and the inhibition of wake vortex contraction, which are both beneficial to the elevation of propulsion efficiency. However, the sheet cavitation behavior of the six propellers aggravates as the tip rake rises. Accordingly, the reasonable range of a tip rake for the design of a Kappel propeller in favor of the propulsion performance is suggested in this paper, exhibiting the promising potential of energy savings for the application to marine vehicles.

Change in Cavitation Regime on NACA0015 Hydrofoil by Heating the Hydrofoil Surface

AbstractAn experimental study of cavitating flow on a heated NACA0015 hydrofoil was conducted in a cavitation tunnel to investigate the influence of the hydrofoil surface temperature on the cavitating flow. The cavitation behavior under different heating conditions was examined using high-speed video, and an image processing method was used to obtain the periodic characteristics of the cavitating flow. The results revealed that attached sheet cavitation and supercavitation occurred on both heated and unheated hydrofoils. However, sheet-cloud cavitation was observed only on the unheated hydrofoil, whereas transient cavitation was observed only on the heated hydrofoil. Transient cavitation also exhibited periodic growth/collapse behavior; however, there was no shedding of a large vapor cloud. Moreover, with a further increase in the hydrofoil surface temperature, transient cavitation turned into open-type cavitation. The cavitating flow exhibited a quasi-steady cavity length with an open cavity closure. It was considered that the surface temperature promoted vapor generation at the cavity leading edge, which enlarged the vapor-filled fore part of the sheet cavity. This enlarged sheet cavity prevented the reentrant flow from moving upstream and thus turned the cavity closure into an open type. Once the cavity closure turned into an open type, the local disturbance led to a smaller adverse pressure gradient, which was not sufficiently strong to create a reentrant flow. In this case, if the vapor generation at the cavity leading edge was sufficiently large to reach a balance with vapor condensation at the open cavity closure, the cavity would be steady.

Cavitation behavior and mixing performance of antisolvent precipitation process in an ultrasonic micromixer

AbstractA facile and robust ultrasonic micromixer was developed to intensify antisolvent precipitation via ultrasonic cavitation. The gas supersaturation created from solvent–antisolvent mixing was found to be a novel driving force which facilitated the generation of cavitation bubbles (CBs). Instead of being attached on the channel wall, numerous CBs translated across the microchannel at a speed up to 1.7 m/s, inducing intense transverse flow over the cross‐section. The unique cavitation behavior enabled rapid mixing (mixing time 15–45 ms at 30 W) of solvent–antisolvent over wide Reynolds number range (70–500) and flow rate ratio (5:1–2:3), providing better operability for antisolvent precipitation. The effects of ultrasonic power, total flow rate, flow rate ratio, and solvent on cavitation behavior and mixing performance were quantitatively studied. Finally, the potential of the ultrasonic micromixer as a new tool for antisolvent precipitation was demonstrated by synthesizing size‐controllable and monodisperse polymeric nanoparticles in a high‐throughput and reproducible manner.

Influence of Inlet Vane and Wrap Angles on Cavitation Behavior of a Centrifugal Pump

This comprehensive study focuses on the relationship between the inlet vane and wrap angles of a centrifugal pump impeller and its cavitation behavior. The objective is to propose a new design for cavitation performance enhancement of the pump by reducing the required net positive suction head (NPSHR). To render a detailed study, the variations of the mentioned angles were examined both at hub and shroud. A three-dimensional two-phase parametric computational fluid dynamics (CFD) study was conducted and variations of inlet blade and wrap angles at hub and shroud were investigated separately. After validating the experimental results with the pump model, the pump parameterization process was carried out, and pump geometry was re-defined with its geometrical properties. The characteristic curves of the parameterized pump and pump model were in agreement with each other. Numerical cavitation tests were performed and the NPSHR values of each design were calculated for four different operating conditions. Results showed that cavitation performance increase was achieved with angle variations at the best efficiency point (BEP) but, this situation led the pump to operate exposed to cavitation at high flows (HF) for some designs. Therefore, the design with the best cavitation performance increased at BEP and HF was proposed as a new design. During numerical simulations, shear stress transport (SST) turbulence model and Rayleigh–Plesset equation were used.

High pressure heat treatment tuning cavitation behavior in FeP metallic glass

High pressure heat treatment tuning cavitation behavior in FeP metallic glass

A study on surface microgrooves in cavitation test of 6061 aluminum alloy

Microgrooves of different widths and microgrooves structures with varying widths were engraved on the surface of 6061 aluminum alloy using fiber laser marking equipment. In order to investigate the influence of the width of microgrooves on its cavitation behavior, cavitation tests on the microgroove structure were performed using an ultrasonic vibration apparatus. The hardness, the surface roughness, and the microscopic morphology of the samples were examined with a digital microhardness tester, a digital three-dimensional video microscope, and a scanning electron microscope, respectively. The results demonstrated that, increasing microgroove size was conducive to inhibition of cavitation erosion while decreasing microgroove size had an opposite effect. The surface microgrooves group elongated the incubation period of aluminum alloy in the cavitation tests, and noticeably increased the cavitation resistance of the aluminum alloy. It was also concluded that, the microgrooves group could transform microjets aiming at the alloy surface to the inside of microgrooves, and absorbed the impacted energy from microjets, leading to a remarkable anticavitation effect.

Effect of section thickness on cavitation behaviour of selective laser sintered polyamide 12

The present study focuses on the results of cavitation resistance of samples obtained by the Selective Laser Sintering technology. All samples are made from Nylon 12 - Polyamide 12 powder, known as PA2200 in the industry, produced by EOS GmbH. The powder, which has been used for building of samples, represent mixture of 50% new powder and 50% of the recycled powder. In the work, samples with different section thicknesses (0.4mm; 0.8mm and 1.0mm) were subjected to the ultrasonically induced cavitation test method to investigate the effect of geometry on their cavitation behaviour. The change in mass loss during different cavitation times was measured on the tested samples. The morphology of cavitation damage was characterized using Scanning Electron Microscopy (SEM). Results obtained in this paper have shown that section thickness of the samples have a significant influence on the cavitation resistance. The highest cavitation resistance was obtained for the samples with 0.4mm thickness.

Cavitation behavior of polypropylene/polyethylene multilayer films during uniaxial tensile deformation: In-situ synchrotron X-ray study

The cavitation of melt-coextruded multilayer films of alternated polypropylene (PP) and polyethylene (PE) during the uniaxial tensile deformation has been investigated. The initiation and evolution of cavities and the relationship between cavitation and plastic deformation have been studied via in-situ SAXS and WAXS techniques. The critical strain for the initiation of cavitation (εcav), crystal shear (εCSh), and yield (εyield) have been estimated from the in-situ experiments. The results show that the sequence of deformation is crystal shear, cavitation and yield, i.e. εCSh<εcav<εyield, indicating that crystal plastic deformation occurs before the cavitation and yield. Additionally, the layer numerosity and annealing temperature (Tanneal) have been discovered to not only modify the mechanical behavior but also regulate cavitation by changing the initial microstructure. The samples with less layer numerosity and high Tanneal improve the macroscopic mechanical strength, whereas the increase of layer numerosity can reduce the stress of cavitation onset (σcav) and retard the onset of cavitation onset (high εcav value). The current study is significant in elucidating the internal mechanism of stretch-induced cavitation behavior in multilayer films.

On the Influence of Cavitation Volume Variations on Propeller Broadband Noise

Low-frequency broadband shipping noise causes a growing concern for marine fauna together with the demand for noise reduction. Detailed analyses of the cavitation behaviour in the time domain serve as a prerequisite for steps toward quieter propellers. Underwater noise measurement data from the propeller of a full-scale container vessel are used for the analysis of the cavitation volume behaviour. Sequencing methods, polynomial models, and stochastic evaluation methods feeding Monte Carlo simulations of unsteady sheet cavitation are applied to identify the cause of an often observed, yet unexplained similarity in shipping noise spectra. Characteristic features of the volume evolution are identified to enhance the understanding of noise generation by sheet cavitation.