Cavitation Bubbles Research Articles

Expansion of the cavitation region using ultrasound focus scanning in the direction of ultrasound propagation for an efficient method of histotripsy

Histotripsy is a non-invasive high-intensity focused ultrasound (HIFU) based therapy using the mechanical effect of cavitation bubbles. In this paper, we experimentally examined the effectiveness of a proposed method of scanning the HIFU focus in the direction of propagation to expand the region of the bubble cloud and increase the treatment throughput. First, the continuous generation of cavitation bubbles was observed with a high-speed camera, and it was confirmed that the region of bubble cloud generation could be expanded by focus scanning. Next, we performed ex vivo experiments. Tissue treated with histotripsy is disrupted and homogenized at the subcellular level, resulting in a decrease in the backscatter intensity of the ultrasound. Therefore, we observed the progression of tissue homogenization with histotripsy by evaluating the reduction of echo intensity in ultrasound imaging. The results suggest that focus scanning can improve the time efficiency of treatment.

The unveiling of a dynamic duo: hydrodynamic cavitation and cold plasma for the degradation of furosemide in wastewater

The degradation in water of furosemide (FUR), a widely used diuretic drug, was herein reported. The method entails an integrated approach based on the hybridisation of hydrodynamic cavitation (HC) with electrical discharge (ED) plasma technology. This dynamic duo could increase the production of oxidising compounds in water, in particular hydroxyl radicals (OH radicals), by triggering the rapid homolytic decomposition of water molecules and avoiding the addition of external oxidants. This study clearly emphasises the effectiveness of an integrated approach to improve the degradation of pollutants in wastewater originating from active pharmaceutical ingredients (APIs). The results of HC/ED-assisted FUR degradation in the presence of radical scavengers highlight the predominant role of the radical oxidation mechanism at the gas–liquid interface of the cavitation bubble during HC/ED treatment. A comparative analysis of the three technologies—HC alone, HC/ED and UV alone—emphasised the promising potential of hybrid HC/ED as a scalable industrial technology. This is demonstrated by the higher degradation rates (100%, 10 min) when treating large volumes (5L) of wastewater contaminated with FUR (50 mg/L), even in the presence of other APIs.

Improvement of contrast ratio between cavitation bubbles and tissue by frequency filtering in triplet pulse ultrasound imaging

Bubble-enhanced high-intensity focused ultrasound treatment requires selective imaging of cavitation bubbles to ensure their localization to the target tissue. Previous studies have proposed the ultrasound imaging of cavitation bubbles with a filtering method, which makes bubble extraction by a triplet pulse sequence more selective. The envelope component as well as harmonic components are generated during the nonlinear propagation of an ultrasonic imaging pulse, but the triplet pulse sequence can significantly reduce only the harmonic components, and its selectivity is degraded by the residual envelope component. In this study, the effects of nonlinear propagation at various intensities of imaging pulse and the frequency filtering to obtain better selectivity are investigated for the triplet pulse sequence with a filtering method. The result shows that the imaging pulse intensity is an important parameter that determines the strength of the effect of nonlinear propagation and that the optimal frequency filtering changes according to it.

Технология предварительной радиальной ИАГ-лазерной факофрагментации в хирургическом лечении катаракты

Purpose. To represent the technology of preliminary radial YAG laser phacofragmentation in the surgical treatment of cataracts. Material and methods. The technology of preliminary radial YAG laser phacofragmentation has been used in the Kaluga branch of the S. Fyodorov Eye Microsurgery Federal State Institution since 2016. The basis of the technology is the transcorneal endocapsular formation of radial cracks of the lens core for its subsequent fragmentation during ultrasonic phacoemulsification of cataracts (FEC). The total number of pulses ranges from 95 to 150. Results. In the Kaluga branch of the S. Fyodorov Eye Microsurgery Federal State Institution, preliminary radial YAG laser phacofragmentation was performed on 9468 eyes with cataracts of 2–4 degrees of density from 2016 to 2023. After YAG laser fragmentation of the lens core, its radial separation occurs according to the «snowflake» type, which consists of 3 layers and «petals» extending from cavitation bubbles that clearly outline the core. The clinical and functional state of the eyes after preliminary YAG laser phacofragmentation indicated the absence of reactive inflammation from the anterior and posterior segment of the eye, which was confirmed by biomicroscopy and ultrasound ophthalmoscanning data. Conclusion. The technology of preliminary radial YAG laser phacofragmentation is a safe and effective method that allows you to achieve uniform separation of lens fibers along the formed fragmentation zones, which correspond to subsequent nuclear fracture zones during the nuclear fragmentation stage during ultrasonic FEC. Key words: radial YAG laser phacofragmentation, cataract, ultrasonic phacoemulsification of cataract

Ultrasonic dehydration of materials without liquid-vapor transition

This study validates the mechanism of ultrasonic dehydration without transition of water into vapor. The process can be realized by cavitation dispersion of liquid initiated by collapse of cavitation bubbles of cylindrical shape formed in capillaries. The developed mathematical model considers the complete life cycle of cavitation bubbles, encompassing three stages: slow growth, rapid expansion with deformation, and collapse. The optimum range of sound pressure level from 150 dB (critical level) to 170 (limit level) at which cavitation dispersion of liquid from capillaries takes place has been determined. The optimum sample size corresponding to the ultrasonic wavelength in gas, at which the dehydrated productivity is maximized, has been determined. The mechanism of ultrasonic dispersion of liquid during drying was confirmed by experiments. Practical implementation of ultrasonic drying of food products (carrots) confirmed effectiveness of implementation of dehydration mechanism and provided a reduction of drying time by 1.9 times with a reduction of power consumption by 1.7 times.

Morphological analysis for thermodynamics of cavitation collapse near fractal solid wall

A fractal geometric boundary with natural wall features is introduced into a hybrid lattice-Boltzmann-method (LBM) multiphase model. The physical model of cavitation bubble collapse near the irregular geometric wall is established to study the thermodynamic characteristics of the bubble collapse. Due to the lack of periodicity, symmetry, spatial uniformity and obvious correlation in the LBM simulation of the bubble collapse near the fractal wall, the morphological analysis based on Minkowski functional is introduced into the thermodynamic investigation of cavitation bubble so as to analyze and obtain the effective information. The results show that the Minkowski functional method can employed to study the temperature information in complex physical fields hierarchically and quantitatively. The high/low temperature region of the cavitation flow is explored, and thermal effect between irregular and fractal geometric wall and cavitation bubble can be revealed. It illustrates that LBM and morphological analysis complement each other, and morphological analysis can also be used as an optional and potential tool in research field of complex multiphase flows.

Study on Non-Spherical Deformation Velocity of a Single Cavitation Bubble

Cavitation bubbles commonly exist in shipbuilding engineering, ocean engineering, mechanical engineering, chemical industry, and aerospace. Asymmetric deformation of the bubble occurs near the boundary and then has strong destructiveness, such as high amplitude loading. Therefore, the research on non-spherical deformation is of great significance, and the objective of this paper is to investigate the non-spherical collapse dynamics of laser-induced cavitation bubbles when near different boundaries. In this study, experimental data, such as the bubble pulsation process and bubble surface velocity distribution, were obtained by high-speed camera techniques and full-field velocity calculations. Near the different boundaries, the results show that the bubbles appeared to have different collapse shapes, such as near-hemispherical, near-ellipsoidal, near-cone, and near-pea shapes, and the surface velocity distribution is extremely non-uniform. When the bubble near the free surface or rigid boundary collapses, the smaller the stand-off r is, the more obvious the repulsive effect of the free surface or the attractive effect of the rigid boundary is. As the stand-off r decreases, the larger the Bjerknes force and the bubble surface velocity difference and the more pronounced the non-spherical shape becomes.

Amplification of Supersonic Microjets by Resonant Inertial Cavitation-Bubble Pair.

We reveal for the first time by experiments that within a narrow parameter regime, two cavitation bubbles with identical energy generated in antiphase develop a supersonic jet. High-resolution numerical simulation shows a mechanism for jet amplification based on toroidal shock wave and bubble necking interaction. The microjet reaches velocities in excess of 1000 m s^{-1}. We demonstrate that potential flow theory established for Worthington jets accurately predicts the evolution of the bubble gas-liquid interfaces unifying compressible and incompressible jet amplification.

Enhanced mitigation of cavitation erosion by means of femtosecond pulsed laser-induced hierarchical surface structures

Hierarchical structures were fabricated on brass surfaces by means of a straightforward 2-step laser-scribing process. We tested the ability of these surface structures to withstand cavitation erosion and compared their performance to untreated brass samples. We found that hierarchical surface structures reduced the eroded volume by a factor between 7.2 and 22.7 times when compared to untreated samples after 800,000 cavitation events. Additionally, the hierarchical surface structures reduced the erosion by a factor between 1.1 and 1.5 times when compared to samples patterned with only microchannel surface structures, for the same amount of cavitation events. Up to 800,000 laser-induced cavitation bubbles were generated at a fixed standoff distance of 0.5 to test the mitigation effect of the scribed surface structures on the eroded volume. The eroded volume was computed by means of confocal microscopy. The results show that additional roughness imposed by the hierarchical surface structure acts as an energy dissipator as observed by comparing the sizes of the higher order rebound cavitation bubbles. These findings provide a promising solution for protecting equipment from cavitation erosion.

Experimental and numerical research on the coupled mechanisms of cavitation effect in a Venturi-type bubble generator

Venturi type bubble generator has a broad application in various fields and its bubble performance is closely related to the strong turbulent flow field. The interaction between bubble breakup and cavitation flow is not fully explained. In present work, the influence of cavitation on the suction performance and gas-phase transport pattern of a Venturi-type bubble generator is investigated by experiments and numerical simulations. The results show that the pressure ratio of 0.58 is the critical cavitation condition and the suction of the Venturi type bubble generator reaches the limiting value. The Venturi type bubble generator almost lost its suction capacity at the pressure ratio decreased to 0.27. However, the cavitation effect has a suppressive effect on the suction volume. The quasi-periodicity of the air inlet velocity pulsation and cavity development is highly consistent. Further research found that the blocking effect formed by return jets and pressure waves from cavity collapse is the main factor in reduced suction volume. The mechanisms of cavity shedding and collapse have a similar evolutionary model to the bubble breakup mechanisms in the Venturi-type generator.

Secondary cavitation bubble dynamics during laser-induced bubble formation in a small container.

We investigated secondary cavitation bubble dynamics during laser-induced bubble formation in a small container with a partially confined free surface and elastic thin walls. We employed high-speed photography to record the dynamics of sub-mm-sized laser-induced bubbles and small secondary bubble clouds. Simultaneous light scattering and acoustic measurements were used to detect the oscillation times of laser-induced bubbles. We observed that the appearance of secondary bubbles coincides with a prolonged collapse phase and with re-oscillations of the laser-induced bubble. We observed an asymmetric distribution of secondary bubbles with a preference for the upstream side of the focus, an absence of secondary bubbles in the immediate vicinity of the laser focus, and a migration of laser-induced bubble toward secondary bubbles at large pulse energies. We found that secondary bubbles are created through heating of impurities to form initial nanobubble nuclei, which are further expanded by rarefaction waves. The rarefaction waves originate from the vibration of the elastic thin walls, which are excited either directly by laser-induced bubble or by bubble-excited liquid-mass oscillations. The oscillation period of thin walls and liquid-mass were Twall = 116 µs and Tlm ≈ 160 µs, respectively. While the amplitude of the wall vibrations increases monotonically with the size of laser-induced bubbles, the amplitude of liquid-mass oscillation undulates with increasing bubble size. This can be attributed to a phase shift between the laser-induced bubble oscillation and the liquid-mass oscillator. Mutual interactions between the laser-induced bubble and secondary bubbles reveal a fast-changing pressure gradient in the liquid. Our study provides a better understanding of laser-induced bubble dynamics in a partially confined environment, which is of practical importance for microfluidics and intraluminal laser surgery.

Experimental investigation on the characteristics of the shock wave emitted by the cavitation bubble near the air bubble

This study explores the mitigation of cavitation damage in hydraulic engineering through air entrainment. The primary aim is to experimentally analyze the shock wave characteristics emitted by cavitation bubbles adjacent to air bubbles affixed to a tube nozzle. The schlieren optical system is utilized to visualize the shock wave, while a hydrophone measures its pressure. Experiments are conducted on cavitation bubbles induced by the spark-generated method in the vicinity of air bubbles, varying the dimensionless distances and sizes of the air bubbles. The results indicate that (1) The introduction of an air bubble noticeably changes the morphology, kinematic behavior, and shock wave features of the cavitation bubble. (2) Four distinct shock wave patterns are identified based on the quantity and shape of the shock wave, with variations in the cavitation bubble's collapsing behavior and shock wave characteristics across different patterns. (3) The dimensionless distance γ and size δ exert significant influence on the shock wave's quantity, pressure peak, shape, and energy. With γ decreases or δ increases, the shock wave quantity increases while the shock wave intensity decreases. This investigation of the interaction between cavitation bubbles and air bubbles is essential for elucidating the mechanism through which air entrainment mitigates cavitation damage.

Investigations on the jets and shock waves of a cavitation bubble collapsing between a wall and a particle

The simultaneous presence of particles and cavitation bubbles has a deleterious effect on the performance and safety of hydraulic machinery through the generation of jets and shock waves. In the present paper, the mechanisms responsible for the generation and the evolution of jets and shock waves from a collapsing cavitation bubble situated between a spherical particle and a wall are simulated using a compressible two-phase flow solver. Specifically, the effects of bubble position on jet and shock wave behavior are qualitatively analyzed. The simulations and experiments reveal three typical cases of jet behavior: a jet toward the wall, double jets, and a jet toward the particle. Needle jets and shock waves are commonly generated by collisions of the bubble interface. In some cases, needle jets are associated with a high impact velocity. It is found that the smaller the distance between the particle and the wall, the higher the pressure generated by the jets and the shock waves on the wall.

Native bubble nuclei for acoustic cavitation in 3D cell cultures

The safety of biomedical ultrasound largely relies on controlling cavitation bubbles in vivo; however, bubble nuclei in biological tissues remain unexplored compared to water. No previous studies have observed where bubble nuclei form in tissues at a microscopic level or how the variation in tissue biomechanical properties can impact the presence of bubble nuclei for acoustic cavitation. In this study, we evaluated whether bubble nuclei form intracellularly or extracellularly in rat epithelial hepatoma (McA-RH7777) and musculoskeletal myoblast (L6) cell lines (n = 5 each), cultured in 3D using Matrigel™ scaffolds. A 3.68 MHz focused ultrasound transducer with f# = 1 was used to induce low-density cavitation using varying pulse lengths (10 to 100 μs) with pressures ranging up to p+ = 29 and p− = 12 MPa. The spatial location of the bubbles was monitored microscopically using high-speed photography at 20 000 fps. Despite significant radiation force on the cell scaffold, preliminary results show that acoustic cavitation bubbles (r = 20 μm approx.) preferentially form extracellularly near the cell membranes. This result suggests that the hydrophobicity in the amphipathic cell membrane may contribute to bubble nuclei formation. Future work includes investigating the distribution of bubble nuclei in healthy versus cancerous cell cultures. [Work supported by NSF CAREER 1943937.]

The collapse of a sonoluminescent cavitation bubble imaged with X-ray free-electron laser pulses

Single bubble sonoluminescence (SBSL) is the phenomenon of synchronous light emission due to the violent collapse of a single spherical bubble in a liquid, driven by an ultrasonic field. During the bubble collapse, matter inside the bubble reaches extreme conditions of several gigapascals and temperatures on the order of 10000 K, leading to picosecond flashes of visible light. To this day, details regarding the energy focusing mechanism rely on simulations due to the fast dynamics of the bubble collapse and spatial scales below the optical resolution limit. In this work we present phase-contrast holographic imaging with single x-ray free-electron laser (XFEL) pulses of a SBSL cavitation bubble in water. X-rays probe the electron density structure and by that provide a uniquely new view on the bubble interior and its collapse dynamics. The involved fast time-scales are accessed by sub-100 fs XFEL pulses and a custom synchronization scheme for the bubble oscillator. We find that during the whole oscillation cycle the bubble’s density profile can be well described by a simple step-like structure, with the radius R following the dynamics of the Gilmore model. The quantitatively measured internal density and width of the boundary layer exhibit a large variance. Smallest reconstructed bubble sizes reach down to R≃0.8μm , and are consistent with spherical symmetry. While we here achieved a spatial resolution of a few 100 nm, the visibility of the bubble and its internal structure is limited by the total x-ray phase shift which can be scaled with experimental parameters.

Vapor compression and energy dissipation in a collapsing laser-induced bubble

The composition of the gaseous phase of cavitation bubbles and its role on the collapse remains to date poorly understood. In this work, experiments of single cavitation bubbles in aqueous ammonia serve as a novel approach to investigate the effect of the vapor contained in a bubble on its collapse. We find that the higher vapor pressure of more concentrated aqueous ammonia acts as a resistance to the collapse, reducing the total energy dissipation. In line with visual observation, acoustic measurements, and luminescence recordings, it is also observed that higher vapor pressures contribute to a more spherical collapse, likely hindering the growth of interface instabilities by decreasing the collapse velocities and accelerations. Remarkably, we evidence a strong difference between the effective damping and the energy of the shock emission, suggesting that the latter is not the dominant dissipation mechanism at collapse as predicted from classical correction models accounting for slightly compressible liquids. Furthermore, our results suggest that the vapor inside collapsing bubbles gets compressed, consistently with previous studies performed in the context of single bubble sonoluminescence, addressing the question about the ability of vapors to readily condense during a bubble collapse in similar regimes. These findings provide insight into the identification of the influence of the bubble content and the energy exchanges of the bubble with its surrounding media, eventually paving the way to a more efficient use of cavitation in engineering and biomedical applications.

Dynamics of cavitation bubbles in viscous liquids in a tube during a transient process

We experimentally, numerically, and theoretically investigate the dynamics of cavitation bubbles in viscous liquids in a tube during a transient process. In experiments, cavitation bubbles are generated by a modified tube-arrest setup, and the bubble evolution is captured with high-speed imaging. Numerical simulations using OpenFOAM are employed to validate our quasi-one-dimensional theoretical model, which effectively characterizes the bubble dynamics. We find that cavitation onset is minimally affected by the liquid viscosity. However, once cavitation occurs, various aspects of bubble dynamics, such as the maximum bubble length, bubble lifetime, collapse time, and collapse speed, are closely related to the liquid viscosity. We further establish that normalized bubble dynamics are solely determined by the combination of the Reynolds number and the Euler number. Moreover, we also propose a new dimensionless number, Ca2, to predict the maximum bubble length, a critical factor in determining the occurrence of liquid column separation.

Theoretical estimation of sonochemical characteristics in a single cavitation bubble under various static pressure conditions

Cavitation bubbles can be generated by introducing ultrasonic waves into the liquid. The growth and collapse of the bubbles transfer energy from ultrasonic waves to the gas mixture, resulting in the formation of an extreme environment with local high pressure and temperature, and then, multiple products (H2, ·OH, H·, O, H2O2, and so on) are produced. In the present study, the sonochemical characteristics inside an oxygen bubble have been investigated by using single bubble dynamics equations taking mass transfer, heat exchange, and chemical reactions into account. The effects of the equilibrium radius and static pressure on the temperature and the yields of H2, ·OH, and total oxidants inside the bubble are analyzed. There are optimal equilibrium radii that maximize gas temperature and the amounts of H2, ·OH, and total oxidants under different static pressures. The results of this paper are in good agreement with the previous results and can be used to explain sonochemical phenomena observed in experiments.

Numerical simulation of the underwater gun using gas-curtain launch

A novel gas-curtain launch technique is proposed to enhance the interior ballistic performance for underwater guns. The size of the initial gas curtain in front of the projectile is a critical factor in determining the subsequent behavior of the gunpowder gas jet flow field once the projectile leaves the muzzle. Hence, a validated two-dimensional unsteady multiphase model is built for the flow field at the muzzle of an underwater gas-curtain launch. The calculation involves determining the development of the initial gas curtain sizes for a 30 mm underwater gun, specifically focusing on the evolution of the precursor jet and gunpowder gas jet flow field. The results indicate that a double three-wave point structure forms within the bottle-shaped shock wave structure of the precursor jet when the initial gas curtain length equals the barrel. As the initial gas curtain size increases, the “bottle” structure elongates along the axial direction and compresses radially. After the projectile exits the muzzle, the gunpowder gas quickly expands toward the front, causing the collapse of the Mach disk of the precursor jet. The gunpowder gas jet then reforms a new bottle-shaped shock wave structure. A larger initial gas curtain can facilitate the expansion of the gunpowder gas, resulting in an increased size of the bottle, delayed formation, and weakened intensity of the Mach disk. Additionally, increasing the size of the initial gas curtain decreases the resistance experienced by the projectile outside the barrel. The initial gas curtain can also affect the cavitation bubble evolution process on the projectile sidewall, showing a growth-(attenuation)-stability trend.

Sono-catalytic syngas production by low-temperature biomass gasification

Syngas holds a crucial role in diverse industrial applications, including chemical synthesis and power generation. It has been traditionally generated through high-temperature processes, such as steam reforming or biomass gasification, demanding temperatures of up to 1200 °C, which results in substantial energy consumption. Consequently, there is a growing interest in exploring alternative, low-temperature biomass gasification processes. This paper introduces an innovative method for syngas production through sono-catalytic biomass conversion at significantly lower temperatures. The approach employs a sonochemical reactor that concentrates acoustic waves to activate inertial cavitation. Furfural, a biomass-derived platform chemical, was chosen as the primary chemical for the study, showcasing the potential of sonochemical syngas production. The reaction converted furfural into various gas products, particularly a mixture of hydrogen and carbon monoxide, with the chemical reaction hypothesized to be triggered by pyrolysis during bubble collapse hot spots. The incorporation of heterogeneous metal foams into the system further enhanced furfural conversion rates. This improvement was attributed to the preferential nucleation of cavitation bubbles on the porous metal foam surface, bringing the hot spots into proximity with furfural molecules. This application of sonochemistry in furfural pyrolysis at low temperatures holds promise for a more economical approach to biomass valorization.