Implosion Of Cavitation Bubbles Research Articles

From cavitation to astrophysics: Explicit solution of the spherical collapse equation.

Differential equationsof the form R[over ̈]=-kR^{γ}, with a positive constant k and real parameter γ, are fundamental in describing phenomena such as the spherical gravitational collapse (γ=-2), the implosion of cavitation bubbles (γ=-4), and the orbital decay in binary black holes (γ=-7). While explicit elemental solutions exist for select integer values of γ, more comprehensive solutions encompassing larger subsets of γ have been independently developed in hydrostatics (see Lane-Emden equation) and hydrodynamics (see Rayleigh-Plesset equation). I here present a universal explicit solution for all real γ, invoking the beta distribution. Although standard numerical ordinary differential equationsolvers can readily evaluate more general second-order differential equations, this explicit solution reveals a hidden connection between collapse motions and probability theory that enables further analytical manipulations, it conceptually unifies distinct fields, and it offers insights into symmetry properties, thereby enhancing our understanding of these pervasive differential equations.

Influence of yeast size on the kinetics of cell disruption in an ultrasonic homogenizer

The results of studies on the disintegration kinetics of the yeast Saccharomyces cerevisiae are presented. The process was carried out in a 500 W ultrasonic homogenizer equipped with a spherical working chamber with a volume of 100 cm 3. The concentration of the suspension of microorganisms was 0.05 g d.m./cm 3. The continuous phase was water solution containing 0.15 M NaCl and 4 mM K 2HPO 4. The kinetics of cell disruption were studied by the direct method. The theory of random transformation of dispersed matter was used to analyze the process. There was significant variation in the size of yeast cells. The range of changes in the values of parameters describing the size of microorganisms was divided into size classes. The kinetics of cell disruption in individual classes was described by a first-order linear differential equation. During the implosion of cavitation bubbles, the transformation volume of individual microorganisms is generated. It has been shown that as the volume of cells in subsequent size classes increases, their transformation volumes do not increase significantly. The safe volume for cells remains unchanged. As the size of the microorganisms increased, there was no increase in the constant rate of cell disruption.

Effects of food to inoculum ratio and ultrasound pre-treatment on biogas production from dissolved air flotation waste from dairy industry

Dissolved air flotation (DAF) waste, a byproduct with high lipid content separated from dairy wastewater, is disposed of by land spreading and causing environmental pollution. To develop a sustainable treatment for DAF waste, this study investigated the effects of food to inoculum (F/I) ratio and ultrasound pre-treatment on the anaerobic digestion of DAF waste. The biochemical methane potential (BMP) of tested DAF waste ranged from 436–566 mL CH4/g VSfed. Increasing the F/I ratio (>1.0) inhibited methane production due to long chain fatty acids (LCFA) accumulation, which high concentrations of oleate inhibited methanogenesis and delayed palmitate degradation. Ultrasound pre-treatment with 30 min pulse (10 s on/ 10 s off) and 15 min continuous operations increased soluble chemical oxygen demand in DAF waste by 82% and 52%, respectively. Moreover, continuous sonication removed 38% of LCFA due to the implosion of cavitation bubbles. The BMP of DAF waste increased by 36% after sonication with F/I ratio 3.0. However, the lag time of methane production was prolonged after sonication due to the fast release of LCFA to the bulk solution. By implementing ultrasound pre-treatment and optimizing the F/I ratio, the energy potential of DAF waste can be harnessed, leading to more sustainable practices in dairy production.

Influence of aging heat treatment at 180 °C on cavitation erosion for aluminum alloy type 5083 in cold rolled state

Aluminum-based alloys have wide applicability in the construction of aircraft, vehicles, and ships. Some of their components, during operation, such as the radiators and the rotors of the cooling pumps in the vehicles, and the propellers of fishing and pleasure boats are affected by the abrasive, chemical and cavitational corrosive action of the water. At certain hydrodynamic flow regimes, the most dangerous becomes the corrosion through cavitation. Operation in such regimes inevitably leads to damaging the structure, due to cyclic stresses of the micro-jets and shock waves generated by the implosion of cavitation bubbles. Although the chemical constitution and alloying with other chemical elements increase the mechanical properties, the service life is still limited when operating in high-intensity cavitation flows. Therefore, researchers are looking for solutions to improve this resistance through various treatments, such as bulk heat. Research heading the same direction, but, made on 5083 alloy, is presented in this paper. The results highlight the behavior of a modified structure compared to the semi-fabricated state (obtained by rolling), through three durations regimes (one hours, 12 hours and 24 hours) of aging heat treatment to 180 °C temperature, after hardening treatment at 450 °C. The cavitation tests were performed in the Laboratory of the Polytechnic University of Timisoara, on the standard vibrating device with piezoceramic crystals. The results were expressed by curves and parameters specific to the evaluation of cavitation resistance, and by macro and microscopic images, showing the unique aspects of the connection between the structure and the mechanical properties obtained through heat treatment regimes. Thus, comparison of the results, including with the delivery state (laminated product), shows that the highest resistance is provided by the treatment at 24 hours. At the same time, the erosion, of pitting and caverns type, and differs from one structure to another.

Degradation and Protection of Materials from Cavitation Erosion: A Review.

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.

Vacancy-Defective Cobalt Nitride Nanostructures for Sonocatalytic Hydrogen Production Using Various Water Resources

The cavitation effect, as a kind of geochemical phenomenon, widely exists under intense hydrodynamic circumstances, turbulent streams, earthquakes, or waterfalls and anywhere else where a shear force abruptly breaks the continuity of liquid surfaces. The development of an efficient and cheap sonocatalyst is hence one of the effective ways to utilize the cavitation effect to harness energy. In this study, we use a flower-like cobalt nitride nanowires catalyst with rich nitrogen-vacancy nanostructures to achieve efficient sonocatalytic hydrogen production in various water resources. In pure water, an exceptional sonocatalytic hydrogen generation rate of 28.5 μmol g–1 h–1 is delivered by the flower-like cobalt nitride nanowires. More interestingly, hydrogen peroxide, a high-value oxidation product, is also detected in the liquid phase after ultrasonic wave vibrations. Due to the acid/alkali resistance and corrosion resistance of the transition metal nitrides (TMNs), cobalt nitride nanowires can also produce hydrogen in acidic water, alkaline water, seawater, and wastewater. Enriched active sites in cobalt nitride nanowires greatly promote the recombination of radicals generated by the implosion of cavitation bubbles, which promotes sonochemical reaction efficiency. In addition, the cobalt nitride nanowire catalyst displays excellent stability and reusability during the sonochemical catalytic reaction. The findings are anticipated to be useful for further research on transition metal nitride materials as prospective sonocatalysts for energy conversion and environmental remediation.

Weapon performance and contest assessment strategies of the cavitating snaps in snapping shrimp

AbstractAnimals compete in contests over limited resources. Contestants forfeit once they ascertain that their opponent has greater resource‐holding potential (RHP; mutual assessment) or once they reach a threshold of costs (self‐assessment). Functional scaling studies of contest behaviour performance can inform how assessment signals, offensive capacity and endurance scale with RHP and thereby elucidate the mechanisms through which each of these assessment types operates.Here, we performed behavioural contest analyses to determine the assessment strategies used in snapping shrimp (Alpheus heterochaelis) contests. Then, we used biomechanical measurements of a common contest behaviour to inform how assessment might operate. We were specifically interested in the snapping behaviour during which snapping shrimp fire imploding cavitation bubbles—hereafter, ‘snaps’—at their opponents.We showed thatA. heterochaelisuse mutual assessment early in contests. Then, when they fire snaps, they switch to cumulative assessment—a type of self‐assessment where contestants endure costs from their own behaviours (e.g. energy) and their opponent's (e.g. injury).Because larger individuals tend to win contests, we then tested how the maximum performance and endurance of snaps scaled with size. We measured the average angular velocity of the snapping dactyl, cavitation bubble duration and pressure of snaps as metrics of performance. We measured 10 snaps per individual (n = 76 individuals). From this series of 10 snaps, we calculated the maximum of each metric as the maximum performance and the attrition of each metric over the course of 10 snaps as a measure of endurance. Maximum performance increased with size, but endurance did not.This suggests that cumulative assessment in snapping shrimp is driven by opponent‐imposed costs. Our results are not consistent with self‐assessment based on endurance; however, the experiment could not fully replicate the quick succession of snaps fired in real contests. Future experiments should better replicate the rapid firing of snaps to test if endurance matters in a more ecologically relevant context.Our framework of integrating biomechanics and behavioural ecology provides a pathway to identify precise mechanisms of contest assessment and animal behaviour more broadly.Read the freePlain Language Summaryfor this article on the Journal blog.

Effect of processing parameters on the development of anisotropic α-Al2O3 platelets during molten salt synthesis

It is of utmost importance to control the size and morphology of anisotropic α-Al2O3 platelets owing to its extensive usage in various applications, including most recent synthetic biomimetic abalone nacre-like composites. In the present article, a wide range of well-developed and well-dispersed α-Al2O3 platelets were produced with diameter and thickness ranging from 4 - 8 μm and 0.6–1 μm respectively, by taking γ-Al2O3 precursor and sodium sulfate as low melting flux. The effects of various processing parameters like calcination temperatures, molar ratios of Al/Na and soaking time on the phase formation and morphology development of the final platelets were investigated in rigor. The results indicated that high calcination temperature of 1200 °C and moderate soaking time (60 min) helped to develop α-Al2O3 platelets with hexagonal morphology and uniform sizes. The sulfate salts created favorable conditions for growth of anisotropic platy α-Al2O3 and Al/Na molar ratio has significant effect in controlling the aspect ratio of the platelets. The impact of deagglomeration treatment by the ultrasound irradiation on the calcined aggregates of platelets was also examined. The breakage of platelets clusters by fracture/erosion due to the interaction with imploding cavitation bubbles under ultrasound energy, reached maximum after 90 min of deagglomeration treatment. The detail phase transformation sequences from γ-Al2O3 to α-Al2O3 was explained by correlating thermal (DT-TGA) and X-ray analysis. The growth mechanism of the anisotropic α-Al2O3 particles in the presence of molten Na2SO4 liquid was also unraveled.

Evolution and implosion of cavitation bubbles towards solid surface

Cavitation bubbles generated via laser-induced breakdown are investigated experimentally. The present work focuses on the direction of the first bubble collapse near a solid surface in distilled water. The solid surface is placed first to the right side in a cuvette filled with distilled water and then placed to the top of the cuvette. In this experiment, it is observed in which direction the cavitation bubble collapses. The cavitation bubble is visualized by a high-speed camera of frequency 68kHz.

Ultrasonication: a process intensification tool for methyl ester synthesis: a mini review

Process intensification has been a promising tool for efficient energy usage, especially in the production of products that are considered energy sources, such as biodiesel. The very mechanism of ultrasound in aiding the reactions lies in the implosion of cavitation bubbles that generate hot regions with extremely high temperatures that reach as high as thousands of degree Celsius on a microsecond timescale. As biodiesel is emerging as an alternate green fuel or extender for fossil diesel that is apparent from the biodiesel mandates across the globe, sonochemistry technology is sought-after as a tool to produce biofuel in a much efficient way. Research and development in this technology is crucial to keep the biodiesel industry relevant by lowering the production cost, as the cost of production is seen as one of the major obstacles in biodiesel commercialization. In addition, by utilizing process intensification tools, the amount of catalyst and associated issues (abundant wastewater generation and treatment, process cycle time) can be reduced, in turn making the process much greener. Ultrasound not only accelerates the reaction rate but also assists in the miscibility of oil and methanol, thus decreasing the amount of catalyst needed for the reaction. While many articles have been issued on ultrasound-assisted biodiesel production, a comprehensive review on the very topic of ultrasound in biodiesel is somehow missing. This review intends to explore the use of ultrasound in transesterification and esterification reactions to produce methyl esters (biodiesel).

Analysis of water coolant pressure fluctuation induced by piston slap

Liner cavitation is caused by water pressure fluctuation in water coolant passage. When the negative pressure falls below the saturated vapor pressure, the impulsive pressure following the implosion of cavitation bubbles causes cavitation erosion on wet cylinder liner surface. Prediction of coolant pressure fluctuation is crucial to relieve liner cavitation erosion. Vibration of internal combustion engine especially liner vibration is thought of as the primary cause of liner cavitation. Piston slap is deemed as the major factor of engine vibration. The present work establishes a coupled system between entire engine structure and water coolant passage acoustic field considering their vibration characteristics by finite element method and boundary element method. Mechanism of piston slap is proposed and the resulting slap forces are applied on cylinder to predict water coolant pressure fluctuation. The influence of sound speed variation of acoustic field on pressure fluctuation is discussed. The contributions of natural modes of engine and water acoustic field to largest negative pressure are analyzed.

Study on the coolant pressure of internal combustion engines through vibro-acoustical analysis of a real cylinder block structure

Liner cavitation is caused by water pressure fluctuation in the water coolant passage of internal combustion engines. The high-speed re-entrant jet and shock wave following the implosion of cavitation bubbles cause cavitation erosion on the wet cylinder liner surface. The present work proposes a numerical method to predict the water pressure fluctuation of engine systems considering acoustic features of water coolant passage. The effect of the geometry modification of water coolant passage is evaluated. The water coolant passage acoustic field is introduced into the engine system containing a crankcase, a gear case, a cylinder head and an injection pump. The water coolant pressure fluctuation and engine vibration are calculated for engine systems with different exciting forces. The cross-sectional pressure distribution of water coolant passage and the longitudinal pressure distribution along thrust side of liner at top dead center are discussed. It is revealed that the pressure distribution is influenced by certain acoustic modes. The pressure fluctuates strongly at the top dead center, which is conductive to bubble formation and explosion.

Ultrasound-Activated Atom-Economical Approach to the Synthesis of Highly Substituted Pyrrolidin-2-ones through a Four-Component Ugi/5-endo-trig Intramolecular Radical Cyclization Reaction

An efficient and diversity-oriented access to functionalized pyrrolidin-2-ones through an Ugi reaction of readily available starting materials with a subsequent transformation is described. A two-step reaction sequence of a four-component Ugi reaction and an intramolecular radical-cyclization reaction leads to the chemo- and regioselective formation of a single product with high atom economy and good to high yields. The radicalization of the pseudopeptides generated from the first step by a cavitational mechanism produces the key intermediate for the ultrasound-activated formation of γ-lactams as the final products by β-Michael addition. Among the advantages of this approach are its use of cavitation bubble implosion as an exclusive path to radicalization of the polyfunctional Ugi adduct, its high selectivity, and its short reaction times.

Damage and Failure of Axonal Microtubule under Extreme High Strain Rate: An In-Silico Molecular Dynamics Study

As a major cytoskeleton element of the axon, the breaking of microtubules (MTs) has been considered as a major cause of the axon degeneration. High strain rate loading is considered as one of the key factors in microtubule breaking. Due to the small size of microtubule, the real-time behavior of microtubule breaking is hard to capture. This study employs fully-atomistic molecular dynamics (MD) simulation to determine the failure modes of microtubule under different loadings conditions such as, unidirectional stretching, bending and hydrostatic expansion. For each loading conditions, MT is subjected to extreme high strain rate (108–109 s−1) loading. We argue that such level of high strain rate may be realized during cavitation bubble implosion. For each loading type, we have determined the critical energy for MT rupture. The associated rupture mechanisms are also discussed. We observed that the stretching has the lowest energy barrier to break the MT at the nanosecond time scale. Moreover, the breakage between the dimers starts at ~16% of total strain when stretched, which is much smaller compared to the reported strain-at-failure (50%) for lower strain rate loading. It suggests that MT fails at a significantly smaller strain states when loaded at higher strain rates.

Numerical modelling of acoustic pressure fields to optimize the ultrasonic cleaning technique for cylinders

Fouling build up is a well-known problem in the offshore industry. Accumulation of fouling occurs in different structures, e.g. offshore pipes, ship hulls, floating production platforms. The type of fouling that accumulates is dependent on environmental conditions surrounding the structure itself. Current methods deployed for fouling removal span across hydraulic, chemical and manual, all sharing the common disadvantage of necessitating halting production for the cleaning process to commence. Conventionally, ultrasound is used in ultrasonic baths to clean a submerged component by the generation and implosion of cavitation bubbles on the fouled surface; this method is particularly used in Reverse Osmosis applications. However, this requires the submersion of the fouled structure and thus may require a halt to production. Large fouled structures such as pipelines may not be accommodated. The application of high power ultrasonics is proposed in this work as a means to remove fouling on a structure whilst in operation. The work presented in this paper consists of the development of a finite element analysis model based on successful cleaning results from a pipe fouled with calcite on the inner pipe wall. A Polytec 3D Laser Doppler Vibrometer was used in this investigation to study the fouling removal process. Results show the potential of high power ultrasonics for fouling removal in pipe structures from the wave propagation across the structure under excitation, and are used to validate a COMSOL model to determine cleaning patterns based on pressure and displacement distributions for future transducer array design and optimization.

The use of Rz roughness parameter for evaluation of materials behavior to cavitation erosion

It is well known that the cavitation eroded surfaces have a porous appearance with a pronounced roughness. The cause is the pitting resulted from the impact with the micro jets as well as the shock waves both determined by the implosion of cavitation bubbles. The height and the shape of roughness is undoubtedly an expression of the resistance of the surface to the cavitation stresses. The paper put into evidence the possibility of using the roughness parameter Rz for estimating the material resistance to cavitation phenomena. For this purpose, the mean depth erosion penetration (MDE-parameter, recommended by the ASTM G32-2010 Standard) was compared with the roughness of three different materials (an annealed bronze, the same bronze subjected to quenching and an annealed alloyed steel), both measured at four cavitation erosion exposure (30, 75, 120 and 165 minutes). The roughness measurements were made in 18 different zones, disposed after two perpendicular diameters, along a measuring lengths of 4 mm. The results confirm the possibility of using the parameter Rz for estimating the cavitation erosion resistance of a material. The differences between the measured values of Rz and those of the characteristic parameter MDE are of the same order of magnitude as those obtained for MDE determination, using more samples of the same material.

Correlation between cavitation erosion resistance and cyclic mechanical properties of different metallic materials

Machine components in contact with flowing fluids are especially prone to cavitation erosion, where plastic deformation and material loss occur due to the repeated implosion of cavitation bubbles in the vicinity of a solid surface. Identifying a correlation between experimentally derivable material properties and resistance against cavitation erosion could help improve the lifetime of cavitation-affected components. Cavitation erosion is a predominantly fatigue-driven phenomenon. In this investigation, we conducted nanoindentation experiments to examine cyclic micromechanical material properties in response to an increasing number of cycles. The experiments were performed on pure iron and different steel grades, i.e., austenitic stainless CrMnCN steels, interstitially alloyed with carbon and nitrogen. We confirmed the view, also proposed in literature, that indentation hardness is inappropriate for ordering the investigated materials by incubation period or maximum erosion rate. We found that the percentage increase of nanoindentation contact stiffness, after an increasing number of cycles, is a promising indicator in terms of the overall ranking of cavitation erosion resistance among the considered materials. Although a single cavitation impact is associated with a significantly higher strain rate than nanoindentation experiments, it is shown that the plastically deformed area around each indent exhibits indications of deformation, such as the formation of slip lines that are also observable after cavitation-induced impacts.

Simultaneous High-Speed Recording of Sonoluminescence and Bubble Dynamics in Multibubble Fields.

Multibubble sonoluminescence (MBSL) is the emission of light from imploding cavitation bubbles in dense ensembles or clouds. We demonstrate a technique of high-speed recording that allows imaging of bubble oscillations and motion together with emitted light flashes in a nonstationary multibubble environment. Hereby a definite experimental identification of light emitting individual bubbles, as well as details of their collapse dynamics can be obtained. For the extremely bright MBSL of acoustic cavitation in xenon saturated phosphoric acid, we are able to explore effects of bubble translation, deformation, and interaction on MBSL activity. The recordings with up to 0.5million frames per second show that few and only the largest bubbles in the fields are flashing brightly, and that emission often occurs repetitively. Bubble collisions can lead to coalescence and the start or intensification of the emission, but also to its termination via instabilities and splitting. Bubbles that develop a liquid jet during collapse can flash intensely, but stronger jetting gradually reduces the emissions. Estimates of MBSL collapse temperature peaks are possible by numerical fits of transient bubble dynamics, in one case yielding 38 000K.

Cavitation erosion mechanisms in stainless steels and in composite metal–ceramic HVOF coatings

Cavitation erosion is a leading cause of hydraulic machinery erosion: imploding cavitation bubbles cause impacts, pitting, and mass loss leading to the component׳s failure. Damage can be mitigated by the use of protective coatings tailored to resist pitting and crack nucleation, to greatly increase the part׳s lifetime. Coatings deposited with the High Velocity Oxy-Fuel (HVOF) process demonstrate low porosity, high hardness and high adhesion. In this work, the cavitation erosion behavior of martensitic and ferritic stainless steels and HVOF coatings prepared from pure Fe3Al powder and Fe3Al reinforced with nitride and boride phases was investigated using the G32 vibratory setup. The results are compared with coatings sprayed from commercial powders: WC–CoCr and Cr3C2–NiCr. HVOF coatings exhibit slightly lower erosion rates than martensitic stainless steels. The mechanical properties were evaluated using depth sensing indentation: higher hardness was associated with better cavitation erosion resistance for steels, but not for the coatings. The composite coatings’ wear mechanisms followed a matrix erosion pattern accompanied by ceramic grain removal.

On the Mechanism of Ultrasound-Driven Deagglomeration of Nanoparticle Agglomerates in Aluminum Melt

One of the promising directions in the technology of composite alloys with improved mechanical properties is reinforcement of the metallic matrix with nanopowders introduced in the liquid metal. Ultrasonic processing is known to significantly improve the introduction of submicrone particles to the metallic melt. This study focuses on the mechanisms of deagglomeration and wettability of such particles by the melt under the action of ultrasound. The suggested mechanism involves the penetration of the liquid metal into the pores and cracks of the agglomerates under the excess pressure created by imploding cavitation bubbles and further destruction of the agglomerate by the sound wave. The main dependences connecting the acoustic parameters and processing time with the physical and chemical properties of particles and the melt are obtained through analytical modeling. The mathematical description of the ultrasonic deagglomeration in liquid metal is presented; a dependence of the threshold intensity of ultrasound for the break-up of agglomerates on their size is reported.