Cavitation In Liquids Research Articles

Dynamics of a Spherical Cavity in a Cavitating Liquid with a Continuously Changing Concentration of Cavitation Nurses

An equation was obtained and the problem of the dynamics of the formation and radiation of a quasi-empty pulsating spherical cavity in a cavitating liquid under the influence of the changing speed of sound in the cavitation zone and the concentration of cavitation nuclei was solved for the first time. Data on the dynamics of the cavity, on radiation and the speed of collapse for the spectrum of internal initial pressure values showed that at the maximum concentration of the gas phase, the pulsations differ in the degree of compression. They have almost the same character — after the first collapse, only one half-cycle occurs, reaching different constant equilibrium radii. The condition of equality of pressure in the cavitation zone and inside the spherical cavity at its boundary made it possible for the first time to establish a dynamic relationship between the volumetric concentration (speed of sound) in the cavitation zone and the radius of the spherical cavity. When calculating and constructing a solution, the condition changes, according to which the initial size of the cavity takes on a value corresponding to the value of the initial pressure. The dependences of the radiation amplitude over the entire range of applied pressures were plotted. It turned out that the radiation amplitude increases by 5 orders of magnitude when the initial pressure in the cavity changes by 3 orders of magnitude from 10–2 atm to 10–5 atm.

К ВЫБОРУ РАСТВОРА ДЛЯ КАВИТАЦИИ В КОМПЛЕКСНОМ ЛЕЧЕНИИ ПОСЛЕРОДОВОГО ЭНДОМЕТРИТА

Relevance. Postpartum endometritis is an infectious and inflammatory process in the endometrium with possible involvement of the myometrium. The main components of the treatment of the disease are antibiotic therapy and removal of necrotic contents of the cavity of the postpartum uterus. From the point of view of caring for the organ, ultrasonic cavitation looks preferable. To increase its effectiveness, various solutions with antiseptic, immunomodulatory or other properties can be used. Aim. The purpose of our study was a comparative assessment of the effectiveness of the use of various liquids during ultrasonic cavitation in the treatment of postpartum endometritis. Materials and methods. 80 patients with mild and moderate severity of the disease were examined and treated. The patients were divided into 4 groups of 20 women: 1) patients of the 1st group received treatment according to the clinical recommendations of the Ministry of Health of the Russian Federation; 2) patients of the 2nd group underwent ultrasound cavitation of the uterine cavity using 0.9% sodium chloride solution; 3) patients of the 3rd group underwent ultrasound cavitation followed by additional irrigation of the uterine cavity 0.25% sodium deoxyribonucleate solution; 4) ultrasound cavitation of the uterine cavity was performed in patients of the 4th group using 0.9% furacilin solution. Results. On the 7th day of treatment for postpartum endometritis, all patients showed an improvement in well-being and objective indicators. At the same time, incomplete reduction of uterine soreness during palpation by the 7th day in patients of the 1st and 3rd groups led to an increase in bed days in these groups. In patients of group 1, there was a slower dynamics of blood parameters such as leukocyte count, C-reactive protein and erythrocyte sedimentation rate. The degree of reduction of tumor necrosis factor alpha and interleukin-10 was the lowest in group 1 and the highest in group 4. The bed day turned out to be the smallest in group 4 and the largest in group 1. Conclusions. Ultrasound cavitation of the uterine cavity significantly increases the effectiveness of complex therapy of postpartum endometritis and shortens the duration of treatment of patients, enhances the positive effect of ultrasonic cavitation by using 0.9% furacilin solution in a dilution of 1: 5000 as a cavitation liquid. Irrigation of the uterine cavity with a solution of sodium deoxyribonucleate does not significantly affect the healing process.

Effect of jet ejector geometry on the supply of a pumping unit preventing wax-deposit

Relevance. Today oil production by installations of electric centrifugal pumps is one of the leading methods of mechanized oil production. The mechanized operation of hard-to-recover oil objects is complicated by the high viscosity of reservoir oil, the formation of wax-deposits in the wellbore. This leads to an increase in hydraulic resistances due to a decrease in the flow section of pipes and other pumping equipment components, a decrease in the productivity of wells and the efficiency of pumping production. In this regard, an urgent task is to develop and improve methods and devices for preventing deposits of wax-deposits in wells. Object. Downhole pumping unit for dosing reagent (inhibitor of wax-deposits) into the well, which is a combination of two technical devices – a pump dosing the reagent and a jet pump. Aim. To analyze the influence of the design parameters of the dosing unit on the efficiency of its operation (reagent consumption, liquid cavitation coefficient in the jet pump). Methods. Mathematical modeling of the operation of a downhole dosing unit for the supply of reagent, based on the application of the laws of conservation of mass and quantity of motion, as well as Bernoulli's law for a moving flow in a jet pump. Results. Based on the simulation results, the nature of the influence of the design parameters of the developed installation on the reagent consumption is established. It is established that the maximum flow rate of the reagent is achieved with a mixing chamber diameter of about 22 mm; an increase in diameter relative to the specified value leads to a decrease in the degree of local pressure reduction, a decrease in the diameter of the mixing chamber – a drop in flow due to an increase in the flow rate in the chamber and an increase in hydraulic resistance. It was found that an increase in the supply of electric centrifugal pumps in the considered range of 100–200 m3 per day has practically no effect on the reagent consumption when the mixing chamber diameter is more than 30 mm. It was found that at confuser length values exceeding 210 mm, the cavitation coefficient, regardless of the mixing chamber diameter, exceeds one, which indicates a smooth and uniform pressure reduction in the device body. In general, it is shown that by regulating the design parameters of a downhole metering unit, it is possible to ensure the required reagent consumption at a known electric centrifugal pump supply (well flow rate).

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.

Some problems of modeling the liquid cavitation degassing. I. Acoustic cavitation.

In recent decades, cavitation methods of liquid degassing have become widely used, which today have practically replaced the traditional time-consuming mechanical and chemical methods of degassing in industry. The application of cavitation methods is based on the fact that a part of the neutral gases present in the liquid is not in a dissolved state, but in a so-called "free" state in the composition of a large number of vapor-gas bubbles, the size of which is measured on the scale of micro- and nanometers. The nature of the stable, long-term existence of such micro-bubbles has not yet found a reasonable explanation and is the subject of debate among researchers. Cavitation methods of degassing, both hydrodynamic and acoustic, are aimed precisely at the rapid removal of these bubbles from the liquid together with the free gas present in them. The advantage of using acoustic cavitation methods is the ability to precisely control the frequency and intensity of ultrasound, as well as the duration of sounding. Acoustic degassing methods are based on two mechanisms: the passage of dissolved gas inside pulsating bubbles due to the effect of "directed diffusion" and the convergence and subsequent coalescence of neighboring bubbles under the influence of force Bjerknes As a result, the growing bubbles quickly float up and leave the liquid together with the free gas. In recent years, a large number of articles on the comprehensive study of acoustic degassing processes have been published. According to the authors of these publications, the mechanism of degassing at the microscopic level and all the diversity of bubble dynamics, depending on the frequency and intensity of the sound, remain unclear. This article examines the main problems of modeling acoustic degassing processes, which confirm the absence of generally accepted clear ideas about the physical nature and mechanisms of cavitation phenomena and a general approach to the analysis of the obtained results. In order to develop research in this direction, the article also presents the results of a computational experiment on the coalescence of pulsating bubbles, conducted by the authors on the basis of a model of the dynamics of a single bubble previously created by them. As a result of the theoretical study, new, previously unknown information about the force interaction of pulsating bubbles of different sizes was obtained, which can be considered as a certain contribution to the understanding of the mechanisms of acoustic degassing.

Acceleration mechanism of abrasive particle in ultrasonic polishing under synergistic physical vibration and cavitation: Numerical study

Ultrasonic technology is widely applied in the engineering ceramic polishing processes without the limitation of material properties and ideally integrated into computer numerical control system. Ultrasonic-induced cavitation and mechanical vibration effect could accelerate the motion of solid abrasives. The individual behaviors of microjet/shockwave of ultrasonic cavitation in gases and liquids, and micro-abrasives with simple harmonic vibrations in solids and liquids has been extensively studied. To conduct a systematic and integrated study of abrasives behavior in the polishing contact region involving abrasive, surround-workpiece wall, ultrasonic physical vibration, and ultrasonic cavitation impact, a novel model integrating the free abrasive motion velocity and fixed abrasive indentation depth under multi-scale contact was proposed according to Hertzian contact theory, Greenwood-Williamson model, indentation deformation theory, the basic equations of cavitation bubble dynamics, cavitation impact control equations, and Newton's law of motion equation. The effects of ultrasonic amplitude, ultrasonic frequency, preloading force and particle size on the proposed model were investigated by theoretical analysis and numerical simulations. Ultrasonic physical vibration mainly influences the dynamic gap and further influence the number of different abrasives. Furthermore, the indentation depth of fixed abrasive depends mainly on the abrasive geometry. As the contact gap and abrasive size decrease, the indentation depth gradually decreases. Under the synergistic effect of cavitation-induced shock wave and microjet, the velocity of free abrasive in this paper is generally 0–150 m/s, and the kinetic energy of free abrasive increases roughly linearly with increasing frequency and approximately as a quadratic function with increasing particle size. Increasing the preloading force leads to a reduction in the abrasive kinetic energy. Besides, the kinetic energy induced by the shock wave has a cliff-like increment at an amplitude of 0.7–0.8 μm. It is revealed that the abrasive kinetic energy is suppressed by the cavitation bubble expansion and collapse at smaller ultrasonic pressure amplitude and surround-wall distance. This research provides a theoretical reference for the modeling of potential defects and material removal on the workpiece surface caused by abrasive motion during polishing, and reduces the trial cost for parameter optimization in actual polishing processing.

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.

Tailoring of residual stress by ultrasonic vibration-assisted abrasive peening in liquid cavitation of metallic alloys

The present study proposes a novel method of ultrasonic vibration assisted-abrasive peening for the enhancement of residual stress on the surface of metals and their alloys. The system employs a vibrating sonotrode that drives the formation and collapse of bubbles within a fluid medium. The imploding bubbles produce pressure waves which transfer momentum to the abrasives which are uniformly distributed in the fluid medium. The abrasives bombard a targeted surface along with intense pressure waves. This induces compressive residual stress through local plastic deformation in a short period. The capability of the ultrasonic-assisted abrasive peening setup is analysed in terms of residual stress by altering the abrasive concentration, peening time, and stand-of-distance between the bottom of the sonotrode and the exposed surface to be treated. The process is able to induce significant residual stress at around 67 % of yield strength for hard material Ti–6Al–4V and more than 80 % of yield strength for ductile materials, Al-6061 and OFHC-Cu. A numerical method coupled with a finite element model is employed to predict the dynamics of the process from cavitation of the bubble to the plastic deformation of the work material. At first, the model estimates the magnitudes of high-pressure waves at the bubble implosion near the solid surface, micro-jet velocity, and abrasive velocity. This information is then fed to Abaqus for numerical modelling of the deformation of work material. The impact of high-speed abrasives in the range of 100 m/s, pressure waves and microjets at the material surface are simulated through the FE model. The simulated results are verified with experimental findings in terms of surface residual stress for different materials, deviating within 10 %.

Hydrogen Embrittlement, Microcracking, and THz Vibrations in the Metal Electrodes of Cold-Fusion Electrolysis Experiments: Repeatability of Nuclear and Stoichiometric Balances

In the last few decades, several scientific papers have reported experimental evidence of anomalous nuclear reactions occurring in condensed matter during electrolytic phenomena or mechanical instabilities such as fracture (in solids) and cavitation (in liquids). Despite the numerous research activities carried out in the field of so-called “Cold Nuclear Fusion”, this phenomenon remains today not fully understood. In recent contributions by the authors, the formation of cracks on the surface of the electrodes used during electrolysis tests, together with chemical composition variations and anomalous sub-atomic particle emissions, were described. A mechanical interpretation of the experimental evidence can be based on low-energy phono-fission reactions, which are a conse- quence of hydrogen embrittlement, microcracking, and THz vibrations. In the present paper, the repeatable results of different laboratory testing programs obtained by means of Pd and Ni are discussed. Preliminary short notes about the energy balance close the paper.

Multiple computations for MHD flow of graphene-oxide nanofluid with radiative heat transfer within porous medium

This paper describes the fundamental characteristics of cavitation in non-Newtonian liquids and bubble dynamics and then applies them to the domains of bioengineering and biomedicine. The goal of this paper is to examine how Newtonian nanomaterial flows hydromagnetically when subjected to a spinning disc considering such biomedical and bioengineering applications. The vertical axis of the disc rotates with a uniform angular frequency. The fundamental mathematical expressions are governed by the Navier–Stokes equations with the Maxwell equations of magnetism, we obtained ordinary differential equations utilizing Von Kármán’s similarity transformations. Additionally, the effects of the magnetic field and radiation restrictions are considered. The RK-4 technique is used to solve the transmuted nonlinear ODEs. The analysis of MATLAB generated flow profiles has looked for changes in the values of key parameters. It is discovered that an increase in the thermal radiation parameter causes a decrease in the nanofluid temperature while an increase in the volume fraction of magnetite nanoparticles causes an increase. The skin-friction and heat-transfer rate at the disc are highly influenced by its rotational, the porosity of the porous media, thermal radiation and nanoparticle size. The rotational parameter, which regulates the disk’s rotation, is a result of the rotating phenomenon. The research demonstrates that when the disk’s rotation increases, the fluid motion accelerates in both the radial and cross-radial directions. Additionally, increasing the Prandtl number significantly improves heat transport, and a higher value for the rotation parameter shows a lesser concentration phenomenon. Additionally, the Nusselt number shows a decrease curve for a changeable thermal conductivity parameter. Finally, the current research can effectively close a gap in the physique of knowledge.

Dual frequency ultrasonic cavitation in various liquids: High-speed imaging and acoustic pressure measurements

Ultrasonic cavitation is used in various processes and applications, utilizing powerful shock waves and high-speed liquid jets generated by the collapsing bubbles. Typically, a single frequency source is used to produce the desired effects. However, optimization of the efficiency of ultrasound reactors is necessary to improve cavitation activity in specific applications such as for the exfoliation of two dimensional materials. This research takes the next step to investigate the effect of a dual frequency transducer system on the bubble dynamics, cavitation zone, pressure fields, acoustic spectra, and induced shock waves for four liquids with a range of physical properties. Using ultra-high-speed imaging and synchronized acoustic pressure measurements, the effect of ultrasonic dual frequencies on bubble dynamics was investigated. The addition of a high frequency transducer (1174 kHz) showed that the bubble fragments and satellite bubbles induced from a low frequency transducer (24 kHz) were able to extend their lifecycle and increase spatial distribution, thus, extending the boundaries of the cavitation zone. Furthermore, this combination of ultrasonic frequencies generated higher acoustic pressures (up to 180%) and enhanced the characteristic shock wave peak, indicating more bubble collapses and the generation of additional shock waves. The dual frequency system also enlarged the cavitation cloud size under the sonotrode. These observations specifically delineated the enhancement of cavitation activity using a dual frequency system pivotal for optimization of existing cavitation-based processing technologies.

Effect of technological parameters on hydrodynamic performance of ultra-high-pressure water-jet nozzle

With the increasing requirement for environmental protection in the area of ship rust removal, ultra-high-pressure (UHP) water-jet technique attaches much attention. Because derusting nozzle is one of the key parts to determine the efficiency of a UHP rust removal system, a better understanding of its technological parameters is required. According to the operation characters associated with UHP water-jet derusting nozzle, the 3D simulations are performed to investigate the nozzle's hydrodynamic performance, taking the cavitation effect, multiphase flow and liquid compressibility models into account. Subsequently, according to the rule of the Latin hypercube sampling (LHS) method, 400 datasets are determined. Pearson correlation, Kendall correlation and Spearman correlation coefficients are selected to analyze the database of UHP water-jet nozzle. It is found that the standoff distance (SOD) and jet angle have the most dominant effect on the magnitude of wall shear stress. Finally, the influence of different SODs and jet angles on hydrodynamic performance of UHP water jet is analyzed by regarding the distribution trends of wall pressure and wall shear stress on target surface as critical contrastive indicators. The distribution rules of the peak wall pressure and wall shear stress on target surface which are attributed to the variation of SODs and jet angles are summarized, and the optimum combination of these two key technological parameters is proposed. This related research provides a reference for the determination of technological parameters.

DYNAMICS OF PNEUMATIC DRIVE. LECTURE CYCLE THE EQUATION OF MOTION OF THE WORKING MEDIUM. MULTIPHASE GAS-LIQUID MIXTURES. CAVITATION AND HYDRATES IN THE DRIVE. TRANSMISSION OF INFORMATION VIA A HYDRAULIC COMMUNICATION CHANNEL Continuation

The paper presents the derivation of a mathematical model of the movement of the working environment; the application of the compiled system of equations of motion of the working medium in a cylindrical coordinate system is shown. The validity and possibility of using a rotary rheometer to determine the rheological characteristics of liquids are mathematically proved. An equation is obtained for the moment of resistance during the movement of Newtonian and non-Newtonian fluids in a coaxially cylindrical developed measuring system, taking into account the rheological parameters of the fluid: “k” is measures of fluid consistency and «n» is characteristics of the degree of non-Newtonian behavior of the material. Verification of the obtained results on the example of two liquids is given, and the corresponding conclusions are drawn. The issues of phase transition in gas-liquid mixtures of adjustable chokes are considered. The criteria for the occurrence of cavitation and hydrate formation in liquid and gaseous media are presented. Equations are described that make it possible to determine the condition for a phase transition from a liquid to a gas-liquid state. The paper presents a modern method of protecting the design of an adjustable throttle from the cavitation phenomenon, which consists in the use of throttle cells or throttling stages. The result of using throttle cells is given. An example of the formation of hydrates in a gas-liquid mixture during its flow through an adjustable throttle is considered. The criterion and method for determining the conditions of hydrate formation in the flow channel of an adjustable throttle are given, which consists in constructing an operating curve of an adjustable throttle, an envelope curve and their intersection with the curve of hydrate formation of a gas-liquid mixture to determine the conditions and areas of hydrate formation. The paper gives an example of the use of a hydraulic communication channel for information transfer. The main mathematical dependences of the mathematical model of the hydraulic communication channel, boundary and initial conditions are given. The form of the pressure pulse is obtained, and one of the main methods of encoding information for a hydraulic communication channel is considered. The condition for ensuring the required purity class of the working fluid for hydraulic systems is determined. The scientific novelty of the work includes the relations obtained, which make it possible to study the hydrodynamics of a fluid with variable viscosity, predict and evaluate the values of the shear stress in the fluid during its movement, the shear strain rate, the moment of friction forces, etc., with known rheological characteristics of the fluid. In addition, the scientific novelty of the work is the formulated criteria for the conditions of the phase transition, as well as the provision of practical recommendations to specialists involved in the design and operation of adjustable chokes. This work is based and is implemented as a course of lectures of the course “Dynamics of Pneumatic drive”, is red by the author at the Bauman Moscow State Technical University at the Department of “Hydromechanics, Hydraulic Machines and Hydropneumoautomatics” (E10), as part of the preparation of masters in the specialty 05.04.13 “Hydraulic machines and hydropneumatic drives”.

Cavitation in cryogenic fluids: A critical research review

Cavitation occurs as the fluid pressure is lower than the vapor pressure at a local thermodynamic state and may result in huge damage to the hydraulic machinery. Cavitation in cryogenic liquids is widely present in contemporary science, and the characteristics of cryogenic cavitation are quite different from those of water due to thermal effects and strong variations in fluid properties. The present paper reviews recent progress made toward performing experimental measurements and developing modeling strategies to thoroughly investigate cryogenic cavitation. The thermodynamic properties of cryogenic fluids are first analyzed, and different scaling laws for thermal effects estimation are then introduced. As far as cryogenic cavitation experimental research is concerned, the progress made in the cavitation visualization and cavity dynamics and the synchronous measurements of the multi-physical field are mainly introduced. As for the study on numerical simulation of cryogenic cavitation, the commonly used cavitation models and turbulence models are, respectively, classified and presented, and the modifications and improvements of the cavitation model and turbulence model for thermal effect modeling of cryogenic cavitation are examined. Then, several advances of critical issues in cryogenic fluid cavitation research are reviewed, including the influences of thermal effects, unsteady shedding mechanisms, cavitation–vortex interactions, and cavitation-induced vibration/noise. This review offers a clear vision of the state-of-the-art from both experimental and numerical modeling viewpoints, highlights the critical study developments and identifies the research gaps in the literature, and gives an outlook for further research on cryogenic cavitation.

DYNAMICS OF PNEUMATIC DRIVE. LECTURE CYCLE. THE EQUATION OF MOTION OF THE WORKING MEDIUM. MULTIPHASE GAS-LIQUID MIXTURES. CAVITATION AND HYDRATES IN THE DRIVE. TRANSMISSION OF INFORMATION VIA A HYDRAULIC COMMUNICATION CHANNEL

The paper presents the derivation of a mathematical model of the movement of the working environment; the application of the compiled system of equations of motion of the working medium in a cylindrical coordinate system is shown. The validity and possibility of using a rotary rheometer to determine the rheological characteristics of liquids are mathematically proved. An equation is obtained for the moment of resistance during the movement of Newtonian and non-Newtonian fluids in a coaxially cylindrical developed measuring system, taking into account the rheological parameters of the fluid: “k” is measures of fluid consistency and «n» is characteristics of the degree of non-Newtonian behavior of the material. Verification of the obtained results on the example of two liquids is given, and the corresponding conclusions are drawn. The issues of phase transition in gas-liquid mixtures of adjustable chokes are considered. The criteria for the occurrence of cavitation and hydrate formation in liquid and gaseous media are presented. Equations are described that make it possible to determine the condition for a phase transition from a liquid to a gas-liquid state. The paper presents a modern method of protecting the design of an adjustable throttle from the cavitation phenomenon, which consists in the use of throttle cells or throttling stages. The result of using throttle cells is given. An example of the formation of hydrates in a gas-liquid mixture during its flow through an adjustable throttle is considered. The criterion and method for determining the conditions of hydrate formation in the flow channel of an adjustable throttle are given, which consists in constructing an operating curve of an adjustable throttle, an envelope curve and their intersection with the curve of hydrate formation of a gas-liquid mixture to determine the conditions and areas of hydrate formation. The paper gives an example of the use of a hydraulic communication channel for information transfer. The main mathematical dependences of the mathematical model of the hydraulic communication channel, boundary and initial conditions are given. The form of the pressure pulse is obtained, and one of the main methods of encoding information for a hydraulic communication channel is considered. The condition for ensuring the required purity class of the working fluid for hydraulic systems is determined. The scientific novelty of the work includes the relations obtained, which make it possible to study the hydrodynamics of a fluid with variable viscosity, predict and evaluate the values of the shear stress in the fluid during its movement, the shear strain rate, the moment of friction forces, etc., with known rheological characteristics of the fluid. In addition, the scientific novelty of the work is the formulated criteria for the conditions of the phase transition, as well as the provision of practical recommendations to specialists involved in the design and operation of adjustable chokes. This work is based and is implemented as a course of lectures of the course “Dynamics of Pneumatic drive”, is red by the author at the Bauman Moscow State Technical University at the Department of “Hydromechanics, Hydraulic Machines and Hydropneumoautomatics” (E10), as part of the preparation of masters in the specialty 05.04.13 “Hydraulic machines and hydropneumatic drives”.

Thermodynamic effects at Venturi cavitation in different liquids

Thermodynamic effects delay the growth of cavitation bubbles and may accumulate to a considerable level in a bubbly cloud. Under thermo-sensitive conditions, due to thermodynamic effects, a bubbly cloud is often believed to behave similarly to a single cavitation bubble with respect to its shape, oscillation, etc. Discrepancies in thermodynamic effects on cavitating flows in previous experimental studies may result from the lack of control of non-dimensional parameter groups under this special condition. In the present paper, we first derive the non-dimensional parameter groups from the dynamics of a single cavitation bubble traveling through a Venturi tube. Among them, three major non-dimensional parameters are proposed for similitude conditions of Venturi cavitation experiments between different liquids, namely, the thermodynamic parameter, the Reynolds number, and the relative cavitation number. Our theory is validated with systematic experiments of Venturi cavitation in water, Freon 113, and fluoroketone in a small-scale closed-circuit cavitation tunnel under well-controlled conditions. Simultaneous high-speed observations from top and front views provide improved measurement of the cavitation characteristics. By comparing the variations of the attached cavity lengths and their oscillation frequencies, we successfully achieve similarities between different working liquids. The results are of particular importance for surrogates, when the original working liquid is too costly or too hazardous, e.g., cryogenic liquid hydrogen LH2 or liquid oxygen LO2.

Cavitation erosion behaviors and damage mechanism of Ti-Ni alloy impacted by water jet with different standoff distances

The cavitation erosion of Ti-Ni alloy is explored on a cavitating liquid jet with different standoff distances. The cavitation erosion characteristics of Ti-Ni alloy specimens are analyzed, and the influences that different standoff distances of the water jet have on cavitation erosion are explored. The results of cavitation erosion outcomes under different standoff distances of 6 mm, 8 mm, 10 mm, 12 mm, 14 mm and 16 mm show slight deformation, grain boundary cracking and formation of initial micro-pits, pits of maximum depth around 50 μm, more pits of maximum depth around 80 μm with micro-cracks, obvious plastic deformation traces with some pits, bulges and slip bands, respectively. When the Ti-Ni alloy is impacted by water jet with a standoff distance of 12 mm for 4 hrs, the surface microstructure undergoes substructural evolution and new fine grains form, with obvious stress concentration and dislocation accumulation appearing on the subsurface.

Burr removal from high-aspect-ratio micro-pillars using ultrasonic-assisted abrasive micro-deburring

The demand for high-aspect-ratio microstructures is ever increasing in the fields of microelectromechanical systems, biomedicine, aerospace, telecommunication, and heat transfer. Mechanical micromachining processes have a distinct advantage over lithography-based processes for machining complex three-dimensional microstructures on a variety of materials with high accuracy and surface finish. But the tool-based micromachining operations face inherent issues in the form of excessive burr formation, which needs to be addressed by post-machining burr removal operations. In this study, an ultrasonic-assisted abrasive micro-deburring process employing a probe sonotrode and abrasive particles has been investigated for deburring high-aspect-ratio micro-pillars machined on aluminium 6061 and copper. Deburring of micromilled pillars of aspect ratio 5:1 has been achieved while maintaining pillar integrity. The mechanism of deburring has been observed to be mainly by the impact of the abrasive particles with a minor role played by liquid cavitation. Burr reduction as high as 88.75% for Al 6061 and 90.1% for copper has been achieved in a short processing time of 10 s. This is a significantly faster process than other ultrasonic cavitation-based deburring processes described in literature (deburring time ranging from 60 min to a few hours). With proper control of the process parameters like stand-off distance and power, burr removal has been achieved while maintaining the integrity of the micro-pillars. Pure water cavitation has also been studied for comparison, which has resulted in a burr removal by 51.5% and 53.1% for Al 6061 and copper, respectively. Upon proper selection of the process parameters, this process can be a viable alternative to existing deburring methods in terms of minimal processing time and structure damage.

Reiner-Rivlin nanofluid over a rotating disk flow

Background and objectiveNon-Newtonian (Reiner-Rivlin) nanofluid is novel prospective in various biology and biomedical (medicine) engineering processes and in many other biological science. In addition, various biological liquids, such as saliva, synovial liquid, blood have non-Newtonian behavior and can demonstrate important viscoelastic characteristics. This treatise elucidates broad feature of cavitation in non-Newtonian liquids and bubble dynamics and applies them to the fields of bioengineering and biomedicine. In view of such biomedical and bioengineering applications the aim of this paper is to discuss the hydromagnetic flow of Reiner-Rivlin nanomaterial subject to a rotating disk is addressed. Disk rotates with constant angular frequency about vertical axis. Reiner’s equation of a general viscous fluid differs from the Navier’s Stokes equation by a quadratic expression describing cross-viscosity coefficient. Energy equation is obtained using thermal radiation and heat generation. Thermodynamics second law investigates the entropy. Multiple slip conditions are analyzed. Thermophoresis and random diffusion behaviors are addressed. First order reaction is also taken into account. MethodologyNonlinear systems are reduced to dimensionless system by employing similarity transformation. ND-solve procedure is implemented on Mathematics software for the computation of nonlinear differential system. ResultsGraphical representation of velocity, temperature and concentration are obtained. Entropy generation has been emphasized. Velocity has decaying trends for magnetic variable. Random diffusion variable have opposite trends for concentration and temperature. An intensification in thermal slip variable reduces temperature.

Numerical prediction of erosion due to a cavitating jet

We numerically investigate the erosion potential of a cavitating liquid jet by means of high-resolution finite volume simulations. As thermodynamic model, we employ a barotropic equilibrium cavitation approach, embedded into a homogeneous mixture model. To resolve the effects of collapsing vapor structures and to estimate the erosion potential, full compressibility is considered. Two different operating points featuring different cavitation intensities are investigated and their erosion potential is estimated and compared. Different methods are used for this purpose, including collapse detection (Mihatsch et al., 2015), maximum pressure distribution on the wall, and a new method of generating numerical pit equivalents. The data of numerical pit equivalents is analyzed in detail and compared with experimental data from the literature. Furthermore, a comprehensive grid study for both operating points is presented.