Single Bubble Research Articles

Physics-informed neural networks for heat transfer prediction in two-phase flows

This paper presents data-driven simulations of two-phase fluid processes with heat transfer. A Physics-Informed Neural Network (PINN) was applied to capture the behaviour of phase interfaces in two-phase flows and model the hydrodynamics and heat transfer of flow configurations representative of established numerical test cases. The developed PINN approach was trained on simulation data derived from physically based Computational Fluid Dynamics (CFD) simulations with interface capturing. The present study considers fundamental problems, including tracking the rise of a single gas bubble in a denser fluid and exploring the heat transfer in the wake of a bubble rising close to a heated wall. Tracking of a rising bubble phase interface of fluids with disparate properties was performed, revealing a maximum error of only 5.2% at the interface edge and a maximum error of 2.8% at the position of the centre of mass. Inferred (hidden variable) flows are studied in addition to a purely extrapolative inverse isothermal bubble case. When no velocity data was supplied, velocity field predictions remained accurate. Rise of an inferred isothermal bubble with unseen fluid properties was found to produce a maximum mean-squared error of 0.28 and centre of mass error of 1.25%. For the case of the rising bubble with a hot wall, the maximum error in the temperature domain using specified boundary conditions was 6.8%, while the bubble position analysis reveals a maximum positional error of 3.6%. These results demonstrate that PINN is agnostic to geometry and fluid properties when studying the combined effects of convection and buoyancy on two-phase flows for the first time. This work serves as a starting point for PINN in multiphase cases involving heat transfer over a range of geometries. Eventually, PINN will be used in such cases to provide solutions for forward, inverse, and extrapolative cases. Each of which represent a dramatic saving in computational cost compared to traditional CFD.

Effect of ultrasonication on rising characteristics of a single gas bubble

In recent years, ultrasonication has been used to enhance flotation process. Gas bubble is the unique carrier during mineral flotation, and thus its characteristics play an important role. However, the bubble rising characteristics under ultrasound action are not clear. Therefore, this paper aims to investigate the effect of ultrasonication on bubble rising behaviors in deionized water and MIBC (Methyl Isobutyl Carbinol) solution. A laboratory visualization system of bubble motion with ultrasonication was designed based on the high-speed dynamic video technology to record the bubble rising process and analyze bubble rising characteristics. Bubble aspect ratio was found to increase with the surfactant concentration increasing, but the rising velocity was in opposite state. In each solution, a significantly higher bubble sphericity was observed with ultrasonication than that without ultrasonication, conversely, the bubble rising velocity was smaller under the action of ultrasonication. A roughly negative linear relationship was found between the bubble shape and rising velocity, and the ultrasonication diminished this relationship. Marangoni effect was considered as the cause of MIBC affecting the bubble motion, and possible explanations of ultrasonication affecting the bubble motion were given from the perspective of bubble surface wave, cavitation bubble oscillation and sound radiation force.

How Nanoparticle Size and Bubble Merging Is Governed by Short‐Range Spatially Controlled Double‐Beam Laser Ablation in Liquids

AbstractPulsed laser ablation in liquid (LAL) is a method for synthesizing nanoparticles with controlled composition and high purity. However, current research predominantly examines isolated cavitation bubbles, overlooking real‐world LAL scenarios where numerous bubbles interact simultaneously. This study addresses this gap by investigating the effects of short‐range micrometric spatially controlled double‐pulse laser ablation in liquids on nanoparticle size distribution. Gold and YAG are used as model materials, and a dimensionless parameter, H*, is introduced to quantify the ratio between double bubble spatial separation and their maximum height. This parameter correlates with cavitation bubble merging time, bubble volume change rate, and subsequent nanoparticle size increase. Shadowgraphs provide valuable insights into bubble contact and fusion dynamics, showcasing phase separation by a thin water film and subsequent merging into a single bubble. Notably, a twofold increase in nanoparticle size is observed for both Au and YAG at H* = 0.25. The research indicates a strong association between nanoparticle size trends and cavitation bubble volume rate change, particularly emphasized at H* = 0.25. Understanding the dynamics of neighboring bubbles during LAL emphasizes the relevance of lateral pulse distances in dual‐beam LAL, impacting particle size distribution in a distance‐dependent manner.

Bubble dynamics and their effects on interfacial heat transfer in one single microchannel

Bubble dynamics are fundamental to understand boiling heat transfer mechanism at microscale. In this study, bubble dynamics in one single confined microchannel was experimentally investigated through vision-assisted technique. Experimental studies were performed to understand the effects of hydraulic diameter (Dh) of channel, flow rate and heat flux on bubble dynamics, which highly affect the boiling heat transfer performance. First of all, experimental results show that Dh has a vital effect on the volume change rate of confined bubble, which can be used to compute the heat flux transported by single bubble. The liquid-vapor (L-V) interfaces were tracked by non-rigid image registration and the velocity and acceleration of L-V interface were estimated through the analysis of recorded videos using vision-based technique. To quantitatively evaluate the impact of bubble dynamics, transient heat transfer rates were presented at different flow rates. Furthermore, the interfacial heat transfer (Nuc) influenced by bubble dynamics was evaluated. Nuc changes with Reb during bubble growth and bubble shrinking. Finally, an analysis of energy distributions by bubble dynamics is conducted. Compared to energy transported by bubble and kinetic energy of bubble, heat flux through interface is significant, dissipating over 96% of total input power.

Effects of surface characteristics on bubble dynamics in nucleation boiling using LBM

In this paper, the hybrid thermal lattice Boltzmann model is adopted to investigate the nucleation boiling. The bubble dynamics behaviors including nucleation, growth, coalescence, and departure, are studied on structured surfaces. Three types of structured surfaces adopting the rectangular, triangular, and trapezoidal structured surfaces are designed with different surface wettability. The numerical results reveal that, firstly, for the single bubble, increasing the opening width of structured surfaces from inside to outside is beneficial for bubble evolution. Then, with the dimensionless separation distance less than 1 between the two nucleation sites for the double bubbles, it presents a more noticeable advantage in the bubble evolution with different surface characteristics. Finally, the dimensionless critical coalescence distance of double bubbles increases significantly with the increment of contact angle on the hydrophobic surface. Besides, the dimensionless bubble critical coalescence distances on the triangular and rectangular structured surfaces are larger than those on the trapezoidal structured surface for the hydrophobic surface.

Hydrodynamics and shape reconstruction of single rising air bubbles in water using high-speed tomographic particle tracking velocimetry and 3D geometric reconstruction

Time-resolved tomographic particle tracking velocimetry (TR-3D-PTV), also called 4D-PTV, is used here to obtain the instantaneous 3D liquid flow field information in the wake of a single rising bubble in water. Simultaneously, the bubble shape, size and velocity are determined by tomographic reconstruction of the 3D bubble shape. Both, tracer particles for PTV and bubbles, are imaged in a shadow mode with background illumination. The Lagrangian method used in this paper, especially combined with the shake the box algorithm, has big advantages compared to particle image velocimetry, in situations, where only low particle per pixel values can be obtained. In this research, single air bubbles of different sizes, with diameters of around 2.4 mm, 4.0 mm, 6.0 mm and 9.6 mm, were injected into stagnant de-ionized water. Their shape was reconstructed in 3D, and an equivalent bubble diameter was determined from this reconstruction. Compared to conventionally used 2D shadow imaging, this diameter is about 13% smaller. The 3D bubble trajectory can be analysed and decomposed into a sinusoidal function curve lateral projection and an ellipsoidal shape vertical projection. As the bubble diameter increases, the radius of the spiral trajectory is decreasing as well as the amplitude of vertical sinusoidal oscillation. The wake structure in the liquid behind the bubbles is also changing with bubble size: from simple vortex pairs for smaller bubbles to an intertwined structure of several twisted vortices for the bigger ones.Graphical abstractThree-dimensional bubble reconstruction (grey surface) and liquid stream lines coloured with velocity magnitude around an ascending air bubble in de-ionized water.

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.

Power law exponents for single bubbles growth in nucleate pool boiling at zero gravity

Nucleate pool boiling is an important boiling mode used in various fields of application. Bubble detachment and new bubble generation at the nucleation site is an important aspect of the process under terrestrial conditions. This sequence prevents prolonged observation of bubble growth phenomena. The problem can be circumvented by performing single bubble growth experiments under zero gravity conditions. Many experiments of this type are performed in a specially designed cell on board the International Space Station. Several combinations of boiling experimental parameters (pressure, heat flux, waiting time, degrees of subcooling) are tested. The bubble size evolution curve was found to represent the influences off the individual parameters best. Fitting attempts show that the experimental bubble growth curves can be nicely described by power law correlations. An analytical solution is given for the evolution of the liquid temperature field within the experimental test cell, in the absence of boiling incidents. It is shown that the time evolving difference between the solid/liquid interfacial temperature and the liquid saturation temperature is the basic factor that determines the bubble growth exponent. As an outcome, the whole experimental information on the bubble growth curves of 160 different boiling conditions is compressed in the form of tables that include the corresponding power law factors. These tables not only allow the reconstruction of the examined boiling curves but can also generate boiling curves in a dense grid of boiling conditions through interpolation of existing boiling data. The latter offers coherence and continuity in boiling computer codes over a broad range of conditions.

Preliminary physical analysis of a single-bubble pool-boiling experiment in space: Effect of subcooling and possible non-condensable residuals

The purpose of this work is to study the boiling heat transfer mechanisms in microgravity. Single bubbles growing without departure up to a centimetric size on a single artificial nucleation site are investigated under well-controlled pool-boiling conditions in the framework of the RUBI experiment on the International Space Station. Subcooling is one of the important parameters defining the bubble growth process. In this work, we conduct a first physical analysis of the experiment. The bubble diameter is evaluated in time using a developed algorithm. Several stages are highlighted. It is shown that subcooling has a significant effect on all stages of bubble life and can even lead to a partial collapse. A numerical model is developed to help a better understanding of the phenomenon. Some observations couldn't be explained without evoking the presence of non-condensable residuals. The amount of those is estimated.

Dynamics of single bubble ascension in stagnant liquid: An investigation into multiphase flow effects on hydrodynamic characteristics using computational simulation

Industrial operations often involve multiphase flows, where the motion of bubbles plays a crucial role in determining hydrodynamic properties. In the context of modern practices, advanced computational solvers are increasingly employed to simulate the interactions and trajectories of bubbles within complex flows. This study stands out in its unique examination of the computational software COMSOL's capability to accurately simulate the upward motion of a single bubble within quiescent water, akin to a liquid-like environment. The novelty lies in the comprehensive coverage of various container diameters (ranging from 10 to 80 mm) and heights (from 25 to 300 mm) relative to the air bubble diameter (ranging from 0.5 to 8 mm). Through meticulous comparisons between nine empirical formulas and numerically projected bubble ascent through a water column, a remarkable level of agreement emerges, underscoring the precision and consistency of the simulations. These simulations unveil intriguing findings, shedding light on the intricate interplay of forces governing bubble behavior. Notably, variations in drag forces induce changes in bubble shapes as a function of diameter, while the ascent of bubbles is accompanied by distinctive vortices, resulting in fascinating asymmetry. Furthermore, vorticity concentrates within the bubble, particularly in lighter fluid regions characterized by reduced pressure. The study also unveils how larger aspect ratios minimize flow drag, consequently boosting ascent velocities, and demonstrates the influence of container diameter on the rising velocity. Gravitational forces are found to reduce ascent velocities at greater column heights, while the rate of air bubble rise escalates with its size. This meticulous exploration of bubble dynamics in multiphase flows yields invaluable insights for diverse industrial applications, ultimately enhancing our understanding of this complex phenomenon. The strong alignment observed between empirical formulations and numerical simulations within the COMSOL framework underscores the utility of such computational tools for the study and design of multiphase flows' intricate dynamics.

Numerical simulation of tritium extraction from liquid PbLi by gas–liquid contactor

As one key component of the fusion reactor, the blanket is in charge of breeding tritium, shielding neutrons and extracting thermal energy for electricity generation. An efficient tritium extraction unit (TEU) is a necessary guarantee for the tritium self-sufficiency in the fusion reactor. The gas–liquid contactor (GLC) is considered to be one of the most efficient devices for the liquid blanket that uses the lead–lithium (PbLi) as the functional materials. Understanding the characteristics of gas–liquid two-phase flow and mass transfer is beneficial for guiding the design and optimization of contactor. However, it is difficult to carry out the tritium experiments due to the scarcity in nature, the strong permeability, as well as the radioactivity. In this paper, the turbulent two-phase model coupled with dilute mass transfer is adopted to numerically study the process of tritium extraction from the liquid PbLi, and the numerical model is evolving step-by-step. Firstly, based on the models of single bubble and helium purge, the effects of different design parameters on the tritium extraction efficiency of the contactor are further investigated (i.e. mass flow rate of helium, initial tritium concentration and liquid PbLi filling height). The results are in good agreement with previous experimental results, and this validates the feasibility of the numerical model used in this work. Then, the entire model of GLC is numerically analyzed, which illustrates that the tritium extraction efficiency of one single unit is only 20.8%. However, the total efficiency can achieve 95% when there are 13 units working together in series. On this basis, the schematic diagram of tritium extraction system is proposed for the fusion blanket.

Acoustically Actuated Flow in Microrobots Powered by Axisymmetric Resonant Bubbles

Bubble‐driven microsystems inspired by the therapeutic use of microbubbles under clinical ultrasound actuation offer innovative remote manipulation in biological settings. Ultrasound‐powered microrobots, benefiting from a distribution of vibrating microbubbles (1–100 μm in diameters), exhibit localized fluid flow for self‐propulsion. Microbubbles also contribute to the design of acoustic metamaterials, where distributed actuation of bubbles enables exotic material properties (e.g., negative refractive index). Herein, a metamaterial‐inspired microrobot design, which exploits the streaming induced by the collective oscillation of microbubble arrays (> 10), is reported. Such a large distribution of bubbles offers twofold advantages: a mesoscale microrobot allowing ease of handling and motion at a considerably low acoustic driving pressure of 50 kPa. In this work, the oscillatory amplitude of a single bubble that acts as a unit cell of the metamaterial‐based microrobot is first characterized. Thereon, this amplitude is related to the flow generated by the collective vibration of all the bubbles close to the theoretically predicted resonant frequency of the bubbles. Finally, the hovering motion of the microrobot induced by the streaming and flow‐assisted debris clearance is demonstrated. Such auxiliary functionalities of the microrobot can be useful for applications like contactless sample extraction in inaccessible biological environments.

Vibrations Analysis of Bubble Evolution in Liquids of Varying Physical Properties

In recent years there is an attempt to control the gas stirring intensity in metal-making ladles with the aid of vibration measurements. Understanding better the induced vibrations in two-phase flows can substantially improve the existing models for gas stirring control. In this work, highly sensitive accelerometers were used for the vibration measurements in a liquid metal alloy; Sn–40 wt pctBi alloy at 200 °C and water at 20 °C. The examination of the liquids was conducted in the ladle mockup integrated into the Liquid Metal Model for Steel Casting facility at Helmholtz-Zentrum Dresden Rossendorf. Single bubbles were generated in the respective liquids by controlled argon injection at low flow rates in the range of 0.01 to 0.15 NL min−1 through a single nozzle installed at the bottom of the ladle. Obtained results demonstrate differences between the induced vibrations in the examined liquids in terms of the magnitude of the root mean square values of vibration amplitude and the shape of the resulting curves with increasing flow rate. Furthermore, continuous wavelet transform reveals variations in the duration and vibrational frequency of the evolved bubble phenomena. The findings suggest that differences in the physical properties of the examined liquids result in variations in the vibrations induced during bubble evolution.

Investigation of aerosol transportation phenomena in pool scrubbing by combining bubble plume measurements and single-bubble mass transfer analysis

The fission product filtration capability of pool scrubbing is an uncertain factor in severe accident risk analysis. Limited discussions on aerosol transportation phenomena exist due to insufficient understanding of aerosol mass transfer from single bubbles and bubble plume behavior. This study aims to investigate aerosol transportation during pool scrubbing by integrating individual bubble mass transfer into the overall bubble plume.Decontamination factor (DF) measurements were conducted for various nozzle submergences, followed by analysis of bubble diameter distributions in the corresponding bubble plume. Findings revealed that the MELCOR model overestimates bubble break-up, contrary to the expected positive impact on DF. To address this discrepancy, a computational fluid dynamics simulation was employed to analyze mass transfer coefficients considering different bubble diameters and aerosol properties. By integrating the mass transfer of single bubbles, the discrepancy in the DF tendencies was attributed to the underestimation of aerosol mass transfer coefficients in individual bubbles.

Investigation into drag coefficient for sub-millimeter bubbles in gas–liquid bubbly flow: Experiments and CFD simulations

The sub-millimeter bubble technique can enhance the gas–liquid inter-phase mass transfer and show immense potential to increase production efficiency. The two-fluid model (TFM), suitable for the CFD simulations on the scale of actual reactors, is a powerful tool for exploring the application of the sub-millimeter bubble technique. Although the accuracy of TFM is largely affected by the drag models, the applicability of the drag models for gas–liquid two-phase flow of sub-millimeter bubbles is scarcely investigated. In the present work, the applicability of the single-bubble drag models was apprised with experimental data of single sub-millimeter bubbles. Then, the bubble swarm effect and its influence on the calculation of drag coefficients were investigated for the gas–liquid two-phase flow of sub-millimeter bubbles under a wide range of gas holdups (0.02–0.21). The accelerating effect was observed in the experiments of gas–liquid two-phase flows. A reasonable explanation for the accelerating effect was discussed based on the bubble size distribution obtained by applying our original image processing method. Based on the experiments, an equation for the drag modification factors was proposed to include the bubble swarm effect. The accuracy and applicability of the proposed equation were validated by applying it together with the accurate single-bubble drag model in the CFD simulation by TFM. The present work investigated the hydrodynamic characteristics of sub-millimeter bubbly flows experimentally and provided an accurate CFD method for further investigation.

Mechanisms underlying the influence of skin properties on a single cavitation bubble in low-frequency sonophoresis

As a safe and effective method for systemic transdermal drug delivery (TDD), sonophoresis has drawn much attention from researchers. Despite numerous studies confirming cavitation as the main reason for sonophoresis, the effect skin has on cavitation bubble dynamics remains elusive due to the difficulty of experimental challenges. For a start, we reveal how single cavitation bubble (SCB) dynamics are affected by skin properties, including elasticity, hydrophilicity and texture. We use polydimethylsiloxane (PDMS) to simulate human skin and record the temporary evolution of SCBs with synchronous ultrafast photography. The influences of skin properties on SCBs are concluded: 1) SCBs collapse later near walls with better elasticities and generate microjets with higher speed; 2) SCBs collapse later near hydrophilic walls with slower microjets; and 3) the existence of a texture structure on walls also delays the time of bubble collapse near them and slows the velocities of microjets (v) during collapses.

Bubble cloud characteristics and ablation efficiency in dual-frequency intrinsic threshold histotripsy

Histotripsy is a non-thermal focused ultrasound ablation method that destroys tissue through the generation and activity of acoustic cavitation bubble clouds. Intrinsic threshold histotripsy uses single-cycle pulses to generate bubble clouds when the dominant negative pressure phase exceeds an intrinsic threshold of ∼25–30 MPa. The ablation efficiency is dependent upon the size and density of bubbles within the bubble cloud. This work investigates the effects of dual-frequency pulsing schemes on the bubble cloud behavior and ablation efficiency in intrinsic threshold histotripsy. A modular 500 kHz:3 MHz histotripsy transducer treated agarose phantoms using dual-frequency histotripsy pulses with a 1:1 pressure ratio from 500 kHz and 3 MHz frequency elements and varying arrival times for the 3 MHz pulse relative to the arrival of the 500 kHz pulse (−100 ns, 0 ns, and +100 ns). High-speed optical imaging captured cavitation effects to characterize bubble cloud and individual bubble dynamics. The effects of dual-frequency pulsing on lesion formation and ablation efficiency were also investigated in red blood cell (RBC) phantoms. Results showed that the single bubble and bubble cloud size for dual-frequency cases were intermediate to published results for the component single-frequencies of 500 kHz and 3 MHz. Additionally, bubble cloud size and dynamics were shown to be altered by the arrival time of the 3 MHz pulse with respect to the 500 kHz pulse, with more uniform cloud expansion and collapse observed for early (−100 ns) arrival. Finally, RBC phantom experiments showed that dual-frequency exposures were capable of generating precise lesions with smaller areas and higher ablation efficiencies than previously published results for 500 kHz or 3 MHz. Overall, results demonstrate dual-frequency histotripsy’s ability to modulate bubble cloud size and dynamics can be leveraged to produce precise lesions at higher ablation efficiencies than previously observed for single-frequency pulsing.

Research on the collapse characteristics of single cavitation bubble near solid particle by the VOF method

In this paper, the collapse behavior of a single cavitation bubble at different distances near a solid particle of typical scales is numerically simulated and researched with the volume of fluid (VOF) method. Based on the key parameters analysis of the pressure field, velocity vector, collapse time the tendency of cavitation bubble collapse characteristics at different distances during the change of particle size is studied with the variable of the distance and relative size between the particle and the cavitation bubble. The dimensionless distance parameter ‘γ’ is specifically presented in the simulation process, the cavitation bubble collapse impact is largely directed to the particle when 3>γ > 2, while the wall hardly affects the interaction between the cavitation bubble and the solid particle as γ > 3. The results illustrate that as the solid particle and wall exist, the distance and particle size affect both the peak collapse pressure and the collapse jet velocity of the cavitation bubble, and the influence of solid wall on the cavitation bubble at the same distance is much greater than that of solid particles. When the particle size increases, the particle gradually affects the cavitation bubble in a way similar to the wall. While as the distance decreases or the particle size increases, the influence of particle and wall on the evolution process of the cavitation bubble expands, meanwhile, the collapse pressure and collapse jet velocity of the cavitation bubble are promoted with the optimized distance and particle size, which brings marvelous cavitation effect. The numerical methods and conclusions of this paper provide a valuable reference for cavitation applications of sand-containing fluids.

Phase field simulation of single bubble behavior under magnetic field

By combining the continuum equation with the momentum equation, phase field and magnetic field, a three-dimensional multi-field coupled model of the single bubble rising dynamics in the gas–liquid two-phase flow is established. The phase field method is used to capture the two-phase interface and simulate the movement of the gas–liquid interface. Compare the model with the numerical simulation under the Level Set method, it turns out that the simulation effect of the model established by the phase field method is better. The effects of different magnetic field intensity on the rise velocity of bubble and bubble deformation under vertical and horizontal magnetic field are analyzed. The results show that the bubble stretches along the magnetic field line under the action of the magnetic field, and the degree of bubble deformation is proportional to the intensity of the magnetic field. The rising speed of the bubble is affected by the magnetic field, which speeds up the overall rising speed of the bubble in the vertical direction and slows down the rising speed of the bubble in the horizontal direction.

Dynamical model and numerical study of cavitation bubble in ultrasonic assisted electrochemical polishing solution of selective laser melting NiTi alloy

In the process of ultrasound assisted electrochemical polishing of selective laser melting (SLM) NiTi alloy, a large number of cavitation bubbles will be generated in the anode and cathode, and these cavitation bubbles will expand and compress rapidly until finally collapse. At the moment of collapse, high temperature and high pressure will occur, and at the same time, pressure shock wave and micro-jet will be produced, which will have a certain impact on material removal during polishing. In order to explore the mechanism of ultrasonic assisted electrochemical polishing, in this paper, the dynamics of cavitation bubbles with free interface and rigid interface are analyzed by ultrasonic assisted electrochemical polishing. The dynamics models of single cavitation bubble and two cavitation bubbles are established. The fourth order Runge–Kutta method was used to solve the model numerically, and the influence of electric field intensity, initial bubble radius, sound pressure amplitude and ultrasonic frequency on the dynamics of cavitation bubble was analyzed. The results show that in the range of f = 1–10 KHz, the initial radius of bubble is 0.01–0.05 micron, the sound pressure amplitude is 103 Pa, and the electric field intensity is 104 V m−1, the cavitation movement gradually becomes regular, and it goes through a complete process of expansion, contraction and then collapse, which is beneficial to the cavitation effect. This provides a theoretical basis for further research on the mechanism of ultrasonic assisted electrochemical polishing of SLM-NiTi alloy, which is of great significance for broadening the processing of additive manufacturing parts with low cost, high efficiency, and consistent quality.