A model for a laser-induced cavitation bubble Zhong, Xiaoxu; Eshraghi, Javad; Vlachos, Pavlos ...
International journal of multiphase flow,
November 2020, 2020-11-00, Letnik:
132
Journal Article
Recenzirano
Odprti dostop
•A model for a laser-induced cavitation bubble is developed.•The predicted bubble radius agrees with the experimental measurements within 10%.•Reduction in bubble radius is primarily due to the ...evaporation and condensation.•The amount of air is less than 1% when the bubble reaches maximum.•Peak pressure can occur at the second collapse depending on evaporation coefficient.
The complex mechanism behind the laser-induced cavitation bubble has led to challenges in its modeling. Current models can only predict the radius of the single laser-induced cavitation bubble over one or two growth and collapse cycles. To fill the gap, we propose a new model that takes into account the liquid compressibility, heat transfer, and non-equilibrium evaporation and condensation. Specifically, we use a new approximation of the temperature gradient at the bubble surface. The four unknown physical parameters in the model are found by fitting to the experimentally measured bubble radius. The predicted bubble radius agrees with the experimental measurements within 10% for several cycles of bubble growth and collapse. The calibrated evaporation coefficient is close to 0.04, which agrees with the value reported in the literature. The maximum potential energy of the bubble is found to have a linear relation with the laser energy. The amount of air is found to be less than 1% when the bubble reaches maximum. Our model predicts that the maximum temperature occurs during the first collapse, but the maximum pressure and extension rate can occur at the second collapse depending on the evaporation coefficient. Evaporation and condensation are found to have a significant effect on the dynamic behavior of the bubble. Increasing the amount of non-condensable air in the bubble helps mitigate the collapsing process, and thus, decreases the maximum pressure, temperature, and extension rate.
Experiments with series of laser-induced single cavitation bubbles were performed on Cu-, Fe-, and Al- base alloys, namely 316LVM, a nickel aluminum bronze (NAB), and pure aluminum. The bubble ...dynamics were recorded by two high-speed cameras, while the resulting surface damage was investigated by a microscope in situ, i.e. between two successive bubbles with the sample remaining in the water. Bubbles with stand-off distances γ (the ratio of distance of the surface from the bubble and the bubble maximum radius) of 1.35 ± 0.5 and bubble radii of about 1.2 mm were directly correlated with the damage they produced. We found a correlation between locally enlarged (“strong”) gas-filled collapse areas (SCAs) during the second bubble collapse and the resulting pits on the sample surface. While all pits could be correlated to a preceding SCA, not all SCAs resulted in pits. This is true on both NAB and 316L. On aluminum, despite the softness of the material, some bubbles did not produce pits, and these where the ones with the most symmetric second-collapse torus. The pits that constitute, in sum, the damage of the material where analyzed in their number and geometry. The pitting rate and the maximum pit depth were roughly inversely depended on the material hardness. Also, beginning wear mechanisms were identified, like emerged grain boundaries on aluminum and light slip lines on steel. Finally, the collapse of a very small, secondary, dissolved-gas bubble close to the surface is documented to cause a pit. This may be one mechanism by which the pits are formed.
•High-speed observation of single-bubble dynamics and in-situ imaging of surface damage.•Pits correlated with locally enlarged (“strong”) gas-filled collapse areas (SCAs).•Material dependence of pitting rate and pit geometry was examined.•Even on aluminum samples, symmetric collapses did not cause damage.•A shockwave-induced collapse of a dissolved gas bubble caused pitting.
In this work, we present an extensive comparative study between novel titanium nitride nanoparticles (TiN NPs) and commercial gold nanorods (GNR), both dispersed in water and exposed to a pulsed ...laser‐induced cavitation process. The optical density, shockwave emission, and bubble formation of these solutions were investigated using shadowgraphy, spatial transmittance modulation, and acoustic measurements. TiN nanoparticle solutions exhibited high stability undser a periodic nanosecond pulsed‐laser irradiation, making these nanomaterials promising agents for high‐power applications. In addition, they demonstrated a stronger nonlinear absorption compared to the GNR solutions, and plasma formation at lower laser energies. This study advances our understanding of the optical properties of TiN and discusses significant differences compared to gold, with important implications for future applications of this material in water treatment, nonlinear signal converting, and laser‐induced cavitation for medical implementations, among others.
•Bubble dynamics investigation near and through a hole in the flat surface.•Laser induced bubbles causes micro pumping action.•Bubble rebound found to be additional pumping driver beside the jetting ...mechanism.•Methodology of bubble tracking suitable for lower temporal resolution visualizations.•Bubble movement follows the power law of rigid boundary till it touches a hole edge.
The laser- induced cavitation bubble, which collapses near a rigid boundary with a hole on a microscale is investigated for liquid pumping applications. The generated bubble and the hole have a comparable size on a scale of 100 μm.
The dynamics of the process are visually tracked near the hole and through the hole. This is made possible by the translucent 3D-printed boundary. The main measurable quantities are the bubble oscillation times and the bubble movement. For the latter, we show that it follows the power law of the Kelvin impulse for the rigid boundary without a hole for small standoff distances up to the moment when the bubble touches the edge of the hole. Further, it was found that the bubble standoff distance has a negligible influence on the first oscillation time, while it increases by almost a factor of two for the second oscillation. During the second oscillation, the bubble enters the hole and displaces all the liquid in the direction of bubble propagation. This indicates a second pumping driver beside the jet produced during the collapse of the primary bubble.
We investigated laser-induced cavitation dynamics in a small container with elastic thin walls and free or partially confined surface both experimentally and by numerical investigations. The cuvette ...was only 8-25 times larger than the bubble in its center. The liquid surface was either free, or two thirds were confined by a piston-shaped pressure transducer. Different degrees of confinement were realized by filling the liquid up to the transducer surface or to the top of the cuvette. For reference, some experiments were performed in free liquid. We recorded the bubble dynamics simultaneously by high-speed photography, acoustic measurements, and detection of probe beam scattering. Simultaneous single-shot recording of radius-time curves and oscillation times enabled to perform detailed investigations of the bubble dynamics as a function of bubble size, acoustic feedback from the elastic walls, and degree of surface confinement. The bubble dynamics was numerically simulated using a Rayleigh-Plesset model extended by terms describing the acoustically mediated feedback from the bubble's environment. Bubble oscillations were approximately spherical as long as no secondary cavitation by tensile stress occurred. Bubble expansion was always similar to the dynamics in free liquid, and the environment influenced mainly the collapse phase and subsequent oscillations. For large bubbles, strong confinement led to a slight reduction of maximum bubble size and to a pronounced reduction of the oscillation time, and both effects increased with bubble size. The joint action of breakdown-induced shock wave and bubble expansion excites cuvette wall vibrations, which produce alternating pressure waves that are focused onto the bubble. This results in a prolongation of the collapse phase and an enlargement of the second oscillation, or in time-delayed re-oscillations. The details of the bubble dynamics depend in a complex manner on the degree of surface confinement and on bubble size. Numerical simulations of the first bubble oscillation agreed well with experimental data. They suggest that the alternating rarefaction/compression waves from breakdown-induced wall vibrations cause a prolongation of the first oscillation. By contrast, liquid mass movement in the cuvette corners result in wall vibrations causing late re-oscillations. The strong and rich interaction between the bubble and its surroundings may be relevant for a variety of applications such as intraluminal laser surgery and laser-induced cavitation in microfluidics.
•A novel numerical method to simulate cavitation induced by long-pulsed laser.•The processes of laser radiation, vaporization, and bubble/fluid dynamics are simulated simultaneously.•An embedded ...boundary method is proposed for laser-fluid coupling, well-posed with 2nd-order accuracy.•The level set method is combined with a phase transition law to track continuous vaporization.•Predictive capability demonstrated by simulations of different laser experiments.
A computational method for simulating thermal cavitation induced by long-pulsed laser is presented. This method accounts for the absorption of laser light by a liquid, the formation of vapor bubbles due to localized heating, and the dynamics of the bubbles and the surrounding liquid. The physical model combines the Euler equations for a compressible inviscid two-phase fluid flow, a reduced form of the radiative transfer equation for laser radiation, and a local thermodynamic model of vaporization. The Euler equations are solved using the FInite Volume method with Exact two-phase Riemann solvers (FIVER). Following this method, numerical fluxes across phase boundaries are computed by constructing and solving one-dimensional bimaterial Riemann problems. The paper focuses on numerical methods for coupling the laser and fluid governing equations and tracking the vapor bubbles. An embedded boundary finite volume method is proposed to solve the laser radiation equation on the same mesh created for the Euler equations, which usually does not resolve the boundary and propagation directions of the laser beam. To impose boundary conditions, ghost nodes outside the laser domain are populated by mirroring and interpolation techniques. The existence and uniqueness of solution are proved for the two-dimensional case, leveraging the special geometry of the laser domain. The order of accuracy of the method is also proved, and verified using numerical tests. A method of latent heat reservoir is proposed to predict the onset of vaporization, which accounts for the accumulation and release of latent heat. A unique challenge associated with long-pulsed laser is that the dynamics of vapor bubbles is driven not only by the inertia of the bubble nuclei, but also by the continuation of vaporization. In this work, the localized level set method is employed to track the bubble surface, and a method of local correction and reinitialization is proposed to account for continuous phase transitions. Several numerical tests are presented to verify the convergence of these methods. Two realistic simulations of laser-induced cavitation are presented at the end, showing that the computational method is able to capture the key phenomena in these events, including non-spherical bubble expansion, shock waves, and the “Moses effect”.
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•Mild steel is processed by massive laser cavitation peening (LCP).•Plastic deformation, residual stress, microhardness, and microstructure after treatment are analyzed.•Understanding ...into the effects of impact times on work hardening and grain refinement.•LCP processing and material strengthening mechanisms are revealed.
A method of laser cavitation peening (LCP) was employed to strengthen the Q235 steel. The plastic deformation, residual stress, microhardness, phase, and microstructure of Q235 steel subjected to laser cavitation peening were investigated through a combination of experiments and simulations. The processing and strengthening mechanisms (LCP impact, plastic strain, grain refinement) were analyzed. Laser-induced cavitation bubble experiences three periodic pulsations during the process of LCP. The strengthening of Q235 steel by LCP can be attributed to the impact of the laser shock wave, bubble collapse shock wave, and water-jet. LCP causes plastic deformation in the surface layer of material and thereby introducing compressive residual stress and enhancing the microhardness. Dislocation structures including dislocation tangles, dislocation walls, and dislocation cells generate within the grains and near grain boundaries after LCP impact. Residual stress, microhardness, and dislocation density increase significantly with the increase of impact times. The high-density dislocation tangles and the sharing of dislocation cells refine the original coarse grains into equiaxed fine grains. The process of grain refinement is accompanied by the dissolution of cementite.
•Research on a novel degradation method with laser technology.•Dynamics of laser-induced cavitation bubbles in suspension has been studied.•Relationship exists between bubble size and degradation ...extent.•Particles have both positive and negative effects.
A method for degrading organic pollutants in suspension by applying laser-induced cavitation is presented. Cavitation bubbles are produced remotely by laser beams, achieving a purpose of non-contact degradation. In this work, laser-induced bubble dynamics in SiO2 sand suspension were studied by high-speed imaging. Pulsating characteristics of cavitaiton bubbles in the infinite domain and near a solid boundary were investigated among various laser energies and sand concentrations. Furthermore, the extent of degradation after processing in suspension and the mechanism were analyzed. Results indicate that solid particles in the liquid medium reduce the extent of degradation. However, the extent of degradation may rebound at a proper sand concentration. In addition, compared to several small bubbles in a bubble string (in the infinite domain), a single larger bubble (near a solid boundary) has a much higher degradation ability.
Cavitation bubbles are widely studied in the fields of hydraulic machinery, medicine, biology and so on. This paper studies different dynamic characteristics of cavitation bubbles in infinite domain ...and attached to a solid wall. The maximum bubble diameter and bubble wall velocity increased with increasing laser energies, which were measured by Matlab software. The bubble pulses several times in infinite domain due to its kinetic energy loss decreases with higher laser energy. However, the fluctuation rules of maximum bubble diameter and bubble wall velocity under different ambient temperatures are different in two conditions. The bubble diameter decreases with the increasing temperature in infinite domain, and the decreasing rate slows down in each oscillation period. An approximate linear relation was proposed to describe the relationship between the maximum bubble diameter and the ambient temperature. Nevertheless, both the bubble diameter and bubble wall velocity increase with the increasing ambient temperature on the solid boundary, which can be ascribed to the decline in liquid viscosity, and the increased phase transition rate on the bubble surface. In addition, the cavitation erosion effect and the variation trend of bubble collapse time under different ambient temperatures was analyzed.
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