Collapse Of Spherical Bubble Research Articles

Effects of heat transfer on the strength of shock waves emitted upon spherical bubble collapse

Effects of heat transfer on the strength of shock waves emitted upon spherical bubble collapse

Numerical Prediction of Cavitation Erosion Intensity in Cavitating Flows around a Clark Y 11.7% Hydrofoil

A numerical prediction method of cavitation erosion is proposed. In this method, the analysis of bubbles in cavitating flows is performed and the intensity of cavitation erosion is evaluated by the impact pressure induced by spherical bubble collapse. In the present study, two-dimensional cavitating flow around the Clark Y 11.7 % hydrofoil is used to examine the proposed numerical prediction method. The proposed numerical method predicts that the intensities of cavitation erosion in noncavitating, attached cavitating and pseudo-supercavitating flows are far weaker than the intensity of cavitation erosion in a transient cavitating flow, and the intensity in the vicinity of the sheet cavity termination is high. These results correspond well to experimental results, and it is confirmed that systematic erosion characteristics are generally captured by this method. Furthermore, the velocity dependence of cavitation erosion is examined, and it is found that the exponent n in the relation between the intensity I and main flow velocity Uin (I ∝ Uinn) becomes large when the bubble radius is large and ranges between 4.3 and 7.0 in the present study. According to the bubble dynamics, the ambient pressure and the rate of increases in pressure increase as the main flow velocity, and the maximum internal pressure increase. Therefore, it is thought that smaller bubbles cause cavitation erosion when the main flow velocity is large.

Spherical bubble collapse in viscoelastic fluids

The collapse of a spherical bubble in an infinite expanse of viscoelastic fluid is considered. For a range of viscoelastic models, the problem is formulated in terms of a generalized Bernoulli equation for a velocity potential, under the assumptions of incompressibility and irrotationality. The boundary element method is used to determine the velocity potential and viscoelastic effects are incorporated into the model through the normal stress balance across the surface of the bubble. In the case of the Maxwell constitutive equation, the model predicts phenomena such as the damped oscillation of the bubble radius in time, the almost elastic oscillations in the large Deborah number limit and the rebound limit at large values of the Deborah number. A rebound condition in terms of ReDe is derived theoretically for the Maxwell model by solving the Rayleigh–Plesset equation. A range of other viscoelastic models such as the Jeffreys model, the Rouse model and the Doi-Edwards model are amenable to solution using the same technique. Increasing the solvent viscosity in the Jeffreys model is shown to lead to increasingly damped oscillations of the bubble radius.

A High-Speed Photographic Study of Ultrasonic Cavitation Near Rigid Boundary

This article investigated an existing steady pattern of collapse and rebound (disintegration and aggregation) of cavitation bubbles near rigid boundary in acoustic field. A deformation process of cavitation bubble was accomplished in two acoustic cycles, namely, a spherical bubble collapsed towards the boundary to its minimum volume and then rebounded and grew into a toroidal bubble (or two individual bubbles) in one acoustic cycle, and the toroidal bubble (or two individual bubbles) collapsed towards the center of ring to its minimum volume, and then rebounded into a spherical bubble in the next acoustic cycle. Inertia force plays a key role in the transition between these two states. The microjet produced during the collapse of spherical bubble and the shock wave produced during the collapse of toroidal bubble (or two individual bubbles) impacts the boundary alternately. A cavitation bubble operating in this pattern can thus be an effective corrosion mechanism of rigid boundary.

Modeling of Shock Wave Emission during Acoustically-Driven Cavitation-Induced Cleaning Processes

Shock wave emission resulting from spherical bubble collapse during cavitation-induced cleaning process on Si wafers is modelled. The velocity of the shock front is calculated as a function of cavitation process parameters and gas state equations.

Shock wave emission upon spherical bubble collapse during cavitation-induced megasonic surface cleaning

When a gas bubble in a liquid interacts with an acoustic wave near a solid surface, the bubble first expands and then collapses. In this paper, a mathematical framework combining the Gilmore model and the method of characteristics is presented to model the shock wave emitted at the end of the bubble collapse. It allows to describe the liquid velocity at the shock front as a function of the radial distance to the bubble center in the case of spherical bubble collapse. Numerical calculations of the liquid velocity at the shock front have shown that this velocity increases with the acoustic amplitude and goes through a maximum as a function of the initial bubble radius. Calculations for different gas state equations inside the bubble show that the Van der Waals law predicts a slightly higher liquid velocity at the shock front than when considering a perfect gas law. Finally, decreasing the value of the surface tension at the bubble/liquid interface results in an increase of the liquid velocity at the shock front. Our calculations indicate that the strength of the shock waves emitted upon spherical bubble collapse can cause delamination of typical device structures used in microelectronics.

A first-order model for bubble dynamics in a compressible viscoelastic liquid

The radial dynamics of a spherical bubble in a compressible viscoelastic liquid is studied by means of a simplified singular-perturbation method to first-order in the bubble-wall Mach number. The three-parameter linear Oldroyd model is adopted to describe the viscoelastic properties of the liquid. The equation of motion for the bubble radius and the pressure equation are derived and numerical calculations are conducted for the case of bubble collapse in a constant-pressure field. It is concluded that the rheology of the liquid strongly influence the behaviour of bubbles only for values of the Reynolds number ( Re=R 0 p ∞ρ ∞ /η where R 0 is the initial radius, p ∞ is the undisturbed liquid pressure, ρ ∞ is the liquid density and η is the liquid viscosity) smaller than 10 2 while for Re ≥ 10 2, sound emission is the main damping mechanism in spherical bubble dynamics. In both cases, the 1/ r law of pressure attenuation through the liquid is not affected by the viscoelastic properties of the liquid. The effect of polymer additives on spherical bubble collapse is also discussed.

Bubble dynamics in a compressible shear-thinning liquid

The radial dynamics of a spherical gas bubble in a compressible shear-thinning liquid is studied by means of a singular perturbation method to first order in the bubble-wall Mach number. The Williamson rheological model is adopted to describe the shear-thinning characteristic of liquid viscosity. The equation of motion for the bubble radius, the equation of the natural frequency of the bubble and the pressure equation are derived. Numerical calculations are presented using the experimental data for two polymer aqueous solutions, viz. HEC and CMC solutions, and water. It is found that the shear-thinning characteristic of liquid viscosity strongly influences only the behaviour of bubbles with initial radii smaller than 10 −1 mm and the rheological parameter with the strongest influence on bubble collapse is the infinite-shear viscosity. The effect of polymer additives, including their surfactant properties, on spherical bubble collapse is also discussed.

Collapse and rebound of a gas-filled spherical bubble immersed in a diagnostic ultrasonic field

This work is concerned with the influence of the finite-amplitude distortion of a driving diagnostic ultrasonic field on the collapse and rebound of a gas-filled spherical microbubble, present in the exposed compressible liquid. Such an analysis is especially important since one of the mechanisms for cavitation damage comes from the very large gas pressures generated at bubble collapse and in the subsequent pressure wave formed by bubble rebound. Gilmore's model [F.R. Gilmore, "The growth or collapse of a spherical bubble in a viscous compressible liquid," Hydrodynamics Lab. Rep. No. 26-4, California Institute of Technology, Pasadena, CA (1952)] for bubble dynamics is used to obtain the motion of the bubble interface when subjected to a pulsed diagnostic ultrasonic field of large amplitude. Knowledge of the bubble motion allows one to derive the pressure distribution around the bubble. Numerical results over a range of initial bubble sizes, acoustic pressures, and frequencies relevant to medical use show that the strength of the pressure spikes radiated by the rebounding bubble depends upon (i) the acoustic frequency (f), (ii) the initial bubble size (R0), and (iii) the magnitude of the pressure amplitude of the fundamental (PF) in a Fourier series description of the distorted pulse. As the pressure spikes propagate outward from the bubble wall, their strength is attenuated as the reciprocal of the distance from the center of collapse.

Optical and acoustic investigations of the dynamics of laser-produced cavitation bubbles near a solid boundary

The dynamics of laser-produced cavitation bubbles near a solid boundary and its dependence on the distance between bubble and wall are investigated experimentally. It is shown by means of high-speed photography with up to 1 million frames/s that jet and counterjet formation and the development of a ring vortex resulting from the jet flow are general features of the bubble dynamics near solid boundaries. The fluid velocity field in the vicinity of the cavitation bubble is determined with time-resolved particle image velocimetry. A comparison of path lines deduced from successive measurements shows good agreement with the results of numerical calculations by Kucera & Blake (1988). The pressure amplitude, the profile and the energy of the acoustic transients emitted during spherical bubble collapse and the collapse near a rigid boundary are measured with a hydrophone and an optical detection technique. Sound emission is the main damping mechanism in spherical bubble collapse, whereas it plays a minor part in the damping of aspherical collapse. The duration of the acoustic transients is 20-30 ns. The highest pressure amplitudes at the solid boundary have been found for bubbles attached to the boundary. The pressure inside the bubble and at the boundary reaches about 2.5 kbar when the maximum bubble radius is 3.5 mm. The results are discussed with respect to the mechanism of cavitation erosion.

Acoustic transient generation by laser-produced cavitation bubbles near solid boundaries

The acoustic transients emitted after breakdown and cavitation bubble collapse upon focusing a Q-switch laser pulse into a liquid are investigated with special emphasis on their modifications induced by a solid boundary. For measuring the form p(t)/pmax of the pressure pulses an optical technique with a resolution of 10 ns has been developed. When p(t)/pmax is known, the pressure amplitude can be determined even when a transducer with a rise time much longer than the pulse duration is used. The duration of the transients (20–30 ns) and their pressure are nearly the same after breakdown and spherical bubble collapse. During spherical collapse, a maximum pressure of about 60 kbar is developed inside a bubble with Rmax=3.5 mm, and on average 73% of the bubble energy loss is transformed into acoustic energy. The sound emission near a solid boundary strongly depends on the normalized distance γ between the bubble and the boundary. The highest pressures at the boundary are achieved for γ→0; for γ=0.2 and Rmax =3.5 mm it has been found that p=2.5 kbar. These results are discussed with respect to the mechanisms of cavitation erosion important for hydraulic cavitation, laser lithotripsy, and ocular surgery.

Spherical vapour bubble collapse

An experimental study of spherical vapour bubble collapse in uniformly subcooled water has been performed, and data have been obtained on bubble radius and pressure histories for subcoolings up to 60°C. A theoretical incompressible equilibrium model of spherical collapse in an infinite sea geometry utilising a finite difference technique to solve the heat conduction equations has been developed, and the predictions are shown to agree with the experimental radius and pressure histories to within 30 per cent, subject to the bubble pressure not exceeding the critical pressure of water. The discrepancies are accounted for in terms of the restricted geometry of the experimental vessel. The noise spectra generated by bubble rebound are shown to extend to beyond 100 kHz in water subcoolings above 40°C.

Laser-Induced Cavitation

When intense laser light is focused into liquids, bubbles can be prod need in the vicinity of the focal point. The dynamics of these bubbles is investigated by high-speed photography with picture repetition rates up to 106 frames/sec. Single spherical bubbles can be produced. In water, they can be said to be the experimental realization of the Rayleigh bubble model. Results on both spherical and nonspherical bubble collapse, rebound, and subsequent collapses and rebounds will be reported showing the sequence of events leading to the cloud of minute bubbles often observed after the collapse of a big bubble. Repeated jet formation of the same bubble seems to be the major suicide mechanism. Shedding of minute bubbles occurs by gas entrainment into the jet. Spherical undisturbed collapsing bubbles remain spherical down to very small radii being heavily distorted a few microseconds later during rebound. Nonlinear spherical bubble oscillations are investigated in silicone oils. The stability of the spherical shape seems to be enhanced by viscosity. A comparison is made with calculated nonlinear bubble oscillations damped by viscosity.

Spherical Bubble Collapse in Uniformly Subcooled Liquids

Spherical Bubble Collapse in Uniformly Subcooled Liquids

Spherical Bubble Collapse in Uniformly Subcooled Liquid

Spherical Bubble Collapse in Uniformly Subcooled Liquid