Bubble Sonoluminescence Research Articles

Diagnosing temperature change inside sonoluminescing bubbles by calculating line spectra

With the numerical calculation of the spectrum of single bubble sonoluminescence, we find that when the maximum temperature inside a dimly luminescing bubble is relatively low, the spectral lines are prominent. As the maximum temperature of the bubble increases, the line spectrum from the bright bubble weakens or even fades away relative to the background continuum. The calculations in this paper effectively interpret the observed phenomena, indicating that the calculated results, which are closely related to the spectrum profile, such as temperature and pressure, should be reliable. The present calculation tends to negate the existence of a hot plasma core inside a sonoluminescing bubble.

Comparison between the single-bubble sonoluminescences in sulfuric acid and in water

Single-bubble sonoluminescence (SBSL) is achieved with strong stability in sulfuric acid solutions. Bubble dynamics and the SBSL spectroscopy in the sulfuric acid solutions with different concentrations are studied with phase-locked integral stroboscopic photography method and a spectrograph, respectively. The experimental results are compared with those in water. The SBSL in sulfuric acid is brighter than that in water. One of the most important reasons for that is the larger viscosity of sulfuric acid, which results in the larger ambient radius and thus the more contents of luminous material inside the bubble. However, sonoluminescence bubble’s collapse in sulfuric acid is less violent than that in water, and the corresponding blackbody radiation temperature of the SBSL in sulfuric acid is lower than that in water.

Dynamics of sonoluminescing bubbles within a liquid hammer device

We studied the dynamics of a single sonoluminescing bubble (SBSL) in a liquid hammer device. In particular, we investigated the phosphoric acid-xenon system, in which pulses up to four orders of magnitude brighter than SBSL in water systems (about 10;{12} photons per pulse) have been previously reported [Chakravarty, Phys. Rev. E 69, 066317 (2004)]. We used stroboscopic photography and a Mie scattering technique in order to measure the radius evolution of the bubbles. Under adequate conditions we may position a bubble at the bottom of the tube (cavity) and a second bubble trapped at the middle of the tube (upper bubble). During its collapse, the cavity produces the compression of the liquid column. This compression drives impulsively the dynamics of the upper bubble. Our measurements reveal that the observed light emissions produced by the upper bubble are generated at its second collapse. We employed a simple numerical model to investigate the conditions that occur during the upper bubble collapse. We found good agreement between numerical and experimental values for the light intensity (fluence) and light pulse widths. Results from the model show that the light emission is increased mainly due to an increase in noble gas ambient radius and not because the maximum temperature increases. Even for the brightest pulses obtained ( 2x10;{13} photons, about 20W of peak power) the maximum temperatures computed for the upper bubble are always lower than 20000K .

Molecular Dynamics of Extreme Mass Segregation in a Rapidly Collapsing Bubble

A molecular dynamic simulation of a mixture of light and heavy gases in a rapidly imploding sphere exhibits virtually complete segregation. The lighter gas collects at the focus of the sphere and reaches a temperature that is several orders of magnitude higher than when its concentration is 100%. Implosion parameters are chosen via a theoretical fit to an observed sonoluminescing bubble with an extreme expansion ratio (25:1) of maximum to ambient radii.

P08 高強度ソノルミネッセンス気泡によるカーボンナノ材料の合成(第II部,ポスター発表)

P08 高強度ソノルミネッセンス気泡によるカーボンナノ材料の合成(第II部,ポスター発表)

Spectral lines of OH radicals and Na atoms in sonoluminescence

With the equations of fluid mechanics, the proper boundary conditions, and the gas properties, we simulate the processes of single-bubble sonoluminescence. The calculation demonstrates the process of the evolution of the radiation energy spectrum with time for bright sonoluminescing bubbles, which clearly shows how the prominence of the OH line near 310 nm gradually merges into the continuous spectral background as the radiation power increases and finally disappears in the spectrum. For the dim bubble, the spectral line of OH radicals or the sodium line near 589 nm is prominent on the spectrum.

Validation of molecular dynamics simulation for a collapsing process of sonoluminescing gas bubbles

Sonoluminescence is light emission associated with the catastrophic collapse of bubble oscillation under ultrasound. Molecular dynamics (MD) simulation of collapsing bubbles with micro- and nano-size equilibrium radii was performed and the results were compared with theoretical calculations. The molecules inside a collapsing gas bubble were modelled as hard spheres, and the instantaneous bubble radius and the bubble wall velocity used in the simulation were obtained from the Keller–Miksis equation with pressure data taken from MD simulation. With a suitable boundary condition at the bubble wall, the MD simulation results for the bubble wall velocity, the gas temperature and pressure around the collapse point for the sonoluminescing bubbles are in acceptable agreement with theoretical predictions. However, these theoretical predictions need validation because estimated thermal conductivity for the gas and liquid were used for the extreme condition achieved at the collapse point. This study also revealed that the collapsing process of a sonoluminescing gas bubble proceeds almost adiabatically.

Stability of a sonoluminescing nitrogen bubble in chilled water

Bubbles are levitated in a resonator driven by an ultrasound wave. Their highly nonlinear oscillations feature a strong collapse, where fluidlike densities and temperatures of several thousand degrees Kelvin are reached, resulting in the emission of ultrashort light pulses. Previous experiments and theories explained the observed stable bubble dynamic and emission on long time scales with the requirement of a noble gas. Recent experiments reveal stable sonoluminescent emission of nitrogen bubbles in chilled water without the presence of a noble gas. Numerical calculations show that a diffusive and dissociative equilibrium can be reached when the temperature within a nitrogen bubble is limited due to the presence of water vapor. Calculated stability lines agree with published experimental results. The results show that noble-gas-free stable single bubble sonoluminescence of nitrogen bubbles is possible.

Trapping an Intensely Bright, Stable Sonoluminescing Bubble

Previous works on single bubble sonoluminescence in sulfuric acid solutions have stressed the fact that the sonoluminescence (SL) emissions are the highest ever found, but at the same time the bubble moves in orbits. We have fixed the SL bubble spatially and at the same time we have reached higher SL emissions using another harmonic acoustic signal to produce the acoustic excitation. Multiple harmonic excitation produces up to a fourfold increase in SL emissions, reaching the peak value of about 40 microW for a moving bubble and 15 microW for a nonmoving bubble. The ability to have a bright stationary bubble also opens new research opportunities. In particular, we develop a new method to measure the absolute radius evolution of the bubble that exploits this stability.

A search for laser heating of a sonoluminescing bubble

Thermodynamic arguments show that a sonoluminescing bubble that acts as a black body can absorb energy from a high power, pulsed laser beam. The mechanism for increasing the temperature of a sonoluminescing bubble is discussed and experiments with a frequency doubled, pulsed Nd:YAG laser are described. A bound for the amount of radiation absorbed is given as no evidence for heating was found at the low radiation intensity employed in the experiments.

Composition and its evolution inside a sonoluminescing bubble by line spectra

The line emissions of OH*, Na, Na-Ar*, and Ar are observed in stable and bright single bubble sonoluminescence (SBSL), which shows that the composition of the bubble consists of at least three parts: the vapor, droplets of the host liquid, and the gas dissolved in the host liquid. The observation of line emissions in SBSL demonstrates that it shares exactly the same spectra with multibubble sonoluminescences (MBSL). The experiments indicate that noble gas plays an important role in all line emissions of both SBSL and MBSL. The time resolved spectra of SBSL show that there is significant mass exchange between the inside and outside of the bubble. The time scale of the mass exchange ranges from less than 1/10 s to tens of seconds. The SBSL in sulfuric acid supports the argon rectification theory. Because stable SBSL in sulfuric acid can just be achieved within a narrow parameter range, only weak rectification is observed in our experiments.

Stability of an imploding spherical shock wave in a van der Waals gas II

The emission of light from a sonoluminescing bubble may depend on whether shock waves launched each acoustic cycle by the imploding surface of the bubble focus on to a sufficiently small volume at the bubble centre. This in turn may depend on whether the shock maintains its stability as it travels inwards. With this application in mind, the linear stability of an imploding spherical shock was studied in Part I, using a van der Waals equation of state for the gas. Conditions for instability were determined, but the subsequent fate of the perturbations of the bubble surface was unknown. Would the instabilities grow and persist at finite amplitude or would they disappear during implosion? The answers to such questions are sought here by integrating the gas dynamics equations using the finite-difference essentially non-oscillatory method of Shu and Osher. The shock is initiated by a nearly spherical 'piston' and its subsequent evolution, including its finite-amplitude deviations from sphericity, is determined. Two types of behaviour are found depending on the parameter b = bp 0 , where b is the van der Waals excluded volume and p 0 is the initial uncompressed density of gas ahead of the shock. When b is sufficiently large, an initially smooth shock front remains smooth as it focuses and, although it is impossible to continue the integrations up to the moment of implosion, it appears that it will focus on a small volume at the centre of the bubble. This is in sharp contrast to what happens at smaller values of b for which the initial distortion of the shock front, if sufficiently large, becomes and remains polygonal shaped. This is consistent with experimental results for cylindrical imploding shocks as well as with earlier theoretical investigations of imploding cylindrical and spherical shocks in an ideal gas (b = 0) that used the Chisnell, Chester and Witham (CCW) approximation or the geometrical shock approximation of Whitham. Plausibly, the polygonal distortions reduce the volume on to which the imploding shock in a sonoluminescing bubble focuses.

Upper Bound for Neutron Emission from Sonoluminescing Bubbles in Deuterated Acetone

An experimental search for nuclear fusion inside imploding bubbles of degassed deuterated acetone at 0 degrees C driven by a 15 atm sound field and seeded with a neutron generator reveals an upper bound that is a factor of 10 000 less than the signal reported by Taleyarkhan et al. The strength of our upper bound is limited by the weakness of sonoluminescence, which we ascribe to the relatively high vapor pressure of acetone.

Temperature and pressure fields due to collapsing bubble under ultrasound

Temperature and pressure fields generated by the collapsing bubble of microsize in liquid under ultrasound are estimated by a set of solutions of the Navier–Stokes equations for the gas inside bubble with considering heat transfer through the bubble wall. The calculation results for the peak temperature and pressure were compared to the observed ones from a sonoluminescing bubble which can be levitated in a spherical cell under ultrasound frequency range of 10–40 kHz. The calculation results are in good agreement with observed ones. However, the Rayleigh–Plesset equation with polytropic relation, a conventional method yields considerably underestimated values in temperature and overestimated ones in pressure. The bubble dynamics model presented in this study may be used as a tool for the design of sonochemical reactor where the peak temperature and pressure and the pressure field due to the bubble collape are important parameters.

Measurement of shock velocity from cavitation collapse in high static pressure liquids using Schlieren and shadowgraphy

High amplitude shock waves due to collapse of a cavitation bubble were photographed using a high power pulsed laser diode driven with an avalanche transistor pulser. The strong implosions of high pressure bubble cavitation travel initially at several times the local speed of sound. This method was used to measure shock wave velocity in water at static pressures up to 300 bars. The photographs were taken between 30 and 60 ns of the bubble implosion. Schlieren and shadowgraphy techniques were used and compared. The purpose is to characterize the pressure conditions that exist shortly after the implosion of a high pressure sonoluminescence bubble. [Work supported by SMDC Contract No. W9113M‐07‐C‐0178.]

Plasma in sonoluminescing bubble

With the new accommodation coefficient of water vapor evaluated by molecular dynamics model, the maximum temperature of a sonoluminescing bubble calculated with the full partial differential equations easily reaches few tens of thousands degrees. Though at this temperature the gas is weakly ionized (10% or less), the gas density inside a sonoluminescing bubble at the moment of the bubble’s flashing is so high that there still forms a dense plasma. The light emission of the bubble is calculated by the plasma model which is compared with that by the bremsstrahlung (electron-ion, electron-neutral atom) and recombination model. The calculation by the two models shows that for the relatively low maximum temperature (<30000 K) of the bubble, the pulse width is independent of the wavelength and the spectrum deviates the black body radiation type; while for the relatively high maximum temperature (∼60000 K), the pulse width is dependent of the wavelength and the spectrum is an almost perfect black body radiation spectrum. The maximum temperature calculated by the gas dynamics equations is much higher than the temperature fitted by the black body radiation formula.

Measurement of Pressure and Density Inside a Single Sonoluminescing Bubble

The average pressure inside a sonoluminescing bubble in sulfuric acid has been determined by two independent techniques: (1) plasma diagnostics applied to Ar atom emission lines, and (2) light scattering measurements of bubble radius vs time. For dimly luminescing bubbles, both methods yield intracavity pressures approximately 1500 bar. Upon stronger acoustic driving of the bubble, the sonoluminescence intensity increases 10,000-fold, spectral lines are no longer resolved, and radius vs time measurements yield internal pressures > 3700 bar. Implications for a hot inner core are discussed.

Theory of light emission in sonoluminescence as thermal radiation

Based on the model proposed by Hilgenfeldt [Nature (London) 398, 401 (1999)], we present here a comprehensive theory of thermal radiation in single-bubble sonoluminescence (SBSL). We first invoke the generalized Kirchhoff's law to obtain the thermal emissivity from the absorption cross section of a multilayered sphere (MLS). A sonoluminescing bubble, whose internal structure is determined from hydrodynamic simulations, is then modeled as a MLS and in turn the thermal radiation is evaluated. Numerical results obtained from simulations for argon bubbles show that our theory successfully captures the major features observed in SBSL experiments.

Dynamics of a Sonoluminescing Bubble in Sulfuric Acid

The spectral shape and observed sonoluminescence emission from Xe bubbles in concentrated sulfuric acid is consistent only with blackbody emission from a spherical surface that fills the bubble. The interior of the observed 7000 K blackbody must be at least 4 times hotter than the emitting surface in order that the equilibrium light-matter interaction length be smaller than the radius. Bright emission is correlated with long emission times (approximately 10 ns), sharp thresholds, unstable translational motion, and implosions that are sufficiently weak that contributions from the van der Waals hard core are small.

Determination of the Size Distribution of Sonoluminescence Bubbles in a Pulsed Acoustic Field

A simple method is described for determining the size of sonoluminescence bubbles generated by acoustic cavitation. The change in the intensity of sonoluminescence, from 4 ms pulses of 515 kHz ultrasound, as a function of the "off" time between acoustic pulses, is the basis of the method. The bubble size determined in water was in the range of 2.8-3.7 mum.