Multibubble sonoluminescence spectra of water which resemble single-bubble sonoluminescence

Multibubble sonoluminescence (MBSL) spectra of water from cavitation clouds were collected in the presence of different noble gases and at different acoustic intensities. Results show that at high acoustic intensity and with xenon as a dissolved gas the emission of the OH* radical becomes indiscernible from the continuum. These spectra resemble single-bubble sonoluminescence (SBSL) spectra. It is concluded that the source of emission in MBSL and SBSL can be the same, the difference in spectra is due to the higher temperature inside the bubble during SBSL.     

Second mode of recycling together with period doubling links single-bubble and multibubble sonoluminescence

We report the existence of a second type of recycling mode that occurs for air-seeded bubbles. Observation of period doubling in both the stable, the first type, and the second type of recycling mode, together with simultaneous measurement of the relative phase of light emission compared to the drive, shows that the instability boundaries of period doubling and bubble extinction are mainly determined by the bubble size irregardless of the gas composition. The second type mode seems to represent a link between single-bubble and multibubble sonoluminescence.     

Scenario of the electric breakdown and UV radiation spectra in single-bubble sonoluminescence

In a preceding paper we put forward the hypothesis that the single-bubble sonoluminescence (SBSL) is caused by strong electric fields arising near the surface of a collapsing gas bubble on account of the flexoelectric effect in water. Here we argue that these fields can indeed provoke a multiple electric breakdown in water, in a micron-size region near the surface of the collapsing gas bubble, and show that the main numerical characteristics of the SBSL can be naturally explained within this mechanism. The SBSL spectra are determined by radiative transitions between high-energy levels of noble-gas atoms excited by hot electrons produced by the strong flexoelectric field in “cold” water. Pis’ma Zh. éksp. Teor. Fiz. 70, No. 7, 428–433 (10 October 1999) Published in English in the original Russian journal. Edited by Steve Torstveit.     

稀土盐水溶液单泡声致发光中的特征光谱

在溶有稀有气体的稀土盐氯化铽水溶液中进行了单泡声致发光光谱的研究. 在固定驱动超声频率、不同驱动声压下, 观察到了一系列OH自由基从第一激发态A²∑⁺到基态X²Π 各振动能级跃迁所产生的谱线, 包括波长307 nm处的(0, 0)跃迁谱线, 335 nm处的(0, 1)跃迁谱线以及276 nm处的(1, 0) 跃迁谱线等. 实验结果表明较高的驱动声压有利于 276 nm处谱线的产生, 而较低的驱动声压则有利于 307 与 335 nm 处谱线的产生. 通过定义线状光谱与连续谱的光强比, 定量地表征了线状光谱在总光谱中的相对强度, 并给出了驱动声压对各跃迁谱线光强比的影响. 关键词： 单泡声致发光 驱动声压 线状光谱 光强比     

Stable multibubble sonoluminescence bubble patterns

Multibubble standing wave patterns can be generated from a flat piezoceramic transducer element radiating into water. By adding a second transducer positioned at 90 degrees from the transducer generating the standing wave, a 3-dimensional volume of stable single bubbles can be established. Further, the addition of the second transducer stabilizes the bubble pattern so that individual bubbles may be studied. The size of the bubbles and the separation of the standing waves depend on the frequency of operation. Two transducers, operating at frequencies above 500 kHz, provided the most graphic results for the configuration used in this study. At these frequencies stable bubbles exhibit a bright sonoluminescence pattern. Whereas stable SBSL is well-known, stable MBSL has not been previously reported. This paper includes discussions of the acoustic responses, standing wave patterns, and pictorial results of the separation of individual bubble sonoluminescence in a multibubble sonoluminescence environment.     

Hydrodynamic approach to multibubble sonoluminescence

The velocity profile and radiation pressure field of a bubble cluster containing several thousand micro bubbles were obtained by solving the continuity and momentum equations for the bubbly mixture. In this study, the bubbles in the cluster are assumed to be generated and collapsed synchronously with an applied ultrasound. Numerical calculations describing the behavior of a micro bubble in a cluster included the effect of the radiation pressure field from the synchronizing motion of bubbles in the cluster. The radiation pressure generated from surrounding bubbles affects the bubble’s behavior by increasing the effective mass of the bubble so that the bubble expands slowly to a smaller maximum size. The light pulse width and spectral radiance from a bubble in a cluster subjected to ultrasound were calculated by adding a radiation pressure term to the Keller–Miksis equation, and the values were compared to experimental values of the multibubble sonoluminescence condition. There was close agreement between the calculated and observed values.     

Ambient acceleration dependence of single-bubble sonoluminescence

Much of the research performed to study SBSL deals with the influence of external parameters (e.g., the host water temperature, the ambient pressure, the type and amount of dissolved gas in the liquid, to name a few) on the bubble dynamics and light emission. In the current paper, work carried out to study the influence of another external parameter-ambient acceleration-is described. The experiments described here were performed on the NASA KC-135 which provided both periods of reduced gravity (10(-3) g) and increased gravity (1.8 g) by flying repeated parabolic maneuvers. The resulting measurements are compared with the predictions of a numerical model and can be understood in the context of the changing hydrostatic head pressure and buoyant force acting on the bubble.     

Line emission in single-bubble sonoluminescence

We report that single-bubble sonoluminescence (SBSL) at low light intensities produces emission bands similar to multibubble sonoluminescence (MBSL) for pure noble gas bubbles. A smooth crossover between SBSL and MBSL behavior can be induced by varying the acoustic pressure amplitude and thereby the intensity of the light emitted. The relative intensity of the band emission depends both on the molecular weight of the noble gas and the water temperature. Our results provide a connection between the mechanisms SBSL and MBSL and show that molecular emission plays a role in SBSL.     

Influence of bubble clustering on multibubble sonoluminescence

Influence of clustering of cavitation bubbles on multibubble sonoluminescence (MBSL) in standing wave fields is studied through measurement of MBSL intensity with a photomultiplier tube and observation of corresponding bubble behavior with a high-speed video camera and an intensified charge-coupled device one. It is clarified that, when the SL is quenched suddenly at excessive ultrasonic power, the behavior of bubbles clearly changes; the bubbles which form dendritic branches of filaments change into clusters due to the secondary Bjerknes force. The cluster is composed of several bubbles surrounded by many tiny bubbles, in which bubbles repeatedly coalesce and fragment, and run away from pressure antinodes. When the clusters are broken up by forced fluid motion, the quenching of MBSL is suppressed.     

Dependence of single-bubble sonoluminescence on ambient pressure

Kondic et al.'s theory makes several specific predictions on the dependence of single-bubble sonoluminescence (SBSL) on ambient pressure. We have carried out experiments to verify these predictions for air bubbles in a water-glycerine mixture at about 17.5 kHz. The results show an increase in SBSL with reduced ambient pressure down to a critical value below which SBSL is extinguished. The results are all in good agreement with Kondic et al.'s theory and are also compatible with the dissociation hypothesis of Lohse et al.     

Influence of ultrasonic frequency on multibubble sonoluminescence

Computer simulations of bubble oscillations are performed under conditions of multibubble sonoluminescence (MBSL) in water for various ultrasonic frequencies. The range of the ambient bubble radius for sonoluminescing bubbles narrows as the ultrasonic frequency increases; at 20 kHz it is 0.1-100 microm while at 1 MHz it is 0.1-3 microm. At 1 MHz, any sonoluminescing bubble disintegrates into a mass of smaller bubbles in a few or a few tens of acoustic cycles, while at 20 kHz and 140 kHz some sonoluminescing bubbles are shape stable. The mechanism of the light emission also depends on the ultrasonic frequency. As the ultrasonic frequency increases, the amount of water vapor trapped inside bubbles at the collapse decreases. As a result, MBSL originates mainly in plasma emissions at 1 MHz while it originates in chemiluminescence of OH radicals and plasma emissions at 20 kHz.     

A new source of radiation in single-bubble sonoluminescence

An unsolved challenge of sonoluminescence phenomenon is the mechanism of light emission at the moment of collapse. In this article, by considering single-bubble sonoluminescence and based on the hydrochemical model and thermal bremsstrahlung approach, for the first time two different origins of light have numerically been studied to describe the Ar bubble radiation in water at the moment of collapse: (a) radiation from the Ar gas inside the bubble and (b) radiation from the thin layer of the surrounding fluid. The results indicate that, contrary to the previous studies, the radiation from the water shell is dominant, and it is about one order of magnitude stronger than the radiation from the gas inside the bubble. This result can decrease the difference between the theoretical results and the previous experimental data. In addition, based on the role of acoustic pressure amplitude on the characteristics of single-bubble sonoluminescence, various parameters such as degree of ionization, gas pressure, temperature and power were calculated. The results are in excellent agreement with the reported experimental measurements.     

Bubble levitation and translation under single-bubble sonoluminescence conditions

Bubble levitation in an acoustic standing wave is re-examined for conditions relevant to single-bubble sonoluminescence. Unlike a previous examination [Matula et al., J. Acoust. Soc. Am. 102, 1522-1527 (1997)], the stable parameter space [Pa,R0] is accounted for in this realization. Forces such as the added mass force and drag are included, and the results are compared with a simple force balance that equates the Bjerknes force to the buoyancy force. Under normal sonoluminescence conditions, the comparison is quite favorable. A more complete accounting of the forces shows that a stably levitated bubble does undergo periodic translational motion. The asymmetries associated with translational motion are hypothesized to generate instabilities in the spherical shape of the bubble. A reduction in gravity results in reduced translational motion. It is hypothesized that such conditions may lead to increased light output from sonoluminescing bubbles.     

Enhancement of sonoluminescence emission from a multibubble cavitation zone

Investigations have been performed on various methods of increasing cavitation activity measured by the intensity of sonoluminescence. It is shown that the effect of the combined action of (a) pulsed modulation of an acoustic field, (b) liquid degassing and cooling and (c) increasing the static pressure considerably exceeds the sum of the effects achieved by each of these methods individually. A more than 250-fold increase of the sonoluminescence intensity has been attained compared with continuous irradiation under normal conditions (room temperature, atmospheric pressure, gas-saturated liquid). An interpretation of the results obtained is proposed.     

水蒸气对声致发光单气泡稳定性的影响

在考虑水蒸气凝结与水的蒸发过程的基础上，推导了球形气泡形状稳定性方程-利用这个方程以及气泡运动时的气体扩散平衡条件，分别研究了环境水温217℃时声驱动频率为206kHz（溶于水中的氩气含量是其饱和度的14％）、环境水温0℃时声驱动频率为319kHz（溶于水中的氮气分压为20kPa，其中含1％氩气），以及环境水温20℃时声驱动频率为338kHz（溶于水中的氮气分压为20kPa，其中含1％氩气）可控制条件下气泡稳定性问题-理论计算结果与前人的实验数据比较，发现考虑水蒸气以后比忽略水蒸气对单气泡稳定区域 关键词： 声致发光 水蒸气 形状不稳定性 扩散平衡     

Argon rectification and the cause of light emission in single-bubble sonoluminescence

In single-bubble sonoluminescence, repeated brief flashes of light are produced in a gas bubble strongly driven by a periodic acoustic field. A startling hypothesis has been made by Lohse and co-workers [Phys. Rev. Lett. 78, 1359 (1997)] that the non-noble gases in an air bubble undergo chemical reaction into soluble products, leaving only argon. In the present work, this dissociation hypothesis is supported by simulations, although the associated temperatures of about 7000 K seem too low for bremsstrahlung, which has been proposed as the dominant light emission mechanism. This suggests that emission from water vapor and its reaction products, heretofore not included, may play an important role.     

Computational simulation of ionization processes in single-bubble and multi-bubble sonoluminescence

The most recent spectroscopic studies of moving-single bubble sonoluminescence (MSBSL) and multi-bubble sonoluminescence (MBSL) have revealed that hydrated electrons (e$_{{rm aq}}^{-}$) are generated in MSBSL but absent in MBSL. To explore the mechanism of this phenomenon, we numerically simulate the ionization processes in single- and multi-bubble sonoluminescence in aqueous solution of terbium chloride (TbCl$_{3}$). The results show that the maximum degree of ionization of single-bubble sonoluminescence (SBSL) is approximately 10000 times greater than that of MBSL under certain special physical parameters. The hydrated electrons (e$_{{{rm aq}}}^{-}$) formed in SBSL are far more than those in MBSL provided these electrons are ejected from a bubble into a liquid. Therefore, the quenching of e$_{{{rm aq}}}^{-}$ to SBSL spectrum is stronger than that of the MBSL spectrum. This may be the reason that the trivalent terbium [Tb(III)] ion line intensities from SBSL in the TbCl$_{3}$ aqueous solutions with the acceptor of e$_{{{rm aq}}}^{-}$ are stronger than those of TbCl$_{3}$ aqueous solutions without the acceptor of e$_{{{rm aq}}}^{-}$. Whereas the Tb(III) ion line intensities from MBSL are not variational, which is significant for exploring the mechanism behind the cavitation and sonoluminescence.     

Effect of noble gases on sonoluminescence temperatures during multibubble cavitation

Sonoluminescence spectra were collected from Cr(CO)6 solutions in octanol and dodecane saturated with various noble gases. The emission from excited-state metal atoms serves as an internal thermometer of cavitation. The intensity and temperature of sonoluminescence increases from He to Xe. The intensity of the underlying continuum, however, grows faster with increasing temperature than the line emission. Dissociation of solvent molecules within the bubble consumes a significant fraction of the energy generated by the collapsing bubble, which can limit the final temperature inside the bubble.     

The role of vapour pressure in multibubble sonoluminescence from organic solvents

The action of high intensity cavitation on several liquid halocarbons (C(2)Cl(4) CCl(4), CHCl(3), C(2)H(2)Br(4)) and other organic solvents (acetone, benzene and their mixtures) was investigated by recording multibubble sonoluminescence UV-Vis spectra over the temperature range between 246 and 298 K. The temperature induced variation of some thermophysical properties of the solvents Favours the interpretations of their role in determining the salient characteristics of the recorded spectra. We observed that high volatility does not necessarily quench sonoluminescence emission and that argon flow plays a key role in the appearance of radical emission lines. While for each investigated substance the intensity of C*(2) emission lines was clearly correlated to temperature, a comparative test between different halocarbons did not show a clear correlation with vapour pressure. Following recently reported results which evidenced the formation of dynamically differentiated populations of emitting bubbles in sulphuric acid, we performed MBSL experiments in liquid mixtures of halocarbons and sulphuric acid to investigate the correlation between the production of emitting species and the halocarbon volatility.     

Influence of dissolved oxygen content on multibubble sonoluminescence with ambient-pressure reduction

The efficiency of chemical reactions in the presence of ultrasound at reduced pressures has been monitored using the influence of dissolved oxygen (DO) content on a luminol solution undergoing multibubble sonoluminescence. From these measurements under the condition of constant ultrasonic frequency and constant amplitude of sound pressure, it is shown that the intensity of sonoluminescence is higher at subatmospheric ambient pressure than at atmospheric pressure under the same degree of saturation. Also, it is found that there is an appropriate content of DO to produce the highest intensity of the luminescence and its value varies with ambient pressure.