Rapid Bubble Collapse Research Articles

Bubble energy generator.

Bubbles have been extensively explored as energy carriers ranging from boiling heat transfer and targeted cancer diagnosis. Yet, despite notable progress, the kinetic energy inherent in small bubbles remains difficult to harvest. Here, we develop a transistor-inspired bubble energy generator for directly and efficiently harvesting energy from small bubbles. The key points lie in designing dielectric surface with high-density electric charges and tailored surface wettability as well as transistor-inspired electrode configuration. The synergy between these features facilitates fast bubble spreading and subsequent departure, transforms the initial liquid/solid interface into gas/solid interface under the gating of bubble, and yields an output at least one order of magnitude higher than existing studies. We also show that the output can be further enhanced through rapid bubble collapse at the air/liquid interface and multiple bubbles synchronization. We envision that our design will pave the way for small bubble-based energy harvesting in liquid media.

Bubble Collapse Phenomenon of Multiphase Flow Field in a Venturi Tube

Microbubbles have various properties and are expected to be used in a wide range of fields. In this research, we focus on one of microbubble generators with a converging- diverging nozzle, i.e. a Venturi tube. In order to control bubble distribution of generated bubble diameter, knowledge of bubble generation mechanism in the tube is required. The purpose of this research is to clarify the effect of complex flow in a Venturi tube on bubble collapse. In this research, we focus on the change of pressure loss coefficient calculated from the pressure distribution in the tube and the sound pressure generated at the time of bubble collapse. For results of the experiment, the pressure loss coefficient increased due to the cavitation in the liquid single-phase flow. The same tendency was further obtained in the bubbly flow. It was also confirmed that the collapse behavior of bubbles differed depending on the inlet conditions, and sound pressure increased under conditions where rapid bubble collapse occurred.

The Chemical History of a Bubble.

Acoustic cavitation (the growth, oscillation, and rapid collapse of bubbles in a liquid) occurs in all liquids irradiated with sufficient intensity of sound or ultrasound. The collapse of such bubbles creates local heating and provides a unique source of energy for driving chemical reactions. In addition to sonochemical bond scission and formation, cavitation also induces light emission in many liquids. This phenomenon of sonoluminescence (SL) has captured the imagination of many researchers since it was first observed 85 years ago. SL provides a direct probe of cavitation events and has provided most of our understanding of the conditions created inside collapsing bubbles. Spectroscopic analyses of SL from single acoustically levitated bubbles as well as from clouds of bubbles have revealed molecular, atomic, and ionic line and band emission riding atop an underlying continuum arising from radiative plasma processes. Application of spectrometric methods of pyrometry and plasma diagnostics to these spectra has permitted quantitative measurement of the intracavity conditions: relative peak intensities for temperature measurements, peak shifts and broadening for pressures, and peak asymmetries for plasma electron densities. The studies discussed herein have revealed that extraordinary conditions are generated inside the collapsing bubbles in ordinary room-temperature liquids: observable temperatures exceeding 15 000 K (i.e., three times the surface temperature of our sun), pressures of well over 1000 bar (more than the pressure at the bottom of the Mariana Trench), and heating and cooling rates in excess of 1012 K·s-1. Scientists from many disciplines, and even nonscientists, have been and continue to be intrigued by the consequences of dynamic bubbles in liquids. As chemists, we are fascinated by the high energy reactions and processes that occur during acoustic cavitation and by the use of SL as a spectroscopic probe of the events during cavitation. Within the chemical realm of SL and cavitation there are many interesting questions that are now answered but also many that remain to be explored, so we hope that this Account reveals to the reader some of the most fascinating of those curiosities as we explore the chemical history of a bubble. The high energy species produced inside collapsing bubbles also lead to secondary reactions from the high energy species created within the collapsing bubble diffusing into the bulk liquid and expanding the range of sonochemical reactions observed, especially in redox reactions relevant to nanomaterials synthesis. Bubbles near solid surfaces deform upon collapse, which lessens the internal heating within the bubble, as shown by SL studies, but introduces important mechanical consequences in terms of surface damage and increased surface reactivity. Our understanding of the conditions created during cavitation has informed the applications of ultrasound to a wide range of chemical applications, from nanomaterials to synthetically useful organic reactions to biomedical and pharmaceutical uses. Indeed, we echo Michael Faraday's observation concerning a candle flame, "There is not a law under which any part of this universe is governed which does not come into play and is touched upon in these phenomena." ( Faraday , M. The Chemical History of a Candle ; Harper & Brothers : New York , 1861 ).

Enhanced flow boiling in microchannels using auxiliary channels and multiple micronozzles (I): Characterizations of flow boiling heat transfer

Flow boiling in parallel microchannels can be dramatically enhanced through inducing self-excited and self-sustained high frequency two-phase oscillations as demonstrated in our previous studies using a two-nozzle microchannel configuration. Two-phase mixing induced by the rapid bubble collapse is shown to be the major enhancement mechanism. However, in the two-nozzle configuration microchannels, the mixing effect is limited to the downstream of the microchannels, meaning that only half length of the entire microchannel is functionalized as designated. In this study, a four-nozzle microchannel configuration is developed with an aim at extending the highly desirable mixing effect to the entire channel. Flow boiling in the four-nozzle configuration microchannels is experimentally studied with deionized water and the mass flux ranging from 120kg/m2 s to 600kg/m2 s. The onset of nucleate boiling temperature is considerably reduced by ∼14% because of more nucleation sites created by the multiple nozzles. Equally important, the improved microchannel configuration successfully extends the mixing to the entire channel as validated by the enhanced heat transfer rate and visualization study. Compared to the previous two-nozzle configuration, the overall heat transfer coefficient (HTC) is significantly improved primarily owing to the enhanced nucleate boiling. For example, the peak overall HTC of 262kW/m2 K is achieved at a mass flux of 150kg/m2 s, accounting for ∼83.7% enhancement. Additionally, the peak effective HTC reaches 97.6kW/m2 K, accounting for ∼67% enhancement.

Enhanced flow boiling in microchannels using auxiliary channels and multiple micronozzles (II): Enhanced CHF and reduced pressure drop

Enhancing critical heat flux (CHF) of flow boiling without escalating pressure drop is highly desirable in thermal management of high power-density electronic devices. Usually, an improved CHF can be achieved by restricting flow or at a higher mass velocity, leading to a higher pressure drop. In this study, compared to the two-nozzle microchannel configuration, the improved microchannel configuration as detailed in the Part (I) of this study can enhance CHF without sacrificing pressure drop. In this part, CHF is experimentally evaluated together with the pressure drop with mass flux ranging from 120kg/m2s to 600kg/m2s. Compared to the two-nozzle configuration, our study shows that CHF can be enhanced up to 32% with a ∼53% reduction of pressure drop at a mass flux of 325kg/m2s. The bubble collapse-removal process is significantly improved because more micronozzles are integrated. The enhanced pumping effect, which is created by rapid bubble collapse processes in the entire main channels, enables a more sustainable liquid supply and hence delays the CHF conditions. Moreover, two-phase flow in terms of pressure drop fluctuations is more stable owing to the effective management of bubble confinement in the entire channel.

Application of cavitation in uranium leaching

Cavitation is mostly considered as an operational problem and not desirable phenomena. The rapid creation and collapse of bubbles can destroy pump and erode other equipment. Recently, cavitation has been explored to enhance mass transfer and also to enhance or alter chemical reactions. Cavitation by definition is the formation, growth and rapid collapse of bubbles. Cavitation can be generated by different techniques. Hydrodynamic (hydraulic) and acoustic cavitations are the results of overcoming the tension existing in a liquid using fluid and sound energy, respectively. Optic, charge particle and steam bubble cavitations are the consequence of local deposition of energy using light, high energy elementary particles beam and steam bubble, respectively. For industrial application, hydrodynamic and acoustic cavitations are more important. Steam bubble cavitation is a recent invention and is a highly promising candidate for industrial applications in future. Improvement in recovery and enhancement in rate of recovery during leaching by ultrasound is documented in literature. Uranium leaching from carnotite ore with ultrasound was reported in 1968 by Russia and ultrasonic leaching of urania impregnated in graphite fuel was reported in 1961 by the USA. There is no other published literature available on uranium leaching with cavitation. However, lot more research has been carried out under sonochemistry for process intensification. Different types of cavitation reactor schemes are proposed by researchers for the process intensification. In this paper, we have reviewed uranium leaching with cavitation using different cavitation mechanisms. Effect of cavitation-aided leaching of uranium from MgF2 has been experimentally established. Uranium leaching of Narwapahar ore with acoustic and hydrodynamic cavitation also has been studied.

The Microstructure and Characteristics of Luminescent Porous Silicon Film Prepared by the Physicochemical

The special physicochemical environment caused by sonic-vacating provides an important outlet for the preparation of highly efficient luminescent porous silicon films. Experimental results show that sonic—chemical treatment is an effective technology for the improvement of the microstructure of porous silicon, and the luminescent efficiency and stability thereof. Luminescent porous silicon films, prepared by ultrasonic—enhanced anode electrochemical etching, display better qualities than the samples prepared by conventional methods widely used at present. This ultrasonic—chemical effect roots in sonic—vacating, i.e. the generation, formation and rapid collapse of bubbles in the etching solution. In the process of the porous silicon being etched, the escape rate and caving-in of hydrogen bubbles in the pores is increased as a result of the work of the ultrasonic waves, which is helpful to the vertical etching of the pores.

Femtosecond laser nano-ablation in fixed and non-fixed cultured cells

To understand the onset and morphology of femtosecond laser submicron ablation in cells and to study physical evidence of intracellular laser irradiation, we used transmission electron microscopy (TEM). The use of partial fixation before laser irradiation provides for clear images of sub-micron intracellular laser ablation, and we observed clear evidence of bubble-type physical changes induced by femtosecond laser irradiation at pulse energies as low as 0.48 nJ in the nucleus and cytoplasm. By taking ultrathin sliced sections, we reconstructed the laser affected subcellular region, and found it to be comparable to the point spread function of the laser irradiation. Laser-induced bubbles were observed to be confined by the surrounding intracellular structure, and bubbles were only observed with the use of partial pre-fixation. Without partial pre-fixation, laser irradiation of the nucleus was found to produce observable aggregation of nanoscale electron dense material, while irradiation of cytosolic regions produced swollen mitochondria but residual local physical effects were not observed. This was attributed to the rapid collapse of bubbles and/or the diffusion of any observable physical effects from the irradiation site following the laser exposure.

Inside a Collapsing Bubble: Sonoluminescence and the Conditions During Cavitation

Acoustic cavitation, the growth and rapid collapse of bubbles in a liquid irradiated with ultrasound, is a unique source of energy for driving chemical reactions with sound, a process known as sonochemistry. Another consequence of acoustic cavitation is the emission of light [sonoluminescence (SL)]. Spectroscopic analyses of SL from single bubbles as well as a cloud of bubbles have revealed line and band emission, as well as an underlying continuum arising from a plasma. Application of spectrometric methods of pyrometry as well as tools of plasma diagnostics to relative line intensities, profiles, and peak positions have allowed the determination of intracavity temperatures and pressures. These studies have shown that extraordinary conditions (temperatures up to 20,000 K; pressures of several thousand bar; and heating and cooling rates of >10(12) K s(1)) are generated within an otherwise cold liquid.

Modeling of hydrodynamic cavitation reactors based on orifice plates considering hydrodynamics and chemical reactions occurring in bubble

In the present work, a model has been developed for predicting the cavitational intensity in a hydrodynamic cavitation reactor based on the use of orifice plates considering the hydrodynamic conditions and the different chemical reactions taking place inside the cavity. The model is based on a set of ordinary differential equations and considers the bubble hydrodynamics and heat exchange including the phase change. It also accounts for the chemical reactions of the various gaseous species in the air–water system and diffusion/dissolution of the reaction products from the cavity. Weber number criterion has been incorporated for the stability of the growing bubble. During rapid bubble collapse a large amount of water vapor is trapped inside the bubble, resulting in an increased heat capacity and endothermic chemical reactions leading to lower temperatures at the end of the collapsing event. Analyzing the reaction thermodynamics within the dense, collapsed bubble, it can be said that the effect of excluded volume of the non-ideal gas results in pronounced suppression of the molecule-producing endothermic reactions using Le-Chatelier's principle. Design correlation in terms of cavitational intensity (in terms of collapse pressure and temperatures) and cavitational yield (in terms of OH radicals) aims at understanding the design information related to the dependency of the cavitational intensity and the radical yield on the operating parameters in the case of the hydrodynamic cavitation.

K-1704 ソノルミネッセンシング・バブルのDSMC法による解析(J08-1 熱流体現象の原子・分子論的アプローチ(1))(J08 熱流体現象の原子・分子論的アプローチ)

To analyze a single sonoluminescing bubble captured in the standing wave, a computational method, which consists of the Direct Simulation Monte Carlo method for the mixture of argon and water molecules inside the bubble and the Yasui's equation for the boundary condition, is proposed, considering the evaporation and condensation of water molecules across the bubble wall as well as the thermal diffusion. The calculation results show agreements of the characteristic histories on the bubble radius and temperature inside the bubble with the experimental one, and the species segregation of mixture gas inside the bubble, which may be associated with the pressure gradient in the interior of bubble during rapid bubble collapse.

Does water vapor prevent upscaling sonoluminescence?

Experimental results for single-bubble sonoluminescence of air bubbles at very low frequency f = 7.1 kHz are presented: In contrast to the predictions of a recent model [S. Hilgenfeldt and D. Lohse, Phys. Rev. Lett. 82, 1036 (1999)], the bubbles are only as bright (10(4)-10(5) photons per pulse) and the pulses as long (approximately 150 ps) as at f = 20 kHz. We can theoretically account for this effect by incorporating water vapor into the model: During the rapid bubble collapse a large amount of water vapor is trapped inside the bubble, resulting in an increased heat capacity and hence lower temperatures, i.e., hindering upscaling. At this low frequency water vapor also dominates the light emission process.

Ultrasonic degradation of cellulose nitrate. II. Effects of temperature, solvent, and other process variables

AbstractCellulose nitrate was degraded ultrasonically at 0 to 85°C. in the alkyl acetates from methyl to heptyl. In each solvent there is a high and low limit temperature where cavitation and degradation both cease. The upper limits are at the temperatures where vapor pressure of the solvent is about one‐half atmosphere, and cavitation evidently ceases because the solvent vapor pressure becomes too great for rapid bubble collapse. The lower limits of pressure and temperature vary in a linear manner, but have not been explained. The results confirm the need for cavitation as an initiator of the degradation mechanism, and explain some effects previously ascribed to solvent viscosity and temperature. When radio frequency power was varied, the rate of degradation was found to be independent of power so long as cavitation was present. In other experiments, degradation was found to be approximately constant to concentrations much lower than previously tested, whereas some proposed mechanisms would require that it should be reduced by dilution. Addition of a nonsolvent reduced the intrinsic viscosity of the polymer solution but did not reduce the extent of degradation; thus degradation is a function of the chain's length but not of its solvation. Finally, comparison of a series of celluloses from diverse sources showed that all gave about the same minimum degradable chain length, of 800–1000 DP. It was concluded that there was no evidence for the existence of weak links in the celluloses at shorter intervals.