Stability of a bubble in a dielectric liquid in an external electrostatic field

Critical instability conditions are found for a gas bubble in a liquid dielectric in a uniform external electrostatic field E ₀. It is shown that they depend both on the magnitude of E ₀ and on the properties of the liquid, as well as on the gas pressure in the bubble. In a linear approximation with respect to the square of the eccentricity of an equilibrium spheroidal form, the equilibrium eccentricity of the bubble exceeds the equilibrium eccentricity of a drop in the field E ₀. The gas pressure in the bubble lowers the critical electric field E ₀ for development of an instability in the bubble. Zh. Tekh. Fiz. 69, 43–48 (August 1999)     

A description of the laser-induced annealing and diffusion behaviour of implanted silicon crystals

Abstract

It is shown that as a result of the Greenwood-Foreman-Rimmer loop punching mechanism applied for helium bubble growth in nickel implanted with 5 keV He⁺ ions at 273 K, a considerable amount of helium remains outside the bubbles which are visible in a transmission electron microscope (TEM). It is also shown that even when it is assumed that there is an energy barrier with an upper limit equal to the formation energy of a self-interstitial atom, not all implanted helium can be accumulated in the bubbles below the critical dose for blistering.

The experimental observation of bubble growth in a helium pre-implanted nickel specimen during 1 MeV e^? irradiation may demonstrate that indeed a significant amount of helium remains between the bubbles visible in TEM.     

Anomalous heat evolution of deuteron implanted al upon electron bombardment III - try to observe the nuclear d-d reaction

In previous papers, one of the authors (K. K.) has observed the anomalous melting of the surface layer of deuteron implanted Al, containing so-called "tunnel structures", on the electron bombardment in transmission electron microscope. In the present paper, we intended to observe the evidence of the d-d nuclear reaction, expecting neutron emission, associated with the melting phenomenon. However, the result was rather unexpected. The melting phenomenon was certainly observed under the same experimental conditions as before. But, in spite of the melting, neutron emission associated with the nuclear reaction was not observed. And, more unexpectedly, X-ray emission of energy less than roughly 400 v keV was observed when specimens with a bubble structure, which never showed melting, were bombarded with electron beams. Several conceivable mechanisms are discussed which, however, are all not convincing to explain the melting. The melting is attributed to some excess energy generation. The error estimation of the radiation measurements was undertaken.     

Self-organization of cavities under irradiation

In the present paper two examples of self-organization in solids under irradiation are considered on the basis of original mechanisms, namely, the ordering of voids in void lattices under high temperature irradiation and the alignment of gas bubbles in bubble lattices under low-temperature gas atom implantation. The ordering of cavities (i.e. voids or gas bubbles) is proposed to arise due to a dissipative interaction between cavities induced by the interstitial dislocation loop absorption and punching, respectively, which represent anisotropic mechanisms of atomic transport.     

On the breakup of gas bubbles in a liquid under the action of a finite-amplitude pressure wave

A mechanism for breaking up gas bubbles in a liquid in a high-intensity pressure wave field is considered. Breakup criteria are obtained. An anomalous dependence of the breakup pressure on the initial bubble radius is found and explained. Zh. Tekh. Fiz. 69, 137–139 (January 1999)     

Interactions between a cavitation bubble and solidification front under the effects of ultrasound: Experiments and lattice Boltzmann modeling

The phenomena of melting and dendritic fragmentation are captured by using an in-situ device during the ultrasound-assisted solidification of a succinonitrile-acetone (SCN-ACE) alloy. The experimental results show that the dendrite arms detach from primary trunk due to the melting of the solid phase, which is caused by a moving ultrasound cavitation bubble. To quantify the interactions between the ultrasound cavitation bubble and the solidification front, a coupled lattice Boltzmann (LB) model is developed for describing the fields of temperature, flow, and solid fraction, and their interactions. The multi-relaxation-time (MRT) scheme is applied in the LB model to calculate the liquid-gas flow field, while the Bhatnagar–Gross–Krook (BGK) equation is executed to simulate the evolution of temperature. The kinetics of solidification and melting are calculated according to the lever rule based on the SCN-ACE phase diagram. After the validation of the LB model by an analytical model, the morphologies of the cavitation bubble and solidification front are simulated. It is revealed that the solidification interface melts due to the increase of the temperature nearby the cavitation bubble in ultrasonic field. The simulated morphologies of the cavitation bubble and solidification front are compared well with the experimental micrograph. Quantitative investigations are carried out for analyzing the melting rate of the solidification front under different conditions. The simulated data obtained from LB modeling and theoretical predictions reasonably accord with the experimental results, demonstrating that the larger the ultrasonic intensity, the faster the melting rate. The present study not only reveals the evolution of the solidification front shape caused by the cavitation bubbles, which is invisible in the ultrasound-assisted solidification process of practical alloys, but also reproduces the complex interactions among the temperature field, acoustic streaming, and multi-phase flows.     

Instability of a bubble in a liquid dielectric in an external electrostatic field

The sizes, charges, and number of daughter bubbles emitted during the development of instability with respect to the polarization charge in a uniform electrostatic field of a gas bubble in a liquid dielectric are found on the basis of the Onsager principle of minimum energy dissipation for nonequilibrium processes. Zh. Tekh. Fiz. 69, 10–13 (November 1999)     

Wigner lattice of ripplopolarons in a multielectron bubble in helium

The properties of ripplonic polarons in a multielectron bubble in liquid helium are investigated on the basis of a path-integral variational method. We find that the two-dimensional electron gas can form deep dimples in the helium surface, or ripplopolarons, to solidify as a Wigner crystal. We derive the experimental conditions of temperature, pressure and number of electrons in the bubble for this phase to be realized. This predicted state is distinct from the usual Wigner lattice of electrons: it melts by dissociation of the ripplopolarons when the electrons shed their localizing dimple as the pressure on the multielectron bubble drops below a critical value. Received 20 February 2003 Published online 11 April 2003 RID="a" ID="a"Also at: TU Eindhoven, Eindhoven, The Netherlands e-mail: devreese@uia.ua.ac.be     

DNS using CLSVOF method of single micro-bubble breakup and dynamics in flow focusing

Numerical simulations are performed to investigate the breakup of air bubble in flow focusing configuration; the CLSVOF (coupled level set with volume of fluid) method is employed to track the interface, which allows a better identification of the liquid–gas interface via a function called level set. The CFD simulations showed that the velocity ratio, the interfacial tension, the outer channel diameter, the continuous phase viscosity, the orifice width and length play an important role in the determination of the air bubble’s size and shape. However, at low capillary number, increasing the flow velocity ratio gives a smaller bubble size in shorter time, while the increase in interfacial tension leads to a bigger bubble. Moreover, the carrier fluid is found to slightly affect the bubbling mechanism, while the smallest bubbles were obtained with the smallest orifice size. In addition, three breakup regimes are observed in this device: disc-bubble (DB), elongated bubble (EB) and the slug bubble (SB) regime flows. This work also demonstrates that the CLSVOF is an effective method to simulate the bubbles breakup in flow focusing geometry. In addition, a comparison of our computational simulations with available experimental results reveals reasonably good agreement.

Graphic abstract

     

Evolution of gas-filled nanocracks in crystalline solids

In this work, the evolution of gas-filled cracks under gas implantation and subsequent annealing is studied on the basis of an elastic continuum approach. The observed growth limitation of He-filled nanocracks in SiC is attributed to their stabilization by the formation of circular dislocation dipoles. The formation and Ostwald ripening of bubble-loop complexes at elevated temperatures is modeled in terms of gas atom exchange between such complexes coupled with local matrix atom exchange between bubbles and loops of the same complex. The scaling laws derived for the time dependence of bubble and loop sizes are found to be in good agreement with experimental data.     

Food technological potentials of CO2 gas hydrate technology for the concentration of selected juices*

ABSTRACT

CO₂ gas hydrate technology seems to be a gentle way to concentrate juices, especially comparing to evaporation processes which achieve high levels of concentration and is furthermore energetically favorable in contrast to freeze concentration processes. CO₂ can form gas hydrates at around 30–80 bar and 274–283 K. For evaluating this new technology, it is not only important to know the phase equilibrium lines of commercial juices like apple and orange juices but also how the application of e.g. a bubble column affects the gas hydrate formation and separation from the concentrated product. In order to support the experimental outcome, numerical modeling seems suitable to understand the physical background of this novel concentration technology. This includes the simulation of temperature, velocity, pressure and concentration fields using finite volume technique. All three work packages combined will lead to a better understanding of the behavior of gas hydrate technology used to concentrate liquid food.     

Theory of sonoluminescence in single bubbles: Flexoelectric energy contribution

An equation of motion for a cavitating gas bubble immersed in a liquid is introduced which includes a flexoelectric energy term. This energy is deduced from the electric field produced by the bubble wall acceleration (pressure gradient) in the fluid (the flexoelectric effect). We show that under conditions of sonoluminescence, this electric field reaches values typical of the electric breakdown field in water. Our theoretical results are consistent with the duration of light emission, minimum bubble radius, and energy release as measured in sonoluminescence experiments in water. Pis’ma Zh. éksp. Teor. Fiz. 68, No. 6, 442–448 (25 September 1998)     

Radiation defects induced by helium implantation in gold-based alloys investigated by positron annihilation spectroscopy

The formation of gas bubbles in metallic materials may result in drastic degradation of in-service properties. In order to investigate this effect in high density and medium-low melting temperature (T _M) alloys, positron annihilation spectroscopy measurements were performed on helium-implanted gold–silver solid solutions after isochronal annealing treatments. Three recovery stages are observed, attributed to the migration and elimination of defects not stabilized by helium atoms, helium bubble nucleation and bubble growth. Similarities with other metals are found for the recovery stages involving bubble nucleation and growth processes. Lifetime measurements indicate that He implantation leads to the formation of small and over-pressurized bubbles that generate internal stresses in the material. A comprehensive picture is drawn for possible mechanisms of helium bubble evolution. Two values of activation energy (0.26 and 0.53 eV) are determined below and above 0.7T _M, respectively, from the variation of the helium bubble radius during the bubble growth stage. The migration and coalescence mechanism, which accounts for these very low activation energies, controls the helium bubble growth.     

Mobility of carbon ions and C+(4P) in helium computed from quantum-mechanical transport cross sections

On the light of a previous work and its recommendations by Matoba et al. [J. Phys. B 41, 145205 (2008)], this paper proposes to look at the mobility of ground and metastable-excited states of C⁺ ions moving into a helium buffer gas. The calculations, based on the three-temperature theory for solving the Boltzmann kinetic equation, are accomplished with quantum-mechanical transport cross sections at the low temperatures 4.3 and 77?K. The obtained mobility results are contrasted with the available theoretical data and experimental measurements, which show acceptable agreements.     

Effect of dissolved gases in water on acoustic cavitation and bubble growth rate in 0.83 MHz megasonic of interest to wafer cleaning

Changes in the cavitation intensity of gases dissolved in water, including H₂, N₂, and Ar, have been established in studies of acoustic bubble growth rates under ultrasonic fields. Variations in the acoustic properties of dissolved gases in water affect the cavitation intensity at a high frequency (0.83 MHz) due to changes in the rectified diffusion and bubble coalescence rate. It has been proposed that acoustic bubble growth rates rapidly increase when water contains a gas, such as hydrogen faster single bubble growth due to rectified diffusion, and a higher rate of coalescence under Bjerknes forces. The change of acoustic bubble growth rate in rectified diffusion has an effect on the damping constant and diffusivity of gas at the acoustic bubble and liquid interface. It has been suggested that the coalescence reaction of bubbles under Bjerknes forces is a reaction determined by the compressibility and density of dissolved gas in water associated with sound velocity and density in acoustic bubbles. High acoustic bubble growth rates also contribute to enhanced cavitation effects in terms of dissolved gas in water. On the other hand, when Ar gas dissolves into water under ultrasound field, cavitation behavior was reduced remarkably due to its lower acoustic bubble growth rate. It is shown that change of cavitation intensity in various dissolved gases were verified through cleaning experiments in the single type of cleaning tool such as particle removal and pattern damage based on numerically calculated acoustic bubble growth rates.     

A Modified Version of the Grimm's Glow Discharge Lamp for Use as a Demountable Hollow Cathode Emission Source. III. Blackening as a Function of Discharge Parameters

Abstract

The influence of anode distance from hollow cathode on the blackening? of spectral lines excited by means of the modified Grimm's lamp was investigated for three representative cathodic materials, i.e. aluminium, copper and graphite using argon as the carrier gas. On the basis of the experimental results as well as voltage-current characteristic curves at distances of 7, 15, 20, 25 and 33 mm, it was possible to conclude that the optimal sets of discharge parameters for all the materials investigated are based on an electrode distance of 20-25 mm. In the case of copper a distance of 33 mm was also found to be highly suitable. An increase in the emission of copper lines at the largest anodic length with increasing pressure of the noble gas was also observed, in contrast with the behavior of the same element at shorter distances. A tentative interpretation of the phenomenon is given.     

Flow of an electrically conducting bubble liquid in the field of an electromagnetic force

Physical processes accompanying the flow of a conducting bubble liquid in crossed electric and magnetic fields are considered. Based on the general equations of mechanics of multiphase media, we develop a one-dimensional model of the flow of and heat exchange in a compressible bubble liquid when the phases are not in thermal and velocity equilibrium. The model is numerically investigated. It is demonstrated that, when the bubble liquid flows along the electromagnetic force vector, the bubbles lag behind the carrying flow and are compressed and warmed up. This causes oscillations of the bubble volume, as well as oscillations of the parameters of both the disperse and carrying phase. In particular, the compression of the bubbles reduces the volumetric gas content, as well as increases the effective conductivity of the flow and the electromagnetic force in the downstream direction. This sets conditions for crisis of the bubble flow when the electromagnetic force expels the bubbles against the main stream. On the basis of the solutions obtained, the efficiency of a gas compressor is calculated.     

Constrained thermal denaturation of DNA under fixed linking number

A DNA molecule with freely fluctuating ends undergoes a sharp thermal denaturation transition upon heating. However, in circular DNA chains and some experimental setups that manipulate single DNA molecules, the total number of turns (linking number) is constant at all times. The consequences of this additional topological invariant on the melting behaviour are nontrivial. Below, we investigate the melting characteristics of a homogeneous DNA where the linking number along the melting curve is preserved by supercoil formation in duplex portions. We obtain the mass fraction and the number of loops and supercoils below and above the melting temperature. We also argue that a macroscopic loop appears at T _c and calculate its size as a function of temperature.     

Sonoluminescence

Abstract

Sonoluminescence is the light emission phenomenon from collapsing bubbles in liquid irradiated by an ultrasonic wave. In the present review, theoretical and experimental studies of the two types of sonoluminescence [single‐bubble sonoluminescence (SBSL) and multibubble sonoluminescence (MBSL)] are described. SBSL is a sonoluminescence from a single stably pulsating bubble trapped at the pressure antinode of a standing ultrasonic wave. MBSL is a sonoluminescence occurring from many bubbles in liquid irradiated by an ultrasonic wave. The theoretical and experimental studies suggest that SBSL originates in emissions from plasma inside the heated bubble at the bubble collapse, whereas MBSL originates both in emissions from plasma and in chemiluminescence inside heated bubbles at the bubble collapse. Unsolved problems of sonoluminescence have also been explained in detail.