Bubble Nucleation Process Research Articles

The use of fast frame video for the study of bubble growth

The kinetics of bubble evolution have received considerable attention in various contexts [l-5]. The process of bubble nucleation electrolytically [6,71, from dissolved gas solutions [8,9], or by the boiling of liquids [l,lO] has been studied in depth as a consequence of its industrial importance. The overall behaviour of bubbles at interfaces may also depend strongly on the process of bubble growth and the closely linked process of bubble detachment, since bubbles that are long-time resident at a potential nucleation site on a gas evolving surface prevent the occurrence of further nucleation events. We show that a fast frame video system may be used to study the growth stage of bubble evolution at surfaces. It should be noted that the filming of bubbles growing either electrolytically or non-electrolytically [6,7] is not a new concept, but the extension of the technique to record the growth cycles of several successive bubbles from their point of nucleation is relatively unexplored. It is expected that a video system may be used to study the nucleation and growth/detachment stages in the same experiment, and thus to determine directly the rate limiting process in bubble evolution. In these experiments, the bubble filming technique has been used to study the radii of either electrolytically or non-electrolytically generated bubbles as a function of time. In some cases it was possible to resolve the points of nucleation and detachment for the bubbles and to

Modelling of Atomization and Vaporization Process in Flash Boiling Spray. 2nd Report, Model Analysis on Atomization and Vaporization Process.

This paper presents the model analysis of atomization and vaporization process in a flash boiling spray based on the experimental results. Two kinds of liquid fuel, n-Pentane and n-Hexane, are injected into quiescent gaseous atmosphere at room temperature with low pressure through a pintle-type injector. Then, in flash boiling spray region where the back pressure is below the saturated vapor pressure of fuel, the bubble nucleation process due to flash boiling is modeled by the nucleation rate equation. Furthermore, fuel vaporization process is assessed by considering bubble growth calculations of vapor cavitation phenomena and fuel evaporation due to heat transfer process. Accordingly, we could estimate quantitatively the transient changes in bubble diameter and vapor mass fraction inside the spray for each back pressure condition.

Phase transitions with sub-critical bubbles

We study the dynamics of cosmological phase transitions initiated from a state of thermal equilibrium. If the effective potential satisfies certain general conditions, a homogeneous phase of false vacuum will form as the Universe expands, and the transition will proceed by well-known bubble nucleation processes. If such conditions do not hold, the Universe may instead be filled with a two-phase emulsion. The evolution of the transition will be determined by the free energy difference between the two phases and by the expansion rate of the Universe. Thermal fluctuations between the phases will determine the final distribution of regions of the Universe in each phase as they freeze out. We develop a method to study the dynamics of such fluctuations, which we call sub-critical bubbles, and apply it to several situations of interest, including the symmetric and asymmetric double-well, and the Coleman-Weinberg scalar potentials. We show that in certain cases it is possible to avoid supercooling, with the transition being completed by sub-critical fluctuations. Possible applications to the electroweak phase transition are briefly discussed.

Measurement of bubble size distributions in vesiculated rocks with implications for quantitative estimation of eruption processes

Abstract This paper outlines methods for determining a bubble size distribution (BSD) and the moments of the BSD function in vesiculated clasts produced by volcanic eruptions. It reports the results of applications of the methods to 11 natural samples and discusses the implications for quantitative estimates of eruption processes. The analysis is based on a quantitative morphological (stereological) method for 2-dimensional imaging of cross-sections of samples. One method determines, with some assumptions, the complete shape of the BSD function from the chord lengths cut by bubbles. The other determines the 1st, 2nd and 3rd moments of distribution functions by measurement of the number of bubbles per unit area, the surface area per unit volume, and the volume fraction of bubbles. Comparison of procedures and results of these two distinct methods shows that the latter yields rather more reliable results than the former, though the results coincide in absolute and relative magnitudes. Results of the analysis for vesiculated rocks from eleven subPlinian to Plinian eruptions show some interesting systematic correlations both between moments of the BSD and between a moment and the eruption column height or the SiO2 content of magma. These correlations are successfully interpreted in terms of the nucleation and growth processes of bubbles in ascending magmas. This suggests that bubble coalescence does not predominate in sub-Plinian to Plinian explosive eruptions. The moment-moment correlations put constraints on the style of the nucleation and growth process of bubbles. The scaling argument suggests that a single nucleation event and subsequent growth with any kind of bubble interaction under continuous depressurization, which leads to an intermediate growth law between the diffusional growth ( R m ∝ t 2 3 ) at a constant depressurization rate and the Ostwald ripening ( R m ∝ t 1 3 ) under a constant pressure, where Rm and t are the mean radius of bubble and the effective time of diffusion respectively, occurred in the eruptions. It is emphasized that the BSD in vesiculated rocks from terrestrial volcanoes can be used to estimate quantitatively eruption processes such as the initial saturation pressure and magma ascent velocity in a volcanic conduit.

Bubble nucleation in polymeric liquids. II. theoretical considerations

AbstractA theory based on classical nucleation theory is developed for bubble nucleation in polymer solutions. The theory requires information on solubility, diffusivity, concentration, surface tension, temperature, and degree of supersaturation. The effects of supersaturation and of the presence of large molecules in a liquid mixture on the free energy of bubble formation are included in the theoretical development. A semiempirical equation for the determination of bubble nucleation rate is developed, with the aid of experimental results reported in part I of this series. Using the experimental data, computer simulations of bubble nucleation in polymer solutions are performed. The consumptions of the volatile component in a liquid mixture, due to bubble nucleation and subsequent growth, and the variation of bubble nucleation rate during the expansion process are included in the simulation of the bubble nucleation process.

THE NUCLEATION OF MICROCELLULAR THERMOPLASTIC FOAM: PROCESS MODEL AND EXPERIMENTAL RESULTS

Abstract Microcellular polymer foams exhibit greatly improved mechanical properties compared to standard foams due to the formers' small bubble size. Typical microcellular foams have bubbles with diameters on the order of 10 microns and volume reductions of 30 to 40%. The presence of these bubbles acts to increase the impact strength of a microfoamed structure to six or seven times that of solid parts of the same linear dimensions due to crack blunting and increased craze initiation in the cell walls. The first step in designing techniques to manufacture parts of microcellular foam is a complete understanding of the bubble nucleation process. To this end, a theoretical model for the nucleation of microcellular foams in thermoplastic polymers has been developed and experimentally confirmed. This model explains the effect of various additives and processing conditions on the number of bubble nucleated. At levels of secondary constituents below their solubility limits, an increase in the concentration of the additive or the concentration of gas in solution with the polymer increases the number of bubbles nucleated. Nucleation in this region is homogeneous. Above the solubility limit of additives, nucleation is heterogeneous and takes place at the interface between second phase inclusions and the polymer. The number of bubbles nucleated is dependent on the concentration of heterogeneous nucleation sites and their relative effect on the activation energy barrier to nucleation.

Modeling of helium effects in metals: High temperature embrittlement

The effects of helium on swelling, creep rupture and fatigue properties of fusion reactor materials subjected to (n, α)-reactions and/or direct α-injection, are controlled by bubble formation. The understanding of such effects requires therefore the modeling of (1) diffusional reactions of He atoms with other defects; (2) nucleation and growth of He bubbles: (3) transformation of such bubbles into cavities under continuous He generation and irradiation or creep stress. The present paper is focussed on the modeling of the (coupled) high temperature bubble nucleation and growth processes within and on grain boundaries. Two limiting cases are considered: di-atomic nucleation described by the simplest possible sets of rate equations, and multi-atomic nucleation described by classical nucleation theory. Scaling laws are derived which characterize the dependence of the bubble densities upon time (He-dose). He generation rate and temperature. Comparison with experimental data of AIS1 316 SS α-implanted at temperatures around 1000 K indicates bubble nucleation of the multi-atomic type. The nucleation and growth models are applied to creep tests performed during α-implantation suggesting that in these cases gas driven bubble growth is the life time controlling mechanism. The narrow (creep stress/He generation rate) range of this mechanism in a mechanism map constructed from these tests indicates that in many reactor situations the time to rupture is probably controlled by stress driven cavity growth rather than by gas driven bubble growth.

Vacuum tension effects on the evolution of domain walls in the early universe

The “vacuum pressure” mechanism of the hadronic bag model is taken as a guide to formulate the dynamics of closed domain walls in the cosmological case. The effective action functional suggested by this analogy is a straightforward generalization of the Einstein-Maxwell action: it involves a 3-index antisymmetric potential whose coupling to matter generates two effective cosmological constants, one inside and one outside the domain wall. It is suggested that this mechanism, which is alternative to the introduction of a Higgs potential, is the source of the bubble nucleation process envisaged in the new inflationary cosmology. The dynamics of a spherical domain in a de Sitter phase is analyzed and is consistent with the geometrical formulation of shell dynamics proposed long ago by Israel.

Bubble nucleation and the Coleman-Weinberg model

Motivated by the “new inflationary universe scenario”, we have made a detailed study of the bubble nucleation process in (nearly) Coleman-Weinberg models with small positive scalar field mass terms. Our goal has been to show the consistency and interrelation between Coleman's analysis of bubble nucleation in flat space, the work of Coleman and De Luccia on bubble nucleation with gravitational effects and the recent dramatically different results of Hawking and Moss on bubble nucleation in Coleman-Weinberg models in a de Sitter background. Many of our results apply to more general classes of potentials.

Velocity dependence of track density in propane and hydrogen bubble chambers

A study of ionization data for charged particles has been made in an underexpanded propane and a normally operated hydrogen bubble chamber. The gap-length distribution is found to be exponential over a wide range of velocity intervals, and the coefficient of this distribution gives a measure of the true track density,g;g is proportional toβ−n, wheren=1.71±0.11 for propane andn=1.86±0.37 for hydrogen. The density of gaps,G, or of blobs,B, defined with good objective criteria, shows a dependence ong, namelyG(ɛ)=g exp [−g(α+ɛ)]; it passes through a maximum value, the position of which is related to the minimum resolvable gap distance (approximately the the average diameter of individual bubbles). The mechanisms of energy loss orδ-ray formation for the process of bubble nucleation have been discussed in view of these measurements. We find the track densityg to be approximately proportional to the rate of energy loss, dE/dX; this would indicate that the bubble nucleation process may not be as simple as has been considered so far.