Bubble Nucleation In Water Research Articles

A Study on Hydrogen Bonding and Energy Variation during Bubble Nucleation in Water on a Grooved Substrate by Molecular Dynamics Simulation.

In this paper, the bubble nucleation process of water was studied by molecular dynamics (MD) simulation. The nucleation mechanism of water on a grooved substrate was revealed from the perspective of hydrogen bond and energy change, and the effect of system pressure on nucleation was studied. The results show that the process of bubble nucleation of water molecules is essentially a process in which the thermal motion of water molecules gradually intensifies and the hydrogen bond continues to break with the increase in kinetic energy. As the hydrogen bond breaks, the kinetic energy of the water molecules is continuously converted to intermolecular potential energy. By analyzing the composition of the hydrogen bond energy, it is found that the electrostatic energy is much greater than the van der Waals energy, so the water nucleation process mainly overcomes the electrostatic force between molecules. With the gradual increase of pressure, although the kinetic energy distribution of molecules does not change significantly, it will cause the potential energy of water molecules to decrease significantly and then lead to the increase of the energy barrier that needs to be crossed for nucleation. Meanwhile, the rise of the nucleation barrier may result in the absence of obvious initial vapor nuclei inside the liquid so that the number of hydrogen bonds cannot be rapidly reduced, which is not conducive to boiling nucleation. The results of this study provide important implications for further understanding of the nucleate boiling process of water.

Onset and critical radius of heterogeneous bubble nucleation

In this work, the onset of heterogeneous bubble nucleation is studied using molecular dynamics (MD) simulations and experiments. In MD simulations, heterogeneous bubble nucleation is initiated in liquid argon by partially heating a platinum surface. Multiple simulations are run by varying the width and temperature of the heated part of the surface; each simulation results in either a collapsing, stable or growing bubble for which Gibbs free energy is estimated and compared. These results atomistically confirm that a critical radius of nucleation exists for heterogeneous nucleation. Based on these simulations, an analytical model is developed to predict the critical width required for bubble nucleation at the nanoscale. Experiments are also conducted on the onset of bubble nucleation in water on a silicon-dioxide surface.

Cavitation Nuclei Regeneration in a Water-Particle Suspension.

Bubble nucleation in water induced by boiling, gas supersaturation, or cavitation usually originates from preexisting gas cavities trapped into solid defects. Even though the destabilization of such gas pockets, called nuclei, has been extensively studied, little is known on the nuclei dynamic. Here, nuclei of water-particle suspensions are excited by acoustic cavitation, and their dynamic is investigated by monitoring the cavitation probability over several thousand pulses. A stable and reproducible cavitation probability emerges after a few thousand pulses and depends on particle concentration, hydrophobicity, and dissolved gas content. Our observations indicate that a stable nuclei distribution is reached at a later time, different from previously reported nuclei depletion in early time. This apparent paradox is elucidated by varying the excitation rate, where the cavitation activity increases with the repetition period, indicating that the nuclei depletion is balanced by spontaneous nucleation or growth of nuclei. A model of this self-supporting generation of nuclei suggests an origin from dissolved gas adsorption on surfaces. The method developed can be utilized to further understand the spontaneous formation and distribution of nanosized bubbles on heterogeneous surfaces.

Homogeneous bubble nucleation in water at negative pressure: A Voronoi polyhedra analysis

We investigate vapor bubble nucleation in metastable TIP4P/2005 water at negative pressure via the Mean First Passage Time (MFPT) technique using the volume of the largest bubble as a local order parameter. We identify the bubbles in the system by means of a Voronoi-based analysis of the molecular dynamics trajectories. By comparing the features of the tessellation of liquid water at ambient conditions to those of the same system with an empty cavity we are able to discriminate vapor (or interfacial) molecules from the bulk ones. This information is used to follow the time evolution of the largest bubble until the system cavitates at 280 K above and below the spinodal line. At the pressure above the spinodal line, the MFPT curve shows the expected shape for a moderately metastable liquid from which we estimate the bubble nucleation rate and the size of the critical cluster. The nucleation rate estimated using Classical Nucleation Theory turns out to be about 8 order of magnitude lower than the one we compute by means of MFPT. The behavior at the pressure below the spinodal line, where the liquid is thermodynamically unstable, is remarkably different, the MFPT curve being a monotonous function without any inflection point.

Bubble cavitation in a microchannel

The effects of microchannel size, mass flow rate and heat flux on boiling incipience or bubble cavitation in a microchannel are studied in this paper. The well-known concept of survival of a bubble cavity is extended, and the classical kinetics of nucleation is introduced to study bubble nucleation in water flowing in a silicon microchannel. The effects of contact angle, dissolved gas, and the existence of microcavities and corners in the microchannel on bubble’s nucleation/cavitation temperature are estimated. With this information, a numerical solution is carried out to study the effects of mass flow rate and heat flux on bubble nucleation/cavitation in microchannels. The results of this analysis provide further physical insight on boiling heat transfer in microchannels.

Kinetic Characteristic of Bubble Nucleation in Superheated Water using Fluid Inclusions

Water in fluid inclusions achieved a superheated condition by isochoric cooling method and the kinetic characteristic of bubble nucleation in water was investigated. The conventional study did not succeed in drawing a picture of bubble nucleation in water. The present study demonstrates that the homogeneous nucleation theory can describe the kinetic property of bubble nucleation in water, and that density fluctuation is a random event which brings about bubble nucleation in superheated water, and the lifetime of superheated water can be predicted with respect to the depth of penetration into the metastable region by the theory.

The crevice model of bubble nucleation

The crevice model for heterogeneous nucleation of bubbles in water in response to a decreasing liquid pressure is studied. The model neglects gas-diffusion effects and is therefore more suited for acoustic than for flow cavitation. It is argued that previous work has overlooked the essential requirement of unstable growth of the interface in the crevice. As a consequence, the available results are incorrect in some cases. Another feature of the model which is considered is the process by which the interface moves out of the crevice. It is concluded that, depending on circumstances, the conditions for this step may be more stringent than those for the initial expansion of the nucleus inside the crevice. Some numerical examples are given to illustrate the complex behavior of nuclei, depending of geometrical parameters, gas saturation, contact angles, and other quantities.

The tribonucleation of bubbles

The theory that tribonucleation of bubbles in liquids occurs in the region of reduced pressure between separating surfaces is quantitatively evaluated. The homogeneous nucleation of bubbles in water appears to be feasible by this mechanism. The effectiveness of the process may be considerably influenced by the nature of the solid surface.

Radiation Nucleation of Bubbles in Water

A charged particle passing through water creates a thermal spike, a region of high temperature along the track. The thermal spike expands explosively, thus producing a pressure wave, and then breaks up because of surface tension into discrete regions of water vapor and hydrogen gas. These vapor-gas microbubbles can act as nucleation centers in superheated or gas supersaturated solutions. Calculations based on this thermal spike model are presented of the total energy and minimum linear energy transfer (LET) required to form nucleation centers of a given size, and the calculations are compared to published data on the radiation nucleation of superheated and supersaturated aqueous solutions. Calculations are also presented of the pressure created by the rapid expansion of the thermal spike, and of the lifetime of the vapor-gas microbubbles under conditions in which they collapse. The calculations cover an LET range of 0.1 to 10 Mev/ mu or, approximately, from the maximum LET of recoil protons in water to the maximum LET of fission fragments in water. The calculations are carried out for a liquid pressure of one atmosphere and two temperature conditions: the minimum temperature at which vapor nuclei of given size will grow and 0 deg C. Themore » effect of high pressures and temperatures on the radiation nucleation of vapor bubbles is discussed briefly in terms of the foam limit. (auth)« less