Fluid Stiction With Mechanical Contact: A Theoretical Model

2016 ◽  
Author(s):  
Rudolf Scheidl ◽  
Hu Zhidong
Keyword(s):  
Evolution Equations ◽  
Outer Boundary ◽  
Bubble Radius ◽  
Growth Dynamics ◽  
Theoretical Work ◽  
Bubble Nucleation ◽  
Mechanical Contact ◽  
Unknown Parameters ◽  
Gap Height ◽  
Bubble Number

Published theoretical work about fluid stiction between two separating plates was so far limited to a finite initial gap. It was shown that pressure and force evolution are well described by fluid film lubrication equations if cavitation is taken into account. The practically important case that plate separation starts from a mechanical contact condition was only studied by experiments. They showed that quite substantial negative pressures can occur in the gap for a very short time and that the peak forces are varying strongly even between consecutive experiments with equal test conditions. In this paper two models are presented which complement the Reynolds equations with dynamical bubble evolution equations. Initial gap height, bubble number density, and initial bubble radius are the three unknown parameters of these models. Initial gap height accounts for surface roughness, the two other parameters refer to the bubble nucleation of the fluid in the small roughness indentations of the gap. A first model employs the Rayleigh-Plesset bubble dynamic model. It requires that the bubbles stay small compared to the gap. Results show that its stiction force dynamics is two orders of magnitude faster than experimentally observed and that the bubble size condition is violated. The second model assumes that bubbles span over the whole gap height and that the flow of the liquid between the bubbles is guided by the Reynolds equation. This model can be brought into reasonable agreement with the experiments. Force variation from experiment to experiment can at least in part be reproduced by a random variation of the initial bubble sizes. The model exhibits a kind of boundary layer behavior close to the outer boundary. This layer represents the interaction zone between bubble growth dynamics, pressure distribution due to viscous flow, and the pressure boundary condition.

scholarly journals Can nanolites enhance eruption explosivity?

Geology ◽  
2020 ◽  
Vol 48 (10) ◽  
pp. 997-1001 ◽  
Author(s):  
Francisco Cáceres ◽  
Fabian B. Wadsworth ◽  
Bettina Scheu ◽  
Mathieu Colombier ◽  
Claudio Madonna ◽  
...  
Keyword(s):  
Volcanic Rocks ◽  
Growth Dynamics ◽  
Nucleation And Growth ◽  
Bubble Nucleation ◽  
Magma Ascent ◽  
Primary Control ◽  
Number Density ◽  
Starting Conditions ◽  
Bubble Number ◽  
Bubble Number Density

Abstract Degassing dynamics play a crucial role in controlling the explosivity of magma at erupting volcanoes. Degassing of magmatic water typically involves bubble nucleation and growth, which drive magma ascent. Crystals suspended in magma may influence both nucleation and growth of bubbles. Micron- to centimeter-sized crystals can cause heterogeneous bubble nucleation and facilitate bubble coalescence. Nanometer-scale crystalline phases, so-called “nanolites”, are an underreported phenomenon in erupting magma and could exert a primary control on the eruptive style of silicic volcanoes. Yet the influence of nanolites on degassing processes remains wholly uninvestigated. In order to test the influence of nanolites on bubble nucleation and growth dynamics, we use an experimental approach to document how nanolites can increase the bubble number density and affect growth kinetics in a degassing nanolite-bearing silicic magma. We then examine a compilation of these values from natural volcanic rocks from explosive eruptions leading to the inference that some very high naturally occurring bubble number densities could be associated with the presence of magmatic nanolites. Finally, using a numerical magma ascent model, we show that for reasonable starting conditions for silicic eruptions, an increase in the resulting bubble number density associated with nanolites could push an eruption that would otherwise be effusive into the conditions required for explosive behavior.

Bubbles and element clusters in rock melts: A chicken and egg problem

2021 ◽  
Author(s):  
Renelle Dubosq ◽  
Pia Pleše ◽  
Brian Langelier ◽  
Baptiste Gault ◽  
David Schneider
Keyword(s):  
Heterogeneous Nucleation ◽  
Homogeneous Nucleation ◽  
Growth Dynamics ◽  
Gas Bubbles ◽  
Atom Probe ◽  
Bubble Nucleation ◽  
Interface Element ◽  
Rich Cluster ◽  
Heterogeneous Distribution ◽  
Rapid Decompression

<p>The nucleation and growth dynamics of gas bubbles and crystals play a vital function in determining the eruptive behaviour of a magma. Their rate and relative timing, among other factors, are controlled by the magma’s ascent rate. Investigating the kinetics of decompression-induced degassing and crystallization processes can thus give us insight into the rheology of magmas. For example, the rapid decompression of magmas inhibits microlite crystallization and bubble nucleation during ascent leading to crystallization and degassing at shallow levels. This results in a drastic increase in viscosity and an over pressured system, which can lead to violent eruptions. Although many experiments and numerical simulations of magma decompression have been carried out, nascent and initial bubble nucleation remain poorly understood. It is widely accepted that there are two ways bubbles can nucleate within a melt: heterogeneous (on a pre-existing surface) and homogeneous nucleation (within the melt), where homogeneous nucleation requires a higher volatile supersaturation. It has since been tentatively suggested that homogeneous nucleation is simply a variety of heterogeneous nucleation where nucleation occurs on the surface of submicroscopic crystals. However, evidence of these crystals is equivocal. Thus, we have combined novel 2D and 3D structural and chemical microscopy techniques including scanning transmission electron microscopy (STEM), electron energy-loss spectroscopy (EELS) mapping, and atom probe tomography (APT) to investigate the presence of sub-nanometer scale chemical heterogeneities in the vicinity of gas bubbles within an experimental andesitic melt. The combined STEM and EELS data reveal a heterogeneous distribution of bubbles within the melt ranging between 20-100 nm in diameter, some of which have Fe and/or Ca element clusters at the bubble-melt interface. Element clusters enriched in Fe, Ca, and Na are also observed heterogeneously distributed within the melt. The reconstructed APT data reveals bubbles as low ionic density regions overlain by a Na-, Ca-, and K-rich cluster and heterogeneously distributed Fe clusters within the bulk of the melt. Based on these observations, our data demonstrate the existence of nano-scale chemical heterogeneities within the melt and at the bubble-melt interface of bubbles that were previously interpreted to be nucleated homogeneously within the melt, therefore contributing to the proposed hypothesis that homogeneous nucleation could in fact be a variety of heterogeneous nucleation. These results highlight the need to redefine homogeneous nucleation and revisit whether bubbles or crystals occur first within volcanic melts. </p>

The effect of nanolites on degassing of silica-rich magma

2020 ◽  
Author(s):  
Francisco Cáceres ◽  
Fabian Wadsworth ◽  
Bettina Scheu ◽  
Mathieu Colombier ◽  
Claudio Madonna ◽  
...  
Keyword(s):  
Ambient Pressure ◽  
Volcanic Eruptions ◽  
Bubble Nucleation ◽  
Magma Ascent ◽  
Explosive Eruptions ◽  
Initial Water Content ◽  
Primary Control ◽  
Number Density ◽  
Bubble Number ◽  
Bubble Number Density

<p>Magma degassing dynamics play an important role controlling the explosivity of volcanic eruptions. Some of the largest explosive eruptions in history have been fed by silica-rich magmas in volcanic systems with complex dynamics of volatiles degassing. Degassing of magmatic water drives bubble nucleation and growth, which in turn increases magma buoyancy and results in magma ascent and an eventual eruption. While micro- to milli-meter sized crystals are known to cause heterogeneous bubble nucleation and to facilitate bubble coalescence, the effects of nanolites remains mostly unexplored. Nanolites have been hypothesized to be a primary control on the eruptive style of silicic volcanoes, however the mechanisms behind this control remains unclear.</p><p>Here we use an experimental approach to show how nanolites dramatically increase the bubble number density in a degassing silicic magma compared to the same magma without nanolites. The experiments were conducted using both nanolite-free and nanolite-bearing rhyolitic glass with different low initial water content. Using an Optical Dilatometer at 1 bar ambient pressure, cylindrical samples were heated at variable rates (1-30 °C min<sup>-1</sup>) to final temperatures of 820-1000 °C. This method allowed us to continuously monitor the volume, and hence porosity evolution in time. X-ray computed microtomography (µCT) and Scanning Electron Microscope (SEM) analyses revealed low and high bubble number densities for the nanolite-free and nanolite-bearing samples respectively.</p><p>Comparing vesicle number densities of natural volcanic rocks from explosive eruptions and our experimental results, we speculate that some very high naturally occurring bubble number densities could be associated with nanolites. We use a magma ascent model with P-T-H<sub>2</sub>O starting conditions relevant for known silicic eruptions to further underpin that such an increase in bubble number density caused driven by the presence of nanolites can feasibly turn an effusive eruption to an eventually explosive behavior.</p>

Investigation of Bubble Nucleation on Platinum Solid Surface Using Molecular Dynamics (MD) Simulation

2010 ◽  
Author(s):  
S. M. Mirnouri Langroudi ◽  
M. Ghasemi ◽  
A. Shahabi ◽  
H. Rezaei Nejad
Keyword(s):  
Molecular Dynamics ◽  
Surface Tension ◽  
Contact Angle ◽  
Solid Surface ◽  
Bubble Radius ◽  
Pair Potential ◽  
Computer Code ◽  
Bubble Nucleation ◽  
Solid Surfaces ◽  
Density Profiles

The main purpose of this paper is to numerically investigate the contact angle of a bubble on a solid surface and the effect of bubble curvature on the surface tension. A computer code based on Molecular Dynamics method is developed. The code carries out a series of simulations to generate bubbles between two planar solid surfaces for different wettabilities. In our simulation, the surface wettability affects the bubble contact angle and curvature. The pair potential for the liquid–liquid and liquid-solid interaction is considered using Lennard-Jones model. Density profiles are locally calculated. Furthermore, surface tension is computed using Young-Laplace equation. It is observed that the gas pressure is independent of the bubble radius. However, the liquid pressure becomes more negative as the radius decreases. In addition, the amount of surface tension decreases by decrease of the radius.

Research on the Change of Energy in the Process of the Micro Bubble Formation with Dissolved Air Method

2013 ◽  
Vol 664 ◽  
pp. 390-394
Author(s):  
Yu Guang Fan ◽  
Zhao Liu ◽  
Jing Ming Li ◽  
San Ping Zhou ◽  
Bing Chen ◽  
...  
Keyword(s):  
Free Energy ◽  
Bubble Formation ◽  
Bubble Radius ◽  
Initial Energy ◽  
Free Energy Change ◽  
Nucleation Theory ◽  
Energy Change ◽  
Micro Bubble ◽  
Bubble Number ◽  
Two Stages

The generation method of dissolved gas micro bubble is introduced in the paper. The micro bubble producing process can be divided into two stages-nucleation and expansion through analysis. The formation process and the free energy change of the micro bubble is analyzed according to the homogeneous nucleation theory, free energy change formula of the two process is derived, and relation between bubble radius and formation bubble number under certain conditions is also discussed. It is concluded that the smaller the radius of formed bubbles, the more free energy change and initial energy are needed according to the analysis of the relation above.

Bubble Formation on the Surface of Laser-Irradiated Nano-Sized Particles

2013 ◽  
Author(s):  
Ho-Young Kwak ◽  
Jaekyoon Oh ◽  
Yungpil Yoo ◽  
Shahid Mahmood
Keyword(s):  
Bubble Formation ◽  
Bubble Radius ◽  
Bubble Nucleation ◽  
Heat Diffusion ◽  
Experimental Result ◽  
Liquid Volume ◽  
Expansion Velocity ◽  
Time Curve ◽  
Large Expansion ◽  
Energy Equations

It is well known that a phase transition from liquid to vapor occurs in the thermal boundary layer adjacent to a nanoparticle that has a high temperature upon irradiation with a high-power laser. In this study, the mechanism by which the evaporated layer adjacent to a laser-irradiated nanoparticle can grow as a bubble was investigated. The pressure of the evaporated liquid volume due to heat diffusion from the irradiated nanoparticle was estimated using a bubble nucleation model based on molecular interactions. The bubble wall motion was obtained using the Keller-Miksis equation. The density and temperature inside the bubble were obtained by solving the continuity and energy equations for the vapor inside the bubble. The evaporation of water molecules or condensation of water vapor at the vapor-liquid interface and the homogeneous nucleation of vapor were also considered. The calculated bubble radius -time curve for the bubble formed on the surface of a gold particle with a diameter of 9 nm is close to the experimental result. Our study reveals that an appropriate size of the evaporated liquid volume and a large expansion velocity are important parameters for the formation of a transient nano-sized bubble. The calculation result suggests that homogeneous condensation of vapor rather than condensation at the interface occurs.

ON THE EFFECT OF OVERBURDEN ON ELECTROMAGNETIC ANOMALIES—A REVIEW

Geophysics ◽  
1970 ◽  
Vol 35 (4) ◽  
pp. 646-659 ◽  
Author(s):  
Amalendu Roy
Keyword(s):  
Theoretical Work ◽  
Unknown Parameters ◽  
Model Studies ◽  
Theoretical Investigations ◽  
Fundamental Objection ◽  
The Many ◽  
Major Objection ◽  
Theoretical Analyses ◽  
Made In

The effect of a conducting overburden in EM prospecting intuitively is considered to be one of degeneration of anomalies, in the sense that the detection of a target and the determination of its unknown parameters become more difficult or ambiguous when an overburden is present than when it is absent. Recently, however, Negi (1967) and Negi and Raval (1969) have suggested on the basis of theoretical work that, if a certain combination of the parameters involved occurs, a conducting overburden can make a target more detectable than it would be without any overburden. These theoretical results and the existing experimental evidence are examined in this paper for the possible existence of “negative screening,” as this effect has been called. Due to a number of incorrect assumptions made in the theoretical analyses by the authors who predicted negative screening, their conclusions do not seem to be valid. A fundamental objection in the case of the stratified sphere, for instance, pertains to the assumption that, in presence of the annulus, the contribution of the inner sphere alone to the total external measurable magnetic field can be obtained by simply subtracting the response of the larger uniform isolated sphere from that of the double sphere. Another major objection concerns the notion in the theoretical analyses that detectability is determined by the contribution from the target alone—a quantity which one can never measure—without regard to the simultaneous contribution from the conducting overburden. Defined on the basis of the measurable total response from the system as a whole, detectability falls progressively with overburden conductivity. Although the existing results of model EM experiments are generally indicative of the absence of a phenomenon like negative screening, no clearcut and indisputable conclusion can be arrived at on the basis of model studies. In some recently published experimental results, there is one solitary instance, unnoticed by the experimenters themselves, which could suggest the existence of negative screening. We believe, however, that, due to the many inherent uncertainties in model EM work, conclusions based on theoretical investigations have to be accepted as more reliable until carefully planned model work is carried out with this specific problem in view.

Bubble Formation on the Surface of Laser-Irradiated Nanosized Particles

2014 ◽  
Vol 136 (8) ◽  
Author(s):  
Ho-Young Kwak ◽  
Jaekyoon Oh ◽  
Yungpil Yoo ◽  
Shahid Mahmood
Keyword(s):  
Bubble Formation ◽  
Bubble Radius ◽  
Bubble Nucleation ◽  
Heat Diffusion ◽  
Experimental Result ◽  
Liquid Volume ◽  
Expansion Velocity ◽  
Time Curve ◽  
Large Expansion ◽  
Nucleation Model

It is well known that a phase transition from liquid to vapor occurs in the thermal boundary layer adjacent to a nanoparticle that has a high temperature upon irradiation with a high-power laser. In this study, the mechanism by which the evaporated layer adjacent to a laser-irradiated nanoparticle can grow as a bubble was investigated through detailed calculations. The pressure of the evaporated liquid volume due to heat diffusion from the irradiated nanoparticle was estimated using a bubble nucleation model based on molecular interactions. The bubble wall motion was obtained using the Keller-Miksis equation. The density and temperature inside the bubble were obtained by solving the continuity and energy equation for the vapor inside the bubble. The evaporation of water molecules or condensation of water vapor at the vapor–liquid interface and the homogeneous nucleation of vapor were also considered. The calculated bubble radius-time curve for the bubble formed on the surface of a gold particle with a diameter of 9 nm is close to the experimental result. Our study reveals that an appropriate size of the evaporated liquid volume and a large expansion velocity are important parameters for the formation of a transient nanosized bubble. The calculation result suggests that homogeneous condensation of vapor rather than condensation at the interface occurs.

A cosmological study of Einstein–Skyrme model in anisotropic Kantowski–Sachs spacetime using Lie and Noether symmetries

2018 ◽  
Vol 15 (06) ◽  
pp. 1850089 ◽  
Author(s):  
Santu Mondal ◽  
Sourav Dutta ◽  
Manjusha Tarafdar ◽  
Subenoy Chakraborty
Keyword(s):  
Lie Algebra ◽  
Evolution Equations ◽  
Einstein Gravity ◽  
Lie Symmetry ◽  
Noether Symmetry ◽  
Noether Symmetries ◽  
Einstein Field Equations ◽  
Field Equations ◽  
Unknown Parameters ◽  
Augmented Space

The present work deals with anisotropic (but zero heat flux) Skyrme fluid in a locally rotational Kantowski–Sachs (KS) spacetime in the background of Einstein gravity. The Lie point symmetry is imposed to the system of Einstein field equations and unknown parameters are either determined or interrelated by the imposition of the symmetry. Subsequently, Noether symmetry, a point-like symmetry of the Lagrangian is used and it is found that the Lie algebra of the Noether symmetry is a subalgebra of the corresponding Lie algebra of the Lie symmetry. Then a point transformation in the 2D augmented space is taken in such a manner that one of the variables becomes cyclic and hence the Lagrangian as well as the evolution equations are simplified to a great extent. Finally, solutions to the physical system are presented and are analyzed physically.

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