Effects of Surface Tension and Bubble Diameter on Bubble Breakage Time under Microgravity

Cavitation is a phenomenon which occurs where the local pressure falls off under the vapor pressure. Over the past few years, numerical simulation models for cavitation have been developed significantly in order to investigate the mechanism of cavitation. In the paper, A local homogeneous cavitation model based on the theory of evaporation and condensation has been deduced, which is used to describe the phase change between water and vapor. The RNG k–ε turbulence model is used to simulate the turbulent flow and the finite volume method is employed to discrete the governing equations. The effects of surface tension of water, pressure fluctuations and non-condensable gases are included in the mass transfer cavitation model. Also in order to neglect the effects of the quantities such as the bubble number and bubble diameter, which is difficult to measure, the relations between the aerodynamic drag and surface tension forces is used to describe the bubble diameter. In order to evaluate the new cavitation model, the two phase cavitation flows around a NACA0015 hydrofoil at different attack angle and different cavitation number are simulated by the new cavitation model, and compared with references, which showed good agreement with the experiments.

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Single Bubble Growth at Different Gravity and the Effects of Microgravity on Marangoni Convection

Volume 5: Fusion Engineering; Student Paper Competition; Design Basis and Beyond Design Basis Events; Simple and Combined Cycles ◽

10.1115/icone20-power2012-54300 ◽

2012 ◽

Author(s):

Yan Yang ◽

Liang-ming Pan ◽

Long-chang Xue

Keyword(s):

Surface Tension ◽

Bubble Growth ◽

Normal Gravity ◽

Bubble Diameter ◽

Single Bubble ◽

Surface Tension Gradient ◽

Multiphase Model ◽

Heating Wall ◽

Marangoni Effects ◽

Energy Equations

In this paper, based on the previous experiment and the VOF (Volume of Fluid) multiphase model, the growth characteristics of a single bubble was numerically investigated in a rectangular pool boiling channel (10 mm × 10 mm × 25 mm) under micro-gravity. The transportation of mass and energy during the phase change was established by adding source term to the mass and energy equations with User Defined Function (UDF). The results showed that under microgravity, the streamline and the temperature field distribution around the bubble were significantly changed compared with the normal gravity, and the flow field and the temperature are no longer a symmetrical distribution. The bubble between microgravity and normal gravity was different from the detachment, and it does not departure from the heating wall directly under the microgravity conditions because of surface tension. But the surface tension gradient caused Marangoni effects are more significant at the smaller microgravity. The bubble growth is more complicated under the conditions of microgravity, and it is connected with the degree of the microgravity: smaller microgravity will result higher bubble growth rate. Moreover, the bubble diameter was changed more fantasticality, under microgravity and the heat transfer coefficient fluctuated more heavily with the increasing of microgravity.

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Application of Dynamic Bubble Departure Model for New, Low-GWP Refrigerants on Enhanced, Structured Surfaces

Volume 8: Heat Transfer and Thermal Engineering ◽

10.1115/imece2017-71324 ◽

2017 ◽

Author(s):

Avinash Shaligram ◽

Sandip Kumar Saha

Keyword(s):

Surface Tension ◽

Bubble Diameter ◽

Surface Tension Force ◽

Nucleate Boiling ◽

Force Model ◽

Dynamic Force ◽

Structured Surfaces ◽

Compact Heat Exchangers ◽

Wall Superheat ◽

Enhanced Surface

Structured surfaces consisting of sub-surface tunnels and openings in the form of pores or gaps are used to enhance boiling heat transfer resulting into compact heat exchangers. One of the applications of enhanced surface tubes is in flooded evaporators in water chillers. The fundamental mechanisms in nucleate boiling on structured surfaces are not still well understood, especially for new, low-GWP refrigerants. In this study, the focus is on bubble departure models. Most of the nucleate boiling models consider the static force model for calculating bubble diameter at the departure. However as per flow visualization studies in published literatures, the process of bubble growth and departure is dynamic and hence three more forces (in addition to buoyancy and surface tension) need to be accounted for while calculating the instantaneous bubble departure diameter. In this study, numerical results are presented for bubble departure diameter for four refrigerants, viz. R134a (the currently used, high GWP refrigerant) and its targeted low-GWP replacements, viz. R1234ze (E), R513A and R450A on enhanced, structured surfaces. Results from the dynamic force model show the bubble departure diameter in the range of 0.78 mm to 0.85 mm for all the four refrigerants. The unsteady growth force ranges from 4.8 × 10−6 N to 1.35 × 10−5 N while the surface tension force ranges from 2.49 × 10−6 N to 1.975 × 10−6 N. Similar results are provided for other forces as a function of wall superheat.

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Simulation Study on Gas Holdup of Large and Small Bubbles in a High Pressure Gas–Liquid Bubble Column

Processes ◽

10.3390/pr7090594 ◽

2019 ◽

Vol 7 (9) ◽

pp. 594 ◽

Cited By ~ 2

Author(s):

Fangfang Tao ◽

Shanglei Ning ◽

Bo Zhang ◽

Haibo Jin ◽

Guangxiang He

Keyword(s):

Surface Tension ◽

High Pressure ◽

Bubble Column ◽

Bubble Diameter ◽

Gas Holdup ◽

Operating Pressure ◽

Gas Velocity ◽

Superficial Gas Velocity ◽

Critical Bubble ◽

Small Bubbles

The computational fluid dynamics-population balance model (CFD-PBM) has been presented and used to evaluate the bubble behavior in a large-scale high pressure bubble column with an inner diameter of 300 mm and a height of 6600 mm. In the heterogeneous flow regime, bubbles can be divided into “large bubbles” and “small bubbles” by a critical bubble diameter dc. In this study, large and small bubbles were classified according to different slopes in the experiment only by the method of dynamic gas disengagement, the critical bubble diameter was determined to be 7 mm by the experimental results and the simulation values. In addition, the effects of superficial gas velocity, operating pressure, surface tension and viscosity on gas holdup of large and small bubbles in gas–liquid two-phase flow were investigated using a CFD-PBM coupling model. The results show that the gas holdup of small and large bubbles increases rapidly with the increase of superficial gas velocity. With the increase of pressure, the gas holdup of small bubbles increases significantly, and the gas holdup of large bubbles increase slightly. Under the same superficial gas velocity, the gas holdup of large bubbles increases with the decrease of viscosity and the decrease of surface tension, but the gas holdup of small bubbles increases significantly. The simulated values of the coupled model have a good agreement with the experimental values, which can be applied to the parameter estimation of the high pressure bubble column system.

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Immunoferritin localization of intracellular antigens in positively stained frozen sections

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s042482010008170x ◽

1978 ◽

Vol 36 (2) ◽

pp. 168-169

Author(s):

K. T. Tokuyasu

Keyword(s):

Surface Tension ◽

Water Surface ◽

Thin Layers ◽

The Other ◽

Positive Staining ◽

Frozen Sections ◽

The Past ◽

Ultrathin Frozen Sections ◽

Definition Of

During the past investigations of immunoferritin localization of intracellular antigens in ultrathin frozen sections, we found that the degree of negative staining required to delineate u1trastructural details was often too dense for the recognition of ferritin particles. The quality of positive staining of ultrathin frozen sections, on the other hand, has generally been far inferior to that attainable in conventional plastic embedded sections, particularly in the definition of membranes. As we discussed before, a main cause of this difficulty seemed to be the vulnerability of frozen sections to the damaging effects of air-water surface tension at the time of drying of the sections.Indeed, we found that the quality of positive staining is greatly improved when positively stained frozen sections are protected against the effects of surface tension by embedding them in thin layers of mechanically stable materials at the time of drying (unpublished).

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The Critical Point Drying Method Applied to Scanning Electron Microscopy of L-929 Cells

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100068382 ◽

1970 ◽

Vol 28 ◽

pp. 278-279

Author(s):

Charles TurnbiLL ◽

Delbert E. Philpott

Keyword(s):

Electron Microscopy ◽

Carbon Dioxide ◽

Surface Tension ◽

Critical Point ◽

Freeze Drying ◽

Attractive Alternative ◽

Crystal Formation ◽

Critical Point Drying ◽

Time Required ◽

Scanning Electron

The advent of the scanning electron microscope (SCEM) has renewed interest in preparing specimens by avoiding the forces of surface tension. The present method of freeze drying by Boyde and Barger (1969) and Small and Marszalek (1969) does prevent surface tension but ice crystal formation and time required for pumping out the specimen to dryness has discouraged us. We believe an attractive alternative to freeze drying is the critical point method originated by Anderson (1951; for electron microscopy. He avoided surface tension effects during drying by first exchanging the specimen water with alcohol, amy L acetate and then with carbon dioxide. He then selected a specific temperature (36.5°C) and pressure (72 Atm.) at which carbon dioxide would pass from the liquid to the gaseous phase without the effect of surface tension This combination of temperature and, pressure is known as the "critical point" of the Liquid.

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The Use of Styrenes as Embedding Media for Electron Microscopy

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100066498 ◽

1971 ◽

Vol 29 ◽

pp. 488-489

Author(s):

Edward D. De-Lamater ◽

Eric Johnson ◽

Thad Schoen ◽

Cecil Whitaker

Keyword(s):

Electron Microscopy ◽

Surface Tension ◽

Ultraviolet Light ◽

Methyl Ethyl Ketone Peroxide ◽

Methyl Ethyl ◽

Styrene Polymerization ◽

Radical Initiation ◽

Tertiary Butyl ◽

Low Viscosity ◽

Free Radical Initiation

Monomeric styrenes are demonstrated as excellent embedding media for electron microscopy. Monomeric styrene has extremely low viscosity and low surface tension (less than 1) affording extremely rapid penetration into the specimen. Spurr's Medium based on ERL-4206 (J.Ultra. Research 26, 31-43, 1969) is viscous, requiring gradual infiltration with increasing concentrations. Styrenes are soluble in alcohol and acetone thus fitting well into the usual dehydration procedures. Infiltration with styrene may be done directly following complete dehydration without dilution.Monomeric styrenes are usually inhibited from polymerization by a catechol, in this case, tertiary butyl catechol. Styrene polymerization is activated by Methyl Ethyl Ketone peroxide, a liquid, and probably acts by overcoming the inhibition of the catechol, acting as a source of free radical initiation.Polymerization is carried out either by a temperature of 60°C. or under ultraviolet light with wave lengths of 3400-4000 Engstroms; polymerization stops on removal from the ultraviolet light or heat and is therefore controlled by the length of exposure.

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The nucleation of cavities at grain boundaries

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100126299 ◽

1987 ◽

Vol 45 ◽

pp. 288-291

Author(s):

P. J. Goodhew

Keyword(s):

Surface Tension ◽

Surface Energy ◽

Grain Boundaries ◽

Radiation Damage ◽

Impurity Concentration ◽

Driving Force ◽

Nucleation And Growth ◽

Phase Boundaries ◽

Cavity Nucleation ◽

Spherical Bubble

Cavity nucleation and growth at grain and phase boundaries is of concern because it can lead to failure during creep and can lead to embrittlement as a result of radiation damage. Two major types of cavity are usually distinguished: The term bubble is applied to a cavity which contains gas at a pressure which is at least sufficient to support the surface tension (2g/r for a spherical bubble of radius r and surface energy g). The term void is generally applied to any cavity which contains less gas than this, but is not necessarily empty of gas. A void would therefore tend to shrink in the absence of any imposed driving force for growth, whereas a bubble would be stable or would tend to grow. It is widely considered that cavity nucleation always requires the presence of one or more gas atoms. However since it is extremely difficult to prepare experimental materials with a gas impurity concentration lower than their eventual cavity concentration there is little to be gained by debating this point.

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