Photographic Observations of Bubble Formation in Flashing Nozzle Flow

1985 ◽  
Vol 107 (4) ◽  
pp. 750-755 ◽  
Author(s):  
R. S. Miller
Keyword(s):  
Bubble Growth ◽  
Growth Models ◽  
Bubble Formation ◽  
Bubble Nucleation ◽  
Gas Content ◽  
Flow Rates ◽  
Noncondensable Gas ◽  
Nucleation Sites ◽  
Spherical Bubbles

Visual observations have been made of bubble growth in the nucleation region of flashing flow of initially subcooled water in a converging-diverging nozzle. Experiments performed under various flow rates, saturation temperatures, turbulence levels, noncondensable gas content, and artificial nucleation sites failed to produce isolated spherical bubbles of the size or density predicted by common bubble nucleation and growth models. Heterogeneous nucleation in the bulk flow was never observed and it is concluded from bubble growth rates that the role of convection in the heat and mass transfer environment of the bubbles is an important consideration in the physics of flashing flows near the nucleation region.

scholarly journals Euler–Lagrange Modeling of Bubbles Formation in Supersaturated Water

2018 ◽  
Vol 2 (3) ◽  
pp. 39 ◽  
Author(s):  
Alessandro Battistella ◽  
Sander Aelen ◽  
Ivo Roghair ◽  
Martin van Sint Annaland
Keyword(s):  
Phase Transition ◽  
Numerical Models ◽  
Bubble Formation ◽  
Industrial Applications ◽  
Bubble Nucleation ◽  
Initial Growth ◽  
Depletion Effect ◽  
Nucleation Sites ◽  
Scale Modelling ◽  
Spherical Bubbles

Phase transition, and more specifically bubble formation, plays an important role in many industrial applications, where bubbles are formed as a consequence of reaction such as in electrolytic processes or fermentation. Predictive tools, such as numerical models, are thus required to study, design or optimize these processes. This paper aims at providing a meso-scale modelling description of gas–liquid bubbly flows including heterogeneous bubble nucleation using a Discrete Bubble Model (DBM), which tracks each bubble individually and which has been extended to include phase transition. The model is able to initialize gas pockets (as spherical bubbles) representing randomly generated conical nucleation sites, which can host, grow and detach a bubble. To demonstrate its capabilities, the model was used to study the formation of bubbles on a surface as a result of supersaturation. A higher supersaturation results in a faster rate of nucleation, which means more bubbles in the column. A clear depletion effect could be observed during the initial growth of the bubbles, due to insufficient mixing.

Review on Bubble Dynamics in Microchannel Heat Sink

2019 ◽  
Author(s):  
Sambhaji T. Kadam ◽  
Ibrahim Hassan ◽  
Ritunesh Kumar ◽  
Aziz Rahman
Keyword(s):  
Bubble Growth ◽  
Bubble Dynamics ◽  
Growth Models ◽  
Flow Boiling ◽  
Nucleation Site ◽  
Bubble Nucleation ◽  
Operating Conditions ◽  
Geometrical Parameters ◽  
Detailed Knowledge ◽  
Diffusion Controlled

Abstract Inception of the boiling, in pool or flow boiling, is the formation of the vapour bubble at active nucleation site. The bubble dynamics plays an important role in the boiling process. It is critical as it unfolds many facets especially when channel size is reduced to submicron. The detailed knowledge of the bubble dynamics is helpful in establishing the thermal and hydraulic flow behaviour in microchannel. In this paper, the bubble dynamics which include bubble nucleation at nucleation site, its growth, departure and motion along the flow in a microchannel are discussed in details. Different models are developed for the critical cavity radius are compiled and observed that they show large variation when compare. The bubble growth models are compiled and concluded that a development of more generalized bubble growth model is necessary to account for the inertia controlled and thermal diffusion controlled regions. The bubble at the nucleation site in a microchannel grows under the influence of various forces such as surface tension, inertia, shear, gravitational and evaporation momentum. Parametric variations of these forces are critically studied and reckoned that the slope of these forces seems to be reduced beyond 500 μm. Eventually, possible impact of the various factors such as operating conditions, geometrical parameters, and thermophysical properties of fluid on bubble dynamics in microchannel has been reported.

Stroboscopic Schlieren Study of Bubble Formation during Megasonic Agitation

2012 ◽  
Vol 187 ◽  
pp. 185-189 ◽  
Author(s):  
Marc Hauptmann ◽  
Steven Brems ◽  
Elisabeth Camerotto ◽  
Paul W. Mertens ◽  
Marc M. Heyns ◽  
...  
Keyword(s):  
Bubble Growth ◽  
Bubble Formation ◽  
Bubble Nucleation ◽  
Nucleation Mechanism ◽  
Thermal Dissipation ◽  
Nucleation Process ◽  
Megasonic Cleaning ◽  
Step Process ◽  
Cleaning Agents ◽  
Fundamental Understanding

An important problem in megasonic cleaning is the nucleation process of bubbles, which act as the cleaning agents. A fundamental understanding of this nucleation process will help to optimize the cleaning parameters for future applications to achieve damage free cleaning. In this work, we use quantitative stroboscopic Schlieren imaging to study the interaction of nucleating bubbles with a travelling acoustic wave. The advantage of this method is that it is non-interfering, meaning that it does not disturb the bubble nucleation. It is revealed that nucleation mechanism is a 2 step process, where a regime of slow bubble growth due to rectified diffusion is subsequently followed by a transient cavitation cycle, where bubbles grow explosively. The latter is accompanied by broadband acoustic emission and enhanced thermal dissipation, leading to the occurrence of thermal convection visible in the Schlieren images.

A Visual Experiment of Single Bubble Growth Processes in a Vertical Rectangular Channel

2018 ◽  
Author(s):  
Ning Cheng ◽  
Yun Guo ◽  
Changhong Peng
Keyword(s):  
Mass Flow ◽  
Bubble Growth ◽  
Rectangular Channel ◽  
Single Bubble ◽  
Growth Processes ◽  
Empirical Parameter ◽  
Equivalent Radius ◽  
Flow Rates ◽  
Nucleation Sites ◽  
Mass Flow Rates

Single bubble growth processes under subcooled boiling condition in a vertical rectangular channel with a gap of 2.8 mm have been visually studied. A high-speed camera was used to observe and record the bubble growth processes at a rate of 6000 frames per second. Four kinds of bubbles with different equivalent radius change trends near the ONB (Onset of Nucleate Boiling) point were observed. The bubble equivalent radius change trends were fitted by traditional empirical formula R(t) = k · tn and found that the value of empirical parameter n was in the range of 0.11 to 0.53 which was smaller than that in literatures, and the value of empirical parameter k had a positive correlation with Ja number. The bubbles generated at the same nucleation point under different heating powers, inlet fluid temperatures and mass flow rates were compared and found that within the experimental range the changes of heating power and inlet fluid temperature had a significant effect on bubble growth rectangular channel which may be used in research nuclear reactor and engineering test reactor. Due to the shape and azimuth of the channel, the bubble behaviors in vertical rectangular channel may be different from those in conventional large-size circular channel or horizontal channel. The investigations reported in the literature generally involved multiple bubbles with complex interactions between the bubbles, and the bubble parameters were usually obtained by averaging the parameters of bubbles generated at different nucleation sites. However, even under the same working condition, bubbles generated by two adjacent nucleation sites may also have big differences. In this experiment, the steady single bubble growth processes in vertical rectangular channel with deionized water as the working fluid were visually investigated. Four kinds of bubbles with different bubble growth curves were observed and the equivalent bubble radius change trends at different heating powers, inlet fluid temperatures and mass flow rates were compared.

Effect of Dual Frequency Ultrasound on the Bubble Formation in a Capillary Tube

2016 ◽  
Author(s):  
Benwei Fu ◽  
Nannan Zhao ◽  
Guoyou Wang ◽  
Hongbin Ma
Keyword(s):  
Bubble Growth ◽  
High Speed ◽  
Capillary Tube ◽  
Bubble Formation ◽  
High Speed Camera ◽  
Dual Frequency ◽  
Heating Section ◽  
Nucleation Sites ◽  
Ultrasonic Sound ◽  
Frequency Ultrasound

A visual experimental was conducted to determine the effect of dual frequency ultrasound on the bubble formation and growth in a capillary quartz tube. The ultrasonic sound was applied to the heating section of a capillary tube by using electrically-controlled piezoelectric ceramics made of Pb-based lanthanum-doped zirconate titanates (PLZTs). The bubble formation and growth were recorded by a high speed camera. Experimental results show that the bubble formation and growth depend on PLZT frequency. When a dual frequency ultrasound (154 kHz and 474 kHz) was used, the nucleation sites for bubble formation were significantly increased and the bubble growth rate enhanced.

Blister-Promoted Bubble Growth in Viscous Polymer Melts

1991 ◽  
Vol 237 ◽  
Author(s):  
Ramon J. Albalák ◽  
Zehev Tadmor ◽  
Yeshayahu Talmon
Keyword(s):  
Bubble Growth ◽  
Polymer Melts ◽  
Bubble Formation ◽  
Cooling Water ◽  
Bubble Surface ◽  
Bubble Nucleation ◽  
General Mechanism ◽  
Volatile Components ◽  
Local Pressure ◽  
Growth Phenomenon

ABSTRACTResidual monomer and other low molecular weight volatile components are removed from polymer melts in a devolatilization step involving bubble formation and growth. Polymer strands containing residual volatiles were extruded into a heated and evacuated devolatilization tank and were then frozen by the flow of cooling water. They were subsequently fractured in liquid nitrogen to reveal their cross-sections and examined in a scanning electron microscope (SEM).SEM observations revealed a previously unknown growth phenomenon in which devolatilization was seen to proceed through a ‘blistering’ mechanism. We discovered that volatile bubbles growing in the melt are fed by the formation of blisters on their inner surfaces. These blisters are formed by the coalescence of a growing bubble and the many satellite micro-bubbles formed around it as it expands. We propose a general mechanism for bubble growth in which we have shown that heterogeneous bubble nucleation in the core, which is governed by the degree of superheat, plays a major role in determining the overall rate of devolatilization. Tensile stresses accompanying bubble growth may result in a local increase in superheat by reducing the local pressure in the melt. This additional superheat combined with the possible accumulation of impurities on the macrobubble surface may be sufficient to increase the nucleation rate of microbubbles in the melt adjacent to the growing bubble, resulting in the large number of blisters formed on the bubble surface.

Gaseous Bubble Nucleation Under Shear Flow

2009 ◽  
Author(s):  
Ho-Young Kwak ◽  
Ki-Moon Kang
Keyword(s):  
Shear Flow ◽  
Atmospheric Pressure ◽  
Room Temperature ◽  
Water Solution ◽  
Bubble Formation ◽  
Bubble Nucleation ◽  
Gas Content ◽  
Methane Gas ◽  
Gaseous Bubble ◽  
Low Shear

A decompression experiment of a water solution, saturated with methane gas at about 68 atm at room temperature, was done to investigate gas bubble nucleation under shear flow. A pressure reduction from 68 atm to atmospheric pressure is well below the decompression pressure required for spontaneous bubble nucleation of the methane gas, about 120 atm. The application of a shear flow from 5 minutes before to 1 minute after the decompression induced active bubble formation and the final gas content in the solution was reduced substantially, even with the application of low shear rate of 25/s.

On the role of separated gas in decompression procedures

1971 ◽  
Vol 178 (1053) ◽  
pp. 389-406 ◽  
Keyword(s):  
Bubble Growth ◽  
Gas Transport ◽  
Decompression Sickness ◽  
Bubble Formation ◽  
Venous System ◽  
The Other ◽  
Single Exposure ◽  
Rate Of Decline ◽  
Kinetics Of

(i) Experiments have been made on the incidence and time of onset of decompression sickness in mice exposed in single or repeated exposures to raised pressures of nitrogen or helium . If a first (conditioning) exposure to pressure is followed 5 min later by a second (test) exposure, the incidence of sickness is considerably higher than that for either exposure alone, or for a single exposure equal in length to the sum of the other two exposures. The same result is obtained if the conditioning exposure is to saturation. Sickness produced by re­peated exposures has a shorter latency of onset than after single exposures. These results are explicable on the basis of asymptomatic bubble formation after decompression. (ii) This latent susceptibility to decompression sickness, as revealed by the test exposure, initially increases with time after decompression, reaches a maximum, and then declines. The rate of decline is faster than can be accounted for on the basis of the decay and local reabsorption of bubbles. It is suggested that gas bubbles are also removed by passage from the tissues through the venous system to the lungs. (iii) The degree to which very short second exposures to pressure (lasting only a few seconds) give rise to the symptoms of decompression sickness cannot be explained on the basis of the kinetics of bubble growth. These symptoms could also arise from compression by the second exposure of bubbles in the tissues, allowing them to enter the venous system and pass to the lungs, where, if expanded by decompression before elimination, they give rise to severe decompression sickness. (iv) These observations are in direct conflict with the principles on which current decompression tables are based. The relative success of the latter must be attributed to the empirical manner in which the tables have been constructed and modified in the light of experience.The results support the theory that separated gas may be present in symptomless decompressions and raise the question of gas transport to the lungs as a factor which should be taken into account in the design of decompression tables.

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