Mechanism of the Initial States of a Bubble Formation and Departure from a Heated Surface in a Subcooled Flow

2021 ◽  
pp. 1-16
Author(s):  
Maryam Medghalchi ◽  
Nasser Ashgriz
Keyword(s):  
Heated Surface ◽  
Bubble Formation ◽  
Subcooled Flow ◽  
Initial States

Vapor Bubble Formation, Forces, and Induced Vibration: A Review

2016 ◽  
Vol 68 (3) ◽  
Author(s):  
Manoj Kumar Gupta ◽  
Dharmendra S. Sharma ◽  
Vikas J. Lakhera
Keyword(s):  
Vapor Bubble ◽  
Flow Boiling ◽  
Heated Surface ◽  
Bubble Formation ◽  
Spherical Shape ◽  
Nucleate Boiling ◽  
Nucleation Site ◽  
Formation Mechanisms ◽  
Subcooled Boiling ◽  
Two Phase

Bubble-induced vibration has become vital during recent investigation and advancement in the area of multiphase boiling. The induced vibration phenomenon can be understood with the help of proper and detailed understanding of vapor bubble formation, growth, collapse, and interaction with the surface. The growth mechanism for the formation of bubbles under nucleate boiling conditions is theoretically investigated. This paper also discusses the dynamics of vapor bubbles during flow in subcooled boiling conditions. In the part of the vapor bubble formation, the characteristics of a bubble emerged from the heated surface at a single nucleation site along with the flow boiling phenomena have been considered for analysis. The bubble is considered to be of spherical shape and detached from a heated surface due to the formation of a microlayer of liquid. The fluid is supposed to be static far away from a vapor bubble. Using well-known models of bubble formation and detachment, equations considering various forces acting over a single bubble have been derived. These equations monitor bubble characteristics in a definite manner according to the derived differential equation for energy conservation developed for the two-phase flow system. To illustrate this phenomenon, two bubble formation mechanisms, inertia-controlled and heat transfer-controlled growth have been considered. The present investigation discusses the governing equations for the bubble growth rate, bubble size and frequency, forces, and the well-known Rayleigh's equation. Also, the vibration characteristic has been reviewed, and the two phenomena, i.e., subcooled boiling induced vibration (SBIV) and flow-induced vibration (FIV) have been discussed in brief. The present review paper aims to reveal the latest evaluation done in the area of bubble-induced vibration and to ascertain the contributions made until now as well as the solution to the upcoming issues.

Analysis of Formation of Vapor Columns in Film Boiling

2007 ◽  
Author(s):  
G. Tomar ◽  
G. Biswas ◽  
A. Sharma
Keyword(s):  
Heat Flux ◽  
Capillary Pressure ◽  
Level Set ◽  
Bubble Growth ◽  
Heated Surface ◽  
Effective Means ◽  
Bubble Formation ◽  
Volume Of Fluid ◽  
Film Boiling ◽  
Column Formation

Boiling is an effective means of enhancing heat transfer from a heated surface. Above a critical superheat and heat flux (Leidenfrost point) stable film boiling is observed. In the film boiling regime, bubble formation occurs periodically in space and time. The site of bubble growth is called a node and the site between two nodes is called an antinode. The spacing between two consecutive nodes is given by the most dangerous Taylor wavelength (Berenson, 1961). An increase in the superheat results in an increase in the frequency of bubble formation and its subsequent detachment. Reimann and Grigull (1975) in their experiments observed that above a critical heat flux, bifurcation from the periodic bubble formation occurs and at the nodes, stable column formation takes place. However, at the antinodes, periodic bubble formation is still observed. On further increasing the heat flux, thin slender vapor columns form at the nodes and antinodes. Bubble formation and detachment in such cases take place from the tip of these stable columns. Numerical simulations of bubble growth in film boiling have been attempted using Volume of Fluid (VOF) methods as well Level Set (LS) methods. We here use a Coupled Level Set and Volume of Fluid (CLSVOF) method to perform simulations of saturated film boiling of water at near critical pressure (21.9MPa). In these simulations, we show that the initial film thickness plays a key role in the prediction of the critical superheat above which stable vapor columns are observed to be formed. Capillary pressure leads to snap-off of the leftover-stem of vapor after bubble detachment. Formation of stable columns is a result of balance between the inertial pressure due to the vapor influx into the column and the capillary pressure.

Void Fractions in Subcooled Flow Boiling

1969 ◽  
Vol 91 (4) ◽  
pp. 471-476 ◽  
Author(s):  
P. S. Larsen ◽  
L. S. Tong
Keyword(s):  
Heat Transfer ◽  
Flow Boiling ◽  
Heated Surface ◽  
Liquid Core ◽  
Heat Removal ◽  
Two Phase ◽  
Subcooled Flow Boiling ◽  
Void Fractions ◽  
Subcooled Flow ◽  
The Difference

A semianalytic model is presented for the prediction of void fractions in subcooled flow boiling at elevated pressures. The model is based on the formation and growth of a bubble boundary layer adjacent to the heated surface at a rate determined by the difference between the imposed surface heat transfer and the heat removal capability of the subcooled liquid core of the flow. The latter heat transfer rate is determined by the analogy between heat and momentum transfer in the liquid employing empirical friction-factor data for low-quality two-phase flow. The analysis is compared to experimental results.

Bubble Formation and Coalescence Under the Influence of Electric Fields

2013 ◽  
Author(s):  
Cila Herman
Keyword(s):  
Electric Fields ◽  
Heated Surface ◽  
Bubble Formation ◽  
Heat Removal ◽  
High Heat ◽  
Gravity Level ◽  
Transfer Rates ◽  
High Heat Transfer ◽  
Industrial Operations ◽  
Bubble Removal

The high heat transfer rates associated with phase-change processes, such as boiling, make them an attractive solution in a range of industrial operations. In terrestrial conditions, the buoyancy force is responsible for bubble removal from the surface, which is essential for heat removal from the surface. Since in space the gravity level is orders of magnitude smaller than on earth, bubbles formed during boiling remain attached at the surface and they also show a tendency to coalesce. As a result, the amount of heat removed from the heated surface is different from terrestrial conditions and it can decrease considerably.

Accurate Estimation of Vaporization Rate in Subcooled Flow Boiling Based on the Results of Visualization Experiment

2016 ◽  
Author(s):  
Kazuhiro Kaiho ◽  
Koji Enoki ◽  
Tomio Okawa
Keyword(s):  
Size Distribution ◽  
Gaussian Distribution ◽  
Bubble Size ◽  
Flow Boiling ◽  
Heated Surface ◽  
Bubble Size Distribution ◽  
Vaporization Rate ◽  
Subcooled Flow Boiling ◽  
Bubble Detachment ◽  
Subcooled Flow

This research presents experimental approaches to accumulate the data for mechanistic model in subcooled flow boiling. A number of photographic studies have been provided to investigate phenomena of bubble nucleation and condensation process for accurate prediction of void fraction such as bubble detachment diameter, bubble detachment frequency and nucleation site density in a subcooled flow boiling. In this work, a transparent heated surface was used to obtain the data from back side of heated surface to avoid overlapping bubbles by using high speed video camera. It enabled to observe bubble nucleation process and active nucleation sites. The experiment was performed in a vertical rectangular channel at atmospheric pressure and the water was used as test fluid. In generally, the computational analysis for a subcooled flow boing deal with mean bubble size as the size of bubbles produced on heated surface. Although, it was found that mean bubble size can represent bubbles produced at same site because they are almost uniform size. Even though the size of bubbles at same site are almost uniform, the difference of the size of bubbles between other sites are considerable value. Therefore, mean bubble size on the surface should not represent bubbles for all site otherwise the serious error may be caused. It seems that bubble detachment diameter should not be given by correlations of mean bubble detachment diameter for accurate prediction of vaporization rate. Some researchers proposed that bubble size distribution should be considered by Gaussian distribution [1–3]. However, it found that bubble size distribution data accumulated in this work cannot be fitted by Gaussian distribution and there are probability that larger bubbles are neglected due to the configuration features of Gaussian distribution. So, Gamma distribution was used to predict the bubble size distribution and it was evaluated in terms of heat flux, wall superheat, mass flux and liquid subcooling. And then, by the experimental approaches, the important dimensionless parameters are identified such as Nusselt number, Jakob number, Reynolds number and dimensionless subcooling. Furthermore, vaporization rate was calculated by correlations of bubble detachment diameter, bubble detachment diameter and nucleation site density and compared with the data. Finally, the effect of using mean bubble size or bubble size distribution on vaporization rate was investigated.

Pool Boiling on Multiple Surfaces in Proximity

2005 ◽  
Author(s):  
Nasser Ghariban ◽  
Ali Rostami
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Critical Heat Flux ◽  
Boiling Heat Transfer ◽  
Heated Surface ◽  
Bubble Formation ◽  
Pool Boiling ◽  
Lower Surface ◽  
Heat Transfer Process ◽  
Test Surface

Information on the boiling heat transfer on a surface when affected by the presence of other surfaces is scares. Pool boiling heat transfer process on multiple surfaces in proximity has been investigated in this work. In particular, the boiling curve and the critical heat flux on a surface located in the heated plume of another surface is studied experimentally. The surfaces are made of two identical wires with known diameter positioned horizontally in a predetermined short distance from each other. Tests were performed by heating the wires up to the critical heat flux in a pool of stationary FC-72 fluid. The boiling curves were experimentally developed for a surface when it is located in the plume of another heated surface. Initial results indicate that the critical heat flux on such a surface drops more than 30% compared to a single isolated wire. The change may be attributed to the plume effects on the bubble formation and bubble dynamics of upper surface as well as the effects on the degree of subcooling in the immediate neighborhood of the test surface. The research focused on the effects of spacing and the degree of subcooling on the boiling and the critical heat flux of the upper surface which is affected by the natural convection and boiling plume of the lower surface. The results of this project are expected to expand the existing knowledge of boiling heat transfer, particularly when it is affected by the presence of other surfaces in the proximity.

Direct observations of radiation-enhanced transformations in glass

1983 ◽  
Vol 41 ◽  
pp. 354-355
Author(s):  
J. F. DeNatale ◽  
D. G. Howitt
Keyword(s):  
Glass Matrix ◽  
Diffusion Mechanism ◽  
Bubble Formation ◽  
Silicate Glasses ◽  
Phase Decomposition ◽  
Direct Observations ◽  
Thin Foils ◽  
Oxygen Bubble ◽  
Electron Energy Loss ◽  
Kinetics Of

The electron irradiation of silicate glasses containing metal cations produces various types of phase separation and decomposition which includes oxygen bubble formation at intermediate temperatures figure I. The kinetics of bubble formation are too rapid to be accounted for by oxygen diffusion but the behavior is consistent with a cation diffusion mechanism if the amount of oxygen in the bubble is not significantly different from that in the same volume of silicate glass. The formation of oxygen bubbles is often accompanied by precipitation of crystalline phases and/or amorphous phase decomposition in the regions between the bubbles and the detection of differences in oxygen concentration between the bubble and matrix by electron energy loss spectroscopy cannot be discerned (figure 2) even when the bubble occupies the majority of the foil depth.The oxygen bubbles are stable, even in the thin foils, months after irradiation and if van der Waals behavior of the interior gas is assumed an oxygen pressure of about 4000 atmospheres must be sustained for a 100 bubble if the surface tension with the glass matrix is to balance against it at intermediate temperatures.

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