Theoretical Model of Bubble Growth in Superheated Ethanol-Water Mixture

2019 ◽  
Author(s):  
Chang Cai ◽  
Hong Liu ◽  
Xi Xi ◽  
Ming Jia ◽  
Weilong Zhang ◽  
...  
Keyword(s):  
Binary Mixture ◽  
Bubble Growth ◽  
Mass Fraction ◽  
Bubble Radius ◽  
Bubble Surface ◽  
Mass Diffusion ◽  
Growth Characteristics ◽  
Initial Mass ◽  
Water Mixture ◽  
Fraction Distribution

Abstract A novel model was developed to investigate the bubble growth characteristics in uniformly superheated ethanol-water (EtOH-H2O) mixture. The influence of the mass fraction of ethanol was discussed in detail. In the proposed model, the energy equation and the component diffusion equation for the liquid were respectively coupled with quadratic temperature and mass fraction distribution within the thermal and concentration boundary layers. The non-random two-liquid equation (NRTL) was adopted to obtain the vapor-liquid equilibrium of the binary mixture at the bubble surface. The comparison between the current calculated bubble radius with the available experimental data demonstrates the accuracy of the bubble growth model. The maximum mass diffusion limited growth rate was also proposed to quantify and illustrate the effect of mass diffusion on bubble growth. The results showed that the later stage of bubble growth in a binary mixture is controlled by both mass diffusion and heat transfer. The bubble growth characteristics strongly depend on the initial mass fraction of ethanol. Within a large concentration range, a higher content of ethanol is adverse to bubble growth at a constant superheat degree. The effect of mass diffusion on bubble growth becomes weaker with an increased initial mass fraction of ethanol.

Mass transfer dominated by thermal diffusion in laminar boundary layers

1997 ◽  
Vol 336 ◽  
pp. 379-409 ◽  
Author(s):  
PEDRO L. GARCÍA-YBARRA ◽  
JOSE L. CASTILLO
Keyword(s):  
Mass Transport ◽  
Boundary Layers ◽  
Thermal Diffusion ◽  
Mass Fraction ◽  
Soret Effect ◽  
Second Order ◽  
Brownian Diffusion ◽  
Diffusion Transport ◽  
Laminar Boundary Layers ◽  
Fraction Distribution

The concentration distribution of massive dilute species (e.g. aerosols, heavy vapours, etc.) carried in a gas stream in non-isothermal boundary layers is studied in the large-Schmidt-number limit, Sc[Gt ]1, including the cross-mass-transport by thermal diffusion (Ludwig–Soret effect). In self-similar laminar boundary layers, the mass fraction distribution of the dilute species is governed by a second-order ordinary differential equation whose solution becomes a singular perturbation problem when Sc[Gt ]1. Depending on the sign of the temperature gradient, the solutions exhibit different qualitative behaviour. First, when the thermal diffusion transport is directed toward the wall, the boundary layer can be divided into two separated regions: an outer region characterized by the cooperation of advection and thermal diffusion and an inner region in the vicinity of the wall, where Brownian diffusion accommodates the mass fraction to the value required by the boundary condition at the wall. Secondly, when the thermal diffusion transport is directed away from the wall, thus competing with the advective transport, both effects balance each other at some intermediate value of the similarity variable and a thin intermediate diffusive layer separating two outer regions should be considered around this location. The character of the outer solutions changes sharply across this thin layer, which corresponds to a second-order regular turning point of the differential mass transport equation. In the outer zone from the inner layer down to the wall, exponentially small terms must be considered to account for the diffusive leakage of the massive species. In the inner zone, the equation is solved in terms of the Whittaker function and the whole mass fraction distribution is determined by matching with the outer solutions. The distinguished limit of Brownian diffusion with a weak thermal diffusion is also analysed and shown to match the two cases mentioned above.

scholarly journals Bubble Dynamics in a Two-Phase Bubbly Mixture

2010 ◽  
Author(s):  
Arvind Jayaprakash ◽  
Sowmitra Singh ◽  
Georges Chahine
Keyword(s):  
Void Fraction ◽  
High Speed ◽  
Bubble Dynamics ◽  
Bubble Radius ◽  
Discharge Voltage ◽  
Large Bubble ◽  
Water Mixture ◽  
Two Phase ◽  
Mixture Density ◽  
Bubbly Medium

The dynamics of a primary relatively large bubble in a water mixture including very fine bubbles is investigated experimentally and the results are provided to several parallel on-going analytical and numerical approaches. The main/primary bubble is produced by an underwater spark discharge from two concentric electrodes placed in the bubbly medium, which is generated using electrolysis. A grid of thin perpendicular wires is used to generate bubble distributions of varying intensities. The size of the main bubble is controlled by the discharge voltage, the capacitors size, and the pressure imposed in the container. The size and concentration of the fine bubbles can be controlled by the electrolysis voltage, the length, diameter, and type of the wires, and also by the pressure imposed in the container. This enables parametric study of the factors controlling the dynamics of the primary bubble and development of relationships between the bubble characteristic quantities such as maximum bubble radius and bubble period and the characteristics of the surrounding two-phase medium: micro bubble sizes and void fraction. The dynamics of the main bubble and the mixture is observed using high speed video photography. The void fraction/density of the bubbly mixture in the fluid domain is measured as a function of time and space using image analysis of the high speed movies. The interaction between the primary bubble and the bubbly medium is analyzed using both field pressure measurements and high-speed videography. Parameters such as the primary bubble energy and the bubble mixture density (void fraction) are varied, and their effects studied. The experimental data is then compared to simple compressible equations employed for spherical bubbles including a modified Gilmore Equation. Suggestions for improvement of the modeling are then presented.

Collective Effects on the Growth of Vapor Bubbles in a Superheated Liquid

1984 ◽  
Vol 106 (4) ◽  
pp. 486-490 ◽  
Author(s):  
G. L. Chahine ◽  
H. L. Liu
Keyword(s):  
Collective Behavior ◽  
Bubble Growth ◽  
Theoretical Study ◽  
Pressure Field ◽  
Bubble Radius ◽  
Significant Inhibition ◽  
Collective Effects ◽  
Superheated Liquid ◽  
Vapor Bubbles ◽  
Bubble Interaction

The problem of the growth of a spherical isolated bubble in a superheated liquid has been extensively studied. However, very little work has been done for the case of a cloud of bubbles. The collective behavior of the bubbles departs considerably from that of a single isolated bubble, due to the cumulative modification of the pressure field from all other bubbles. This paper presents a theoretical study on bubble interaction in a superheated liquid during the growth stage. The solution is sought in terms of matched asymptotic expansions in powers of ε, the ratio between rb0, a characteristic bubble radius and l0, the interbubble distance. Numerical results show a significant inhibition of the bubble growth rate due to the presence of interacting bubbles. In addition, the temperature at the bubble wall decreases at a slower rate. Consequently, the overall heat exchange during the bubble growth is reduced.

scholarly journals Kalina-Flash Cycle Performance Analysis and Parametric Optimization

2019 ◽  
Author(s):  
Raveendra Nath R ◽  
C. Vijaya Bhaskar Reddy ◽  
K.Hemachandra Reddy
Keyword(s):  
Mass Fraction ◽  
Parametric Optimization ◽  
Pressure Ratio ◽  
Cycle Performance ◽  
Second Law ◽  
Water Mixture ◽  
Objective Functions ◽  
Thermodynamic Investigation ◽  
Kalina Cycle ◽  
Multi Objective Genetic Algorithm

In this paper, a thermodynamic investigation is done on a Kalina-flash cycle. This work is initially validated with the Kalina cycle power plant, Wich is commissioned in Husavic. Low-temperature Kalina-flash is considered for this study. This cycle is working with the ammonia-water mixture. The Kalina-flash cycle was optimized in the view of exergy and thermal efficiency. A multi-objective genetic algorithm is used to accomplish optimization. The optimum values of the objective functions are observed to be 40.20 and 11.70% respectively. At last, The influence of the separator inlet dryness fraction, basic ammonia mass fraction, temperature and flash pressure ratio on the first and second law efficiencies are analysed.

scholarly journals Bubble dynamics in a compressible liquid in contact with a rigid boundary

2015 ◽  
Vol 5 (5) ◽  
pp. 20150048 ◽  
Author(s):  
Qianxi Wang ◽  
Wenke Liu ◽  
A. M. Zhang ◽  
Yi Sui
Keyword(s):  
Shock Waves ◽  
Thin Layer ◽  
High Speed ◽  
Bubble Radius ◽  
Time History ◽  
Bubble Surface ◽  
Boundary Integral ◽  
Boundary Integral Method ◽  
Imaging Method ◽  
Rigid Boundary

A bubble initiated near a rigid boundary may be almost in contact with the boundary because of its expansion and migration to the boundary, where a thin layer of water forms between the bubble and the boundary thereafter. This phenomenon is modelled using the weakly compressible theory coupled with the boundary integral method. The wall effects are modelled using the imaging method. The numerical instabilities caused by the near contact of the bubble surface with the boundary are handled by removing a thin layer of water between them and joining the bubble surface with its image to the boundary. Our computations correlate well with experiments for both the first and second cycles of oscillation. The time history of the energy of a bubble system follows a step function, reducing rapidly and significantly because of emission of shock waves at inception of a bubble and at the end of collapse but remaining approximately constant for the rest of the time. The bubble starts being in near contact with the boundary during the first cycle of oscillation when the dimensionless stand-off distance γ = s / R m < 1, where s is the distance of the initial bubble centre from the boundary and R m is the maximum bubble radius. This leads to (i) the direct impact of a high-speed liquid jet on the boundary once it penetrates through the bubble, (ii) the direct contact of the bubble at high temperature and high pressure with the boundary, and (iii) the direct impingement of shock waves on the boundary once emitted. These phenomena have clear potential to damage the boundary, which are believed to be part of the mechanisms of cavitation damage.

OS2-22 Effect of Mass Fraction of Ammonia on OTEC Systemwith Ammonia/water Mixture as Working Fluid

2007 ◽  
Vol 2007.12 (0) ◽  
pp. 367-368
Author(s):  
Yasuyuki IKEGAMI ◽  
Hiroyuki ASOU ◽  
Takeshi YASUNAGA ◽  
Hirokazu MANDA ◽  
Junichi INADOMI
Keyword(s):  
Mass Fraction ◽  
Working Fluid ◽  
Water Mixture ◽  
Ammonia Water

Considerations on the Design Principles for a Binary Mixture Heat Recovery Boiler

1992 ◽  
Vol 114 (4) ◽  
pp. 701-706 ◽  
Author(s):  
S. S. Stecco ◽  
U. Desideri
Keyword(s):  
Heat Transfer ◽  
Binary Mixture ◽  
Binary Mixtures ◽  
Heat Recovery ◽  
Combined Cycle ◽  
Working Fluid ◽  
Heat Recovery Boiler ◽  
Water Mixture ◽  
Volume Viscosity ◽  
Recovery Boiler

The use of a binary mixture as a working fluid in bottoming cycles has in recent years been recognized as a means of improving combined cycle efficiency. There is, however, quite a number of studies dealing with components of plants that employ fluids other than water, and particularly binary mixtures. Due to different specific volume, viscosity, thermal conductivity, and Prandtl number, heat recovery boilers designed to work with water require certain modifications before they can be used with binary mixtures. Since a binary mixture is able to recover more heat from the exhaust fumes than water, the temperature difference between the hot and the cold fluids is generally lower over the whole recovery boiler; this necessitates greater care in sizing the tube bundles in order to avoid an excessive heat transfer surface per unit of thermal power exchanged. The aim of this paper is to provide some general criteria for the design of a heat recovery boiler for a binary mixture, by showing the influence of various dimensional parameters on the heat surface and pressure drop both in the cold and the hot side. Heat transfer coefficients and pressure drops in the hot side were computed by means of correlations found in the literature. A particular application was studied for an ammonia-water mixture, used in the Kalina cycles, which represents one of the most interesting binary cycles proposed so far.

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