Bubble Dynamics From Artificial Nucleation Sites During Subcooled Pool Boiling

2009 ◽  
Author(s):  
Xipeng Lin ◽  
David M. Christopher ◽  
Yanshen Li ◽  
Hui Li
Keyword(s):  
High Speed ◽  
Bubble Dynamics ◽  
Stokes Equations ◽  
Liquid Pool ◽  
Numerical Results ◽  
Bottom Surface ◽  
Heating Rates ◽  
Bubble Generation ◽  
Vof Model ◽  
Nucleation Sites

The bubble dynamics of ethanol vapor bubbles growing, coalescing and condensing in a subcooled ethanol liquid pool were investigated experimentally and numerically for a range of subcoolings and heating rates. The bubbles were generated from an artificial pair of nucleation sites made of microscale tubes mounted flush with the bottom surface of the liquid pool with the vapor supplied by a vapor generator. Observations of the bubble generation with a high speed camera show the various coalescence modes with no coalescence at low heating rates and high subcoolings and horizontal and/or vertical coalescence depending on the heating rate and subcooling. At very low subcoolings, the bubbles grew quite large with various types of coalescence. The numerical results using solutions of the Navier-Stokes equations with the VOF model and using a simplified one dimensional model also describe the bubble dynamics and the conditions for coalescence. The numerical results suggest that the condensation rate at the interface is probably much higher than predicted by the model due to significant convection in the liquid pool or due to significant disturbance of the interface by the vapor jet entering the bubble.

scholarly journals Efficient and Accurate 3-D Numerical Modelling of Landslide Tsunami

Water ◽  
2019 ◽  
Vol 11 (10) ◽  
pp. 2033 ◽  
Author(s):  
Guodong Li ◽  
Guoding Chen ◽  
Pengfeng Li ◽  
Haixiao Jing
Keyword(s):  
Numerical Model ◽  
Mesh Generation ◽  
Water Waves ◽  
High Speed ◽  
Stokes Equations ◽  
Computational Cost ◽  
Similarity Criterion ◽  
Numerical Results ◽  
Mesh Resolution ◽  
Landslide Tsunami

High-speed and accurate simulations of landslide-generated tsunamis are of great importance for the understanding of generation and propagation of water waves and for prediction of these natural disasters. A three-dimensional numerical model, based on Reynolds-averaged Navier–Stokes equations, is developed to simulate the landslide-generated tsunami. Available experiment data is used to validate the numerical model and to investigate the scale effect of numerical model according to the Froude similarity criterion. Based on grid convergence index (GCI) analysis, fourteen cases are arranged to study the sensitivity of numerical results to mesh resolution. Results show that numerical results are more sensitive to mesh resolution in near field than that in the propagation field. Nonuniform meshes can be used to balance the computational efficiency and accuracy. A mesh generation strategy is proposed and validated, achieving an accurate prediction and nearly 22 times reduction of computational cost. Further, this strategy of mesh generation is applied to simulate the Laxiwa Reservoir landslide tsunami. The results of this study provide an important guide for the establishment of a numerical model of the real-world problem of landslide tsunami.

A Direct Numerical Simulation of the Unsteady Development of a Deformable Rising Bubble in a Quiescent Liquid

2008 ◽  
Author(s):  
Alpana Agarwal ◽  
C. F. Tai ◽  
J. N. Chung
Keyword(s):  
Weber Number ◽  
Bubble Dynamics ◽  
Stokes Equations ◽  
Control Volume ◽  
Density Ratio ◽  
Simulation Method ◽  
Liquid Pool ◽  
Accurate Information ◽  
Two Phase ◽  
Wide Range

An accurate finite-volume based numerical method for the simulation of an isothermal two-phase flow, consisting of a deformable bubble rising in a quiescent, unbounded liquid, is presented. This direct simulation method is built on a sharp interface concept and developed on an Eulerian, Cartesian fixed grid with a cut-cell scheme and marker points to track the moving interface. The unsteady Navier-Stokes equations in both liquid and gas phases are solved separately. The mass continuity and momentum flux conditions are explicitly matched at the true phase boundary to determine the interface shape and movement of the bubble. The highlights of this method are that it utilizes a combined Eulerian-Lagrangian approach, and is capable of treating the interface as a sharp discontinuity. A fixed underlying grid is used to represent the control volume. The interface, however, is denoted by a separate set of marker particles which move along with the interface. A quadratic curve fitting algorithm with marker points is used to yield smooth and accurate information of the interface curvatures. This numerical scheme can handle a wide range of density and viscosity ratios. The bubble is assumed to be spherical and at rest initially, but deforms as it rises through the liquid pool due to buoyancy. Additionally, the flow is assumed to be axisymmetric and incompressible. The bubble deformation and dynamic motion are characterized by the Reynolds number, the Weber number, the density ratio and the viscosity ratio. The effects of these parameters on the translational bubble dynamics and shape are given and the physical mechanisms are explained and discussed. Results for the shape, velocity profile and various forces acting on the bubble are presented here as a function of time until the bubble reaches terminal velocity. The range of Reynolds numbers investigated is 1 < Re < 100, and that of Weber number is 1 < We < 10.

scholarly journals Bubble Dynamics in a Narrow Gap Flow under the Influence of Pressure Gradient and Shear Flow

Fluids ◽  
2020 ◽  
Vol 5 (4) ◽  
pp. 208
Author(s):  
Peter Reinke ◽  
Jan Ahlrichs ◽  
Tom Beckmann ◽  
Marcus Schmidt
Keyword(s):  
Shear Flow ◽  
Pressure Gradient ◽  
High Speed ◽  
Bubble Dynamics ◽  
Three Dimensional ◽  
High Speed Imaging ◽  
Two Phase ◽  
Bubble Generation ◽  
Gap Flow ◽  
The Impact

The volume-of-flow method combined with the Rayleigh–Plesset equation is well established for the computation of cavitation, i.e., the generation and transportation of vapor bubbles inside a liquid flow resulting in cloud, sheet or streamline cavitation. There are, however, limitations, if this method is applied to a restricted flow between two adjacent walls and the bubbles’ size is of the same magnitude as that of the clearance between the walls. This work presents experimental and numerical results of the bubble generation and its transportation in a Couette-type flow under the influence of shear and a strong pressure gradient which are typical for journal bearings or hydraulic seals. Under the impact of variations of the film thickness, the VoF method produces reliable results if bubble diameters are less than half the clearance between the walls. For larger bubbles, the wall contact becomes significant and the bubbles adopt an elliptical shape forced by the shear flow and under the influence of a strong pressure gradient. Moreover, transient changes in the pressure result in transient cavitation, which is captured by high-speed imaging providing material to evaluate transient, three-dimensional computations of a two-phase flow.

Deposition Process of Droplets Impacting on a Horizontal Surface

2011 ◽  
Vol 354-355 ◽  
pp. 579-584 ◽  
Author(s):  
Jing Yin Li ◽  
Qiang Han ◽  
Yan Jie Zhao ◽  
Xiao Fang Yuan
Keyword(s):  
Impact Velocity ◽  
High Speed ◽  
Droplet Impact ◽  
Numerical Results ◽  
Horizontal Surface ◽  
Experimental Investigations ◽  
Impact Process ◽  
Vof Model ◽  
Spread Factor ◽  
The Impact

The results of the experimental investigations and numerical simulations of droplet impact on a stationary horizontal surface are presented. The impact process of a droplet with high impact energy on a horizontal surface was photographed by a high-speed CCD. In addition, two-dimensional numerical simulation of the impact process was also performed using the VOF model. Comparison between the experimental and numerical results shows that the chosen computational model is suitable to simulate such impact processes. Furthermore, the effect of the droplet impact velocity and diameter on the impact process was studied in detailed. The numerical results show that the variation in droplet impact velocity has a significant effect on the maximum spread factor and spread speed, whereas, the variation in droplet diameter considerably influences the maximum spread factor and the oscillation of the drop in the receding phase.

Three-Dimensional Volume of Fluid Simulations of Air Bubble Dynamics in a Converging Nozzle

2018 ◽  
Author(s):  
Deify Law ◽  
Thomas G. Shepard
Keyword(s):  
High Speed ◽  
Bubble Dynamics ◽  
Liquid Velocity ◽  
Three Dimensional ◽  
Volume Of Fluid ◽  
Ansys Fluent ◽  
Air Bubble ◽  
Vof Model ◽  
Time Trace ◽  
Velocity Information

The present work relates to the dynamics of single bubbles accelerating through a converging nozzle. There are two main aspects to this study. First, this expands upon a previously used two-dimensional model [1] by providing three-dimensional volume of fluid (VOF) simulations that show better agreement with experiments. The VOF model is employed to perform simulations using the commercial computational fluid dynamics (CFD) code ANSYS FLUENT. Second, the present work uses experimental high-speed camera results in conjunction with simulation results to demonstrate bubble time trace and velocity information. Time series of the average liquid velocity at the atomizer exit orifice when the bubble exits as determined via simulation are reported. The passing of a bubble through the nozzle is found to cause a significant fluctuation in the exit velocity that is coupled to the liquid and gas dynamics upstream of the exit.

Theoretical Modeling and Experimental Measurements of Single Bubble Dynamics From a Submerged Orifice in a Liquid Pool

2007 ◽  
Author(s):  
S. K. Kasimsetty ◽  
A. Subramani ◽  
R. M. Manglik ◽  
M. A. Jog
Keyword(s):  
Flow Rate ◽  
High Speed ◽  
Bubble Dynamics ◽  
Bubble Diameter ◽  
Liquid Pool ◽  
Orifice Diameter ◽  
Equivalent Diameter ◽  
Bubble Behavior ◽  
Balance Of Forces ◽  
Submerged Orifice

The dynamics of a single gas bubble, emanating from a submerged orifice in stagnant water has been explored both theoretically and experimentally. The mathematical model represents a fundamental balance of forces due to buoyancy, viscosity, surface tension, liquid inertia, and gas momentum transport, and the consequent motion of the gas-liquid interface. Theoretical solutions describe the dynamic bubble behavior (incipience, growth and necking) as it grows from a tip of a sub-millimeter-scale capillary orifice in an isothermal pool of water. These results are also found to be in excellent agreement with a set of experimental data that are obtained from optical high-speed micro-scale flow visualization. Variations in bubble shape, equivalent diameter, and growth times with capillary orifice diameter and air flow rates are outlined. These parametric trends suggest a two-regime ebullient transport: (a) a constant volume regime where the bubble diameter is not affected by the flow rate, and (b) a growing bubble regime where bubble size increases with flow rate.

Effect of Ambient Pressure on Bubble Growth in Micro-Channel and Its Pumping Effect

2010 ◽  
Author(s):  
F. Mobadersani ◽  
M. Eskandarzade ◽  
S. Azizi ◽  
S. Abbasnezhad
Keyword(s):  
Atmospheric Pressure ◽  
Bubble Growth ◽  
Bubble Dynamics ◽  
Stokes Equations ◽  
Ambient Pressure ◽  
Three Dimensional ◽  
Numerical Results ◽  
Micro Channel ◽  
Bubble Volume ◽  
Explosive Boiling

Over the last two decades, explosive boiling has been widely used in industry, many researches have been dedicated to study its aspects. Some applications of explosive boiling are in thermal bubble jet printers, micro-injectors and micro-medicine devices. In such applications ambient pressure is not usually the atmospheric pressure. To have a good design, there is a great need to simulate the bubble growth under non-atmospheric pressure. In this research a three dimensional numerical analysis of growth and collapse of a bubble in a micro-channel under four different ambient pressures is presented. Flow3D package which solves the Navier-Stokes equations with surface tension effects, is used to reach this aim. Leinhard’s equation is used to compute the temperature of explosive boiling in various pressures. It is considered that the internal pressure of the bubble has an exponential form. Bubble dynamics relations have been used to obtain time constant of the bubble. The bubble volume and the flow rates from both ends of the microchannel are obtained. It has been shown that increasing in the ambient pressure causes decreasing in the bubble volume. Numerical results for the growth and collapse of the bubble in the micro-channel are compared with those of experiments under similar conditions. Results of the growth and collapse of the bubble in the micro-channel of a printer, BJ-80, have been used to validation. Comparisons show that the bubble evolution is well predicted by the numerical results.

Numerical simulation of a two-phase flow in the electrospinning process

2014 ◽  
Vol 24 (8) ◽  
pp. 1755-1761 ◽  
Author(s):  
Lan Xu ◽  
HongYing Liu ◽  
Na Si ◽  
Eric Wai Ming Lee
Keyword(s):  
Numerical Simulation ◽  
Two Phase Flow ◽  
Stokes Equations ◽  
Electrospinning Process ◽  
Numerical Results ◽  
Phase Flow ◽  
Fiber Morphology ◽  
Two Phase ◽  
Content Type ◽  
Vof Model

Purpose – An electrospinning process is a multi-phase and multi-physics process. The purpose of this paper is to numerically simulate the two-phase flow in the electrospinning process. The numerical results can offer in-depth insight into physical understanding of many complex phenomena which cannot be fully explained experimentally. Design/methodology/approach – The two-phase flow can be calculated by solving the modified Navier-Stokes equations under the influence of electric field and the interface between the two fluids has been determined by using the Volume of Fluids (VOF) method. A realizable k-e model is used to model the turbulent viscosity. The numerical results can be obtained using Computational Fluid Dynamics (CFD) techniques. Findings – The numerical simulation is a powerful tool to controlling over electrospinning parameters such as voltage, flow rate, and others. Research limitations/implications – The numerical simulation of two-phase flow model will take into account solvent evaporation and solidification of the jet, which play pivotal roles in determining the internal fiber morphology of the jet to be described here. Originality/value – This paper deals with studying numerically the two-phase flow in the electrospinning process by applying CFD techniques. And the flow is modeled by ANSYS(FLUENT) using the VOF model.

Bubble Growth During Nucleate Boiling in Microchannels

2010 ◽  
Author(s):  
David M. Christopher ◽  
Xipeng Lin
Keyword(s):  
Heat Transfer ◽  
Bubble Growth ◽  
High Speed ◽  
Stokes Equations ◽  
Electronics Cooling ◽  
Nucleate Boiling ◽  
Nucleation Site ◽  
High Heat Flux ◽  
Transfer Coefficients ◽  
Vof Model

The flow and heat transfer in microchannels has been of great interest for some years now due to the significantly higher heat transfer coefficients useful for enhancing the heat transfer in very small but high heat flux applications such as electronics cooling. Nucleate boiling heat transfer in microchannels is also of great interest for generating even higher heat transfer rates; however, numerous studies have shown that the bubble formation immediately fills the entire microchannel with vapor significantly reducing the heat transfer since the bubble size is normally of the same size as the microchannel. The bubble growth process is very fast and difficult to study experimentally, even with high speed cameras. This study numerically analyzes the flow and bubble growth in a microchannel for various conditions by solving the Navier-Stokes equations with the VOF model with an analytical microlayer model to provide the large amount of vapor produced by the curved region of the microlayer. As each bubble forms, the large pressure drop around the bubble causes the bubble to quickly break away from the nucleation site and move quickly downstream. The bubbles are quite small with the size depending on the bulk flow velocity, subcooling and the heating rate. The numerical results compare quite well with preliminary experimental observations of bubble growth on a microheater embedded in the channel wall for FC-72 flowing in a microchannel.

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