Numerical Simulation of Liquid Droplet Coalescence and Breakup

2020 ◽  
Vol 142 (10) ◽  
Author(s):  
Shuxia Yuan ◽  
Ramin Dabirian ◽  
Ovadia Shoham ◽  
Ram S. Mohan
Keyword(s):  
Weber Number ◽  
Recovery Time ◽  
Relative Velocity ◽  
Shape Recovery ◽  
Liquid Droplet ◽  
Fluid Dynamic ◽  
Droplet Diameter ◽  
Continuous Phase ◽  
Collision Time ◽  
Coalescence Time

Abstract This paper studied the evolution of binary droplet collision in liquid and also a mathematical calculation method of coalescence time. Binary droplet collisions occur in many engineering applications; however, the accurate models to predict the collision of droplets in the liquid are still lacking. In this work, the binary collision processes of droplets were simulated through computational fluid dynamic (CFD) method, where the interfaces between the two phases were tracked by the volume of fluid (VOF) approach. The results reveal that Weber number determines the results of the head-on collisions, and the cases with the same Weber number present similar evolution processes. If coalescence happens, the collision time decreases with increase in relative velocity, whereas the shape recovery time is independent with the relative velocity, but depends on droplet diameter. It is derived from this research that the collision time is proportional to the droplet diameter, and the shape recovery time is proportional to the 3/2 power of droplet diameter. The droplet moving directions play an important role in the collision results, and the case of two droplets moving toward each other with equal velocity is the easiest way to coalesce. When two droplets with different sizes collide, besides relative velocity, the coalescence and breakup are determined by the absolute velocities, the size, and size ratio of the two droplets. The increase in viscosity of continuous phase results an increase in collision time, but decrease in coalescence time.

Liquid Droplet Impact Over Hydrophobic Mesh Surfaces and Assessment of Weber Number Dependent Characteristics

2022 ◽  
Author(s):  
Abba Abdulhamid Abubakar ◽  
Bekir Sami Yilbas ◽  
Hussain Al-Qahtani ◽  
Anwaruddin Siddiqui Mohammed
Keyword(s):  
Weber Number ◽  
Liquid Droplet ◽  
Droplet Diameter ◽  
Mesh Size ◽  
Vertical Axis ◽  
Capillary Length ◽  
Flat Surfaces ◽  
Mesh Surface ◽  
Droplet Behavior ◽  
Fluid Penetration

Abstract Impacting droplets and droplet ejection from hydrophobic mesh surfaces have interest in biomedicine, heat transfer engineering, and self-cleaning of surfaces. The rate and the size of newborn droplets can vary depending on, the droplet fluid properties, Weber number, mesh geometry, and surface wetting states. In the present study, impacting water droplets onto hydrophobic mesh surface is investigated and impact properties including, spreading, rebounding, and droplet fluid penetration and ejection rates are examined. Droplet behavior is assessed using high recording facilities and predicted in line with the experiments. The findings reveal that the critical Weber number for droplet fluid penetrating/ejecting from mesh screen mainly depends on the droplet fluid capillary length, and hydrophobic mesh size. The contact time of impacting droplet over mesh surface reduces with increasing droplet Weber number, which opposes the case observed for impacting droplets over flat hydrophobic surfaces. The restitution coefficient attains lower values for impacting droplets over mesh surfaces than that of flat surfaces. The rate and diameter of the ejected droplet from the mesh increases as droplet Weber increases. At the onset of impact, streamline curvature is formed inside droplet fluid, which creates a stagnation zone with radially varying pressure at the droplet fluid mesh interface. This reduces the ejected droplet diameter from mesh cells as mesh cells are located away from the impacting vertical axis.

Numerical Simulation of Droplet Generation in Series Co-Flow Capillaries

2009 ◽  
Author(s):  
Yanxi Song ◽  
Jinliang Xu
Keyword(s):  
Reynolds Number ◽  
Disperse Phase ◽  
Weber Number ◽  
Three Dimensional ◽  
Continuous Phase ◽  
Disperse Flow ◽  
Double Emulsions ◽  
Wide Range ◽  
In Series ◽  
Dispersed Phases

We study the production and motion of monodisperse double emulsions in microfluidics comprising series co-flow capillaries. Both two and three dimensional simulations are performed. Flow was determined by dimensionless parameters, i.e., Reynolds number and Weber number of continuous and dispersed phases. The co-flow generated droplets are sensitive to the Reynolds number and Weber number of the continuous phase, but insensitive to those of the disperse phase. Because the inner and outer drops are generate by separate co-flow processes, sizes of both inner and outer drops can be controlled by adjusting Re and We for the continuous phase. Meanwhile, the disperse phase has little effect on drop size, thus a desirable generation frequency of inner drop can be reached by merely adjusting flow rate of the inner fluid, leading to desirable number of inner drops encapsulated by the outer drop. Thus highly monodisperse double emulsions are obtained. It was found that only in dripping mode can droplet be of high mono-dispersity. Flow begins to transit from dripping regime to jetting regime when the Re number is decreased or Weber number is increased. To ensure that all the droplets are produced over a wide range of running parameters, tiny tapered tip outlet for the disperse flow should be applied. Smaller the tapered tip, wider range for Re and we can apply.

Jet Breakup and Droplet Formation in Immiscible Liquid-Liquid System

2016 ◽  
Author(s):  
Shimpei Saito ◽  
Yuzuru Iwasawa ◽  
Yutaka Abe ◽  
Akiko Kaneko ◽  
Tetsuya Kanagawa ◽  
...  
Keyword(s):  
Weber Number ◽  
Droplet Diameter ◽  
Droplet Formation ◽  
Liquid System ◽  
Immiscible Liquid ◽  
Satellite Droplet ◽  
Breakup Length ◽  
Jet Breakup ◽  
Fundamental Process ◽  
Median Diameter

Mitigative measures against the event of a core disruptive accident (CDA) are of the importance from the viewpoint of safety of a sodium-cooled fast reactor (SFR). If the CDA occurs, the so-called post-accident heat removal must be surely achieved. The present study focuses on the scenario that the molten materials are injected into the lower plenum as jets. The jet breakup behavior during the CDA will be very complicated. Therefore, a specialized study on the fundamental process during the jet breakup is believed to be an effective approach. The aim of this paper is to understand the fundamental process of hydrodynamic interaction of jet breakup and droplet formation Using the immiscible liquid-liquid system, water and silicon oil as the test fluids, visualization via high-speed videography was performed. From the visualization results, the breakup length and droplet diameter were measured by image processing. The experimental data were scaled with ambient Weber number. When the Weber number was smaller than 1, the droplet diameter was close to the nozzle diameter, and distribution of droplet size was not observed. When the Weber number exceeded 1, the breakup length became longer and the generated droplet diameter possessed a distribution with two peaks due to satellite droplet formation. In both cases, the droplet formed at the leading edge of jet. In case that Weber number is around 100, the droplets were formed by entrainment of interfacial wave at jet side. From the mass median diameter data, we can see that the increase of the Weber number caused the decrease of median diameter and the increase of the width of the distribution.

scholarly journals Thermal Decomposition of a Single AdBlue® Droplet Including Wall–Film Formation in Turbulent Cross-Flow in an SCR System

Energies ◽  
2019 ◽  
Vol 12 (13) ◽  
pp. 2600
Author(s):  
Kaushal Nishad ◽  
Marcus Stein ◽  
Florian Ries ◽  
Viatcheslav Bykov ◽  
Ulrich Maas ◽  
...  
Keyword(s):  
Thermal Decomposition ◽  
Relative Velocity ◽  
Pipe Wall ◽  
Film Formation ◽  
Droplet Diameter ◽  
Cross Flow ◽  
Operating Conditions ◽  
Wall Film ◽  
Wall Interaction ◽  
Scr System

The selective catalytic reduction (SCR) methodology is notably recognized as the widely applied strategy for NOX control in exhaust after-treatment technologies. In real SCR systems, complex unsteady turbulent multi-phase flow phenomena including poly-dispersed AdBlue® spray evolve with a wide ranging relative velocity between the droplet phase and carrier gas phase. This results from an AdBlue® spray that is injected into a mixing pipe which is cross-flowing by a hot exhaust gas. To reduce the complexity while gaining early information on the injected droplet size and velocity needed for a minimum deposition and optimal conversion, a single droplet with a specified diameter is addressed to mimic a spray featuring the same Sauter Mean Diameter. For that purpose, effects of turbulent hot cross-flow on thermal decomposition processes of a single AdBlue® droplet are numerically investigated. Thereby, a single AdBlue® droplet is injected into a hot cross-flowing stream within a mixing pipe in which it may experience phase change processes including interaction with the pipe wall along with liquid wall–film and possible solid deposit formation. First of all, the prediction capability of the multi-component evaporation model and thermal decomposition is evaluated against the detailed simulation results for standing droplet case for which experimental data is not available. Next, exploiting Large Eddy Simulation features the effect of hot turbulent co- and cross-flowing streams on the dynamic droplet characteristics and on the droplet/wall interaction is analyzed for various droplet diameters and operating conditions. This impact is highlighted in terms of droplet evaporation time, decomposition efficiency, droplet trajectories and wall–film formation. It turns out that smaller AdBlue® droplet diameter, higher gas temperature and relative velocity lead to shorter droplet life time as the droplet evaporates faster. Under such conditions, possible droplet/wall interaction processes on the pipe wall or at the entrance front of the monolith may be avoided. Since the ammonia (NH3) gas generated by urea decomposition is intended to reduce NOX emission in the SCR system, it is apparent for the prediction of high NOX removal performance that UWS injector system which allows to realize such operating conditions is favorable to support high conversion efficiency of urea into NH3.

Shielding Nozzle Design and Analysis for Atomization-Based Cutting Fluid Systems in Micromachining

2015 ◽  
Vol 3 (2) ◽  
Author(s):  
Andressa Lunardelli ◽  
John E. Wentz ◽  
John P. Abraham ◽  
Brian D. Plourde
Keyword(s):  
Fluid Dynamic ◽  
Continuous Phase ◽  
Computational Fluid Dynamic Model ◽  
Parameter Analysis ◽  
Cutting Fluid ◽  
Nozzle Design ◽  
Fluid Systems ◽  
Cutting Surface ◽  
Droplet Tracking ◽  
Cooling And Lubrication

Atomization-based cutting fluid systems (ACFs) are increasingly being used in micromachining applications to provide cooling and lubrication to the tool–chip interface. In this research, a shielding nozzle design is presented. A computational fluid dynamic model is developed to perform parameter analysis of the design. The numerical simulations were accomplished using the Eulerian approach to the continuous phase and a Lagrangian approach for droplet tracking. Based on the results of the simulations it is determined that the shielding nozzle is effective at providing droplets to the cutting surface at an appropriate speed and size to create a lubricating microfilm.

Experimental Evaluation of Control Fluid Fallback During Off-Bottom Well Control

2002 ◽  
Author(s):  
Fernando S. Flores-Avila ◽  
John Rogers Smith ◽  
Adam T. Bourgoyne ◽  
Darryl A. Bourgoyne
Keyword(s):  
Liquid Flow ◽  
Liquid Droplet ◽  
Drilling Fluid ◽  
Terminal Velocity ◽  
Continuous Phase ◽  
Flow Conditions ◽  
Fluid Accumulation ◽  
Well Control ◽  
Water Based ◽  
Control Fluid

This study measured the liquid fallback during simulated blowout conditions. The purpose of the study was to establish a basis for developing a procedure for controlling blowouts that relies on the accumulation of liquid kill fluid injected while the well continues to flow. The results from full-scale experiments performed with natural gas and water based drilling fluid in a vertical 2787-foot deep research well are presented. The results show that the critical velocity that prevents control fluid accumulation can be predicted by adapting Turner’s model of terminal velocity based on the liquid droplet theory to consider the flow conditions, velocity and properties of the continuous phase when determining the drag coefficient. Similarly, the amount of liquid that flows countercurrent into and accumulates in the well can be predicted based on the concept of zero net liquid flow (ZNLF) holdup.

Research on the Process of Liquid Droplet Impinging on the Liquid Film

2014 ◽  
Vol 933 ◽  
pp. 295-299
Author(s):  
Z.H. Wang ◽  
X. Meng
Keyword(s):  
Liquid Film ◽  
Fusion Reactor ◽  
Liquid Droplet ◽  
Flow Behavior ◽  
Droplet Diameter ◽  
High Heat ◽  
High Heat Flux ◽  
Experiment Research ◽  
Fluid Properties ◽  
Secondary Drop

The impacting of liquid droplet on the liquid film appears in many engineering processes. In the fusion reactor, liquid metal is used as the heat transfer media, moderator and breeder in the condition of high heat flux. The paper analyzes the flow behavior of liquid droplet impinging on the liquid film from the aspects of experiment research. In the impinging, splashing means the production of secondary drop coming from the cusp of the crown flow or Worthington jet. Impinging velocity, liquid film thickness, droplet diameter, fluid properties and impinging angle have been analyzed separately.

Spray Flame Characteristics of Bio-Derived Fuels in a Simulated Gas Turbine Burner

2019 ◽  
Author(s):  
Heena Panchasara ◽  
Pankaj S. Kolhe ◽  
Ajay K. Agrawal
Keyword(s):  
Gas Turbine ◽  
Axial Velocity ◽  
Alternative Fuels ◽  
Dynamic Models ◽  
Fuel Injection ◽  
Fluid Dynamic ◽  
Droplet Diameter ◽  
Distribution Functions ◽  
Turbulent Dispersion ◽  
Radial Profiles

Abstract Fuel injection plays an important role in liquid fueled gas turbine combustion. The strong interdependence of liquid breakup and atomization, turbulent dispersion of these droplets, droplet evaporation, and fuel-air mixing make the spray modeling an extremely challenging task. The physical processes are even more difficult to predict for alternative fuels with different thermophysical properties. In this study, spray flames of unheated and preheated vegetable oil (VO) produced by an air-blast atomizer in a swirl stabilized combustor are investigated experimentally. Phase Doppler particle analyzer (PDPA) is used to measure the instantaneous diameter and axial velocity of droplets at different axial and radial locations in both flames. Experiments are conducted at an equivalence ratio of 0.79 and atomizing air to liquid ratio (ALR) by mass of 2.5 to obtain stable VO flames. Radial profiles of mean axial velocity and Sauter mean diameter are presented to show the effect of fuel preheating. Joint Probability Density Functions (joint PDF) are presented to show the correlation between droplet diameter and axial velocity. Results are analyzed to show that both sprays exhibit self-similar droplet diameter distributions at different axial and radial locations when normalized properly. Thus, the vast amount of PDPA data in the spray can be reduced to simple distribution functions. A method to reconstruct the joint PDF from experimentally determined distribution functions is presented. We envision that the joint PDF approach outlined in this study could be implemented in high-fidelity computational fluid dynamic models to improve spray predictions in future studies.

Experiments on Liquid Droplet Impinging Erosion

2010 ◽  
Author(s):  
Takayuki Yamagata ◽  
Nobuyuki Fujisawa ◽  
Akiharu Ikarashi ◽  
Daichi Hama ◽  
Tsuyoshi Takano
Keyword(s):  
Erosion Rate ◽  
Liquid Droplet ◽  
Droplet Diameter ◽  
Optical Measurements ◽  
Light Extinction ◽  
Number Density ◽  
Direct Imaging ◽  
Threshold Velocity ◽  
Type Apparatus ◽  
Aluminum Material

In the present paper, liquid droplet impinging erosion is studied using a newly developed spray-jet-type apparatus to evaluate the erosion rate of aluminum material due to the droplets having a diameter of tens of micrometers. In order to characterize the droplet properties, such as velocity, diameter and number density, optical measurements have been introduced using PIV, direct imaging and light extinction method, respectively. While, the erosion rate of aluminum material is evaluated using the spray-jet apparatus. The present measurements indicate that the non-dimensional erosion rate agrees closely with the previous result obtained at larger droplet diameters. However, the threshold velocity was estimated to be larger than that of the previous result, suggesting the influence of droplet diameter on the threshold velocity.

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