Dynamics of Liquid Sheet Breakup in Splash Plate Atomization

2017 ◽  
Vol 140 (1) ◽  
Author(s):  
G. Thunivumani ◽  
Hrishikesh Gadgil
Keyword(s):  
Solid Surface ◽  
Weber Number ◽  
Jet Impingement ◽  
Liquid Sheet ◽  
Force Balance ◽  
Impingement Angle ◽  
Wide Range ◽  
Perforated Sheet ◽  
Sheet Breakup ◽  
Regime Map

An experimental study was conducted to investigate the breakup of a liquid sheet produced by oblique impingement of a liquid jet on a plane solid surface. Experiments are carried out over a wide range of jet Weber number (80–6300) and various jet impingement angles (30 deg, 45 deg, and 60 deg) are employed to study the sheet dynamics. The breakup of a liquid sheet takes place in three modes, closed rim, open rim, and perforated sheet, depending upon the Weber number. The transitions across the modes are also influenced by the impingement angle with the transition Weber number reducing with increase in impingement angle. A modified regime map is proposed to illustrate the role of impingement angle in breakup transitions. A theoretical model based on force balance at the sheet edge is developed to predict the sheet parameters by taking the shear interaction between the sheet and the solid surface into account. The sheet shape predicted by the model fairly matches with the experimentally measured sheet shape. The breakup length and width of the sheet are measured and comparisons with the model predictions show good agreement in closed rim mode of breakup.

scholarly journals Breakup of the Water Sheet Formed by Two Liquid Impinging Jets

2019 ◽  
Vol 2019 ◽  
pp. 1-8
Author(s):  
Yakang Xia ◽  
Lyes Khezzar ◽  
Shrinivas Bojanampati ◽  
Arman Molki
Keyword(s):  
Weber Number ◽  
Reynolds Numbers ◽  
Impinging Jets ◽  
Liquid Jets ◽  
Liquid Jet ◽  
Impingement Angle ◽  
Number Range ◽  
Breakup Length ◽  
Sheet Breakup ◽  
Visualization Experiments

Flow visualization experiments are carried out to study the flow regimes and breakup length of the water sheet generated by two impinging liquid jets from an atomizer made of two identical tubes 0.686 mm in diameter. These experiments cover liquid jet Reynolds numbers based on the pipe diameter in the range of 1541 to 5394. The effects of the jet velocities and impingement angle between the two jets on the breakup performance are studied. Four spray patterns are recognized, which are presheet formation, smooth sheet, ruffled sheet, and open-rim sheet regimes. Water sheet breakup length is found to be consistent with previous experimental and theoretical results in the lower Weber number (based on water jet diameter and velocity) range. In the relatively high Weber number range, the breakup length tends to a constant value with increasing Weber number, and some discrepancies between experimental and theoretical predictions do exist. Measured water sheet area increases with increasing liquid jet Reynolds numbers and impingement angle within the range of the current study.

A non-linear model for impinging jets atomization

2008 ◽  
Vol 222 (2) ◽  
pp. 213-224 ◽  
Author(s):  
E A Ibrahim ◽  
B E Outland
Keyword(s):  
Linear Model ◽  
Weber Number ◽  
Drop Size ◽  
Impinging Jets ◽  
Liquid Sheet ◽  
Linear Perturbation ◽  
Breakup Length ◽  
Half Wavelength ◽  
Non Linear ◽  
Sheet Breakup

The problem considered is predicting the characteristics of the spray produced by atomization of an attenuating liquid sheet formed by the impingement of two liquid jets of equal diameters and momenta. A second-order non-linear perturbation analysis is employed to model the evolution of harmonic instability waves that lead to sheet distortion and fragmentation. The onset of atomization occurs when the uneven surface modulations of the thinning sheet bring its upper and lower interfaces in contact. It is found that the sheet is torn into ligaments at each half wavelength. The instability of the ligaments causes their eventual disintegration into drops. The results indicate that sheet breakup length, time, and resultant drop size decrease as Weber number is increased. A higher Weber number induces a greater sheet breakup thickness. The breakup length, thickness, time, and drop size are diminished at larger impingement angles. The theoretical predictions of the present non-linear model are in good agreement with available experimental data and empirical correlations for sheet breakup length and drop size.

Effect of Weber Number on Disintegration of Liquid Sheet With Co-Flowing Gas

2014 ◽  
Author(s):  
Mohammad Ali ◽  
Mohammed S. Mayeed ◽  
A. K. M. Sadrul Islam ◽  
M. Quamrul Islam
Keyword(s):  
Weber Number ◽  
Gaseous Medium ◽  
Normal Force ◽  
Surface Force ◽  
Liquid Sheet ◽  
Navier Stokes ◽  
Stokes Systems ◽  
Sheet Breakup ◽  
Surface Tension Forces ◽  
Moving Liquid

The disturbances on the surface of a moving liquid sheet in a moving gaseous medium are studied to analyze the dynamics and breakup of the liquid sheet with co-flowing gas. The problem, composed of the Navier-Stokes systems associated with surface tension forces, is solved by the Volume of Fluid (VOF) technique with a Continuum Surface Force (CSF) manner artificially smoothing the discontinuity present at the interface. The investigation provides the insights into the dynamics and breakup processes. The inlet velocities of liquid and gas are determined by liquid and gas Weber number, respectively. It is found that the disturbances occurred by the gas Weber number controls the instability process for the liquid sheet breakup. The results show that there is a range of gas Weber number for the occurrence of droplet. In this range, the gas Weber number causes an aerodynamic normal force at the tip of the liquid sheet which is able to form a droplet from the tip of the liquid sheet. Below that range of gas Weber number, the aerodynamic normal force at the tip of the sheet is too low to produce a droplet and above the range, the aerodynamic normal force stretches the liquid sheet too much and no droplet occurs.

Symmetric and Asymmetric Disturbances in the Rayleigh Zone of an Air-Assisted Liquid Sheet: Theoretical and Experimental Analysis

2020 ◽  
Vol 142 (7) ◽  
Author(s):  
V. Sivadas ◽  
S. Karthick ◽  
K. Balaji
Keyword(s):  
Growth Rate ◽  
Weber Number ◽  
High Speed ◽  
Low Frequency ◽  
Maximum Growth ◽  
Temporal Analysis ◽  
Average Frequency ◽  
Liquid Sheet ◽  
Number Ratio ◽  
Sheet Breakup

Abstract The temporal analysis of symmetric (dilatational) and asymmetric (sinusoidal) perturbations at the interface of a water sheet in a coflowing air stream focuses on low gas Weber number region (Weg < 0.4), namely, Rayleigh breakup zone. The motive for this investigation is to acquire a better insight of breakup phenomena involved, rather than technical relevance, by utilizing Kelvin–Helmholtz instability. Accordingly, perturbations are introduced on the basic flow whose stability is to be examined by the method of normal (Fourier) modes. The temporal growth-rate of perturbations is traced to extract the wavenumber associated with maximum growth-rate. Thus, the critical wavelength, in conjunction with the phase velocity of the disturbance will facilitate to obtain the corresponding breakup frequency of the liquid sheet. The analytical findings on liquid sheet breakup frequency with increasing Weber number ratio exhibit the dominance of symmetric wave over asymmetric wave. It also shows independent evolution of breakup frequency with respect to Weber number ratio for the respective perturbation modes, which appears to be a pointed profile. That is, the frequency contour for dilatational mode dips, whereas it rises for the sinusoidal mode and at the Weber number ratio of 0.518 the crossover occur. The theoretical results were substantiated by high-speed flow visualization studies that discern the coexistence of low-frequency (primary) and high-frequency (intermediate) breakup events. Furthermore, the empirical average frequency data track reasonably well with the dilatational instability.

scholarly journals Is contact angle a cause or an effect? – A cautionary tale

2020 ◽  
Vol 146 ◽  
pp. 03004
Author(s):  
Douglas Ruth
Keyword(s):  
Contact Angle ◽  
Solid Surface ◽  
Contact Angles ◽  
Two Dimensions ◽  
Experimental Results ◽  
Flow In Porous Media ◽  
Two Dimensional ◽  
Wide Range ◽  
Fluid Drop ◽  
Surrounding Fluid

The most influential parameter on the behavior of two-component flow in porous media is “wettability”. When wettability is being characterized, the most frequently used parameter is the “contact angle”. When a fluid-drop is placed on a solid surface, in the presence of a second, surrounding fluid, the fluid-fluid surface contacts the solid-surface at an angle that is typically measured through the fluid-drop. If this angle is less than 90°, the fluid in the drop is said to “wet” the surface. If this angle is greater than 90°, the surrounding fluid is said to “wet” the surface. This definition is universally accepted and appears to be scientifically justifiable, at least for a static situation where the solid surface is horizontal. Recently, this concept has been extended to characterize wettability in non-static situations using high-resolution, two-dimensional digital images of multi-component systems. Using simple thought experiments and published experimental results, many of them decades old, it will be demonstrated that contact angles are not primary parameters – their values depend on many other parameters. Using these arguments, it will be demonstrated that contact angles are not the cause of wettability behavior but the effect of wettability behavior and other parameters. The result of this is that the contact angle cannot be used as a primary indicator of wettability except in very restricted situations. Furthermore, it will be demonstrated that even for the simple case of a capillary interface in a vertical tube, attempting to use simply a two-dimensional image to determine the contact angle can result in a wide range of measured values. This observation is consistent with some published experimental results. It follows that contact angles measured in two-dimensions cannot be trusted to provide accurate values and these values should not be used to characterize the wettability of the system.

Nonlinear instability of plane liquid sheets

2000 ◽  
Vol 406 ◽  
pp. 281-308 ◽  
Author(s):  
SEYED A. JAZAYERI ◽  
XIANGUO LI
Keyword(s):  
Weber Number ◽  
Density Ratio ◽  
Perturbation Expansion ◽  
Liquid Sheet ◽  
Fundamental Wave ◽  
Liquid Density ◽  
Initial Amplitude ◽  
Nonlinear Stability Analysis ◽  
Liquid Sheets ◽  
Breakup Time

A nonlinear stability analysis has been carried out for plane liquid sheets moving in a gas medium at rest by a perturbation expansion technique with the initial amplitude of the disturbance as the perturbation parameter. The first, second and third order governing equations have been derived along with appropriate initial and boundary conditions which describe the characteristics of the fundamental, and the first and second harmonics. The results indicate that for an initially sinusoidal sinuous surface disturbance, the thinning and subsequent breakup of the liquid sheet is due to nonlinear effects with the generation of higher harmonics as well as feedback into the fundamental. In particular, the first harmonic of the fundamental sinuous mode is varicose, which causes the eventual breakup of the liquid sheet at the half-wavelength interval of the fundamental wave. The breakup time (or length) of the liquid sheet is calculated, and the effect of the various flow parameters is investigated. It is found that the breakup time (or length) is reduced by an increase in the initial amplitude of disturbance, the Weber number and the gas-to-liquid density ratio, and it becomes asymptotically insensitive to the variations of the Weber number and the density ratio when their values become very large. It is also found that the breakup time (or length) is a very weak function of the wavenumber unless it is close to the cut-off wavenumbers.

Modeling of Gas Turbine Fuel Nozzle Spray

1997 ◽  
Vol 119 (1) ◽  
pp. 34-44 ◽  
Author(s):  
N. K. Rizk ◽  
J. S. Chin ◽  
M. K. Razdan
Keyword(s):  
Gas Turbine ◽  
Fuel Injection ◽  
Near Field ◽  
Continuous Phase ◽  
Liquid Sheet ◽  
Vapor Concentration ◽  
Fuel Vapor ◽  
Fuel Injector ◽  
Gas Temperature ◽  
Sheet Breakup

Satisfactory performance of the gas turbine combustor relies on the careful design of various components, particularly the fuel injector. It is, therefore, essential to establish a fundamental basis for fuel injection modeling that involves various atomization processes. A two-dimensional fuel injection model has been formulated to simulate the airflow within and downstream of the atomizer and address the formation and breakup of the liquid sheet formed at the atomizer exit. The sheet breakup under the effects of airblast, fuel pressure, or the combined atomization mode of the airassist type is considered in the calculation. The model accounts for secondary breakup of drops and the stochastic Lagrangian treatment of spray. The calculation of spray evaporation addresses both droplet heat-up and steady-state mechanisms, and fuel vapor concentration is based on the partial pressure concept. An enhanced evaporation model has been developed that accounts for multicomponent, finite mass diffusivity and conductivity effects, and addresses near-critical evaporation. The presents investigation involved predictions of flow and spray characteristics of two distinctively different fuel atomizers under both nonreacting and reacting conditions. The predictions of the continuous phase velocity components and the spray mean drop sizes agree well with the detailed measurements obtained for the two atomizers, which indicates the model accounts for key aspects of atomization. The model also provides insight into ligament formation and breakup at the atomizer exit and the initial drop sizes formed in the atomizer near field region where measurements are difficult to obtain. The calculations of the reacting spray show the fuel-rich region occupied most of the spray volume with two-peak radial gas temperature profiles. The results also provided local concentrations of unburned hydrocarbon (UHC) and carbon monoxide (CO) in atomizer flowfield, information that could support the effort to reduce emission levels of gas turbine combustors.

Experimental Studies on Cooling Effectiveness of the Double-Decker Air Jet Impingement With Film Outflow

2007 ◽  
Author(s):  
Junkui Mao ◽  
Wen Guo ◽  
Zhenxiong Liu ◽  
Jun Zeng
Keyword(s):  
Infrared Radiation ◽  
Experimental Studies ◽  
Jet Impingement ◽  
Experimental Results ◽  
Thermal Camera ◽  
Local Cooling ◽  
Cooling Effectiveness ◽  
Air Jet ◽  
Double Decker ◽  
Wide Range

Experiments were carried out to investigate the cooling effectiveness of a lamellar double-decker impingement/effusion structure. Infrared radiation (I.R.) thermal camera was used to measure the temperature on the outside surface of the lamellar double-decker. Experimental results were obtained for a wide range of governing parameters (blowing rate M (0.0017∼0.0066), the ratio of the jet impingement distance to the diameter of film hole H/D (0.5∼1.25), the ratio of the distance between the jet hole and film hole to the diameter of the film hole P/D (0, 3, 4), and the material of double-decker (Steel and Copper)). It was observed that the local cooling effectiveness η varies with all these parameters in a complicated way. All the results show that higher cooling effectiveness η is achieved in larger blowing rate cases. A certain range of H/D and P/D can be designed to result in the maximum cooling effectiveness η. And η is less sensitive to the material type compared with those parameters such as H/D, M and P/D.

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.

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