NUMERICAL STUDY OF SCALE AND SHAPE PARAMETERS OF DROPLET-SIZE DISTRIBUTION IN AIR-ASSISTED ATOMIZER

The article is devoted to the development of approach to study the atomization in an air-assisted atomizer by the volume- of-fluid method. Received through the simulations in the axisymmetric swirl approximation, the ligament-size distributions were approximated by the translated Weibull distribution, which is determined by the scale, shape and location parameters. The dependences of the latter two parameters on the surface tension, viscosity, density and flow rate of the atomized liquid are a subject of this research. Since the problem hasn’t been well studied before, there is no convenient approach to determine the location parameter and as a result, we use two ways to find it. The first one is by changing the parameters of the translated Weibull distribution with aim to fit the ligament-size distribution as best as possible. The second one is by equating the location parameter to the minimal ligament size where the ligament-size distribution is zero. The choice of the approach not only changes values of the parameters, but also leads to appearance or disappearance of the dependence of the location parameter on the properties of the atomized liquid. Nevertheless, if the very weak decrease of the shape parameter on the surface tension is neglected, this parameter of the Weibull distribution doesn’t depend on the parameters of the liquid. Moreover, this conclusion is the same for both approach to determine the location parameter.

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Dropwise condensation of low surface tension fluids on lubricant-infused surfaces: Droplet size distribution and heat transfer

International Journal of Heat and Mass Transfer ◽

10.1016/j.ijheatmasstransfer.2021.121149 ◽

2021 ◽

Vol 172 ◽

pp. 121149

Author(s):

J.Y. Ho ◽

K.F. Rabbi ◽

S. Sett ◽

T.N. Wong ◽

N. Miljkovic

Keyword(s):

Heat Transfer ◽

Surface Tension ◽

Size Distribution ◽

Droplet Size ◽

Droplet Size Distribution ◽

Dropwise Condensation

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Numerical Study of the Effects of Droplet Size Distribution on Fuel Transport and Air-Fuel Mixing in a Gasoline Direct-Injection Engine

10.4271/2003-01-3100 ◽

2003 ◽

Cited By ~ 1

Author(s):

Edwin Y. L. Yeoh ◽

Martin H. Davy

Keyword(s):

Size Distribution ◽

Droplet Size ◽

Numerical Study ◽

Direct Injection ◽

Droplet Size Distribution ◽

Gasoline Direct Injection ◽

Direct Injection Engine ◽

Gasoline Direct Injection Engine ◽

Fuel Mixing

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Breakage, coalescence and size distribution of surfactant-laden droplets in turbulent flow

Journal of Fluid Mechanics ◽

10.1017/jfm.2019.772 ◽

2019 ◽

Vol 881 ◽

pp. 244-282 ◽

Cited By ~ 8

Author(s):

Giovanni Soligo ◽

Alessio Roccon ◽

Alfredo Soldati

Keyword(s):

Surface Tension ◽

Turbulent Flow ◽

Size Distribution ◽

Droplet Size Distribution ◽

Lower Surface ◽

Field Method ◽

Phase Field Method ◽

Shear Stresses ◽

Elasticity Number ◽

Surface Tension Forces

In this work, we compute numerically breakage/coalescence rates and size distribution of surfactant-laden droplets in turbulent flow. We use direct numerical simulation of turbulence coupled with a two-order-parameter phase-field method to describe droplets and surfactant dynamics. We consider two different values of the surface tension (i.e. two values for the Weber number, $We$, the ratio between inertial and surface tension forces) and four types of surfactant (i.e. four values of the elasticity number, $\unicode[STIX]{x1D6FD}_{s}$, which defines the strength of the surfactant). Stretching, breakage and merging of droplet interfaces are controlled by the complex interplay among shear stresses, surface tension and surfactant distribution, which are deeply intertwined. Shear stresses deform the interface, changing the local curvature and thus surface tension forces, but also advect surfactant over the interface. In turn, local increases of surfactant concentration reduce surface tension, changing the interface deformability and producing tangential (Marangoni) stresses. Finally, the interface feeds back to the local shear stresses via the capillary stresses, and changes the local surfactant distribution as it deforms, breaks and merges. We find that Marangoni stresses have a major role in restoring a uniform surfactant distribution over the interface, contrasting, in particular, the action of shear stresses: this restoring effect is proportional to the elasticity number and is stronger for smaller droplets. We also find that lower surface tension (higher $We$ or higher $\unicode[STIX]{x1D6FD}_{s}$) increases the number of breakage events, as expected, but also the number of coalescence events, more unexpected. The increase of the number of coalescence events can be traced back to two main factors: the higher probability of inter-droplet collisions, favoured by the larger number of available droplets, and the decreased deformability of smaller droplets. Finally, we show that, for all investigated cases, the steady-state droplet size distribution is in good agreement with the $-10/3$ power-law scaling (Garrett et al., J. Phys. Oceanogr., vol. 30 (9), 2000, pp. 2163–2171), conforming to previous experimental observations (Deane & Stokes, Nature, vol. 418 (6900), 2002, p. 839) and numerical simulations (Skartlien et al., J. Chem. Phys., vol. 139 (17), 2013).

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Numerical study on pre-film atomization mechanism and characteristics by a coaxial swirl injector

Proceedings of the Institution of Mechanical Engineers Part A Journal of Power and Energy ◽

10.1177/0957650919844045 ◽

2019 ◽

Vol 233 (8) ◽

pp. 1022-1038

Author(s):

Qun Zhang ◽

Xin Wang ◽

Rui Kou ◽

Chaochao Li ◽

Peng Zhang ◽

...

Keyword(s):

Liquid Film ◽

Size Distribution ◽

Droplet Size ◽

Numerical Study ◽

Droplet Size Distribution ◽

Venturi Tube ◽

Experimental Results ◽

Two Stage ◽

Spray Cone ◽

Fuel Flow

The overall process and mechanism of the centrifugal pre-film atomization with double swirling flow were studied using the methods of large Eddy simulation and volume of fluid. The atomization process includes a centrifugal jet under the primary swirl and a pre-film atomization under the two-stage counter-rotating swirl at the venturi outlet. The fuel is ejected from the outlet of the centrifugal nozzle and undergoes the transient process of reaching the venturi throat. The breaking mechanism of liquid film in this process is the same as that of the formation mechanism of the mushroom-shaped tip of liquid jet. The numerical simulation results are highly consistent with the experimental results. For the formation and development of the liquid film on the venturi wall, collision and wave action promote the expansion of the liquid film. At the outlet position of the venturi tube, the short wave mode and the two-stage reverse swirling structure play major roles in the fragmentation process of the flake liquid film, which coincides with the flow characteristics given by the experiment. It is found that the spray cone angle increases as the fuel flow rate increases, and the numerical results are basically consistent with the predicted values of the empirical formula under different fuel flow rates. The droplet size distribution showed a Poisson distribution during the atomization of centrifugal jets and pre-film, and the peak position and variation trend of the droplet size distribution at the outlet of the venturi tube were basically consistent with experimental results.

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