Droplet collision dynamics

M. Richer, A. Frohn. Navier-Stokes simulation of droplet collision dynamics. In Proceedings of the 7th ISCFD in Beijing, China, 1997 (to be published). 

T. Inamuro, S. Tajima, F. Ogino Lattice Boltzmann simulation of droplet collision dynamics, Int. J. Heat Mass Transfer 47, 4649 657 (2004). 

Chandra and Avedisian 411] studied the collision dynamics of a liquid (n-heptane) droplet on a polished, solid, stainless steel surface, and on a liquid film created by deposition of a preceding droplet using a flash photographic method. They presented a comprehensive series of clear images of droplet shape, morphology, and structure during the deformation process. In their experiments, the... 

Ashgriz, N. and Givi, P. (1987). Binary collision dynamics of fuel droplets. Inter. J. Heat Fluid Flow, 8 205-210. 

One alternative to solving the equations of change of continuum mechanics for simulating droplet collisions is the lattice-Boltzmann approach [63-67]. This technique describes the liquid dynamics on the basis of the dynamics of particle motion, which represents the liquid dynamic behavior and is governed by the lattice-Boltzmann... 

C. K. Law Dynamics of droplet collision. Proceedings of the lUTAM Symposium Mechanics and Combustion of Droplets and Sprays, Tainan, Taiwan, pp. 99-118 (1994). 

B. Sakakibara, T. Inamuro Lattice Boltzmann simulation of collision dynamics of two unequal-size droplets, Int. J. Heat Mass Transfer 51, 3207-3216 (2008). 

Figure 6.12 illustrates the various processes that occur during emulsification Break up of droplets, adsorption of surfactants and droplet collision (which may or may not lead to coalescence) [8]. Each of these processes occurs numerous times during emulsification and the time scale of each process is very short, typically a microsecond. This shows that the emulsification is a dynamic process and events that occur in a microsecond range could be very important. 

In this work, we have investigated binary collisions of shear-thinning, non-isoviscous, and viscoelastic droplets by means of DNS with the VOF-code FS3D. Our aim is to tmderstand the influence of the liquid rheology on the collision outcome as well as on the flow dynamics inside the collision complex and to give an improved prediction of the outcome of droplet collisions. 

The algorithm of lamella stabilization is a key technique in the numerical simulation. At high Weber numbers extremely thin lamellae appear in droplet collisions. If an insufficient fine mesh is used in the simulatimi, the lamella can rupture which leads to wrong results. The idea to circumvent the problem is to prevent the curvature computation in the lamella region from being affected by the opposite lamella surface. Both in the cases of head-on and off-center collisions, our developed algorithm of lamella stabilization avoids the numerical rupture of a lamella and is able to capture the collision dynamics in agreement with experiment. 

Multiscale descriptions of particle-droplet interactions in spray processing of composite particles are realized based on Multiphase Computational Fluid Dynamics (M-CFD) models, in which processes such as liquid atomization and particle-droplet mixing spray (macro-scale), particle-droplet collision (mesoscale), and particle penetration into droplet (micro-scale) are taken into account as shown in Fig. 18.52. Thereby, the incorporation efficiency and sticking efficiency of solid particles in matrix particles are correlated with the operatiOTi conditions and material properties. 

Pan and Suga [171], for example, performed 3D dynamic simulations of binary droplets collisions for cases of different Weber numbers and impact parameters. The systems used are water drops in air and tetradecane drops in nitrogen at atmospheric conditions. The bulk fluids are considered incompressible. The simulations cover the four major regimes of binary collision bouncing, coalescence, reflexive separation. 

IV. System 2 Deformation Dynamics of Liquid Droplet in Collision with a Particle with Film-Boiling Evaporation... 

Ge and Fan (2005) developed a 3-D numerical model based on the level-set method and finite-volume technique to simulate the saturated droplet impact on a superheated flat surface. A 2-D vapor-flow model was coupled with the heat-transfer model to account for the vapor-flow dynamics caused by the Leidenfrost evaporation. The droplet is assumed to be spherical before the collision and the liquid is assumed to be incompressible. 

Detailed modeling study of practical sprays has a fairly short history due to the complexity of the physical processes involved. As reviewed by O Rourke and Amsden, 3l() two primary approaches have been developed and applied to modeling of physical phenomena in sprays (a) spray equation approach and (b) stochastic particle approach. The first step toward modeling sprays was taken when a statistical formulation was proposed for spray analysis. 541 Even with this simplification, however, the mathematical problem was formidable and could be analyzed only when very restrictive assumptions were made. This is because the statistical formulation required the solution of the spray equation determining the evolution of the probability distribution function of droplet locations, sizes, velocities, and temperatures. The spray equation resembles the Boltzmann equation of gas dynamics[542] but has more independent variables and more complex terms on its right-hand side representing the effects of nucleations, collisions, and breakups of droplets. 

For percolating microemulsions, the second and the third types of relaxation processes characterize the collective dynamics in the system and are of a cooperative nature. The dynamics of the second type may be associated with the transfer of an excitation caused by the transport of electrical charges within the clusters in the percolation region. The relaxation processes of the third type are caused by rearrangements of the clusters and are associated with various types of droplet and cluster motions, such as translations, rotations, collisions, fusion, and fission [113,143]. 

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