Bouncing, coalescence, and separation in head-on collision of unequal-size droplets

Tang, Chenglong; Zhang, Peng; Law, Chung K.

doi:10.1063/1.3679165

Cited by 126 publications

(135 citation statements)

References 15 publications

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“…The dominant phenomena in this stage are droplet collision, coalescence and deformation, which are similar to those observed in the collision of two nonreactive droplets [25,37] . A slightly dark "tail" behind the WFNA droplet is the shadow of NA vapor, which is negligible during this stage because of the relatively low droplet temperature and the short time.…”

Section: Descriptions Of Ignition Phenomenasupporting

confidence: 59%

“…Previous studies [25][26][27] have demonstrated that droplet separation is suppressed and hence droplet coalescence is promoted by increasing the size ratio. It is known that droplet separation occurs, at relatively high Weber numbers, when the surface tension of the temporarily coalesced droplet cannot hold the excess kinetic energy of the collision.…”

Section: Collision Dynamics and Internal Mixing Of Dropletsmentioning

confidence: 99%

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Hypergolic ignition by head-on collision of N,N,N′,N′ −tetramethylethylenediamine and white fuming nitric acid droplets

Zhang

Yuan

et al. 2016

Combustion and Flame

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a b s t r a c tHypergolic ignition by the head-on collision of a smaller N,N,N ,N −tetramethylethylenediamine (TMEDA) droplet and a larger white fuming nitric acid (WFNA) droplet was experimentally investigated by using a droplet collision experimental apparatus equipped with a time-resolved shadowgraph, a photodetector and an infrared detector. The investigation was focused on understanding the influence of droplet collision and mixing, which vary with the collisional Weber number ( We = 20 −220) and the droplet size ratio ( = 1.2 −2.9) while have a fixed Ohnesorge number (Oh = 2.5 ×10 −3 ), on the hypergolic ignitability and the ignition delay times. The hypergolic ignition was found to critically rely on the heat release from of the liquid-phase reaction of TMEDA and nitric acid, which is subsequent to and enhanced by the effective mixing of the droplets of proper size ratios. Consequently, the ignitability regime nomogram in the We-space shows that the hypergolic ignition favors small s and large We s; the ignition delay times tend to decrease with either decreasing , or increasing We , or both. A non-monotonic variation of the ignition delay times with We was observed and attributed to the non-monotonic emergence of jet-like mixing patterns that enhance the droplet mixing and hence the liquid-phase reaction.

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Section: Descriptions Of Ignition Phenomenasupporting

confidence: 59%

Section: Collision Dynamics and Internal Mixing Of Dropletsmentioning

confidence: 99%

Hypergolic ignition by head-on collision of N,N,N′,N′ −tetramethylethylenediamine and white fuming nitric acid droplets

Zhang

Yuan

et al. 2016

Combustion and Flame

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“…With decreasing size ratio the boundary line is shifted remarkably to the right, to higher We. However, this is not in accordance with the studies of Tang et al (2012) where  = 0.4 results in a shift to Wec ~ 40. A shift of this boundary line to the right was also observed by Kuschel and Sommerfeld (2013) and Sommerfeld and Kuschel (2016) when increasing the dynamic viscosity of the liquid, similar to the work of Gotaas et al (2007).…”

Section: Theoretical Boundary Linescontrasting

confidence: 53%

“…One result of Rabe et al (2010) for different sized water droplets is also found in this region. This point is just included for illustrating the fact that decreasing size ratio yields a shift of the triple point as well as Wec to the right (see Tang et al 2012). The data points for the Diesel/water emulsion droplets are initially above and for higher water content, and hence larger viscosity, below the correlation, which suggests a slightly lower slope of such correlation (Chen et al 2017).…”

Section: Characteristic Points In the Collision Mapsmentioning

confidence: 99%

Numerical analysis of sprays with an advanced collision model

Sommerfeld

Laı́n

2017

Proceedings ILASS–Europe 2017. 28th Conference on Liquid Atomization and Spray Systems

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Modelling of collisions between liquid droplets in the frame of a Lagrangian spray simulation has still many open issues, especially when considering higher viscous droplets and if colliding droplets have a large size difference. A generalisation of the collision maps is attempted based on the behaviour of characteristic points, namely the triple point where bouncing, coalescence and stretching separation coincide and the critical Weber-number where reflexive separation first occurs in head-on collisions. This is done by correlating experimental data with respect to the Capillary number with the Ohnesorge-number for the triple point and the critical Weber-number is also well described by a correlation the Ohnesorge-number. Based on these results the boundary line between stretching separation and coalescence is found by adapting the Jiang et al. (1992) correlation. For the upper boundary of reflexive separation the shifted Ashgriz and Poo (1990) correlation is used. It was however so far not possible to predict the lower bouncing boundary through the Estrade et al. (1999) boundary line correctly. The proposed boundary-line models were validated for various liquid, however still considering only a size ratio of one. With the developed three-line boundary model Euler/Lagrange numerical calculations for a simple spray system were conducted and the droplet collisions were analysed with respect to their occurrence. Droplet collision modelling is performed on the basis of the stochastic droplet collision model, also considering the influence of impact efficiency, which so far was neglected for most spray simulations. The comparison with measurements showed reasonable good agreement for all properties. KeywordsDroplet collisions, stochastic collision model, impact efficiency, collision outcomes, Euler/Lagrange calculations, spray simulations. IntroductionIn numerous technical and industrial spraying systems higher viscous liquids, suspensions or solutions are being atomised. Examples are liquid fuels (including bio-fluids) in combustion systems, liquid melts or other mineral melts in the field of materiel science and spray drying of foodstuff or pharmaceutical materials. Therefore, in a numerical calculation of such spraying systems, mostly done with an Euler/Lagrange approach, the resulting different liquid properties have to be accounted for. Here the focus is related to droplet collision modelling. Hence, established droplet collision models have to be generalized regarding liquid properties, mainly viscosity and surface tension. Since colliding droplets may have considerable different size also the droplet size ratio is an important parameter to be considered in droplet collision modelling. In order to model droplet collisions in the frame of the Lagrangian droplet parcel concept, where only pointmasses are tracked, applied to spraying systems several elementary processes have to be considered (Sommerfeld and Kuschel 2016). The first step is the detection of possible collisions between two droplets. In orde...

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“…A similar variety of processes is observed for colliding drops: they can merge (minimizing their surface energy) if the impact is slow and well-centred. But air between them does not always have the time to escape during the shock, so that they can also bounce off each other (Tang, Zhang & Law 2012) -an effect recently exploited to generate levitation of drops on a bath of the same liquid, by shaking the bath at high enough frequency and acceleration (Couder et al 2005).…”

Section: Introductionmentioning

confidence: 99%

Water colliding with oil

Quéré

2012

J. Fluid Mech.

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The collision of two liquid drops is both an applied question (in rain formation or combustion, for example) and a beautiful basic situation, where impact involves liquid phases, making this problem worth studying in its own right. In a stimulating paper, Planchette, Lorenceau & Brenn (J. Fluid Mech., this issue, vol. 702, 2012, pp. 5-25) consider collisions between oil and water, which often lead to water drops protected by a shell of oil. By looking at the deformations during impact, they characterize the dynamical conditions leading to single encapsulation, and derive a criterion for avoiding fragmentation.

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Bouncing, coalescence, and separation in head-on collision of unequal-size droplets

Cited by 126 publications

References 15 publications

Hypergolic ignition by head-on collision of N,N,N′,N′ −tetramethylethylenediamine and white fuming nitric acid droplets

Hypergolic ignition by head-on collision of N,N,N′,N′ −tetramethylethylenediamine and white fuming nitric acid droplets

Numerical analysis of sprays with an advanced collision model

Water colliding with oil

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