Experimental investigation of water droplet binary collisions and description of outcomes with a symmetric Weber number

Rabe, Christophe; Malet, J.; Feuillebois, François

doi:10.1063/1.3392768

Cited by 78 publications

(71 citation statements)

References 12 publications

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“…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%

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: 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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“…Interestingly, all VOF simulations for water droplets (Saroka et al 2012) of different size are clustered above the correlation, which indicates that some phenomena are not captured properly by these simulations. 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).…”

Section: Characteristic Points In the Collision Mapsmentioning

confidence: 57%

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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“…with vd , a viscous dissipation coefficient, found experimentally to be equal to 0.92 and with dimensionless number ref/stre that is found to be 0.28 according to experimental results (Rabe, 2010). These three models describing the transition curves between collision regimes are described more in detail in Rabe (2010).…”

Section: Modelling Of Droplet Polydispersionmentioning

confidence: 99%

“…Rabe et al [27] proposed simple formulae expressing the boundaries of collision outcomes fields as a function of the symmetric Weber number. The final equation for the critical impact parameter ( represents the impact parameter for which the transition between two regimes is observed) at which the transition between reflexive separation and coalescence occurs is then Based on another balance of energies, the critical impact parameter for the transition between coalescence and stretching separation can be expressed as stre-coal = √We 2 stre + 8We stre We − We stre 4We…”

Section: Modelling Of Droplet Polydispersionmentioning

confidence: 99%

See 1 more Smart Citation

Dispersed Two-Phase Flow Modelling for Nuclear Safety in the NEPTUNE_CFD Code

Mimouni

Benguigui

Fleau

et al. 2017

Science and Technology of Nuclear Installations

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The objective of this paper is to give an overview of the capabilities of Eulerian bifluid approach to meet the needs of studies for nuclear safety regarding hydrogen risk, boiling crisis, and pipes and valves maintenance. The Eulerian bifluid approach has been implemented in a CFD code named NEPTUNE CFD. NEPTUNE CFD is a three-dimensional multifluid code developed especially for nuclear reactor applications by EDF, CEA, AREVA, and IRSN. The first set of models is dedicated to wall vapor condensation and spray modelling. Moreover, boiling crisis remains a major limiting phenomenon for the analysis of operation and safety of both nuclear reactors and conventional thermal power systems. The paper aims at presenting the generalization of the previous DNB model and its validation against 1500 validation cases. The modelling and the numerical simulation of cavitation phenomena are of relevant interest in many industrial applications, especially regarding pipes and valves maintenance where cavitating flows are responsible for harmful acoustics effects. In the last section, models are validated against experimental data of pressure profiles and void fraction visualisations obtained downstream of an orifice with the EPOCA facility (EDF R&D). Finally, a multifield approach is presented as an efficient tool to run all models together.

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Experimental investigation of water droplet binary collisions and description of outcomes with a symmetric Weber number

Cited by 78 publications

References 12 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

Dispersed Two-Phase Flow Modelling for Nuclear Safety in the NEPTUNE_CFD Code

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