Dynamics of internal jets in the merging of two droplets of unequal sizes

Tang, Chenglong; Zhao, Jiaquan; Zhang, Peng; Law, Chung K.; Huang, Zuohua

doi:10.1017/jfm.2016.218

Cited by 47 publications

(56 citation statements)

References 30 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: 58%

“…Another important aspect of droplet coalescence is the subsequent internal mixing, which has gained increasing attentions in recent years for its relevance in the microfluidics and hypergolic propellant systems involving liquid-phase reactions [32][33][34][35][36][37][38] . An important understanding gained from the recent studies is that the internal mixing is minimal for the head-on collision of two identical droplets due to the intrinsic symmetry across the collision plane.…”

Section: Collision Dynamics and Internal Mixing Of Dropletsmentioning

confidence: 99%

“…Tang et al . [37] investigated experimentally and numerically the internal mixing of unequal-size droplets and identified the jet-like mixing patterns varying with We and , as shown in Fig. 2 .…”

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: 58%

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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“…Turbulent internal flow can improve mixing, but is difficult to generate and sustain at typical droplet length scales. Laminar internal flows can include complex flow structures, such as internal jets, that are crucial for enabling efficient mixing within passively mixed systems [11][12][13].…”

Section: Introductionmentioning

confidence: 99%

Surface jets and internal mixing during the coalescence of impacting and sessile droplets

Sykes

Castrejón‐Pita

et al. 2020

Phys. Rev. Fluids

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The internal dynamics during the coalescence of a sessile droplet and a subsequently deposited impacting droplet, with either identical or distinct surface tension, is studied experimentally in the regime where surface tension is dominant. Two color high-speed cameras are used to capture the rapid internal flows and associated mixing from both side and bottom views simultaneously by adding an inert dye to the impacting droplet. Given sufficient lateral separation between droplets of identical surface tension, a robust surface jet is identified on top of the coalesced droplet. Image processing shows this jet is the result of a surface flow caused by the impact inertia and an immobile contact line. By introducing surface tension differences between the coalescing droplets, the surface jet can be either enhanced or suppressed via a Marangoni flow. The influence of the initial droplet configuration and relative surface tension on the long-term dynamics and mixing efficiency, plus the implications for emerging applications such as reactive inkjet printing, are also considered. * mm13tcs@leeds.ac.uk † M.Wilson@leeds.ac.uk

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“…For the highly viscous droplets, noticeable mixing was however not observed in their experiments, and instead, the smaller droplet simply lodges onto the larger droplet after coalescence. Recently, Tang et al 10 experimentally investigated the coalescence of two unequal-sized droplets with nonzero Weber numbers and observed the non-monotonic emergence of the jet-like mixing with increasing . Specifically, the jet-like mixing emerged at small s, in accordance with previous observations for initially stationary droplet coalescence 30,31 , but such a mixing was absent at higher s as the increased droplet deformation absorbed the impact energy and therefore suppressed the jet formation.…”

Section: Introductionmentioning

confidence: 99%

Vortex-ring-induced internal mixing upon the coalescence of initially stationary droplets

Xia

et al. 2017

Phys. Rev. Fluids

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This study employs an improved volume of fluid method and adaptive mesh refinement algorithm to numerically investigate the internal jet-like mixing upon the coalescence of two initially stationary droplets of unequal sizes. The emergence of the internal jet is attributed to the formation of a main vortex ring, as the jet-like structure shows a strong correlation with the main vortex ring inside the merged droplet. By tracking the evolution of the main vortex ring together with its circulation, we identified two mechanisms that are essential to the internal-jet formation: the vortex-ring growth and the vortex-ring detachment. Recognizing that the manifestation of the vortex-ring-induced jet physically relies on the competition between the convection and viscous dissipation of the vortex ring, we further developed and substantiated a vortex-ring-based Reynolds number ( = /4 ) criterion, where is the circulation of the detached main vortex ring and is the liquid kinematic viscosity, to interpret the occurrence of the internal jet at various Ohnesorge numbers and size ratios. For the merged droplet with apparent jet formation, the average mixing rate after jet formation increases monotonically with , which therefore serves as an approximate measure of the jet strength. In this respect, stronger internal jet is responsible for enhanced mixing of the merged droplet. _____________________________a) The first and second authors contributed equally to this work. b) Author to whom correspondence should be addressed. Electronic

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Dynamics of internal jets in the merging of two droplets of unequal sizes

Cited by 47 publications

References 30 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

Surface jets and internal mixing during the coalescence of impacting and sessile droplets

Vortex-ring-induced internal mixing upon the coalescence of initially stationary droplets

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