A new model for the bouncing regime boundary in binary droplet collisions

Al-Dirawi, Karrar H.; Bayly, Andrew E.

doi:10.1063/1.5085762

Cited by 36 publications

(29 citation statements)

References 21 publications

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“…Our experimental set-up and methodology are described in detail by Al-Dirawi & Bayly (2019, 2020). Briefly, fluid was driven through custom-made monodisperse (110, 160 and 210 m) nozzles to create a continuous jet; square-wave signals applied to piezos built into the nozzle caused the jet to breakup into a stream of equal-sized droplets.…”

Section: Experimental Methodsmentioning

confidence: 99%

Inertial stretching separation in binary droplet collisions

et al. 2021

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Binary droplet collisions exhibit a wide range of outcomes, including coalescence and stretching separation, with a transition between these two outcomes arising for high Weber numbers and impact parameters. Our experimental study elucidates the effect of viscosity on this transition, which we show exhibits inertial (viscosity-independent) behaviour over an order-of-magnitude-wide range of Ohnesorge numbers. That is, the transition is not always shifted towards higher impact parameters by increasing droplet viscosity, as it might be thought from the existing literature. Moreover, we provide compelling experimental evidence that stretching separation only arises if the length of the coalesced droplet exceeds a critical multiple of the original droplet diameters (3.35). Using this as a criterion, we provide a simple but robust model (without any arbitrarily chosen free parameters) to predict the coalescence/stretching-separation transition.

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Section: Experimental Methodsmentioning

confidence: 99%

Inertial stretching separation in binary droplet collisions

et al. 2021

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“…Naturally, this diagram is not unique and different combinations of the liquid and gas properties (e.g., drop viscosity, type of liquids, ambient gas pressure, etc.) lead to different collision maps [226,[262][263][264][265][266].…”

Section: Drop Size Distribution and Advancementsmentioning

confidence: 99%

Turbulent Flows With Drops and Bubbles: What Numerical Simulations Can Tell Us—Freeman Scholar Lecture

Soligo

Roccon

Soldati

2021

Journal of Fluids Engineering

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Turbulent flows laden with large, deformable drops or bubbles are ubiquitous in nature and in a number of industrial processes. These flows are characterized by a physics acting at many different scales: from the macroscopic length scale of the problem down to the microscopic molecular scale of the interface. Naturally, the numerical resolution of all the scales of the problem, which span about eight to nine orders of magnitude, is not possible, with the consequence that numerical simulations of turbulent multiphase flows impose challenges and require methods able to capture the multi-scale nature of the flow. In this review, we start by describing the numerical methods commonly employed and discussing their advantages and limitations, and then we focus on the issues arising from the limited range of scales that can be possibly solved. Ultimately, the droplet size distribution, a key result of interest for turbulent multiphase flows, is used as a benchmark to compare the capabilities of the different methods and to discuss the main insights that can be drawn from these simulations. Based on this, we define a series of guidelines and best practices that we believe important in the simulation analysis and in the development of new numerical methods.

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“…Droplet collisions have been extensively studied in past decades (Ashgriz & Poo 1990;Jiang, Umemura & Law 1992;Qian & Law 1997;Estrade et al 1999;Brenn, Valkovska, & Danov 2001;Pan, Law & Zhou 2008;Pan, Chou & Tseng 2009;Zhang & Law 2011;Tang, Zhang, & Law 2012;Kwakkel, Breugem, & Boersma 2013;Huang & Pan 2015;Li 2016;Pan et al 2016Pan et al , 2019Sommerfeld & Kuschel 2016;Hu et al 2017;Al-Dirawi & Bayly 2019;Huang, Pan & Josserand 2019;Chubynsky et al 2020) due to significant relevance to a variety of systems in natural and technological situations. Examples are seen in raindrop formation (Gunn 1965;Strangeways 2006), medical therapy (May 1973;Feng et al 2016), disease transmission (Tellier 2009;Gralton et al 2011) and combustion processes in engines (Chiu 2000;Zhang et al 2016).…”

Section: Introductionmentioning

confidence: 99%

Transitions of bouncing and coalescence in binary droplet collisions

Huang

Pan

2021

J. Fluid Mech.

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In droplet impacts, transitions between coalescence and bouncing are determined by complex interplays of multiple mechanisms dominating at various length scales. Here we investigate the mechanisms and governing parameters comprehensively by experiments and scaling analyses, providing a unified framework for understanding and predicting the outcomes when using different fluids. Specifically, while bouncing had not been observed in head-on collisions of water drops under atmospheric conditions, it was found in our experiments to appear on increasing the droplet diameter sufficiently. Contrarily, while bouncing was always observed in head-on impacts of alkane drops, we found it to disappear on decreasing the diameter sufficiently. The variations are related to gas draining dynamics in the inter-droplet film and suggest an easier means for controlling bouncing as compared to alternating the ambient pressure usually sought. The scaling analysis further shows that for a given Weber number, enlarging droplet diameter or fluid viscosities, or lowering surface tension contributes to a larger characteristic minimum thickness of the gas film, thus enhancing bouncing. The key dimensionless group $(O{h_{g,l}},\;O{h_l},\;{A^\ast })$ is identified, referred to as the two-phase Ohnesorge number, the Ohnesorge number of liquid and the Hamaker constant, respectively. Our thickness-based model indicates that as ${h^{\prime}_{m,c}} > 21.1{h_{cr}}$ , where ${h^{\prime}_{m,c}}$ is the maximum value of the characteristic minimum film thickness $({h_{m,c}})$ and ${h_{cr}}$ is the critical thickness, bouncing occurs in both head-on and off-centre collisions. That is, when $1.2O{h_{g,l}}/(1 - 2O{h_l}) > \sqrt[3]{{{A^\ast }}}$ , a fully developed bouncing regime occurs, thereby yielding a lower coalescence efficiency. The transitional Weber number is found universally to be 4.

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A new model for the bouncing regime boundary in binary droplet collisions

Cited by 36 publications

References 21 publications

Inertial stretching separation in binary droplet collisions

Inertial stretching separation in binary droplet collisions

Turbulent Flows With Drops and Bubbles: What Numerical Simulations Can Tell Us—Freeman Scholar Lecture

Transitions of bouncing and coalescence in binary droplet collisions

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