Bulletin of the American Physical Society
72nd Annual Meeting of the APS Division of Fluid Dynamics
Volume 64, Number 13
Saturday–Tuesday, November 23–26, 2019; Seattle, Washington
Session B22: Drops: Coalescence II |
Hide Abstracts |
Chair: Kyoo-Chul Park, Northwestern University Room: 604 |
Saturday, November 23, 2019 4:40PM - 4:53PM |
B22.00001: Droplet Encapsulation Vatsal Sanjay, Utkarsh Jain, Maziyar Jalaal, Devaraj van der Meer, Detlef Lohse When a millimetric water drop is gently deposited on a silicone oil bath, it reaches a temporarily stable shape supported by a thin lubricating air layer. Upon the drainage of this layer, a triple contact line (between air, water, and oil) forms. Owing to the positive spreading coefficient of silicone oil, it tries to maximize its surface area. This configuration results in encapsulation of droplet by the liquid pool. We focus on the temporal dynamics of the encapsulation process.\\ We study the problem using experiments and numerical simulations. In experiments, we use high-speed imaging at 50k fps to capture the process of encapsulation. In simulations, we first find the initial static shape of the droplet by using the Young-Laplace equation. We then solve the Navier-Stokes equations using a Finite Volume Method implemented by [Popinet 2014, Basilisk, http://basilisk.fr]. We have modified this numerical framework to solve for the triple contact line implicitly.\\ The present work provides information on the physics of the interaction of droplets with a free surface and presents a new methodology for modeling triple contact lines. This method can be used in a wide range of applications involving three immiscible liquids. [Preview Abstract] |
Saturday, November 23, 2019 4:53PM - 5:06PM |
B22.00002: Partial coalescence of a droplet with a pool of different viscosity Abdullah Al Alhareth, Sigurdur T. Thoroddsen The partial coalescence of a drop with a liquid surface is a critical factor during the coarsening of emulsions, as this process can produce smaller droplets. It is well-known that increased liquid viscosity or reduced drop size will eventually stop the satellite pinch-off at a critical Ohnesorge number. On the other hand, similar satellites can be pinched off during the rapid spreading of a drop on a solid surface, if it is strongly hydrophilic. Herein we study this process when the substrate transitions from low to high viscosity liquid, modeled to approach the boundary conditions of a solid. We use miscible silicone oils, with a low-viscosity drop and a large range of pool viscosities up to a million times that of the drop. We observe non-monotonic behavior and as the viscosity increases we see a propensity for second-stage pinch-off1. We connect the observed critical Ohnesorge numbers to the spreading behavior. 1. Zhang, Li {\&} Thoroddsen, Phys. Rev. Lett. 102,104502 (2009). [Preview Abstract] |
Saturday, November 23, 2019 5:06PM - 5:19PM |
B22.00003: Characteristics of coalescence mechanism of two unequal sized drops at liquid-liquid interface. Swati Singh, Arun K. Saha The drop coalescence is important in many applications such as formation of rain drops in cloud and mixing in microdevices. In the present work, the dynamics of satellite drop generation during the coalescence of two drops of unequal size are studied. The mechanism depends on five non-dimensional parameters: Ohnesorge number for both liquids, Bond number, Atwood number and the diameter ratio of two drops. We have performed two-dimensional, axisymmetric simulations using Coupled Level set and Volume of fluid method (CLSVOF) to unveil the underlying physics of coalescence process under varying drop diameter ratio (1.0-9.0) and Ohnesorge number. The Bond number is kept less than 0.1. Result shows the three different pinch-off scenario depending on drop diameter ratio: (i) the mother drop deforms after coalescence resulting in necking and subsequent satellite drop pinches off following the similar sequence as that of a drop coalescence with a flat liquid pool, (ii) occurrence of mother drop pinch-off happens with necking but without intermediate detachment of satellite drop, (iii) mother drop completely coalesces into the father drop without any evidence of satellite drop generation. [Preview Abstract] |
Saturday, November 23, 2019 5:19PM - 5:32PM |
B22.00004: Two Fluid Coalescence of Drops in an Exterior Fluid Christopher Anthony, Michael Harris, Osman Basaran The coalescence of drops and bubbles has been investigated in numerous experimental, numerical and theoretical studies due to its prevalence in industrial and natural processes. In many studies to date, either the interior/dispersed phase (e.g. the gas inside bubbles) or the exterior/continuous phase (e.g. the air surrounding drops) has been treated as dynamically inert in order to simplify the analysis. However, in many systems of interest, the interior and the exterior phases are fluids of comparable viscosities and/or densities, and treating one as dynamically inert may be inappropriate. Indeed, theoretical arguments by Eggers et al. suggest that the interior fluid will always play a role at some early time but that this could occur at length scales below the continuum limit (e.g. with bubbles). To date, the scaling behavior predicted by Eggers et al. for viscous drops in a viscous medium has been contradicted by experimental observations and no numerical study has been able to resolve this contradiction. Here, we explore through high fidelity numerical simulations drop coalescence in an exterior medium paying particular attention to the high viscosity or creeping flow limit while also considering a limited number of cases of finite viscosity. [Preview Abstract] |
Saturday, November 23, 2019 5:32PM - 5:45PM |
B22.00005: Non-continuum tangential resistivity functions for two spheres suspended in a gas Melanie Li Sing How, Donald L. Koch, Lance R. Collins In the limit of absence of gas-phase inertia, the motion of two spheres is described by the Stokes equation for large separations and by the linearized Boltzmann equation for separations comparable with the mean-free path of the gas. The forces and torques the gas exerts on each sphere are described by five resistivity functions (Jeffrey \& Onishi, J. Fluid Mech. 139: 261-290 1984). The resistivity functions undergo a transition as the separation distance between the spheres approaches the mean free path of the gas. In particular, the divergences of the Stokes resistivity functions as the spheres approach contact are reduced by non-continuum effects. We present modified tangential resistivity functions that are uniformly valid through this transition (i.e., from the continuum limit at distant separations to separations where the lubrication flow near contact is a free molecular flow). We apply the modified resistivity functions to two illuminating cases: (i) a sphere falling in close proximity to a vertical wall; and (ii) two spheres settling under gravity. The results show qualitative differences from the classical Stokes flow solution and are applied to the study of coalescing cloud droplets settling under gravity. [Preview Abstract] |
Saturday, November 23, 2019 5:45PM - 5:58PM |
B22.00006: Coalescence dynamics of two unequal size water droplets in air Nitin Goyal, Atul Sharma Coalescence dynamics of two water droplets falling under gravity in air, is studied for various diameter ratio (d$_{\mathrm{bottom}}$/d$_{\mathrm{top}})$ D$_{\mathrm{r}}=$0.15-6 and Ohnesorge number Oh$=$0.001-0.025 at a Bond number Bo$=$0.092. Axisymmetric simulations are done using sharp interface level set method based in-house code. We presented a regime map for the various Oh and D$_{\mathrm{r}}$, with partial coalescence at smaller as well as larger values of D$_{\mathrm{r}}$ and full coalescence at intermediate value of D$_{\mathrm{r}}$. For a transition in the coalescence dynamics, the present work reports a smaller and a larger critical value of D$_{\mathrm{r}}$ as compared to one critical D$_{\mathrm{r}}$ (the larger one) reported in the literature. Over the range of Oh studied here, there is a monotonic increase in both the critical D$_{\mathrm{r}}$ with increasing Oh -- from 1.5 to 5.7 for the larger critical D$_{\mathrm{r}}$ and from 0.3 to 0.4 for the smaller critical D$_{\mathrm{r}}$. The pinch-off height of satellite droplet is larger for partial coalescence at the larger D$_{\mathrm{r}}$ as compared to that at the smaller D$_{\mathrm{r}}$. The partial coalescence regime at the smaller D$_{\mathrm{r}}$ is presented here for the first time. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2020 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
1 Research Road, Ridge, NY 11961-2701
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700