Bulletin of the American Physical Society
77th Annual Meeting of the Division of Fluid Dynamics
Sunday–Tuesday, November 24–26, 2024; Salt Lake City, Utah
Session X08: Surface Tension Effects: Capillary Phenomena |
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Chair: Sadaf Sobhani, Cornell University Room: Ballroom H |
Tuesday, November 26, 2024 8:00AM - 8:13AM |
X08.00001: OpenFOAM Simulations of Passive Bubble Separations Analogous to Capillary Nucleate Boiling in Microgravity Ward M Cereck, Josh McCraney, Kjell Lindgren, Mark Weislogel, Sarah E Morris Steady nucleate boiling is readily achieved on Earth as lighter vapor bubbles are removed from the heated surface by buoyancy forces due to gravity. Can steady nucleate boiling take place in the low-gravity environment of space? In 2022, NASA astronaut Kjell Lindgren injected air into the vertex of an expanding partially-liquid-filled rhombic channel aboard the International Space Station. The wetting liquid is driven toward the vertex along the interior corners of the container by capillary forces. The liquid flows break up the gas into asymmetric ullages that are driven passively away from the vertex by the displacing liquid. The bubbles 'rise' to near-inscribed locations where they coalesce, flowing further into new inscribed locations, eventually merging with the liquid free surface. Analogous to bubbles rising during the boiling process due to gravity, these bubbles 'rise' in microgravity due to the combined effects of surface tension, wetting, and conduit geometry. The maximum stable gas flow rate might be considered as analogous to the maximum vapor production rate for steady nucleate boiling in low-g environments. Our research aims to develop a numerical tool to predict such large-scale low-g bubble migrations using the open-source CFD software OpenFOAM with a multi-phase incompressible volume of fluid solver. These isothermal simulations are benchmarked against the rare experimental results catalogued by bubble volumes, overall gas flow rate, conduit geometry, and fluid properties, and the liquid flux (liquid co-flow) around the bubble is measured as a function of bubble height. |
Tuesday, November 26, 2024 8:13AM - 8:26AM |
X08.00002: Continuous dip-coating flow in the presence of a liquid-liquid interface Jishnu Goswami, Farzam Zoueshtiagh, Sreenivas Sreenivas Dip-coating is a widely utilized industrial process for applying protective coatings over substrates. Landau and Levich's theoretical analysis highlighted the key viscous-capillary interactions. The process becomes complex with liquid-liquid interfaces, as seen in multilayered coatings. This study explores the continuous dip-coating of a wire in a two-immiscible liquid system, focusing on the fluid dynamics at the liquid-liquid interface and the resulting film coating. Both experimental and numerical analysis reveals multiple flow regimes: visco-capillary, visco-inertial, boundary layer-dominated, and visco-gravitational. Our findings extend the Landau-Levich law beyond the classical capillary number values and show a distinct visco-inertial regime with a sharp, delayed transition. At high inertia, boundary layer effects reduce film thickness, while a visco-gravitational regime emerges when inertia is minimal and diminishing capillary suction effectiveness. |
Tuesday, November 26, 2024 8:26AM - 8:39AM |
X08.00003: Experimental Study of Wetting effect on Capillary-gravity Wave Scattering from a Barrier Zhengwu Wang, Guoqin Liu, Likun Zhang The wetting phenomenon at three-phase boundaries (solid, liquid, and gas) affects capillary-gravity wave scattering from barriers, but there is a lack of experimental data and comparison with simulations. The scattering is affected by surface tension and the contact lines at the three-phase boundary. When the solid surface conditions vary, the contact angle and the shape of the meniscus generated by the wetting effect change accordingly. It is possible to measure the influence of the wetting effect on the scattering by coating the barrier surface to be hydrophobic or hydrophilic. Our previous work focused on how the scattering is affected by the portion of the barrier immersed under the water surface with a pinned contact line. In this study, we will coat the barrier surface to experimentally measure how the wetting with different coatings affect the scattering. A comparison of the experimental measurements with numerical simulations of potential flow of the waves will be potentially included. |
Tuesday, November 26, 2024 8:39AM - 8:52AM |
X08.00004: Capillary Rise between Elastic Fibers and the Dynamics of the Transition to a Coalesced Equilibrium Katie Wu, Suzie Protière, Camille Duprat, Howard A Stone When slender elastic fibers separated by a small gap are partially submerged in a reservoir of wetting liquid, attractive capillary forces may cause them to draw nearer to each other and snap into contact. After the fibers make contact, the system transitions via capillary rise towards a stable coalesced equilibrium state in which the two fibers are joined by a capillary bridge whose equilibrium height is determined by a balance between elasticity and capillarity. The dynamics of this transition to a coalesced equilibrium state were investigated experimentally. Data were acquired for different fiber diameters, lengths, and elastic moduli. We report measurements of the rates of capillary rise of liquid into the narrow gap between the fibers and their simultaneous self-assembly into a corner-like configuration. In all cases, we observe an intermediate regime in which capillary rise is characterized by power-law growth. Although the exponent appears to be constant, the prefactor depends on both the radius and elastic modulus of the fibers. We will rationalize these findings as well as other results regarding the late stages of rise and the final approach of the capillary bridge to its equilibrium height. |
Tuesday, November 26, 2024 8:52AM - 9:05AM |
X08.00005: Inertial Period Corner Rise in the Interstice of Circular Tubes Chitransh Atre, K Arul Prakash, Baburaj A Puthenveettil
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Tuesday, November 26, 2024 9:05AM - 9:18AM |
X08.00006: On the transport of droplets and bubbles through density transition layers Damir Juric, Abdullah M Abdal, Lyes Kahouadji, Seungwon Shin, Jalel Chergui, Colm-Cille P Caulfield, Omar K Matar The transport of droplets or bubbles through density interfaces is a common phenomenon in nature. For instance, in the ocean, oil droplets from spills or rising air bubbles may encounter variations in the surrounding fluid's temperature. These temperature differences can significantly alter the density and viscosity of the ambient fluid, thereby affecting the transport dynamics and fateof the droplets or bubbles.In this work, we consider the rising motion of a droplet or bubble through a sharp density interface. The study considers varying the droplet/bubble Bond number (Bo), Galilei number (Ga)and the stratification strength of the ambient fluid, which is governed by the Froude number (Fr). The simulations are implemented viathree-dimensional DNS using a LevelContour Reconstruction Method (LCRM) -a hybrid level-set front-tracking method to accurately capture the motion and the interaction of the droplet or bubble with the sharp density interface. The Galilei numbers considered in this work are relatively moderate(Ga<100), and the density stratification is modeled using an error function formulation, ρf(z)=ρ1+ 0.5(ρ2−ρ1)[(1−erf(z/H)], where z indicates the vertical position, H is the height of the density transition layer, and ρ1 and ρ2 are the undisturbed fluid densities above and below the stratification interface, respectively. This study begins by examining how density variations in the ambient fluid, caused by temperature differences, affect the transport of droplets or bubbles. The work then investigates the role of coupling the effects of variable fluid viscosity on their transportand deformation |
Tuesday, November 26, 2024 9:18AM - 9:31AM |
X08.00007: Rib formation in inertial liquid entrainment Jean-Philippe Matas, Pierre Trontin, J John Soundar Jerome We present findings on pattern formation under high-speed liquid entrainment conditions on the outer surface of a rotating cylinder. Our observations for two liquids (water, and a 100 times more viscous mixture of water and UCON oil), reveal that this inertial coating flow produces a series of vertical parallel thin liquid sheets, as fluid is entrained and ballistically ejected by the rotating wall. The observed wavelength, of the order of a few centimeters, is surprisingly almost unchanged when velocity and the viscosity of the fluid are modified, even when the liquid sheets are strongly fragmented and droplet ejection occurs. We demonstrate that these axial patterns arise from a primary instability driven by an adverse pressure gradient in the meniscus region of the rotary Landau-Levich-Derjaguin flow. According to our model, the rib spacing is proportional to the capillary length lc, even though the observed wavelength is itself much larger than lc. Additionally, we conducted Direct Numerical Simulations using Basilisk, which evidence the central role of pressure in the entrained film in driving this instability. The numerical simulation replicates well the experimental data, and corroborate the predictions of our model when the density and surface tension are numerically varied. |
Tuesday, November 26, 2024 9:31AM - 9:44AM |
X08.00008: Droplet motion over a chemical step Sacha Szkudlarek Controlling and understanding the mechanisms of droplet motion on physically and chemically structured substrates is relevant to application in microfluidics. |
Tuesday, November 26, 2024 9:44AM - 9:57AM |
X08.00009: Cascading rupture of oil droplets Shenghao Tan, Nate J Cira Certain types of oil droplets display unique cyclic motions of rupture and recovery on immiscible liquid substrates. This phenomenon differs from the hole nucleation by spinodal dewetting by the critical thickness of the oil film. We demonstrate that multiple factors are required to achieve such behavior: 1) The oil must display pseudo-partial wetting on the liquid substrate, 2) Surface-active compounds must be present within the oil or substrate, and 3) Substrate-air interface must be actively created. We show that the critical thickness and number of hole nucleation events are dependent on the concentration of surface-active compounds, suggesting spatially dependent dynamic surface tension potentially playing a role in the phenomenon. Here we describe and characterize the thinning, rupture, and recovery of these oil droplets then propose a model to explain this unique behavior. |
Tuesday, November 26, 2024 9:57AM - 10:10AM |
X08.00010: Wettability study of porous pattern membranes inspired by banana leaf KURADA V KRISHNASRI, Ayush Ranjan, Ankita Chakraborty, Pratyush Bhatt Janus wettability, characterized by the coexisting hydrophilic and hydrophobic domains on single material is gaining considerable attention owing to its potential to alter solid-liquid interactions and subsequent interesting outcomes. Banana leaf is a classic example of this with adaxial side exhibiting stronger wettability characetristics compared to the abaxial side owing to structural differences in terms of nanopillars dimensions. The leafs are observed to be composed of longitudinal patterns of two different length scales along with intermittent nanopillars present in between in random orientation. Present work attempts to prepare a porous replica of banana leaf pattern (both abaxial and adaxial) with cellulose acetate as base polymer using nonsolvent induced phase separation process and study the effect on surface wettability. The pattern formation has been confirmed from the FESEM analysis both for the substrate and the replica, with nanopillars replicating as nanodents. The additional effect of chemical composition of leaf surface on the wettability is explored. Such porous patterned membranes can be tailor-made to prepare biological scaffolds with desirable wettability properties and also find applications in water treatment membranes. |
Tuesday, November 26, 2024 10:10AM - 10:23AM |
X08.00011: Passive Control of Capillary Rise Dynamics in Micro-Channels Aniruddha Saha, Joshua Krsek, Giancarlo D'Orazio, Sadaf Sobhani Capillary rise, a fundamental fluid-structure interaction, is influenced by channel geometries and fluid properties. This study investigates the dynamics of capillary rise in micro-channels using numerical methods to develop passive control strategies. We implemented sinusoidal variations in the channel cross-section and investigated a wide range of contact angles, and demonstrated precise control over the fluid front's ascent rate. The benefits achieved over conventional capillaries have therefore influenced the design of architected capillaries. Scaling of the liquid height is performed to reveal the rate of liquid rise for multiple contact angles collapsing into a single curve. This demonstrates the presence of a new mixed regime of fluid flow which is different from purely inertia dominated (~t) and viscous dominated (~t2) regimes that which governs the rate of rise. |
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