Bulletin of the American Physical Society
75th Annual Meeting of the Division of Fluid Dynamics
Volume 67, Number 19
Sunday–Tuesday, November 20–22, 2022; Indiana Convention Center, Indianapolis, Indiana.
Session Z31: Drops: Impact, Bouncing, Wetting and Spreading V |
Hide Abstracts |
Chair: Javad Eshraghi, Purdue University; Constantine Megaridis, University of Illinois at Chicago Room: 239 |
Tuesday, November 22, 2022 12:50PM - 1:03PM |
Z31.00001: Wetting Dynamics of Volatile Hydrofluoroether (HFE) Liquid Droplets Manish Kumar, Senthil K Parimalanathan, Alexey Rednikov, Pierre Colinet The present work reports the wetting dynamics of a series of Hydrofluoroether liquids, having low surface tension and an appreciable volatility. As the series number increases from HFE-7100 to 7500, the volatility of the liquid decreases without any significant change in surface tension. The high-speed shadowgraphy technique is employed to observe the spreading of HFE-liquid droplets of different sizes on glass and sapphire substrates. Droplets of HFE-7500 liquid show the strongest wetting behavior compared to other HFE-liquids. For a given volume, the maximum wetted diameter of droplets decreases as the series number decreases from HFE-7500 to 7100. In contrast, the final (evaporation-driven) contact angle increases with the decrement in the series number. During the spreading stage, the higher volatile liquid spreads slower, with an apparent wetting exponent ranging from 1/11 to 1/18, which is smaller than the Tanner's law exponent of 1/10. Apart from immediate evaporative losses, this wetting behavior may also be affected by the larger evaporative cooling of the higher volatile liquid at the droplet interface, which induces thermal Marangoni stresses in the opposite direction of the contact line motion, thereby restricting the spreading of the droplet. |
Tuesday, November 22, 2022 1:03PM - 1:16PM |
Z31.00002: Capillary-Driven Liquid Transport of Low-Surface-Tension Liquids Shashwata Moitra, Constantine M Megaridis There has been extensive research on capillary-driven transport of high surface tension liquids (e.g. water, glycerol, etc.), but only limited attention has been given to contact-line confined transport of liquids with low surface tension (e.g. oils, alcohols, etc.). When the fluid surface tension drops below 40 mN/m, repellency becomes extremely difficult. This situation is encountered in many engineering applications and thus is of high technological importance. In this work, we use a fluorinated nanocomposite coating deposited on a surface textured by laser etching, a scalable technique that requires no lithography implementation. The approach results in the repellency of liquid hydrocarbons with surface tensions as low as 21mN/m. The repellency of several liquids with surface tensions in the range 21-72mN/m is experimentally investigated. Comparisons are performed between the velocities acquired by fluids transported pumplessly on a wedge-shaped wettability-patterned track, due to confinement imposed by the superomniphobic background surrounding the wettable track. Finally, travel distance and velocities of low-surface tension liquids transported on inclined ramps against gravity on similar wedge-shaped wettability-patterned tracks are compared. |
Tuesday, November 22, 2022 1:16PM - 1:29PM |
Z31.00003: Drop penetration of fur-like fiber arrays Gene Patrick P Rible, Michael Spinazzola, Rachel Constantin, Andrew Dickerson In this experimental study we combine of drop impact onto porous media and impacts onto single fibers to study drop impact into fiber arrays inspired by mammalian fur coats. In our 3D-printed arrays, we can vary the packing density, fiber alignment and shape, and wettability. Drops impact fibers fixed at both ends, inertially penetrating and spreading across the upper surface. Using image analysis we measure penetration depth, wetted diameter, and volume of penetration into the array. Impact Weber number and a modified porosity define penetration, retraction, and rebound. As packing density increases and porosity decreases, penetration is replaced by inertial spreading, which is of course no surprise. However, our results indicate that as density grows past what we can manufacture, toward the density of lying hairs, penetration of fibrous arrays by falling drops is nearly zero. Thus we expect mammalian skin to remain dry in the most violent rainfall. |
Tuesday, November 22, 2022 1:29PM - 1:42PM |
Z31.00004: Conversion of drops into bubbles upon impact on a porous membrane with gas discharge Lukas Weimar, Luyang Hu, Tobias Baier, Steffen Hardt The impact of drops on a porous membrane with high contact-angle hysteresis and gas discharge is studied experimentally and based on CFD simulations. Four different impact modes are identified, ranging from complete repulsion to fast immobilization of a drop. The rebound time of a drop is proportional to the inertial-capillary timescale, similar to the case of drop impact in the Leidenfrost regime. The most remarkable aspect of the dynamics is the transformation of a drop into a bubble, which occurs when the drop just overcomes the repulsion by the gas flow and wets the surface. In that case, the contact line of the drop on the membrane surface gets immobilized, while the bottom surface of the drop gets displaced away from the membrane, resulting in a bubble with a diameter significantly larger than the diameter of the impacting drop. The inflation of the gas bubble is due to the expanding gas cushion below the drop, fed by the gas discharge through the membrane. The transition to the regime in which a drop is transformed into a bubble is well described by a simple scaling relationship based on a balance between inertia and the repulsive force due to the gas flow. |
Tuesday, November 22, 2022 1:42PM - 1:55PM |
Z31.00005: Early-time splash jet dynamics in high-speed droplet impacts on textured and lubricant-infused surfaces Nathaniel Henman, Frank Smith, Manish Tiwari The high-speed impact of liquid droplets onto surfaces with different properties is a research area of huge practical importance. Recent advances in surface engineering have focussed heavily on nature inspired lubricant-infused surfaces and the present study considers a computational model of the delicate early stages of droplet impact onto such surfaces. An idealised two-dimensional model is utilised for a normal impact of an incompressible liquid droplet onto a surface of rectangular asperities and a thin layer of lubricant. The effects that the parameters pertaining to a lubricant-infused surface, namely the surface topology, lubricant depth and lubricant viscosity, have on the extent of the thin splash jet ejected at impact are investigated in turn. It’s found that changes in all three have a clear and discernible effect on the extent of the splash jet at early stages after impact, which is likely to have a key influence on the overall dynamics. Various different splashing behaviours are observed and are presented in a phase diagram which emphasises the relationship between the surface parameters and the impact velocity. Comparisons of a lubricant-infused surface to a textured, superhydrophobic surface, with no lubricant present, highlight the importance of the surface topology. |
Tuesday, November 22, 2022 1:55PM - 2:08PM |
Z31.00006: Alcohol vapor-induced water drop bouncing on hydrophilic surfaces Jongsu Jeong, Kyung Chun Kim, Seungho Kim It is generally conceived that an impacting water drop of low Weber number completely bounces off superhydrophobic surfaces. Here we show that the impacting drop can jump off hydrophilic surfaces when Isopropyl alcohol (IPA) vapor is subjected to the surfaces. IPA molecules consist of hydrophilic hydroxy head and hydrophobic alkyl tail similar to surfactant molecules. The supply of IPA vapor leads to the adsorption of the hydrophilic head of IPA molecules onto hydrophilic solid surfaces, and it allows the hydrophobic tail of IPA molecules to be oriented toward the gas phase, which induces the droplet bouncing. Experiments revealed that a critical Weber number exists for the drop bouncing and the surface wettability of the IPA-adsorbed surface turns into its original hydrophilic state by removing the surrounding IPA vapor. We visualize such novel drop behaviors with a high-speed camera and analyze their prominent features by combining experiments and theory. |
Tuesday, November 22, 2022 2:08PM - 2:21PM |
Z31.00007: Probing dissipation length-scale in spreading drops using granular suspensions Alice Pelosse, Elisabeth L Guazzelli, Matthieu Roché Granular suspensions are used to gain a better understanding of the multiscale physics of spreading drops. In a previous work, monomodal granular suspensions were shown to obey the Cox Voinov law which relates the capillary number to the dynamical contact angle, provided one uses an apparent viscosity. Contrary to the bulk viscosity of monomodal suspensions which solely depends on particle volume fraction, the apparent wetting viscosity was shown to depend both the particle concentration and size: it is maximum for the smallest particles and decrease to almost the suspending fluid viscosity above a cut-off diameter of 100 μm, even for dense suspensions. The origin of this cut-off size is investigated and linked to the dissipation length-scale of this multiscale problem. Tuning dissipation can be achieved by using the confinement constraint of the particles by the contact line. |
Tuesday, November 22, 2022 2:21PM - 2:34PM |
Z31.00008: Capillary adsorption of droplets into a funnel-like structure Yanchen Wu, Fei Wang, Weidong Huang, Michael Selzer, Britta Nestler The penetration of liquid from an infinite reservoir into a capillary tube has been studied for more than a century. However, if the size of the droplet is comparable to the pore size, a mathematical description of the penetration criterion, which is influenced by the droplet size, the intrinsic wettability, and the opening angle of the capillary tube, remains a knotty issue. In this contribution, we theoretically and numerically address the penetration criterion of the droplets with limited volume into a funnel-like pore structure. Our results show that there is a critical contact angle below which a certain-sized droplet can penetrate a hydrophobic pore. This critical contact angle is closely related to the opening angle and droplet size. Remarkably, our predictions extend the limit of the maximum contact angle for the complete penetration of droplets into capillary tubes in the literature. The critical contact angle becomes invariant for a given droplet size when the opening angle is larger than a certain threshold. Furthermore, we find that for a constant opening angle, the critical contact angle decreases as the droplet size increases. As the droplet volume tends to become infinity, the opening angle has almost no effect on the penetration, and the critical contact angle asymptotically approaches 90°, which is consistent with previous works. Our observations shed light on a specific mechanism for a precise control of droplets in filtration systems and microfluidic platforms. |
Tuesday, November 22, 2022 2:34PM - 2:47PM |
Z31.00009: Modeling Directional Droplet Transport on Wettability-Confined Wedge Tracks Harshad s Gaikwad, Arani Mukhopadhyay, Subramanian Sankaranarayanan, Constantine M Megaridis Wettability-confined tracks facilitate the spontaneous pumpless transport of droplets on open-surface microfluidic devices. In recent experimental and computational studies, the speed of the advancing front of such self-propelled droplets on the hydrophilic or superhydrophilic wedges has been shown to vary with the wedge angle, volume of the droplet, and the shear-thinning nature of the liquid. However, the influence of wettability difference between the two domains, as described by the difference between the contact angle of the hydrophilic wedge and the surrounding hydrophobic surface, is less well understood. In this study, we analyze the effect of such wettability difference on the droplet transport under consideration. To do so, we setup the FEM-based multiphase simulations in COMSOL Multiphysics software and show the variation in the speed of the advancing front of the droplets with respect to different combinations of hydrophobic and hydrophilic contact angles. The multiphase flow simulations are modelled using the Phase-Field method. The results are validated against published experiments. |
Tuesday, November 22, 2022 2:47PM - 3:00PM |
Z31.00010: Volume-of-Fluid based simulation of the withdrawing tape problem using a novel implementation of the generalized Navier boundary condition Mathis Fricke, Yash Kulkarni, Tomas Fullana, Stephane L Zaleski The (static or dynamic) contact angle boundary condition is the classical approach to model the wettability of the solid surface in a two-phase flow model of dynamic wetting. It prescribes the orientation of the interface normal at the contact line. In addition, the Navier slip condition is a frequent choice to regularize the moving contact line singularity. The “generalized Navier boundary condition” (GNBC), introduced by Qian et al., combines the modeling of both effects into one single boundary condition for the fluid velocity at the solid boundary. The uncompensated Young stress enters the force balance between friction and viscous stress at the contact line. Hence, the GNBC leads to a dynamic relaxation of the contact angle. |
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. |
© 2024 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
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700