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 J06: Drops: Dynamic Surface Interactions |
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Chair: Mehdi Mortazavi, Worcester Polytechnic Institute Room: Ballroom F |
Sunday, November 24, 2024 5:50PM - 6:03PM |
J06.00001: Novel Droplet Accelerator for Aircraft Icing Research Ru-Ching Chen, Charles Ruggeri Aircraft icing occurs when clouds of supercooled water droplets strike and freeze on various parts of an aircraft. This ice formation poses significant hazards to aviation. A crucial factor in determining the size and shape of the ice is the liquid water content (LWC), which measure the mass of water per unit volume of air. Various probes, such as hot-wire probes, have been developed to measure LWC. However, these measurements are influenced by aerodynamic, splashing, and evaporative efficiencies. Conducting fundamental experiments to investigate these phenomena is challenging due to the small sizes and high speeds of the droplets involved. |
Sunday, November 24, 2024 6:03PM - 6:16PM |
J06.00002: Evaporation-driven coalescence of two droplets undergoing freezing Sivanandan Kavuri, George Karapetsas, Chander Shekhar Sharma, Kirti Sahu We examine the evaporation-induced coalescence of two droplets undergoing freezing through numerical simulations using the lubrication approximation. When two sessile droplets freeze in close proximity on a substrate, they interact through the gaseous phase, involving simultaneous evaporation and condensation. In an unsaturated environment, the evaporation flux over the two volatile droplets is asymmetric, with lower evaporation in the region between them. This flux asymmetry generates an asymmetric curvature in each droplet, resulting in a capillary flow that drives the droplets closer together, eventually leading to coalescence. The capillary flow driven by evaporation competes with the upward movement of the freezing front, depending on the relative humidity of the surrounding environment. Higher relative humidity reduces the evaporative flux, delaying capillary flow and impeding coalescence by restricting contact line motion. At a constant relative humidity, substrate temperature governs the coalescence phenomenon, with resulting condensation potentially accelerating the process. Interestingly, lower substrate temperatures facilitate faster propagation of the freezing front, thereby restricting coalescence. |
Sunday, November 24, 2024 6:16PM - 6:29PM |
J06.00003: How Leidenfrost drops are propelled on textured surfaces via spontaneous symmetry breaking Songlin Shi, Chen Ma, Steffen Hardt, Cunjing Lv The directional motion of Leidenfrost drops on textured surfaces has been observed for textures that break the mirror symmetry along their direction of propulsion, for example ratchet structures. Here, we report Leidenfrost propulsion on mirror-symmetric spatially periodic surfaces, which raises the question about the origin of the propulsion mechanism. We map the underlying physics that entails gas and liquid flow as well as the dynamics of the gas-liquid interface to a comparatively simple model of two harmonic oscillators, which represent the regions close to the gas-liquid interface on both sides of a single fin of the texture. The restoring force of these oscillators is due to surface tension, and the oscillators are coupled through the gas flow between the solid surface and the gas-liquid interface. The oscillator model predicts that once a drop is moving relative to the texture, the gas-liquid interface experiences a deformation that breaks the mirror symmetry and in turn gives rise to a propulsion force. The origin of this propulsion force is the pressure field within the asymmetric gas flow. The experiments conducted on mirror-symmetric textures demonstrate a strong propulsion, with drop velocities of more than 10 cm/s. |
Sunday, November 24, 2024 6:29PM - 6:42PM |
J06.00004: How Surface Macrotextures Influence the Interactions between an Impacting Water Drop and a Non-Wetting Substrate in Supercooled Conditions? Naumi Noshin Chowdhury, Yang Yang, Samira Shiri When a water drop impacts a supercooled surface, it may freeze and adhere to it. Superhydrophobic surfaces are widely used as anti-icing solutions due to their ability to delay icing and reduce ice adhesion strength. Previous studies have shown that adding macrotextures to a superhydrophobic surface can reduce the contact time of an impacting drop by splitting it into smaller droplets. However, it remains unclear how an impacting water drop interacts with macrotextured non-wetting surfaces at freezing temperature. In this study, we demonstrate how surface macrotextured geometry can influence impact dynamics and freezing, with the goal of enhancing the anti-icing capability of the substrate. This research aims to provide deeper insights into optimizing surface designs for better water repellency below its freezing point. |
Sunday, November 24, 2024 6:42PM - 6:55PM |
J06.00005: Unraveling the influence of polymer brush thickness on droplet impact behavior on quasi-liquid surfaces Lingxuan Hao, Bei Fan The droplet impinging dynamics on surfaces represent a key phenomenon in various engineering and industrial applications, such as anti-icing, droplet electricity generation, printing. Understanding this phenomenon can assist in optimizing fabrication procedure and enhancing performance in these applications. Recently, quasi-liquid surfaces (QLS) prepared by grafting flexible polydimethylsiloxane (PDMS) chains onto substrate surfaces have garnered widespread attention due to their unique liquid repellency and excellent durability. These surfaces have shown outstanding potential in various industrial applications, including anti-icing and steam condensation. The QLS can be fabricated with different thicknesses under varying conditions, which could influence the surface wetting properties and droplet impinging dynamics on the surfaces. In this work, we utilized high-speed cameras to capture the dynamic impact behavior of water droplets on QLS surfaces with varying thicknesses and structures. By studying the transverse and longitudinal dynamic responses of the droplets, we obtained the energy dissipation during the impact process. Previous reports indicate that smoother surfaces result in less energy loss and higher rebound heights during droplet impact. In our experiments, although thicker QLS provides smoother surfaces, they exhibit greater energy dissipation. This suggested that the QLS could act as a soft cushion and absorb a portion of the kinetic energy during the impact process. These findings can be used to guide the selection of optimal preparation processes tailored to the specific requirements of various industrial applications, including inkjet printing, spray coating, and spray cooling technologies aiming to achieve the best droplet impact characteristics. |
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