Bulletin of the American Physical Society
76th Annual Meeting of the Division of Fluid Dynamics
Sunday–Tuesday, November 19–21, 2023; Washington, DC
Session A20: Superhydrophobic Surfaces |
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Chair: Hui Hu, Iowa State University Room: 146C |
Sunday, November 19, 2023 8:00AM - 8:13AM |
A20.00001: Transient Heat Transfer to Rolling or Sliding Drops on Inclined Heated Superhydrophobic Surfaces Daniel Maynes, Joseph Furner, Julie Crockett, Brian D Iverson This presentation examines the time resolved heat transfer to drops rolling or sliding along inclined, heated non-wetting surfaces. Results were experimentally obtained using IR imaging for a smooth hydrophobic surface and post as well as rib structured superhydrophobic surfaces of varying solid fraction (0.06 - 0.5). Tests were performed at varying inclination angle (10, 15, 20, and 25°), drop volume (12, 20, 30, and 40 <!--[if gte msEquation 12]>μL), and surface temperature (50, 65, and 80 °C). Rib structured superhydrophobic surfaces were explored for drops moving parallel and perpendicular to the rib structures. The findings indicate that transient heat transfer is predominantly influenced by the surface’s solid fraction and the velocity of the drops, with a secondary dependence on drop volume. Surfaces with low solid fraction show a significant reduction in initial heating rate (up to 80% reduction) to the drop, when compared with that of the smooth surface. The drop velocity depends on surface solid fraction and inclination angle, with drop volume exerting smaller influence. Rib structured surfaces impact heat transfer by enhancing heat transfer rate for drops that move along the rib direction compared with drops that move perpendicular to the ribs. The difference is likely due to increased drop velocity that exists for the parallel rib orientation. Correlations that enable prediction of the heat transfer to rolling drops on superhydrophobic surfaces are presented that show excellent collapse of the experimental data. |
Sunday, November 19, 2023 8:13AM - 8:26AM |
A20.00002: Exploring Dynamics of Water Drop Transport on Vibrating Superhydrophobic Surfaces schon gabriel fusco, Miguel Ángel Rodriguez Valverde, Miguel Ángel Cabrerizo Vílchez The control of water drop transport is a challenging problem in many scientific field. Mechanical vibration rises as an effective mechanism to move drops. |
Sunday, November 19, 2023 8:26AM - 8:39AM |
A20.00003: Quantifying microdroplet contact-line friction using atomic force microscope Dan Daniel, Xue Qi Koh, Calvin Thenarianto, Ville Jokinen Controlling the wetting and spreading of microdroplets is key to technologies such as microfluidics, ink-jet printing, and surface coating. Contact angle goniometry is commonly used to characterize surface wetting by droplets, but the technique is ill-suited for sub-millimetric droplets. Here, we attach a micrometric-sized droplet to an Atomic Force Microscope (AFM) cantilever to directly quantify contact-line friction on different surfaces (superhydrophobic and underwater superoleophobic) with sub-nanonewton force resolutions. We demonstrate the versatility of our approach by performing friction measurements using different liquids (water and oil droplets) and under different ambient environments (in air and under water). Finally, we show that underwater superoleophobic surfaces can be qualitatively different from superhydrophobic surfaces: contact-line friction is highly sensitive to contact-line speeds for the former but not for the latter surface. |
Sunday, November 19, 2023 8:39AM - 8:52AM |
A20.00004: Experimental Study on the Dynamic Droplet Impingement Force on Surfaces with Various Wettability at High Weber Number Haiyang Hu, Hui Hu Understanding the fundamental of the durability degradation of water/ice-phobic coatings is crucial to the development of the novel anti-/de-icing technology. In the present study, an experimental investigation was conducted to evaluate the dynamic water droplet impact force on surfaces with different wettability at high Weber numbers. Three surfaces (i.e., Hydrophilic, Hydrophobic, and Super Hydrophobic surfaces) were utilized as the substrate during the impingement process of the water droplet at both room temperature and supercooled level. The impact force is measured by a piezoelectric impact force sensor synchronized with a high-speed image technique to characterize the dynamic collision force as well as the dynamic impingement morphology. The result shows that, at the kinematic stage, the force for impingement experiences a sharp increase which is followed by the self-similar prediction when the droplet is compressed to a truncated sphere. The dynamic impact force would drive away from the theoretical prediction when the spreading stage began and reach the maximum as the self-similar high-pressure region propagates to the apex of the droplet. Then, it is followed by long-time decay to zero before the receding stage. While the impingement morphology varies significantly with different surface hydrophobicity, the variation of impact force at different surfaces maintains within the small range. It shows a limited effect of dynamic impact force on the various wettability. The findings derived from the present study are very helpful in understanding the fundamental water erosion effect, which can be beneficial to the development of a more durable water/ice repellence coating. |
Sunday, November 19, 2023 8:52AM - 9:05AM |
A20.00005: On jet impingement on the underside of complex surfaces Ozgur Orun, Rodrigo Blanco, Simo A Makiharju Interaction of multiphase flow boundary layers with surfaces of complex distributed roughness and hydrophobic properties cannot be reliably predicted, despite their potential for a wide range of applications from frictional drag reduction to heat exchangers. Superhydrophobic surfaces (SHS) in particular are of great interest because of their ability to trap small air pockets (plastrons) between the liquid-solid interface and hence modify heat and momentum transport. However, a thorough understanding of the heterogeneous wetting mechanism on SHS is lacking due to the complicated nature of the surface. To glean physical insight, we first focus on a repeatable experiment observing the water patch topology resulting from a vertically impinging jet on the underside of various surfaces. Weber numbers ranged from 50 to 800, and impingement on 9 distinct surfaces with equilibrium contact angles ranging from 40 to 150° was examined. The equivalent sand-grain roughness (0.06 < ks < 40 μm) for each surface was also measured. Referencing the Cassie-Baxter theory, the role of surface chemistry and geometry on wetting characteristics was explored through an energy argument that compares the energies associated with the attached and detached states of the previously impinged liquid film. |
Sunday, November 19, 2023 9:05AM - 9:18AM |
A20.00006: An Advanced Aircraft Deicing Analysis: Supercooled Liquid Dynamics under Ultrasonic Frequency and Surface Roughness Effects Kevin Thomas Fernandez, Olivier Coutier-Delgosha Structural icing is a significant engineering challenge that has prompted extensive research into thermal, mechanical, and cavitation preventive measures. Common solutions involve, high-power consumption that add to the aircraft weight and the spray of anti-icing chemicals, but new complexities arise from water droplets freezing at supercooled levels, leading to increased weight, drag, and de-icing power requirements. To address this, a novel approach combines Ultrasonic-Guided Waves (UGW) with piezoelectric (PZT) actuators and explores surface roughness variation of a superhydrophobic surface. This research builds upon previous work on rough surfaces and briefly discusses two suitable fabrication methods. A gap in the literature exists for controlled environment frequencies above 20 kHz, which is being addressed through the development of a custom environment featuring precise temperature control and other equipment. The study spans various heights and frequencies (20 kHz to 51 kHz) to determine the optimal range. The focus is on constructing a specialized experimental setup based on insights gained from experiments at Argonne National Laboratory and from the work that has been previously done in the project. Two core aspects are emphasized: ultrasonic actuation with a focus on atomization and the study of droplet dynamics at temperatures below -15°C within a controlled environment. The experimental methodology involves adjusting frequency, amplitude, and velocity parameters to draw relevant conclusions. Aluminium is used as the substrate for its accuracy and reliability. In conclusion, the research aims to tackle structural icing through the innovative combination of Ultrasonic-Guided Waves and PZT actuators, while also exploring the impact of surface roughness and droplet dynamics during the water-to-ice transition. The custom-built environment ultrasonic wave actuation using disk actuator integration offer promising solutions for more efficient and cost-effective de-icing methods. |
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