Symmetry-Breaking Drop Bouncing on Superhydrophobic Surfaces with Continuously Changing Curvatures

Controlling the residence time of drops on the solid surface is related to a wide spectrum of engineering applications, such as self-cleaning and anti-icing. The symmetry-breaking dynamics induced by the initial drop shape can promote drop bouncing. Here, we study the bouncing features of spherical and ellipsoidal drops on elliptical surfaces that continuously change curvatures inspired by natural succulent leaves. The bounce characteristics highly depend on the geometric relations between the ellipsoidal drops and curved surfaces. Numerical results show that ellipsoidal shapes of the drops amplify asymmetries of the mass and momentum in synergy with an influence of the surface curvature during the impact, which is verified by experiments. Effects of the surface anisotropy and drops’ ellipticity on the residence time are investigated under various surface morphologies and Weber numbers. The residence time is closely associated with an initial surface curvature at the apex. The underlying principle of modifying the residence time via the drops’ ellipticity and initial surface curvature is elucidated based on momentum asymmetry. The understanding of the bouncing features on curved surfaces will offer practical implications for enhanced heat transfer performances and controlled water repellency, etc.

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Effect of Viscosity on Bouncing Dynamics of Elliptical Footprint Drops on Non-Wettable Ridged Surfaces

Polymers ◽

10.3390/polym13244296 ◽

2021 ◽

Vol 13 (24) ◽

pp. 4296

Author(s):

Sungchan Yun

Keyword(s):

Residence Time ◽

Underlying Mechanism ◽

Textured Surfaces ◽

Viscous Liquids ◽

Drop Shape ◽

Viscous Drops ◽

Fundamental Understanding ◽

Initial Drop ◽

Density Surface ◽

The Impact

An initial drop shape can alter the bouncing dynamics and significantly decrease the residence time on superhydrophobic surfaces. Elliptical footprint drops show asymmetric dynamics owing to a pronounced flow driven by the initial drop shape. However, the fundamental understanding of the effect of viscosity on the asymmetric dynamics has yet to be investigated, although viscous liquid drop impact on textured surfaces is of scientific and industrial importance. Here, the current study focuses on the impact of elliptical footprint drops with various liquid properties (density, surface tension, and viscosity), drop sizes, and impact velocities to study the bouncing dynamics and residence time on non-wettable ridged surfaces numerically by using a volume-of-fluid method. The underlying mechanism behind the variation in residence time is interpreted by analyzing the shape evolution, and the results are discussed in terms of the spreading, retraction, and bouncing. This study provides an insight on possible outcomes of viscous drops impinging on non-wettable surfaces and will help to design the desired spraying devices and macro-textured surfaces under different impact conditions, such as icephobic surfaces for freezing rain or viscous liquids.

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An Experimental Investigation Into the Relationship Between Temperature-Time History and Surface Roughness in the Spray Quenching of Aluminum Parts

Journal of Engineering Materials and Technology ◽

10.1115/1.2805925 ◽

1996 ◽

Vol 118 (1) ◽

pp. 127-134 ◽

Cited By ~ 15

Author(s):

John D. Bernardin ◽

Issam Mudawar

Keyword(s):

Surface Roughness ◽

Photoelectron Spectroscopy ◽

Hydrogen Diffusion ◽

Wide Spectrum ◽

Time History ◽

Cooling Curve ◽

Initial Surface ◽

Milled Sample ◽

The Impact ◽

Temperature Time

Repeated heat-quench cycles of Al-1100 samples resulted in increased surface roughness and corresponding shifts in the temperature-time cooling curve towards shorter overall quench periods. Three different types of initial surface roughness were applied to the test samples: polished, particle blasted, and milled finishes. For each of the three test surfaces, cooling curve shifts during repeated heat-quench cycles were accompanied by surface roughening, the shift was smallest with the milled sample. The surface roughness was examined with the aid of scanning electron microscopy, surface contact profilometry, and X-ray photoelectron spectroscopy. Surface profiles obtained via the profilometer revealed, on a relative basis, significant changes in surface roughness on the polished and particle blasted surfaces but not on the milled (roughest) surface. The roughening was the result of (a) hydrogen diffusion associated with oxidation, (b) oxidation buildup, and, to a lesser extent, (c) expulsion of impurities along dendrite boundaries. The hydrogen diffusion caused localized pressure buildup within the surface and along grain boundaries resulting in the formation of both microscopic (1 to 10 μm) features on the polished and particle blasted surfaces and relatively large (20 to 1000 μm) bumps and blisters on the particle blasted surface. It is shown how these wide spectrum surface roughness features affect cooling rate by (a) raising the Leidenfrost temperature separating the film and transition boiling regimes, (b) increasing the number of boiling sites on the quenched surface, and (c) altering the impact dynamics of the spray drops.

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A Survey of Electromagnetic Influence on UAVs from an EHV Power Converter Stations and Possible Countermeasures

Electronics ◽

10.3390/electronics10060701 ◽

2021 ◽

Vol 10 (6) ◽

pp. 701

Author(s):

Yanchu Li ◽

Qingqing Ding ◽

Keyue Li ◽

Stanimir Valtchev ◽

Shufang Li ◽

...

Keyword(s):

Electromagnetic Interference ◽

Wide Spectrum ◽

Electromagnetic Emission ◽

Power Converter ◽

Electromagnetic Environment ◽

Communication Circuits ◽

Electromagnetic Emissions ◽

Surrounding Space ◽

Extra High Voltage ◽

The Impact

It is inevitable that high-intensity, wide-spectrum electromagnetic emissions are generated by the power electronic equipment of the Extra High Voltage (EHV) power converter station. The surveillance flight of Unmanned Aerial Vehicles (UAVs) is thus, situated in a complex electromagnetic environment. The ubiquitous electromagnetic interference demands higher electromagnetic protection requirements from the UAV construction and operation. This article is related to the UAVs patrol inspections of the power line in the vicinity of the EHV converter station. The article analyzes the electromagnetic interference characteristics of the converter station equipment in the surrounding space and the impact of the electromagnetic emission on the communication circuits of the UAV. The anti-electromagnetic interference countermeasures strive to eliminate or reduce the threats of electromagnetic emissions on the UAV’s hardware and its communication network.

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The Impact of Fluid Loss and Carbohydrate Consumption during Exercise, on Young Cyclists’ Fatigue Perception in Relation to Training Load Level

International Journal of Environmental Research and Public Health ◽

10.3390/ijerph18063282 ◽

2021 ◽

Vol 18 (6) ◽

pp. 3282

Author(s):

Leonardo Cesanelli ◽

Berta Ylaitė ◽

Giuseppe Messina ◽

Daniele Zangla ◽

Stefania Cataldi ◽

...

Keyword(s):

Perceived Exertion ◽

Wide Spectrum ◽

Load Level ◽

Training Load ◽

Fluid Loss ◽

Young Athletes ◽

Carbohydrate Consumption ◽

Significant Difference ◽

Training Impulse ◽

The Impact

High-level young athletes need to face a wide spectrum of stressors on their journey to élite categories. The aims of the present study are (i) to evaluate session rate of perceived exertion (sRPE) at different training impulse (TRIMP) categories and the correlations between these two variables and, (ii) evaluate the correlations between sRPE, fluid loss, and carbohydrate consumption during exercise. Data on Edward’s TRIMP, sRPE, body mass loss pre- and post- exercise (∆), and carbohydrate consumption (CHO/h) during exercise have been acquired from eight male junior cyclists during a competitive season. One-way ANOVA and correlation analysis with linear regression have been performed on acquired data. sRPE resulted in a significant difference in the three TRIMP categories (p < 0.001). sRPE resulted in being very largely positively associated with TRIMP values (p < 0.001; R = 0.71). ∆ as well as CHO/h was largely negatively related with sRPE in all TRIMP categories (p < 0.001). The results confirmed the role of fluid balance and carbohydrate consumption on the perception of fatigue and fatigue accumulation dynamics independently from the training load. Young athletes’ training load monitoring and nutritional-hydration support represent important aspects in athlete’s exercise-induced fatigue management.

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Acute Management Should Be Optimized in Patients with Less Specific Stroke Symptoms: Findings from a Retrospective Observational Study

Journal of Clinical Medicine ◽

10.3390/jcm10051143 ◽

2021 ◽

Vol 10 (5) ◽

pp. 1143

Author(s):

Simona Halúsková ◽

Roman Herzig ◽

Dagmar Krajíčková ◽

Abduljabar Hamza ◽

Antonín Krajina ◽

...

Keyword(s):

Wide Spectrum ◽

Intravenous Thrombolysis ◽

National Institutes Of Health ◽

Vascular Territory ◽

Anterior Circulation ◽

Point Increase ◽

Single Center Study ◽

Mouth Corner ◽

Specific Symptoms ◽

The Impact

Anterior circulation stroke (ACS) is associated with typical symptoms, while posterior circulation stroke (PCS) may cause a wide spectrum of less specific symptoms. We aim to assess the correlation between the initial presentation of acute ischemic stroke (AIS) symptoms and the treatment timeline. Using a retrospective, observational, single-center study, the set consists of 809 AIS patients treated with intravenous thrombolysis (IVT) and/or endovascular treatment (EVT). We investigate the impact of baseline clinical AIS symptoms and the affected vascular territory on recanalization times in patients treated with IVT only and EVT (±IVT). Regarding the IVT-only group, increasing the National Institutes of Health Stroke Scale (NIHSS) score on admission and speech difficulties are associated with shorter (by 1.59 ± 0.76 min per every one-point increase; p = 0.036, and by 24.56 ± 8.42 min; p = 0.004, respectively) and nausea/vomiting with longer (by 43.72 ± 13.13 min; p = 0.001) onset-to-needle times, and vertigo with longer (by 8.58 ± 3.84 min; p = 0.026) door-to-needle times (DNT). Regarding the EVT (±IVT) group, coma is associated with longer (by 22.68 ± 6.05 min; p = 0.0002) DNT, anterior circulation stroke with shorter (by 47.32 ± 16.89 min; p = 0.005) onset-to-groin time, and drooping of the mouth corner with shorter (by 20.79 ± 6.02 min; p = 0.0006) door-to-groin time. Our results demonstrate that treatment is initiated later in strokes with less specific symptoms than in strokes with typical symptoms.

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Superhydrophobicity in perfection: the outstanding properties of the lotus leaf

Beilstein Journal of Nanotechnology ◽

10.3762/bjnano.2.19 ◽

2011 ◽

Vol 2 ◽

pp. 152-161 ◽

Cited By ~ 285

Author(s):

Hans J Ensikat ◽

Petra Ditsche-Kuru ◽

Christoph Neinhuis ◽

Wilhelm Barthlott

Keyword(s):

Chemical Composition ◽

Water Repellency ◽

Contact Angles ◽

Dense Layer ◽

Lotus Effect ◽

Nano Structure ◽

Lotus Leaf ◽

Water Drops ◽

The Impact ◽

Unique Chemical

Lotus leaves have become an icon for superhydrophobicity and self-cleaning surfaces, and have led to the concept of the ‘Lotus effect’. Although many other plants have superhydrophobic surfaces with almost similar contact angles, the lotus shows better stability and perfection of its water repellency. Here, we compare the relevant properties such as the micro- and nano-structure, the chemical composition of the waxes and the mechanical properties of lotus with its competitors. It soon becomes obvious that the upper epidermis of the lotus leaf has developed some unrivaled optimizations. The extraordinary shape and the density of the papillae are the basis for the extremely reduced contact area between surface and water drops. The exceptional dense layer of very small epicuticular wax tubules is a result of their unique chemical composition. The mechanical robustness of the papillae and the wax tubules reduce damage and are the basis for the perfection and durability of the water repellency. A reason for the optimization, particularly of the upper side of the lotus leaf, can be deduced from the fact that the stomata are located in the upper epidermis. Here, the impact of rain and contamination is higher than on the lower epidermis. The lotus plant has successfully developed an excellent protection for this delicate epistomatic surface of its leaves.

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Effect of initial surface curvature on frictionally excited thermoelastic phenomena

Wear ◽

10.1016/0043-1648(74)90033-7 ◽

1974 ◽

Vol 27 (2) ◽

pp. 195-207 ◽

Cited By ~ 9

Author(s):

R.A. Burton ◽

V. Nerlikar

Keyword(s):

Surface Curvature ◽

Initial Surface

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The role of drop shape in impact and splash

Nature Communications ◽

10.1038/s41467-021-23138-4 ◽

2021 ◽

Vol 12 (1) ◽

Author(s):

Qingzhe Liu ◽

Jack Hau Yung Lo ◽

Ye Li ◽

Yuan Liu ◽

Jinyu Zhao ◽

...

Keyword(s):

Electromagnetic Field ◽

Spherical Geometry ◽

Impact Dynamics ◽

Helmholtz Instability ◽

Liquid Drops ◽

Drop Shape ◽

Spreading Dynamics ◽

Solid Substrates ◽

The Impact

AbstractThe impact and splash of liquid drops on solid substrates are ubiquitous in many important fields. However, previous studies have mainly focused on spherical drops while the non-spherical situations, such as raindrops, charged drops, oscillating drops, and drops affected by electromagnetic field, remain largely unexplored. Using ferrofluid, we realize various drop shapes and illustrate the fundamental role of shape in impact and splash. Experiments show that different drop shapes produce large variations in spreading dynamics, splash onset, and splash amount. However, underlying all these variations we discover universal mechanisms across various drop shapes: the impact dynamics is governed by the superellipse model, the splash onset is triggered by the Kelvin-Helmholtz instability, and the amount of splash is determined by the energy dissipation before liquid taking off. Our study generalizes the drop impact research beyond the spherical geometry, and reveals the potential of using drop shape to control impact and splash.

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Evaluating ‘homegrown’ research networks in Africa

South African Journal of Science ◽

10.17159/sajs.2018/20170070 ◽

2018 ◽

Vol 114 (3/4) ◽

Cited By ~ 1

Author(s):

Camilla Adelle ◽

Nico Elema ◽

Ereck Chakauya ◽

David Benson

Keyword(s):

Wide Spectrum ◽

Evaluation Framework ◽

Evidence Based ◽

Regional Research ◽

Research Networks ◽

Sustainable Resources ◽

Science Policy Interface ◽

Mere Existence ◽

The Impact

Attempts to improve the policy environment have led to a growing pressure on governments in Africa to embark on policymaking that is more evidence based and considers a wide spectrum of scientific and indigenous knowledge. Local – or ‘homegrown’ – research networks on the continent can help strengthen the role of scientific knowledge in policymaking by increasing the capacity of researchers and by enhancing the visibility and communication of the research produced. While a large number of regional and sub-regional research networks have sprung up in Africa, the mere existence of networks does not guarantee their success. In reality, the impact of research networks on the science–policy interface depends on how well the networks operate in practice. We present a framework for evaluating the effectiveness of research networks in a way that is comparable across networks. The evaluation framework was used to evaluate two sub-regional research networks: the NEPAD Southern African Networks of Water Centres of Excellence (SANWACTE) and the NEPAD Southern African Network for Biosciences (SANBio). The evaluation revealed some shared constraints limiting the effectiveness of both networks, including uneven regional representation, asymmetry between network members, and difficulties in securing sufficient, diverse and sustainable resources. Further research into network design and funding models is suggested in order to enhance the role of these networks in providing locally appropriate knowledge for policymaking on the continent.

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The impact of rotational speed and water volume on textile translational motion in a front-loading washer

Textile Research Journal ◽

10.1177/0040517518809042 ◽

2018 ◽

Vol 89 (16) ◽

pp. 3401-3410 ◽

Cited By ~ 1

Author(s):

Hong Liu ◽

R Hugh Gong ◽

Pinghua Xu ◽

Xuemei Ding ◽

Xiongying Wu

Keyword(s):

Residence Time ◽

Rotational Speed ◽

High Speed ◽

Translational Motion ◽

Processing System ◽

Water Volume ◽

Motion Path ◽

Rotational Axis ◽

Passive Region ◽

The Impact

Textile motion in a front-loading washer has been characterized via video capturing, and a processing system developed based on image geometric moment. Textile motion significantly contributes to the mass transfer of the wash solution in porous materials, particularly in the radial direction (perpendicular to the rotational axis of the inner drum). In this paper, the velocity profiles and residence time distributions of tracer textiles have been investigated to characterize the textile dynamics in a front-loading washer. The results show that the textile motion varies significantly with the water volume and rotational speed, and that the motion path follows certain patterns. Two regions are observed in the velocity plots: a passive region where the textile moves up with low velocity and an active region where the textile falls down with relatively high speed. A stagnant area in the residence time profile is observed. This corresponds to the passive region in the velocity profile. The stagnant area affects the mechanical action, thus influencing washing efficiency and textile performance. The findings on textile dynamics will help in the development of better front-loading washers.

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