scholarly journals Vibration-Enhanced Droplet Motion Modes: Simulations of Rocking, Ratcheting, Ratcheting With Breakup, and Ejection

2019 ◽  
Vol 141 (7) ◽  
Author(s):  
Ryan A. Huber ◽  
Matthew Campbell ◽  
Nicole Doughramaji ◽  
Melanie M. Derby
Keyword(s):  
Contact Angle ◽  
Contact Angle Hysteresis ◽  
Vertical Surface ◽  
Water Recovery ◽  
Droplet Motion ◽  
Droplet Ejection ◽  
First Case ◽  
Wide Range ◽  
Diameter Droplet ◽  
Boltzmann Method

Power plant water usage is a coupling of the energy–water nexus; this research investigates water droplet motion, with implications for water recovery in cooling towers. Simulations of a 2.6 mm-diameter droplet motion on a hydrophobic, vertical surface were conducted in xflow using the lattice Boltzmann method (LBM). Results were compared to two experimental cases; in the first case, experimental and simulated droplets experienced 30 Hz vibrations (i.e., ±0.1 mm x-direction amplitude, ±0.2 mm y-direction amplitude) and the droplet ratcheted down the surface. In the second case, 100 Hz vibrations (i.e., ±0.8 mm x-direction amplitude, ±0.2 mm y-direction amplitude) caused droplet ejection. Simulations were then conducted for a wide range of frequencies (i.e., 10–100 Hz) and amplitudes (i.e., ±0.018–50 mm), resulting in maximum accelerations of 0.197–1970 m/s2. Under low maximum accelerations (e.g., <7 m/s2), droplets rocked upward and downward in rocking mode, but did not overcome the contact angle hysteresis and, therefore, did not move. As acceleration increased, droplets overcame the contact angle hysteresis and entered ratcheting mode. For vibrations that prompted droplet motion, droplet velocities varied between 10–1000 mm/s. At capillary numbers above approximately 0.0044 and Weber numbers above 3.6, liquid breakup was observed in ratcheting droplets (e.g., the formation of smaller child droplets from the parent droplet). It was noted that both x- and y-direction vibrations were required for droplet ejection.

scholarly journals Amphiphobic Nanostructured Coatings for Industrial Applications

Materials ◽  
2019 ◽  
Vol 12 (5) ◽  
pp. 787 ◽  
Author(s):  
Federico Veronesi ◽  
Giulio Boveri ◽  
Mariarosa Raimondo
Keyword(s):  
Surface Tension ◽  
Contact Angle ◽  
Photoelectron Spectroscopy ◽  
Contact Angle Hysteresis ◽  
Contact Angles ◽  
Friction Reduction ◽  
Hybrid Coatings ◽  
Wetting Behavior ◽  
Wide Range ◽  
Solid Liquid

The search for surfaces with non-wetting behavior towards water and low-surface tension liquids affects a wide range of industries. Surface wetting is regulated by morphological and chemical features interacting with liquid phases under different ambient conditions. Most of the approaches to the fabrication of liquid-repellent surfaces are inspired by living organisms and require the fabrication of hierarchically organized structures, coupled with low surface energy chemical composition. This paper deals with the design of amphiphobic metals (AM) and alloys by deposition of nano-oxides suspensions in alcoholic or aqueous media, coupled with perfluorinated compounds and optional infused lubricant liquids resulting in, respectively, solid–liquid–air and solid–liquid–liquid working interfaces. Nanostructured organic/inorganic hybrid coatings with contact angles against water above 170°, contact angle with n-hexadecane (surface tension γ = 27 mN/m at 20 °C) in the 140–150° range and contact angle hysteresis lower than 5° have been produced. A full characterization of surface chemistry has been undertaken by X-ray photoelectron spectroscopy (XPS) analyses, while field-emission scanning electron microscope (FE-SEM) observations allowed the estimation of coatings thicknesses (300–400 nm) and their morphological features. The durability of fabricated amphiphobic surfaces was also assessed with a wide range of tests that showed their remarkable resistance to chemically aggressive environments, mechanical stresses and ultraviolet (UV) radiation. Moreover, this work analyzes the behavior of amphiphobic surfaces in terms of anti-soiling, snow-repellent and friction-reduction properties—all originated from their non-wetting behavior. The achieved results make AM materials viable solutions to be applied in different sectors answering several and pressing technical needs.

3-D Numerical Simulation of Contact Angle Hysteresis for Slug Flow in Microchannel

2007 ◽  
Author(s):  
Chen Fang ◽  
Carlos Hidrovo ◽  
Fumin Wang ◽  
Julie Steinbrenner ◽  
Eonsoo Lee ◽  
...  
Keyword(s):  
Contact Angle ◽  
Produced Water ◽  
Volume Fraction ◽  
Piecewise Linear ◽  
Contact Angle Hysteresis ◽  
Pem Fuel Cells ◽  
Angle Distribution ◽  
Confined Space ◽  
Interface Position ◽  
Wide Range

Water management that ensures the effective removal of produced water in the microchannel at the cathode is critical for the performance of PEM fuel cells. The small dimension and confined space of channels leads to the importance of the surface force in determining the dynamics of inside liquid slugs. The present study focuses on the simulation of the slug detachment process in the micro-channel, using a contact angle hysteresis model within the framework of VOF approach. Based on solving the nonlinear equations accounting for the relationship among volume fraction, interface position, and contact angle, a special model is developed to replicate the hysteresis effect. In addition, a special algorithm is introduced to simulate the thin liquid/gas films. A systematic comparison between experiment and simulation has been conducted and the quantitative match in terms of slug dimensions is achieved for a wide range of flow conditions. The simulation reveals that the contact angle distribution along the slug profile could be approximated using piecewise linear function. The calculation also shows that the contact angle hysteresis might be responsible for several phenomena observed in experiment, such as slug instability.

Thermally Actuated Droplet Motion on Chemically Homogeneous, Striated, and Defected Surfaces

2008 ◽  
Author(s):  
Jian-Zhang Chen
Keyword(s):  
Contact Angle ◽  
Contact Angle Hysteresis ◽  
Three Dimensional ◽  
Droplet Radius ◽  
Three Dimensional Model ◽  
Thermocapillary Force ◽  
Droplet Motion ◽  
Viscous Forces ◽  
Hydrophobic Coating ◽  
Numerical Predictions

Experiments have demonstrated thermocapillary actuation on uniformly grafted partial-wettable surfaces. Droplet mobilization only occurs above a threshold thermal gradient or threshold droplet radius [1]. We characterized the motion instead in terms of a threshold depinning force, which successfully describes all the liquids tested. Above the depinning transition, the droplet speed, which is controlled by thermocapillary, capillary and viscous forces, increases monotonically with this reduced force parameterization. These results agree well to numerical predictions of a generalized Ford and Nadim model by using two fitting parameters, the slip coefficient and the magnitude of contact angle hysteresis [2–3]. In this follow-up study, we developed a doubly grafted surface, on which alkyltrichlorosilane coated stripes are surrounded by a more hydrophobic coating, perfluoroctyl-trichlorosilane. The quality of alkyltrichlorosilane coated stripes was still good for the thermocapillary droplet actuation, in which droplets were driven on the alkyltrichlorosilane surface and confined by the perfluoroctyl-trichlorosilane. The experimental results are also well described by a derived approximate three-dimensional model equation, which resembles the parameterization. The droplets are driven by thermocapillary force and retarded by contact angle hysteretic force, represented as contact angle hysteresis. This contact angle hysteresis is caused by chemical heterogeneity, surface roughness etc [4]. In the last part of this presentation, we will also present the thermocapillary droplet motion on a designed defected surface, which shows a tiny defect can severely hinge the droplet.

Studying of Contact Angle Friction and Contact Angle Hysteresis (CAH) Though Force Measurements

2012 ◽  
Author(s):  
Qi Ni ◽  
Timo Marschke ◽  
Samuel Steele ◽  
Najafi Seyed ◽  
Nathan B. Crane
Keyword(s):  
Contact Angle ◽  
Contact Line ◽  
Contact Angle Hysteresis ◽  
Contact Angles ◽  
Force Measurements ◽  
Droplet Motion ◽  
Characterization Methods ◽  
Receding Contact ◽  
Novel Method ◽  
Contact Line Friction

A novel method of measuring contact line friction and contact angle hysteresis is described. In this method, a droplet is constrained between two surfaces while the surface of interest initiates motion. The results are compared to conventional characterization methods such as measuring the angle of inclined plane for droplet motion and measuring advancing and receding contact angles by infusing/withdrawing liquid from the substrate. At slow speeds, the proposed method provides a measure of the hysteresis but can also capture information about the contact line friction and viscous affects. Droplet force dependence on droplet size (height/width) is also investigated.

Surprising Lack of Influence on Water Droplet Motion by Hydrophilic Microdomains on Checkerboard-like Surfaces with Matched Contact Angle Hysteresis

Langmuir ◽  
2020 ◽  
Vol 36 (27) ◽  
pp. 7835-7843 ◽  
Author(s):  
Brandon Becher-Nienhaus ◽  
Guojun Liu ◽  
Richard J. Archer ◽  
Atsushi Hozumi
Keyword(s):  
Contact Angle ◽  
Water Droplet ◽  
Contact Angle Hysteresis ◽  
Droplet Motion

scholarly journals Direct and accurate measurement of size dependent wetting behaviors for sessile water droplets

2015 ◽  
Vol 5 (1) ◽  
Author(s):  
Jimin Park ◽  
Hyung-Seop Han ◽  
Yu-Chan Kim ◽  
Jae-Pyeong Ahn ◽  
Myoung-Ryul Ok ◽  
...  
Keyword(s):  
Contact Angle ◽  
Focused Ion Beam ◽  
Ion Beam ◽  
Contact Angle Hysteresis ◽  
Dependent Manner ◽  
Water Droplets ◽  
Formation Pathway ◽  
Size Dependent ◽  
Three Phase ◽  
Wide Range

Abstract The size-dependent wettability of sessile water droplets is an important matter in wetting science. Although extensive studies have explored this problem, it has been difficult to obtain empirical data for microscale sessile droplets at a wide range of diameters because of the flaws resulting from evaporation and insufficient imaging resolution. Herein, we present the size-dependent quantitative change of wettability by directly visualizing the three phase interfaces of droplets using a cryogenic-focused ion beam milling and SEM-imaging technique. With the fundamental understanding of the formation pathway, evaporation, freezing and contact angle hysteresis for sessile droplets, microdroplets with diameters spanning more than three orders of magnitude on various metal substrates were examined. Wetting nature can gradually change from hydrophobic at the hundreds-of-microns scale to super-hydrophobic at the sub-μm scale and a nonlinear relationship between the cosine of the contact angle and contact line curvature in microscale water droplets was demonstrated. We also showed that the wettability could be further tuned in a size-dependent manner by introducing regular heterogeneities to the substrate.

Lattice Boltzmann modeling for the coalescence between a free droplet in gases and a sessile droplet on wettable substrate with contact angle hysteresis

2017 ◽  
Vol 232 (3) ◽  
pp. 431-444 ◽  
Author(s):  
Lei Wang ◽  
Jianglong Sun
Keyword(s):  
Contact Angle ◽  
Kinetic Energy ◽  
Lattice Boltzmann ◽  
Capillary Wave ◽  
Contact Angle Hysteresis ◽  
Typical Characteristic ◽  
Ohnesorge Number ◽  
Sessile Droplet ◽  
Two Phase ◽  
Boltzmann Method

The coalescence between a free droplet and a sessile droplet on wettable substrate is numerically studied. The axisymmetric lattice Boltzmann method for two-phase flows is used in modeling. Here the contact angle hysteresis (prescribed by advancing angle [Formula: see text] and receding angle [Formula: see text]) is taken into account. The effects of Ohnesorge number ( Oh), contact angle and its hysteresis, and the radius of the free droplet on the coalescence dynamics are investigated in detail. The Oh numbers ranging from 0.02 to 0.15 here makes the radius of the liquid bridge r and the time t follow power law. Also, Oh has remarkable impact on the development of capillary wave and on the amount of kinetic energy released from coalescence. It is found that the curve of the wetting radius varying with time includes several plateau stages, which is a typical characteristic for the effect of contact angle hysteresis. The larger window of contact angle hysteresis would result in smaller steady wetting radius after coalescence. Compared with the existence of contact angle hysteresis, the absence of contact angle hysteresis makes the droplets system release more kinetic energy during the coalescence but the released kinetic energy decays more rapidly and soon reduces to zero. Oppositely, if the contact angle hysteresis exists, the released kinetic energy would oscillate for a period of time before approaching zero.

A NEW APPROACH TO INVESTIGATE CONTACT ANGLE HYSTERESIS

2018 ◽  
Author(s):  
Qiao Liu ◽  
Abbasali Abouei Mehrizi ◽  
Hao Wang
Keyword(s):  
Contact Angle ◽  
Contact Angle Hysteresis ◽  
New Approach
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