Separating Wickability and Wetting Effects During Water Droplet Evaporation on Superhydrophilic Nanoporous Surfaces

2019 ◽  
Author(s):  
Alanna Y. Cooney ◽  
Emma R. McClure ◽  
Samuel Cabrera ◽  
Van P. Carey
Keyword(s):  
Contact Angle ◽  
Impact Velocity ◽  
High Speed ◽  
Experimental Results ◽  
Nanostructured Surface ◽  
Water Droplets ◽  
Droplet Spreading ◽  
Wetting Contact Angle ◽  
Vof Model ◽  
Nanoporous Surfaces

Abstract The dynamic behavior of impinging water droplets is studied in the context of varying surface wettability and wickability on smooth and nanostructured superhydrophilic surfaces. This study distinguishes the separate effects of wetting (contact angle), wickability, and inertia on the spreading and vaporization of water droplets deposited on nanoporous surfaces by considering experimental results in tandem with axisymmetric, volume of fluid (VOF) simulations of droplet spreading. High speed videos were obtained for water droplets spreading on nanoporous surfaces which exhibit very low (< 15°) contact angle and high wickability. In this study, the effect of wickability was assessed by comparing the experimental results, which include the low contact angle and high wickability effects, to predictions of the VOF model, which include only the ultralow contact angle. While a droplet touched to the nanostructured surface demonstrates spreading driven by wicking, droplets which hit the surface with a non-zero impact velocity demonstrate spreading characteristics similar to the smooth surface, which are driven by inertia and ultra-low contact angle. The presence of the nanoporous layer impacts the equilibrium position of the contact line and the final spread radius changes with impact velocity on the nanostructured surface. These results provide fundamental input for modeling of spray cooling systems with nanostructured surfaces.

Experimental study of spreading characteristics of droplet impacting on canopy fabric surface

2017 ◽  
Vol 31 (34) ◽  
pp. 1750325 ◽  
Author(s):  
Han Cheng ◽  
Chao Qiu ◽  
Changchun Zhou ◽  
Xuebin Sun ◽  
Rui Yang
Keyword(s):  
Experimental Study ◽  
Kinetic Energy ◽  
Impact Velocity ◽  
Working Conditions ◽  
Experimental Results ◽  
Initial Kinetic Energy ◽  
Droplet Spreading ◽  
Visualization Technology ◽  
Fabric Surface ◽  
The Impact

A new experiment based on visualization technology is designed to study the spreading characteristics of droplet impacting on canopy fabric. The processes of droplet impacting on 66 type polyamide grid silk are captured. The experimental results show that the spreading characteristics are also affected by fabric pretension and fabric permeability. The pretension is favorable for the droplet to reach the final equilibrium stage. The impact velocity determines the initial kinetic energy and plays a major role in the droplet spreading. The fabric permeability determines the wettability and has different effects on spreading characteristics under different working conditions. In addition, the above factors can enhance the two competitive processes of spreading and imbibing at the same time. The spreading characteristics depend on which process is the dominant one.

Deposition Process of Droplets Impacting on a Horizontal Surface

2011 ◽  
Vol 354-355 ◽  
pp. 579-584 ◽  
Author(s):  
Jing Yin Li ◽  
Qiang Han ◽  
Yan Jie Zhao ◽  
Xiao Fang Yuan
Keyword(s):  
Impact Velocity ◽  
High Speed ◽  
Droplet Impact ◽  
Numerical Results ◽  
Horizontal Surface ◽  
Experimental Investigations ◽  
Impact Process ◽  
Vof Model ◽  
Spread Factor ◽  
The Impact

The results of the experimental investigations and numerical simulations of droplet impact on a stationary horizontal surface are presented. The impact process of a droplet with high impact energy on a horizontal surface was photographed by a high-speed CCD. In addition, two-dimensional numerical simulation of the impact process was also performed using the VOF model. Comparison between the experimental and numerical results shows that the chosen computational model is suitable to simulate such impact processes. Furthermore, the effect of the droplet impact velocity and diameter on the impact process was studied in detailed. The numerical results show that the variation in droplet impact velocity has a significant effect on the maximum spread factor and spread speed, whereas, the variation in droplet diameter considerably influences the maximum spread factor and the oscillation of the drop in the receding phase.

Capillary Driven Fluid Flow in Medical Devices

2008 ◽  
Author(s):  
Fiachra A. O’Leary ◽  
Philip C. Griffin
Keyword(s):  
Contact Angle ◽  
High Speed ◽  
Computational Models ◽  
Fluid Velocity ◽  
Initial Pressure ◽  
Cardiac Risk ◽  
Cross Sectional ◽  
Aspect Ratios ◽  
Vof Model ◽  
Epoxy Material

Microscale fluid dynamics has played a significant role in the development of many applications in the medical diagnostic sector and in recent years many devices have implemented advances in this field. Capillary driven assays are commonly used in diagnostic areas, such as, cardiac risk, fertility, drug abuse and infectious diseases1. Typically a platform is used where bodily fluids or samples are taken, filtered and by means of small microchannels, transported and mixed with a variety of antibodies2. In order to perform correctly, these antibodies need to bind to the proteins in the fluid. It is therefore essential that the exposure of the proteins to the antibodies is maximized. To achieve this, capillary dimensions can be altered to obtain the required flow rates and exposure times3. This paper focuses on controlling these parameters. In this paper, a study was conducted in which the flows in four straight rectangular microchannels of varying cross sectional areas were assessed. The four microchannels were fabricated from an epoxy material. The microchannel widths varied from 100μm to 1000μm with each channel having a dept of 200μm. The four microchannels had aspect ratios of 0.5, 1, 2 and 10. The microchannels were sealed using a heat sealing hydrophilic tape. Fluid velocity rates were measured experimentally using an X-Stream XS-4 high speed camera at 500 frames per second. Preliminary contact angle results between water and the epoxy material gave a contact angle of 81.5 degrees +/− 6 degrees. Computational models of the four microchannels were performed using a Volume Of Fluid (VOF) model in Fluent 6.2.16, a commercially available CFD code. The computational models had four boundary types: pressure inlet, pressure outlet, epoxy wall and hydrophilic tape wall. The inlet boundary has an initial pressure applied to it, capillary pressure between the water and air interface in the microchannel. It was found that as the dimensions of the microchannels increased, the governing equations were less accurate in predicting the experimental fluid velocity in the microchannels.

scholarly journals Enhancement of Sensitivity and Accuracy of Micro/Nano Water Droplets Detection Using Galvanic-Coupled Arrays

Sensors ◽  
2019 ◽  
Vol 19 (20) ◽  
pp. 4500 ◽  
Author(s):  
Rekha Goswami Shrestha ◽  
Tatsuya Ando ◽  
Yukihiro Sakamoto ◽  
Jin Kawakita
Keyword(s):  
Contact Angle ◽  
Water Droplet ◽  
High Speed ◽  
Current Response ◽  
Water Droplets ◽  
Galvanic Current ◽  
Moisture Sensor ◽  
Average Value ◽  
Small Water ◽  
Working Principle

A moisture sensor has been reported that detects invisibly small water droplets and distinguishes their particle size with high accuracy and high speed. This sensor uses narrow lines of dissimilar metals as electrodes, arranged with gaps of 0.5 to 10 μm. The working principle for this sensor is that it measures the galvanic current generated when a water droplet forms a bridge-like structure between the electrodes. In addition, the surface of the sensor was controlled by using hydrophilic polymer, GL, and hydrophobic polymer, PMMA. The study of the relationship between the contact angle, projected area of water droplets and current response from the sensor with a modified surface showed that in the case of GL, the contact angle was small (wettability increased) and the average value and distribution of the projected water droplet area and the sensor’s response increased. This enhanced the sensor’s sensitivity. On the other hand, in the case of PMMA, the contact angle was large (wettability decreased), the area of the water droplet and its distribution became small and the accuracy of discriminating the water droplet’s diameter by the sensor enhanced. Therefore, by rendering sensor’s surface hydrophilic and hydrophobic, the sensitivity and accuracy of the sensor could be enhanced.

Gas-Assisted Droplet Impact on a Solid Surface

2016 ◽  
Vol 138 (8) ◽  
Author(s):  
Andres J. Diaz ◽  
Alfonso Ortega
Keyword(s):  
Solid Surface ◽  
High Speed ◽  
Liquid Droplet ◽  
High Speed Photography ◽  
Droplet Deformation ◽  
Droplet Spreading ◽  
Carrier Gas ◽  
Air Jet ◽  
Vof Model ◽  
Theoretical Predictions

An experimental, numerical, and theoretical investigation of the behavior of a gas-assisted liquid droplet impacting on a solid surface is presented with the aim of determining the effects of a carrier gas on the droplet deformation dynamics. Experimentally, droplets were generated within a circular air jet for gas Reynolds numbers Reg = 0–2547. High-speed photography was used to capture the droplet deformation process, whereas the numerical analysis was conducted using the volume of fluid (VOF) model. The numerical and theoretical predictions showed that the contribution of a carrier gas to the droplet spreading becomes significant only at high Weo and when the work done by pressure forces is greater than 10% of the kinetic energy. Theoretical predictions of the maximum spreading diameter agree reasonably well with the experimental and numerical observations.

Effect of Impact Velocity and Substrate Temperature on Boiling of Water Droplets Impinging on a Hot Stainless Steel Surface

Volume 3 ◽  
2004 ◽  
Author(s):  
N. Z. Mehdizadeh ◽  
S. Chandra
Keyword(s):  
Stainless Steel ◽  
Substrate Temperature ◽  
Impact Velocity ◽  
Steel Surface ◽  
Bubble Nucleation ◽  
Test Surface ◽  
Stainless Steel Surface ◽  
Water Droplets ◽  
Droplet Spreading ◽  
The Impact

We photographed high velocity impact of small water droplets (0.55 mm) on a heated stainless steel surface. To achieve high impact velocities the test surface was mounted on the rim of a rotating flywheel, giving linear velocities of up to 50 m/s. Two cartridge heaters were inserted in the substrate and used to vary substrate temperature. A CCD video camera was used to photograph droplets impinging on the substrate. By synchronizing the ejection of a single droplet with the position of the rotating flywheel and triggering of the camera, different stages of droplet impact were photographed. Substrate temperature was varied from 100–240°C and the impact velocity from 10–30 m/s. High-resolution photographs were taken of vapor bubbles nucleating sites inside the thin films produced by spreading droplets. For a given impact velocity, the extent of droplet spreading increased with substrate temperature. The superheat needed to initiate bubble nucleation decreased with impact velocity. We derived an analytical expression for the amount of superheat required for vapor bubble nucleation as a function of impact velocity.

Modification of Polishing Putty: A Study on Inorganic Filler

2011 ◽  
Vol 84-85 ◽  
pp. 509-513
Author(s):  
Chun Bo Bi ◽  
Jian Guang Lin ◽  
Zeng Chuan Hao
Keyword(s):  
Contact Angle ◽  
Atomic Force Microscope ◽  
Coupling Agent ◽  
Experimental Results ◽  
Microstructure Analysis ◽  
Inorganic Filler ◽  
Talcum Powder ◽  
Wetting Contact Angle ◽  
Atomic Force ◽  
The Relationship

The microstructure of talcum powder added with the KH550、KH560 and silane composite coupling agent were studied by atomic force microscope, the modified effect of KH560 coupling agent was the best, which verified through the microstructure analysis and the wetting contact Angle proved law method. The relationship between the dosage of KH560 coupling agent and contact angle was analyzed by the wetting contact Angle proved law method. The optimum dosage of KH560 coupling agent was determined by the experimental results of the viscosity of polishing putty.

Effects of Ambient Air Relative Humidity and Surface Temperature on Water Droplet Spreading Dynamics

2018 ◽  
Author(s):  
M. Jadidi ◽  
M. A. Farzad ◽  
J. Y. Trepanier ◽  
A. Dolatabadi
Keyword(s):  
Contact Angle ◽  
Relative Humidity ◽  
Surface Temperature ◽  
Air Temperature ◽  
Water Droplet ◽  
Superhydrophobic Surface ◽  
High Speed ◽  
Ambient Air ◽  
Dew Point ◽  
Droplet Spreading

Water droplet impact on horizontal glass, aluminum, and superhydrophobic surfaces is experimentally investigated using high speed imaging. Experiments are performed at three different relative humidities (i.e. 10, 20 and 30%) and three surface temperatures (i.e. 20, 2 and −2°C) to ascertain their effects on droplet spreading and recoil behaviors. In this study, the droplet Weber number, Reynolds number, and the ambient air temperature are fixed at 16.2, 1687, and 23°C, respectively. The high-speed images of impact, spreading and recoil of the droplets as well as the temporal variations of droplet spreads are prepared. Results show that the ratio of surface temperature to dew point temperature (which depends on the air temperature and relative humidity) has a significant influence on droplet spreading, recoil, and contact angle. When this ratio is less than one, condensation and frost formation become important. Decreasing the mentioned ratio (it can be done by decreasing the surface temperature or increasing the relative humidity) causes the droplet spreading factor for hydrophilic surfaces to increase significantly. For superhydrophobic surface, decreasing this ratio (within the mentioned range) does not influence the maximum spreading. However, the recoiling phase is slowed down and the droplet detachment time form the superhydrophobic surface is increased noticeably. In addition, the equilibrium contact angle decreases as the mentioned ratio decreases.

Yaw Galloping of a TLWP Platform Under High Speed Currents by Analytical Methods and its Comparison With Experimental Results

2017 ◽  
Author(s):  
Francisco Lamas ◽  
Miguel A. M. Ramirez ◽  
Antonio Carlos Fernandes
Keyword(s):  
High Speed ◽  
Production Systems ◽  
Experimental Tests ◽  
Experimental Results ◽  
Analytical Methodology ◽  
New Approach ◽  
Laboratory Facilities ◽  
Polynomial Curve ◽  
Computational Fluid Dynamics Cfd ◽  
Cfd Analyses

Flow Induced Motions are always an important subject during both design and operational phases of an offshore platform life. These motions could significantly affect the performance of the platform, including its mooring and oil production systems. These kind of analyses are performed using basically two different approaches: experimental tests with reduced models and, more recently, with Computational Fluid Dynamics (CFD) dynamic analysis. The main objective of this work is to present a new approach, based on an analytical methodology using static CFD analyses to estimate the response on yaw motions of a Tension Leg Wellhead Platform on one of the several types of motions that can be classified as flow-induced motions, known as galloping. The first step is to review the equations that govern the yaw motions of an ocean platform when subjected to currents from different angles of attack. The yaw moment coefficients will be obtained using CFD steady-state analysis, on which the yaw moments will be calculated for several angles of attack, placed around the central angle where the analysis is being carried out. Having the force coefficients plotted against the angle values, we can adjust a polynomial curve around each analysis point in order to evaluate the amplitude of the yaw motion using a limit cycle approach. Other properties of the system which are flow-dependent, such as damping and added mass, will also be estimated using CFD. The last part of this work consists in comparing the analytical results with experimental results obtained at the LOC/COPPE-UFRJ laboratory facilities.

The Effect of Strain Rate on the Material Characteristics of Nickel-Based Superalloy Inconel 718

2007 ◽  
Vol 340-341 ◽  
pp. 283-288 ◽  
Author(s):  
Jung Han Song ◽  
Hoon Huh
Keyword(s):  
Dynamic Response ◽  
High Strain Rate ◽  
Strain Rate ◽  
Turbine Blade ◽  
Inconel 718 ◽  
High Speed ◽  
High Strain ◽  
Split Hopkinson Pressure Bar ◽  
Experimental Results ◽  
Stress Wave Propagation

The dynamic response of the turbine blade materials is indispensable for analysis of erosions of turbine blades as a result of impulsive loading associated with gas flow. This paper is concerned with the dynamic material properties of the Inconel 718 alloy which is widely used in the high speed turbine blade. The dynamic response at the corresponding level of the strain rate should be acquired with an adequate experimental technique and apparatus due to the inertia effect and the stress wave propagation. In this paper, the dynamic response of the Inconel 718 at the intermediate strain rate ranged from 1/s to 400/s is obtained from the high speed tensile test and that at the high strain rate above 1000/s is obtained from the split Hopkinson pressure bar test. The effects of the strain rate on the dynamic flow stress, the strain rate sensitivity and the failure elongation are evaluated with the experimental results. Experimental results from both the quasi-static and the high strain rate up to 3000/s are interpolated in order to construct the constitutive relation that should be applied to simulate the dynamic behavior of the turbine blade made of the Inconel 718.

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