Measurement of Liquid Droplet Evaporation Rate under the Conditions of Intense Heating

2014 ◽  
Vol 698 ◽  
pp. 603-608 ◽  
Author(s):  
Evgenija Orlova ◽  
Dmitriy Feoktistov
Keyword(s):  
Contact Angle ◽  
Contact Line ◽  
Evaporation Rate ◽  
Liquid Droplet ◽  
Droplet Evaporation ◽  
Solid Substrate ◽  
Anodized Aluminum ◽  
Specific Evaporation Rate ◽  
Contact Line Pinning ◽  
Contact Diameter

This paper presents an experimental study of the evaporation of a sessile water-sodium chlorides solution drop to open atmosphere on the solid substrate (anodized aluminum) under the varying heat flux. The main parameters defining drop profile, i. e., contact diameter, contact angle, and height of the drop have been obtained. Specific evaporation rate has been calculated. According to the data analysis it was found, that the sessile water-sodium chlorides solution drop with the highest concentration (16.7%) evaporates in the "reverse depinning" mode. So, there is movement of the contact line in the direction of increasing the surface occupied by the drop. The sessile water and water-sodium chlorides solution drop with 4.8% and 9.1% concentration evaporates in the contact line pinning mode. The influence of the initial concentration of the evaporated solution on the contact angle and the specific evaporation rate was found out.

Numerical Study of Water Droplet Evaporation on a Superhydrophobic Surface

2013 ◽  
Author(s):  
Zhenhai Pan ◽  
Susmita Dash ◽  
Justin A. Weibel ◽  
Suresh V. Garimella
Keyword(s):  
Contact Angle ◽  
Water Droplet ◽  
Evaporation Rate ◽  
Numerical Study ◽  
Liquid Droplet ◽  
Current Model ◽  
Solid Substrate ◽  
Analytical Models ◽  
Vapor Concentration ◽  
Constant Contact Angle

A comprehensive numerical model is developed to predict evaporation of a water droplet from an unheated superhydrophobic substrate. Analytical models that only consider vapor diffusion in the gas domain, and assume the system to be isothermal, over-predict the evaporation rates by ∼25% compared to experiments conducted on such surfaces. The current model solves for conjugate heat and mass transfer in the solid substrate, liquid droplet, and surrounding gas. Evaporative cooling of the interface is accounted for, and vapor concentration is coupled to local temperature at the interface. Buoyancy-driven convective flows in the droplet and vapor domains are also simulated. A droplet evaporating in a constant-contact-angle mode with an initial volume of 3 μl and contact angle of 160 deg is considered at an ambient temperature of 21°C and 29% relative humidity, to match conditions of related experiments. The interface cooling effect suppresses the evaporation rate significantly; however, natural convection in the gas and liquid domains has a negligible impact on the evaporation rate. The local evaporation flux along the droplet interface predicted by the model is compared to that predicted by an analytical diffusion-based model. The numerically calculated total evaporation rate agrees with experimental results to within 2%. The large deviations between past analytical models and the experimental data on superhydrophobic surfaces are reconciled.

WATER DROPLET EVAPORATION IN A CHAMBER ISOLATED FROM THE EXTERNAL ENVIRONMENT

2020 ◽  
Vol 6 (3) ◽  
pp. 8-22
Author(s):  
KSENIA A. Batishcheva ◽  
ATLANT E. Nurpeiis
Keyword(s):  
Water Vapor ◽  
Evaporation Rate ◽  
External Environment ◽  
Heat Removal ◽  
Droplet Evaporation ◽  
Droplet Volume ◽  
Evaporation Time ◽  
Aluminum Alloy Amg6 ◽  
Evaporation Of Droplets ◽  
Contact Diameter

With an increase in the productivity of power equipment and the miniaturization of its components, the use of traditional thermal management systems becomes insufficient. There is a need to develop drip heat removal systems, based on phase transition effects. Cooling with small volumes of liquids is a promising technology for microfluidic devices or evaporation chambers, which are self-regulating systems isolated from the external environment. However, the heat removal during evaporation of droplets into a limited volume is a difficult task due to the temperature difference in the cooling device and the concentration of water vapor that is unsteady in time depending on the mass of the evaporated liquid. This paper presents the results of an experimental study of the distilled water microdrops’ (5-25 μl) evaporation on an aluminum alloy AMg6 with the temperatures of 298-353 K in an isolated chamber (70 × 70 × 30 mm3) in the presence of heat supply to its lower part. Based on the analysis of shadow images, the changes in the geometric dimensions of evaporating drops were established. They included the increase in the contact diameter, engagement of the contact line due to nano roughening and chemical composition inhomogeneous on the surface (90-95% of the total evaporation time) of the alloy and a decrease in the contact diameter. The surface temperature and droplet volume did not affect the sequence of changes in the geometric dimensions of the droplets. It was found that the droplet volume has a significant effect on the evaporation time at relatively low substrate temperatures. The results of the analysis of droplet evaporation rates and hygrometer readings have shown that reservoirs with salt solutions can be used in isolated chambers to control the concentration of water vapor. The water droplets evaporation time was determined. The analysis of the time dependences of the evaporation rate has revealed that upon the evaporation of droplets in an isolated chamber under the conditions of the present experiment, the air was not saturated with water vapor. The latter did not affect the evaporation rate.

Anomalous Contact Angle Hysteresis of a Captive Bubble: Advancing Contact Line Pinning

Langmuir ◽  
2011 ◽  
Vol 27 (11) ◽  
pp. 6890-6896 ◽  
Author(s):  
Siang-Jie Hong ◽  
Feng-Ming Chang ◽  
Tung-He Chou ◽  
Seong Heng Chan ◽  
Yu-Jane Sheng ◽  
...  
Keyword(s):  
Contact Angle ◽  
Contact Line ◽  
Contact Angle Hysteresis ◽  
Contact Line Pinning

Ring-Shaped Sessile Droplet

2011 ◽  
Author(s):  
Svyatoslav S. Chugunov ◽  
Douglas L. Schulz ◽  
Iskander S. Akhatov
Keyword(s):  
Contact Angle ◽  
Liquid Droplet ◽  
Liquid Structure ◽  
Solid Substrate ◽  
Contact Angles ◽  
Equilibrium Contact Angle ◽  
Sessile Droplet ◽  
System Equilibrium ◽  
Energy Consideration ◽  
External Forces

It is recognized that small liquid droplet placed on the solid substrate forms equilibrium contact angle that can be obtained from well-known Young’s law. Previously, deviations from Young’s law were demonstrated for the droplets exposed to external fields (gravity, electric, etc) and for the droplets on non-homogeneous substrates. This work reveals that the Young’s equilibrium contact angle can be altered by geometrical reasons only. We consider a ring-shaped droplet on a solid substrate as a test structure for our discussion. We use the global energy consideration for analysis of system equilibrium for the case of freely deposited liquid with no external forces applied. The theoretical analysis shows that steady ring-shaped liquid structure on a solid substrate does exist with contact angles on both contact lines to be different from the Young’s equilibrium contact angle.

Contact Line Pinning and Depinning Prior to Rupture of an Evaporating Droplet in a Simulated Soil Pore

2020 ◽  
Author(s):  
Partha P. Chakraborty ◽  
Melanie M. Derby
Keyword(s):  
Contact Line ◽  
Pressure Difference ◽  
Liquid Droplet ◽  
Liquid Droplets ◽  
Water Contact ◽  
Marginal Rate ◽  
Vapor Interface ◽  
Hydrophobic Pore ◽  
Contact Line Pinning ◽  
Liquid Vapor

Abstract Altering soil wettability by inclusion of hydrophobicity could be an effective way to restrict evaporation from soil, thereby conserving water resources. In this study, 4-μL sessile water droplets were evaporated from an artificial soil millipore comprised of three glass (i.e. hydrophilic) and Teflon (i.e. hydrophobic) 2.38-mm-diameter beads. The distance between the beads were kept constant (i.e. center-to-center spacing of 3.1 mm). Experiments were conducted in an environmental chamber at an air temperature of 20°C and 30% and 75% relative humidity (RH). Evaporation rates were faster (i.e. ∼19 minutes and ∼49 minutes at 30% and 75% RH) from hydrophilic pores than the Teflon one (i.e. ∼24 minutes and ∼52 minutes at 30% and 75% RH) due in part to greater air-water contact area. Rupture of liquid droplets during evaporation was analyzed and predictions were made on rupture based on contact line pinning and depinning, projected surface area just before rupture, and pressure difference across liquid-vapor interface. It was observed that, in hydrophilic pore, the liquid droplet was pinned on one bead and the contact line on the other beads continuously decreased by deforming the liquid-vapor interface, though all three gas-liquid-solid contact lines decreased at a marginal rate in hydrophobic pore. For hydrophilic and hydrophobic pores, approximately 1.7 mm2 and 1.8–2 mm2 projected area of the droplet was predicted at 30% and 75% RH just before rupture occurs. Associated pressure difference responsible for rupture was estimated based on the deformation of curvature of liquid-vapor interface.

Sculpting and Aerosolizing Pinned Liquid Films With Localized Acoustic Pressures of Surface Acoustic Waves

2012 ◽  
Author(s):  
Daniel Taller ◽  
Hsueh-Chia Chang ◽  
David B. Go
Keyword(s):  
Contact Angle ◽  
Numerical Modeling ◽  
Contact Line ◽  
Acoustic Waves ◽  
Acoustic Pressure ◽  
Surface Acoustic Waves ◽  
Liquid Films ◽  
Solid Substrate ◽  
Planar Surface ◽  
Bulk Film

Due to viscous decay, a planar surface acoustic wave (SAW) diffracting from a solid substrate into a liquid film produces a time-averaged, exponentially decaying acoustic pressure in the film. We show that if the film is pinned against a bounding wall, the localized acoustic pressure generates a sequence of surface drops at the contact line, whose dimensions decay in the same exponential manner as the localized acoustic pressure. The undulating interfacial profile near the contact line also inherits this exponential decay, such that the averaged contact angle is exponentially small. The bulk film topology and the aerosolization mechanism are hence insensitive to the wettability of the surface but are controlled only by the localized acoustic pressure and the decaying undulations it produces at the contact line. The size distribution of surface drops is collapsed under the exponential scaling that depends only on the SAW decay rate and amplitude. Numerical modeling based on the Young-Laplace equation is used to model the liquid profile and to predict two aerosolization regimes.

scholarly journals On-demand contact line pinning during droplet evaporation

2020 ◽  
Vol 312 ◽  
pp. 127983
Author(s):  
Wei Wang ◽  
Qi Wang ◽  
Kaidi Zhang ◽  
Xubo Wang ◽  
Antoine Riaud ◽  
...  
Keyword(s):  
Contact Line ◽  
Droplet Evaporation ◽  
On Demand ◽  
Contact Line Pinning

scholarly journals Evaporation of sessile drops: a three-dimensional approach

2015 ◽  
Vol 772 ◽  
pp. 705-739 ◽  
Author(s):  
P. J. Sáenz ◽  
K. Sefiane ◽  
J. Kim ◽  
O. K. Matar ◽  
P. Valluri
Keyword(s):  
Contact Angle ◽  
Contact Line ◽  
Evaporation Rate ◽  
Three Dimensional ◽  
Complex Case ◽  
Interface Temperature ◽  
Angle Distribution ◽  
Moving Contact Line ◽  
Moving Contact ◽  
Sessile Drops

The evaporation of non-axisymmetric sessile drops is studied by means of experiments and three-dimensional direct numerical simulations (DNS). The emergence of azimuthal currents and pairs of counter-rotating vortices in the liquid bulk flow is reported in drops with non-circular contact area. These phenomena, especially the latter, which is also observed experimentally, are found to play a critical role in the transient flow dynamics and associated heat transfer. Non-circular drops exhibit variable wettability along the pinned contact line sensitive to the choice of system parameters, and inversely dependent on the local contact-line curvature, providing a simple criterion for estimating the approximate contact-angle distribution. The evaporation rate is found to vary in the same order of magnitude as the liquid–gas interfacial area. Furthermore, the more complex case of drops evaporating with a moving contact line (MCL) in the constant contact-angle mode is addressed. Interestingly, the numerical results demonstrate that the average interface temperature remains essentially constant as the drop evaporates in the constant-angle (CA) mode, while this increases in the constant-radius (CR) mode as the drops become thinner. It is therefore concluded that, for increasing substrate heating, the evaporation rate increases more rapidly in the CR mode than in the CA mode. In other words, the higher the temperature the larger the difference between the lifetimes of an evaporating drop in the CA mode with respect to that evaporating in the CR mode.

Study of Microdroplet Growth on Homogeneous and Patterned Surfaces Using Lattice Boltzmann Modeling

2019 ◽  
Vol 141 (6) ◽  
Author(s):  
Nilesh D. Pawar ◽  
Sunil R. Kale ◽  
Supreet Singh Bahga ◽  
Hassan Farhat ◽  
Sasidhar Kondaraju
Keyword(s):  
Contact Angle ◽  
Contact Line ◽  
Lattice Boltzmann ◽  
Growth Dynamics ◽  
Hydrophobic Surface ◽  
Droplet Growth ◽  
Patterned Surfaces ◽  
Hydrophobic Region ◽  
Hydrophilic Region ◽  
Contact Line Pinning

We present droplet growth dynamics on homogeneous and patterned surfaces (surface with hydrophilic and hydrophobic region) using two-dimensional thermal lattice Boltzmann method (LBM). In the first part, we performed 2D simulations on homogeneous hydrophobic surfaces. The result shows that the droplet grows at higher rate on a surface with higher wettability which is attributed to low conduction resistance and high solid–liquid contact area. In the later part, we performed simulations on patterned surface and observed that droplet preferentially nucleates on the hydrophilic region due to lower energy barrier and grows in constant contact line (CCL) mode because of contact line pinning at the interface of hydrophilic–hydrophobic region. As the contact angle reaches the maximum value of hydrophobic surface, contact line depins and droplet shows constant contact angle (CCA) growth mode. We also discuss the effect of characteristic width of hydrophilic region on growth of droplet. We show that contact angle of the droplet increases rapidly and reaches the contact angle of hydrophobic region on a surface with a lower width of the hydrophilic surface.

Transient Interface Shape and Deposition Profile Left by Desiccation of Colloidal Droplets on Multiple Surfaces

2015 ◽  
Author(s):  
Peter D. Dunning ◽  
Collin T. Burkhart ◽  
Michael J. Schertzer
Keyword(s):  
Contact Angle ◽  
Electric Fields ◽  
Particle Deposition ◽  
Medical Diagnostics ◽  
Initial Contact ◽  
Interface Shape ◽  
Deposition Pattern ◽  
Deposition Patterns ◽  
Contact Line Pinning ◽  
Contact Diameter

Control of deposition patterns left by desiccated colloidal droplets is valuable in applications ranging from medical diagnostics to inkjet printing. This investigation presents an experimental method to monitor the transient interface shape of a colloidal droplet during desiccation and to quantify the deposition pattern left by the colloidal material optically. Transient image profiles and particle deposition patterns are examined for droplets containing fluorescent particles that were desiccated on glass and on the photoresist SU-8 3005. Contact line pinning was more prevalent on glass, where the contact diameter remained approximately constant throughout the process and the contact angle decreased with time. On SU-8, the contact diameter was initially constant, but decreased after the contact angle was reduced. The initial contact diameter on glass was similar to the diameter of the deposition pattern. The diameter of the deposition pattern on SU-8 was approximately half of the initial contact diameter. The deposition on SU-8 was also observed to be more uniform than that left on glass. These results suggest that selection of an appropriate substrate is an important consideration for colloidal deposition. The method presented will be used to in future investigations to characterize the effectiveness of coffee stain suppression through the application of external electric fields.

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