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.

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 a Small Droplet Movement in a Microchannel under Heat Source

2019 ◽  
Vol 894 ◽  
pp. 104-111
Author(s):  
Thanh Long Le ◽  
Jyh Chen Chen ◽  
Huy Bich Nguyen
Keyword(s):  
Contact Angle ◽  
Heat Source ◽  
Water Droplet ◽  
Stokes Equations ◽  
Numerical Study ◽  
Dynamic Contact Angle ◽  
Dynamic Contact ◽  
Initial Position ◽  
Immiscible Fluids ◽  
Two Phase

In this study, the numerical computation is used to investigate the transient movement of a water droplet in a microchannel. For tracking the evolution of the free interface between two immiscible fluids, we employed the finite element method with the two-phase level set technique to solve the Navier-Stokes equations coupled with the energy equation. Both the upper wall and the bottom wall of the microchannel are set to be an ambient temperature. 40mW heat source is placed at the distance of 1 mm from the initial position of a water droplet. When the heat source is turned on, a pair of asymmetric thermocapillary convection vortices is formed inside the droplet and the thermocapillary on the receding side is smaller than that on the advancing side. The temperature gradient inside the droplet increases quickly at the initial times and then decreases versus time. Therefore, the actuation velocity of the water droplet first increases significantly, and then decreases continuously. The dynamic contact angle is strongly affected by the oil flow motion and the net thermocapillary momentum inside the droplet. The advancing contact angle is always larger than the receding contact angle during actuation process.

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.

Numerical Study on Evolution of Sessile Water Droplets During Evaporation

2012 ◽  
Author(s):  
Dinghua Hu ◽  
Huiying Wu ◽  
Xinyu Wu
Keyword(s):  
Contact Angle ◽  
Numerical Study ◽  
Concentration Field ◽  
Marangoni Effect ◽  
Simple Expression ◽  
Vapor Concentration ◽  
Contact Radius ◽  
Iteration Algorithm ◽  
Dimensionless Time ◽  
Water Droplets

The evaporation of sessile water droplets has been investigated numerically in this paper. A numerical model based on the quasi-stationary assumptions is established for describing the evaporation dynamics. Droplets are assumed to be pinned and axisymmetric on a substrate during the evaporation, and the influence of Marangoni effect on the evaporation has been taken into account. In a self-consistent way, the vapor concentration field in the gas phase, the velocity field in the liquid phase, and the temperature field in both liquid and gas phases have been calculated using the finite element method (FEM). A novel iteration algorithm is proposed to study the time evolution of contact angle. From the numerical results, we derived a universal correlation of the contact angle with the dimensionless time. The correlation, which is validated against experimental data from open literature, is independent on the contact radius, substrate temperature and ambient humidity. Base on this correlation, a simple expression has been further developed to estimate the evaporation time, and the predictions are in good agreement with the experimental results from open literature. The work in this paper provides an extensive understanding of the evaporation of sessile droplets.

Well productivity enhancement by applying nanofluids for wettability alteration

2018 ◽  
Vol 58 (1) ◽  
pp. 121 ◽  
Author(s):  
Saurabh Naik ◽  
Gabriel Malgaresi ◽  
Zhenjiang You ◽  
Pavel Bedrikovetsky
Keyword(s):  
Contact Angle ◽  
Gas Production ◽  
Analytical Models ◽  
Wettability Alteration ◽  
Two Phase ◽  
Well Productivity ◽  
Productivity Decline ◽  
Water Blocking ◽  
Water Cut ◽  
Constant Contact Angle

Water blocking is a frequent cause for gas productivity decline in unconventional and conventional fields. It is a result of the capillary end effect near the wellbore vicinity. It creates significant formation damage and decreases gas well productivity. The alteration of the rock wettability by nanofluids is an effective way to reduce water blockage and enhance gas production. Presently, several types of surfactants and nanofluids are used in the industry for contact angle alteration. In this study, we developed an analytical model and analysed the sensitivity to several parameters. After the treatment, the porous medium in the well vicinity (or along the core) will have a stepwise constant contact angle profile. We derive analytical models for compressible steady-state two-phase linear and axi-symmetric flows, accounting for the piecewise-constant contact angle and contact-angle-dependent capillary pressure and relative permeability. The modelling reveals a complex interplay between the competing effects of compressibility, viscous and capillary forces, which influence the optimal contact angle for treatment. The optimal contact angle for treatment will depend on the initial wettability of the formation, the water cut and the capillary-viscous ratio.

3D Numerical Study of the Transport Characteristics of an Evaporating Water Droplet Sessile on Heated Superhydrophobic Substrates

2019 ◽  
Author(s):  
Yikun Peng ◽  
Shanshan Li ◽  
Zhenhai Pan
Keyword(s):  
Substrate Temperature ◽  
Water Droplet ◽  
Evaporation Rate ◽  
Numerical Study ◽  
Fundamental Problem ◽  
Heating Temperature ◽  
Evaporative Cooling ◽  
Computational Domain ◽  
Vapor Diffusion ◽  
Recirculation Flow

Abstract Evaporation of sessile droplets on superhydrophobic substrates is an important fundamental problem. Classic diffusion-based model only considers vapor diffusion and assumes an isothermal profile along the droplet interface. The diffusion based model extremely overestimates the evaporation rate for droplets evaporating on heated superhydrophobic substrates, and results in a deviation of evaporation lifetime up to 52.5%. The present 3D numerical model considers various effects including vapor diffusion, buoyancy-driven flow and evaporative cooling, etc., with conjugate heat and mass transfer solved throughout the computational domain. Evaporation of a sessile water droplet with an initial volume of 3 μL is investigated on superhydrophobic substrates (contact angle: 160 deg) with heating temperature ranging from 40 °C to 60 °C. The deviation of evaporation lifetime is less than 2% for 40 °C and 50 °C substrates. A single-roll asymmetric vortex is produced inside the droplet rather than the symmetric recirculation flow predicted by 2D axisymmetric simulation. The evaporative cooling along the droplet interface is observed, but the coolest point appears on the one side of the droplet instead of the droplet top owing to the asymmetrical rolling flow inside the droplet. It is seen that the buoyancy-driven convection significantly speeds up the evaporation as the substrate temperature increases. Influence of relative humidity is also discussed and indicates a stronger impact for low substrate temperature. The present model not only precisely predicts the instantaneous evaporation rate and the total evaporation time, but also reveals the important underlying transport characteristics, which provides new insights into evaporation of water droplets resting on heated superhydrophobic substrates.

A THEORETICAL AND EXPERIMENTAL STUDY OF THE EVAPORATION RATE OF METHANOL DROPLETS ON A HORIZONTAL SURFACE

2013 ◽  
Vol 21 (03) ◽  
pp. 1350019
Author(s):  
BIN LIU ◽  
BIHAO CAI ◽  
YUN SU ◽  
XIAOYONG DONG
Keyword(s):  
Contact Angle ◽  
Evaporation Rate ◽  
Transitional Stage ◽  
Theoretical Conclusion ◽  
Spherical Cap ◽  
Droplet Shape ◽  
Three Stages ◽  
Base Radius ◽  
Constant Contact Angle ◽  
Contact Diameter

The evaporation of droplet on a substrate is a hot topic. Considering the droplet shape as a spherical cap, the equations about the droplet evaporation rate of the constant contact angle stage, the constant contact diameter stage and the transitional stage are theoretically analyzed and verified by experiments. The results show that three stages are shown in the evaporation process, and the evaporation rates in these three stages coincident with the theoretical conclusion. In the constant contact angle stage, the evaporation rate is proportional to the square of base radius. While in the constant contact diameter stage, the evaporation rate is proportional to the cube of base radius. The evaporation rate in the transitional stage approximates to that of the constant contact angle stage.

scholarly journals On the lifetimes of evaporating droplets

2014 ◽  
Vol 744 ◽  
Author(s):  
J. M. Stauber ◽  
S. K. Wilson ◽  
B. R. Duffy ◽  
K. Sefiane
Keyword(s):  
Contact Angle ◽  
Solid Substrate ◽  
Contact Radius ◽  
Constant Contact Angle

AbstractThe complete description of the lifetime of a droplet on a solid substrate evaporating in a ‘stick–slide’ mode is obtained. The unexpectedly subtle relationship between the lifetime of such a droplet and the lifetimes of initially identical droplets evaporating in the extreme modes (namely the constant contact radius and constant contact angle modes) is described and summarised in an appropriate master diagram. In particular, it is shown that the lifetime of a droplet is not, in general, constrained by the lifetimes of the extreme modes.

scholarly journals Numerical study of low-speed droplets impacting on the fabric surface

Mechanika ◽  
2019 ◽  
Vol 25 (6) ◽  
pp. 449-454
Author(s):  
Guo Qilei
Keyword(s):  
Contact Angle ◽  
Impact Velocity ◽  
Numerical Study ◽  
Liquid Droplet ◽  
Morphological Evolution ◽  
Droplet Diameter ◽  
Flow Characteristics ◽  
Shape Distortion ◽  
Proposed Model ◽  
Fabric Surface

In this approach, the numerical model of the fluid dynamics of liquid droplets impacting on the fabric surface with VOF method is proposed. The results obtained by the proposed model are well in agreement with the experimental results. The mechanism of the liquid droplet morphological evolution is investigated by pressure distribution and velocity vector, and the obvious bubble entrapment, which cannot be observed in experimenal results, is captured by the proposed model. The evolution laws of the spreading factor and the contact angle at the liquid-porous interface are obtained and the reason why the contact angle is dynamic is analyzed. The effects of droplet diameter and impact velocity on the fluid flow characteristics are also discussed. Usually, droplet diameter increasing leads more dramatic shape distortion of the liquid droplet, and impact velocity increasing leads shorter time to reach the maximum spreading stage. Finally, based on the properties of the impacting droplet by the proposed model, the important references of optimizing the parachute design for severe weather are built.

Numerical Investigation of Water Droplet Impact on Solid Surface in Microgravity

2013 ◽  
Vol 390 ◽  
pp. 65-70
Author(s):  
Jun Jun Tao ◽  
Jun Qin ◽  
Xue Han ◽  
Yong Ming Zhang
Keyword(s):  
Solid Surface ◽  
Water Droplet ◽  
Normal Gravity ◽  
Numerical Study ◽  
Liquid Droplet ◽  
Water Mist ◽  
Droplet Impact ◽  
Gravity Level ◽  
Vof Model ◽  
Fuel Vapour

A numerical study based on VOF model has been carried out to investigate the dynamics of water droplet impact on solid surface in microgravity in comparison with that in normal gravity to discuss the differences of the extinguishing mechanism of water mist in different gravity level. Water droplets with different initial diameters and impact velocities were considered. The simulated results show that the deformation process in microgravity lags behind that in normal gravity. And it was also found that Dmaxand spread velocities are smaller in microgravity as the potential energy decreases and the time taken for a liquid droplet to reach its maximum spread has no obvious regularity. Hence, the effect of cooling the fuel surface and diluting fuel vapour with water mist in microgravity may be not as good as that in normal gravity.The critical impact Weber number for water droplet breaking up in microgravity is lower than that in normal gravity as the reduction of the value of Bond number, which may result in diluting fuel vapour with water mist in microgravity being more effective than that in normal gravity in some case.

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