Evaporation of a Sessile Microdroplet on a Heated Hydrophobic Substrate
04 Dec 2014-International Journal of Micro-nano Scale Transport (Multi Science Publishing)-Vol. 5, Iss: 2, pp 51-58
TL;DR: In this article, an in-house, experimentally validated finite-element numerical model was employed to simulate internal fluid flow and heat transfer during the evaporation of sessile water microdroplets on heated hydrophobic glass substrate.
Abstract: We investigated evaporation of sessile water microdroplets on heated hydrophobic glass substrate. An in-house, experimentally validated finite-element numerical model was employed to simulate internal fluid flow and heat transfer during the evaporation. We also validated the non-uniform evaporative flux for water droplets having different initial wetting angles with theoretical results from literature. During evaporation, the fluid flow is radially outward due to the largest evaporative flux near the wetting line. The isotherms are almost horizontal which indicates that the conduction between the droplet and substrate dominates over internal convection during the evaporation. The evolution of wetted radius and wetting angle indicates a two-stage evaporation process:during the first stage of the evaporation, wetted radius remains constant and wetting angle decreases with time; while in the second stage, wetting angle remains constant and wetted radius decreases with time. The droplet volume shows a linear ...
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TL;DR: In this paper, the effects of substrate temperature, substrate wettability, and particle concentration are experimentally investigated for evaporation of a sessile water droplet containing colloidal particles.
Abstract: Effects of substrate temperature, substrate wettability, and particle concentration are experimentally investigated for evaporation of a sessile water droplet containing colloidal particles. Time-varying droplet shapes and temperature of the liquid–gas interface are measured using high-speed visualization and infrared thermography, respectively. The motion of the particles inside the evaporating droplet is qualitatively visualized by an optical microscope and the profile of the final particle deposit is measured by an optical profilometer. On a nonheated hydrophilic substrate, a ring-like deposit forms after the evaporation, as reported extensively in the literature, while on a heated hydrophilic substrate, a thinner ring with an inner deposit is reported in the present work. The latter is attributed to Marangoni convection, and recorded motion of the particles as well as measured temperature gradient across the liquid–gas interface confirms this hypothesis. The thinning of the ring scales with the substr...
114 citations
TL;DR: In this paper, the effect of pitch of the pillars and impact velocity on the impact dynamics of a microliter water droplet on a micropillared hydrophobic surface was studied qualitatively by high-speed photography and quantitatively by the temporal variation of wetted diameter and droplet height.
96 citations
Cites background from "Evaporation of a Sessile Microdropl..."
...2 cooling via spray evaporative cooling [5] and on spatially varying wettability surfaces [6]....
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...…hysteresis [°] μ dynamic viscosity [Pa.s] ρ density [kg/m3] 1 Bergeron et al. (2000) 2 Truesdell et al. (2006) 3 Antonini et al. (2011) 4 Bixler and Bhushan (2014) 5 Patil and Bhardwaj (2014) 6 Attinger et al. (2014) 7 Bhardwaj et al. (2010) 8 Yarin (2006) 9 Richard and Quéré (2000) 10 Rioboo et…...
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Posted Content•
TL;DR: A first-order model corroborates the liquid-gas interface temperature measurements and variation in the measured ring profile with the substrate temperature, and proposes a regime map for predicting three types of deposits-namely, ring, thin ring with inner deposit, and inner deposit-for varying substrate temperature.
Abstract: Effects of substrate temperature, substrate wettability and particles concentration are experimentally investigated for evaporation of a sessile water droplet containing colloidal particles. Time-varying droplet shapes and temperature of the liquid-gas interface are measured using high-speed visualization and infrared thermography, respectively. The motion of the particles inside the evaporating droplet is qualitatively visualized by an optical microscope and profile of final particle deposit is measured by an optical profilometer. On a non-heated hydrophilic substrate, a ring-like deposit forms after the evaporation, as reported extensively in the literature; while on a heated hydrophilic substrate, a thinner ring with an inner deposit is reported in the present work. The latter is attributed to Marangoni convection and recorded motion of the particles as well as measured temperature gradient across the liquid-gas interface confirms this hypothesis. The thinning of the ring scales with the substrate temperature and is reasoned to stronger Marangoni convection at larger substrate temperature. In case of a non-heated hydrophobic substrate, an inner deposit forms due to very early depinning of the contact line. On the other hand, in case of a heated hydrophobic substrate, the substrate heating as well as larger particle concentration helps in the pinning of the contact line, which results in a thin ring with an inner deposit. We propose a regime map for predicting three types of deposits namely, ring, thin ring with inner deposit and inner deposit - for varying substrate temperature, substrate wettability and particles concentration. A first-order model corroborates the liquid-gas interface temperature measurements and variation in the measured ring profile with the substrate temperature.
52 citations
Cites background from "Evaporation of a Sessile Microdropl..."
...ion along droplet and substrate thickness in the control volume with these assumptions simplifies to, 2 2 0 dT dz (3) The boundary condition at the bottom surface of the substrate is, T z T( 0) s (4) 21 The boundary condition at the top boundary of the control volume is jump energy boundary condition and is given by, L dT k dz (5) where, J apex is the evaporative mass flux at the apex of the d...
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TL;DR: In this article, an in-house, experimentally validated, finite element method-based computational model is employed to simulate the droplet impact dynamics and transient fluid flow within the liquid-gas interface.
Abstract: We numerically investigate bouncing and non-bouncing of droplets during isothermal impact on superhydrophobic surfaces. An in-house, experimentally validated, finite element method-based computational model is employed to simulate the droplet impact dynamics and transient fluid flow within the droplet. The liquid–gas interface is tracked accurately in Lagrangian framework with dynamic wetting boundary condition at three-phase contact line. The interplay of kinetic, surface and gravitational energies is investigated via systematic variation of impact velocity and equilibrium contact angle. The numerical simulations demonstrate that the droplet bounces off the surface if the total droplet energy at the instance of maximum recoiling exceeds the initial surface and gravitational energy, otherwise not. The non-bouncing droplet is characterized by the oscillations on the free surface due to competition between the kinetic and surface energy. The droplet dimensions and shapes obtained at different times by the simulations are compared with the respective measurements available in the literature. Comparisons show good agreement of numerical data with measurements, and the computational model is able to reconstruct the bouncing and non-bouncing of the droplet as seen in the measurements. The simulated internal flow helps to understand the impact dynamics as well as the interplay of the associated energies during the bouncing and non-bouncing. A regime map is proposed to predict the bouncing and non-bouncing on a superhydrophobic surface with an equilibrium contact angle of 155°, using data of 86 simulations and the measurements available in the literature. We discuss the validity of the computational model for the wetting transition from Cassie to Wenzel state on micro- and nanostructured superhydrophobic surfaces. We demonstrate that the numerical simulation can serve as an important tool to quantify the internal flow, if the simulated droplet shapes match the respective measurements utilizing high-speed photography.
42 citations
TL;DR: In this article, a quasi-dynamic contact angle model based on experimental inputs is implemented to model the dynamic wetting of a droplet, impacting on a hydrophobic or a superhydrophobic surface.
25 citations
References
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TL;DR: In this article, the authors ascribe the characteristic pattern of the deposition to a form of capillary flow in which pinning of the contact line of the drying drop ensures that liquid evaporating from the edge is replenished by liquid from the interior.
Abstract: When a spilled drop of coffee dries on a solid surface, it leaves a dense, ring-like deposit along the perimeter (Fig 1a) The coffee—initially dispersed over the entire drop—becomes concentrated into a tiny fraction of it Such ring deposits are common wherever drops containing dispersed solids evaporate on a surface, and they influence processes such as printing, washing and coating1,2,3,4,5 Ring deposits also provide a potential means to write or deposit a fine pattern onto a surface Here we ascribe the characteristic pattern of the deposition to a form of capillary flow in which pinning of the contact line of the drying drop ensures that liquid evaporating from the edge is replenished by liquid from the interior The resulting outward flow can carry virtually all the dispersed material to the edge This mechanism predicts a distinctive power-law growth of the ring mass with time—a law independent of the particular substrate, carrier fluid or deposited solids We have verified this law by microscopic observations of colloidal fluids
5,553 citations
"Evaporation of a Sessile Microdropl..." refers background in this paper
...The evaporative flux on the free surface is non-uniform and the largest evaporation near the contact line generates evaporative-driven radially outward and transient internal flow [6, 7]....
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01 Jan 2004
TL;DR: The first € price and the £ and $ price are net prices, subject to local VAT as discussed by the authors, and prices and other details are subject to change without notice. All errors and omissions excepted.
Abstract: The first € price and the £ and $ price are net prices, subject to local VAT. Prices indicated with * include VAT for books; the €(D) includes 7% for Germany, the €(A) includes 10% for Austria. Prices indicated with ** include VAT for electronic products; 19% for Germany, 20% for Austria. All prices exclusive of carriage charges. Prices and other details are subject to change without notice. All errors and omissions excepted. P.-G. de Gennes, F. Brochard-Wyart, D. Quere Capillarity and Wetting Phenomena
2,414 citations
TL;DR: Key advances in the understanding and fabrication of surfaces with controlled wetting properties are about to make the dream of a contamination-free (or 'no-clean') surface come true.
Abstract: In the 19th century, Oscar Wilde stated “We live, I regret to say, in an age of surfaces”. Today, we do so even more, and we do not regret it: key advances in the understanding and fabrication of surfaces with controlled wetting properties are about to make the dream of a contamination-free (or 'no-clean') surface come true. Two routes to self-cleaning are emerging, which work by the removal of dirt by either film or droplet flow. Although a detailed understanding of the mechanisms underlying the behaviour of liquids on such surfaces is still a basic research topic, the first commercial products in the household-commodity sector and for applications in biotechnology are coming within reach of the marketplace. This progress report describes the current status of understanding of the underlying mechanisms, the concepts for making such surfaces, and some of their first applications.
2,114 citations
Book•
08 Mar 2013
TL;DR: Capillarity: Unconstrained Interfaces / Capillarity and gravity / Hysteresis and Elasticity of Triple Lines / Wetting and Long-Range Forces b/ Hydrodynamics of Interfaces -- Thin Films, Waves, and Ripples as discussed by the authors.
Abstract: Capillarity: Unconstrained Interfaces / Capillarity and Gravity / Hysteresis and Elasticity of Triple Lines / Wetting and Long-Range Forces b/ Hydrodynamics of Interfaces -- Thin Films, Waves, and Ripples / Dynamics of the Triple Line / Dewetting / Surfactants / Special Interfaces / Transport Phenomena
1,550 citations
TL;DR: In this article, the evaporation of a sessile droplet with a pinned contact line was investigated experimentally, by analytic theory and by computation using the finite element method (FEM).
Abstract: The evaporation of a sessile droplet with a pinned contact line is investigated experimentally, by analytic theory and by computation using the finite element method (FEM). Because of the low value of R2/Dtf = cv(1 − H)/ρ = 1.4 × 10-5, where R is the contact-line radius, D is the water vapor diffusivity, cv is the saturated water vapor concentration, H is the relative humidity, and ρ is the liquid water density, the evaporation can be considered as a quasi-steady-state process. Hence, the vapor concentration distribution above the droplet satisfies the Laplace equation but with a time-varying droplet surface. It is found both theoretically and experimentally that the net evaporation rate from the droplet remains almost constant with time for a small initial contact angle (θ < 40°), even though the evaporation flux becomes more strongly singular at the edge of the droplet as the contact angle decreases during evaporation. We also measured the critical contact angle at which the contact line starts to reced...
1,302 citations
"Evaporation of a Sessile Microdropl..." refers background in this paper
...The evaporative flux on the free surface is non-uniform and the largest evaporation near the contact line generates evaporative-driven radially outward and transient internal flow [6, 7]....
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