PINNING OF A SOLID–LIQUID–VAPOR INTERFACE

We propose a macroscopic Hamiltonian approach to study the pinning (sticking) of a solid–liquid–vapor contact line by pinning centers on the solid. We have so far studied the case of a vertical solid immersed into a liquid in the presence of gravity, but the method is general and can easily be extended to other geometries with and without gravity. Using computer simulations the method can be used to give a nonperturbative estimate for whether pinning centers interact cooperatively or independently in the pinning of the contact line.

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

ASME 2020 18th International Conference on Nanochannels, Microchannels, and Minichannels ◽

10.1115/icnmm2020-1091 ◽

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.

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A new method for determining the interfacial molecules and characterizing the surface roughness in computer simulations. Application to the liquid–vapor interface of water

Journal of Computational Chemistry ◽

10.1002/jcc.20852 ◽

2008 ◽

Vol 29 (6) ◽

pp. 945-956 ◽

Cited By ~ 126

Author(s):

Lívia B. Pártay ◽

György Hantal ◽

Pál Jedlovszky ◽

Árpád Vincze ◽

George Horvai

Keyword(s):

Surface Roughness ◽

Computer Simulations ◽

New Method ◽

Vapor Interface ◽

Liquid Vapor

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Numerical Study of Evaporation Heat Transfer From the Liquid-Vapor Interface in Wick Microstructures

Volume 9: Heat Transfer, Fluid Flows, and Thermal Systems, Parts A, B and C ◽

10.1115/imece2009-11326 ◽

2009 ◽

Cited By ~ 4

Author(s):

Ram Ranjan ◽

Jayathi Y. Murthy ◽

Suresh V. Garimella

Keyword(s):

Heat Transfer ◽

Numerical Study ◽

Saturated Vapor ◽

Wire Mesh ◽

Liquid Meniscus ◽

Vapor Interface ◽

Evaporation Heat ◽

Evaporation Heat Transfer ◽

Solid Liquid ◽

Liquid Vapor

A numerical model of the evaporating liquid meniscus under saturated vapor conditions in wick microstructures has been developed. Four different wick geometries representing the common wicks used in heat pipes, viz., wire mesh, rectangular grooves, sintered wicks and vertical microwires, are modeled and compared for evaporative performance. The solid-liquid combination considered is copper-water. Steady evaporation is modeled and the liquid-vapor interface shape is assumed to be static during evaporation. Liquid-vapor interface shapes in different geometries are obtained by solving the Young-Laplace equation using Surface Evolver. Mass, momentum and energy equations are solved numerically in the liquid domain, with the vapor assumed to be saturated. Evaporation at the interface is modeled by using appropriate heat and mass transfer rates obtained from kinetic theory. Thermo-capillary convection due to non-isothermal conditions at the interface is modeled for all geometries and its role in heat transfer enhancement from the interface is quantified for both low and high superheats. More than 80% of the evaporation heat transfer is noted to occur from the thin-film region of the liquid meniscus. Very small Capillary and Weber numbers arising due to small fluid velocities near the interface for low superheats validate the assumption of static liquid meniscus shape during evaporation. Solid-liquid contact angle, wick porosity, solid-vapor superheat and liquid level in the wick pore are varied to study their effects on evaporation from the liquid meniscus.

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