Capillary forces and wetting dynamics by diffuse-interface modeling

Author

Fanny Thomas, CUNY City CollegeFollow

Date of Award

2020

Document Type

Dissertation

Department

Chemical Engineering

First Advisor

Jeffrey F Morris

Keywords

Multiphase flow, Capillary forces, Contact line dynamics, Numerical modeling, Wetting

Abstract

Wetting phenomena underlie many natural and industrial processes, from the proper functioning of the lungs to the thin coating of surfaces. The three-phase interactions involved at microscopic scales play a critical role. Adding solid particles to an emulsion, for example, can drastically change the flow behavior due to capillary bridging between the particles. The study of these three-phase systems is especially relevant to the petroleum industry, where gas hydrates forming large clusters in subsea pipelines during crude oil transportation is a major concern. The dynamics of such systems is also of great interest from a fundamental perspective. Indeed describing non-equilibrium situations involving a 3-phase contact line is a long-standing problem that has never been explicitly resolved. The well-known moving contact line problem falls outside the scope of classical hydrodynamics, and requires the use of approaches inclusive of both local phenomena and larger scale effects.

In the first part of this dissertation, the dynamics of capillary bridges and the motion of the three-phase contact line are studied within the framework of the diffuse interface theory. The key to understanding the dynamics of interfacial systems lies in an accurate description of the capillary forces. In this work, we combine the diffuse interface theory with a multiphase lattice Boltzmann algorithm to develop a description of the capillary forces in 2D binary systems. The forces and the surface tension are derived on a continuum level through the use of the capillary stress tensor. This approach provides a unified picture between fluid dynamics and thermodynamics, consistent with the multi-scale nature of the problem. The method is implemented for ``pair" systems, composed of a liquid bridge connecting two solid elements. We identify the mechanisms governing the motion of the three-phase contact line and how the model handles the contact line singularity in comparison with the classic sharp-interface approach. We describe the two-way coupling between the dynamics of the solid elements and the fluid flow and discuss numerical challenges associated with moving curved boundaries, and the tracking of the interface. Numerical results are compared with theoretical predictions at equilibrium, and the capillary forces obtained in non-equilibrium situations are examined.

The interparticle forces due to capillary bridging depend on the wetting conditions of the solid surface. But these properties are not always well characterized: for example, the wetting characteristics of clathrate hydrates strongly influence their behavior in flow assurance situations, but direct experimental measurements are not prevalent in the literature. In the second part of this dissertation, a new experimental method is proposed for measuring the contact angle of various liquids on cyclopentane hydrate, a structure II clathrate hydrate that forms at atmospheric pressure. This method includes a protocol to obtain a smooth hydrate surface, followed by standard image-based contact angle measurements. The contact angle of halogenated organics drops immersed in brine is measured on cyclopentane hydrate and ice. Both the hydrate and ice surfaces are found to be water-wetting. Finite contact angles are obtained on the hydrate substrate but not on ice.

Recommended Citation

Thomas, Fanny, "Capillary forces and wetting dynamics by diffuse-interface modeling" (2020). CUNY Academic Works.
https://academicworks.cuny.edu/cc_etds_theses/952