“Fluid transport through nanoporous media in the presence of phase transitions

Abstract

Clean potable water is among the most precious commodities in the world. Even though water is not sparse on the planet’s surface, it is not sufficiently accessible for about 4 billion people, who are experiencing serious water shortages for at least one month each year. Most of the current methods, which are trying to tackle that problem, are treating seawater and brackish water to obtain fresh water. The most common techniques face the challenge of a high energy input and large production costs.

A primary motivation of this thesis was therefore to contribute to the development of a vapor-gap membrane that can be used in a process that combines seawater desalination and energy production. When a gas-permeable liquid-repelling membrane, also called vapor-gap membrane, is in contact with liquids on both sides and a temperature difference is applied, mass transport across the membrane is induced by evaporation on one side and condensation on the other. Mass is thus transported in the vapor phase across the membrane, away from a contaminated liquid. The permeate flux may then be used to run a turbine.

Transport of fluid across a vapor-gap membrane involves liquid-vapor phase transitions, and the membrane pore sizes can reach down to the nanometer scale. Therefore, we have been particularly concerned with the effect of interfaces (liquid-vapor and fluid-solid) on fluid transport across the membrane, as well as with the fundamental definition and description of the driving forces involved. On a broader scale, we aimed to develop a general thermodynamic framework for the description of fluid flow across a nanoporous medium.