Water transport in porous media: From pore scale to biological applications

Abstract

Water transport in porous media can be observed at various scales, and scientific principles applied at microscales also affect the transport behavior at the macroscale. It is therefore essential to understand the water transport in small confined geometries such as thin adsorbed films surrounding the pore wall and capillary tubes; representative examples of fine pore structure. In this thesis, we study various topics within computational fluid dynamics, numerical methods, and classical and non-equilibrium thermodynamics to investigate water transport in the small systems found in porous media. We study how each of the intrinsic and extrinsic factors affects water transport in porous media, for instance, these intrinsic factors include pore complexity, porosity, pore size and type and wall material properties. The extrinsic factors include fluid properties such as surface tension, viscosity, pressure and temperature. The first chapter describes the details of the mentioned theories.

Chapter 2, which contains Paper I, deals with how extrinsic factors such as pressure and surface tension affect the transport of water in the capillary tube. In particular, the two-phase flow of wetting and non-wetting fluids, which can be represented by water and air bubbles, are studied. We reveal how the size of the air bubble varies along the tube position and how this change depends on the applied pressure in the system of pore scale, which is affected by capillary force. We also investigate how the volumetric flow rate of the fluids is affected. This chapter becomes the first milestone in building a 3D network model as an example of a study of water transport in the macroscale of porous media.

In Chapter 3, which contains Paper II, we review general historical discoveries, developments in theories and models, comparisons between models and phenomena

and applications of water adsorption in porous media. Adsorption is found in the thin film surrounding the pore wall and we examine how extrinsic factors applied in adsorption are integrated into adsorption isotherm models and how each isotherm is categorized depending on the size of the pore. Various interfacial phenomena are involved in thin adsorbed films of porous media and properties of adsorption are reviewed with statistical approaches used for applying adsorption isotherms models to study experimental results.

Chapter 4, which includes Paper III and IV, deals with the transport of water vapor within the pores of the mucous membrane and air passage in a seal nose, which is a relevant biological system. This chapter covers not only the transport of the water at the macroscale from the ambient air to the inside of the seal nose, but also the transport of the water at the microscale as evaporation and condensation on the mucus lining at the pore wall surface. We show the result of temperature and water mass fraction profiles relating to the morphology and complexity of the seal nose and the loss of heat and entropy production based on the mentioned profiles. Various indicators described above show that the more complex nose structure of seals living in the Arctic regions is advantageous to survive in extremely dry and cold environments. In addition, we conducted an extended study to find the effects of variables such as nose length among the intrinsic factors of porous media. Tidal volume, nose maxilloturbinate length and respiration frequency, which are important extrinsic parameters of flow in the porous nose maxilloturbinate, are investigated. We reveal that the Arctic seal has the actual physiological properties of the mentioned variables that confirm the efficient function of respiration.