Studies on processes involving liquid -to -gas phase change in porous media.

摘要

Liquid-to-gas phase change and subsequent growth of the produced gas phase within a porous medium, is involved in a wide variety of processes of significant scientific and commercial interest. While significant progress towards the understanding of the problem has been achieved, a number of important questions still remain unanswered. Advancing this understanding is the objective of this work.;We conducted experimental and theoretical work considering both continuum and discrete approaches and at different length scales. Processes of interest included drying and evaporation, where the mass transfer that drives the process occurs in the gas phase. It also included solution gas-drive and internal steam drive where the mass or heat transfer, respectively, occurs in the liquid phase.;Concepts of immiscible displacement driven by mass transfer were used to model aspects of drying of porous media. Visualization experiments were utilized to identify the mechanisms concerning the motion of gas-liquid interfaces at the pore-scale and subsequently were introduced in a pore-network approach. A linear stability analysis, in the absence of capillarity, showed that the drying front is stable due to diffusion in the gas phase. The presence of capillarity resulted in inducing a viscous flow. The developing pressure gradients effectively limit the extent of the front to a finite width. A power-law scaling relation of the front width with a diffusion-based capillary number was then developed. A continuum description for the regime upstream of the front was also introduced. The effect of high pressures on the evaporation process was examined using a continuum approach.;In a subsequent investigation, we derived an effective continuum model to describe the nucleation and subsequent growth of a gas phase from a supersaturated, slightly compressible binary liquid in a porous medium, driven by solute diffusion, as observed in solution gas-drive processes. The case of internal steam drive, where heat transfer drives the phase change of a single component liquid, was also considered. The evolution of the gas resulted either from the reduction of the system pressure at a constant rate, or from the withdrawal of the liquid at a constant rate. The model addressed two stages before the onset of bulk gas flow, nucleation and gas phase growth. Important quantities characterizing the process, such as the fraction of pores that host activated sites, the deviation from thermodynamic equilibrium, the maximum supersaturation in the system and the critical gas saturation depend crucially on the nucleation characteristics of the medium. (Abstract shortened by UMI.).