Dissertation/Thesis Abstract

The effects of gravity and thermal gradient on the drying processes in porous media
by Tajer, Seyed Ehsan, Ph.D., University of Southern California, 2011, 120; 3466112
Abstract (Summary)

This dissertation focuses on analyzing the compound effects of capillarity and gravity driven viscous flow through macroscopic liquid films during both isothermal and non-isothermal drying processes of porous materials. A mathematical model is developed to describe the drying process in a pore-network representation of porous media. The problem is characterized by a series of dimensionless parameters, and particularly a diffusion-based capillary number, Caf, and the gravity Bond number, Bx, in addition to the various geometrical parameters of the pore network.

Results on the evolution of the liquid saturation, the isolated liquid clusters and the drying rates are obtained as a function of dimensionless time and the dimensionless parameters in the two cases when gravity and/or thermal gradient oppose or aid the process (corresponding to positive or negative Bond numbers) respectively. In the first case, the fronts are stabilized, while in the second they are destabilized. As a result, gravity-controlled film flow is a major transport mechanism in the drying of porous media, its effect being dominant when gravity controls the process. Under strong capillarity conditions, the films span across the whole block, enhancing significantly liquid flow from distant clusters and improving recovery rates. The results are established first through an analytical solution of the problem in 1-D and later through the two-dimensional pore-network. The results of the pore-network in 1D are validated by the analytical solutions.

During non-isothermal drying, the emphasis is on understanding evaporation phenomena and the combined effects of capillarity and viscous forces as are modified by the presence of thermal gradients and an applied temperature gradient. The temperature dependence of equilibrium vapor concentration and surface tension are included. Strong evaporation effects under thermal conditions, associated with the variation of equilibrium concentrations, are clearly shown, with higher temperatures accelerating the process, as expected. The influence of surface tension variation induced by thermal gradients leads to destabilizing or stabilizing invasion percolation fronts, depending on the direction of the thermal gradient and have corresponding effects on the process.

The recovery of volatile oils from the matrix of fractured porous media can be significantly aided through gas injection. Within certain assumptions, this process operates similar to that of drying of porous media. For example, recovery is controlled by mechanisms involving capillary, viscous and gravity forces in the liquid and the liquidgas interfaces, and mass diffusion and convection in the gas phase.

In petroleum reservoirs, commonly, two immiscible liquid phases and a gas phase coexist in equilibrium. The crude oil and the natural gas are mixtures of hydrocarbon components. In such case, a liquid phase with higher solid affinity may spread on the rock surface, and the second liquid (assuming it has higher affinity with the first liquid compared to the gas phase) may form corner films on the wetting liquid, while the gas phase fills the pore center. Such case with more complicated fluid configurations and flow dynamics are not addressed in this study. Also, phase equilibrium calculation is needed to determine the concentration of each component in each phase. The current study, only addressed the evaporation of a single-component liquid.

The work finds application to the recovery of volatile oils from fractured or heterogeneous reservoirs, as well as a wide variety of drying processes in general (for example, in pharmaceuticals, ceramics and building material, electronic devices, food, paper and textile industries).

Indexing (document details)
Advisor: Yortsos, Yannis C.
Commitee: Ershaghi, Iraj, Ghanem, Roger G.
School: University of Southern California
Department: Petroleum Engineering
School Location: United States -- California
Source: DAI-B 72/10, Dissertation Abstracts International
Subjects: Chemical engineering, Petroleum engineering
Keywords: Drying, Evaporative recovery, Invasion percolatoin, Porous media, Thermal gradients
Publication Number: 3466112
ISBN: 978-1-124-78902-6
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