Page 10 - gas transport in porous media

Ho and Webb
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relatively little cross-fertilization of these studies and findings into other disciplines
such as engineering. Some processes such as enhanced vapor diffusion have been
investigated by researchers in soil sciences as far back as the 1950s and 1960s, but
they are only recently being considered in engineering applications such as drying of
porous materials.
Another motivation for this book is to identify applications where gas and vapor
transport are important or dominant mechanisms. Often, the importance of gas and
vapor transport mechanisms is overlooked or overshadowed by studies of liquid-
flow processes. However, advances in numerical modeling and experimental methods
have allowed the simulation of coupled gas- and liquid-flow processes in complex
media, and we are now able to distinguish the relative importance of mechanisms
in various applications. Examples of recent applications in which gas and vapor
transport processes are significant include nuclear waste disposal in geologic media
and detection of unexploded ordnance in the subsurface.
This book is divided into three parts: Part 1 – Processes and Models; Part 2 –
Measurement and Monitoring; and Part 3 – Applications. The first part, Processes
and Models, presents fundamental processes associated with gas and vapor transport
in porous media. Beginning with gas transport mechanisms, it describes advection
and diffusion processes, including the Dusty-Gas Model. Vapor transport processes
are then described in a similar manner, illustrating important features of a condensable
gas in porous media such as enhanced vapor diffusion and vapor-pressure lowering.
Vapor-solid sorption is also discussed because of its importance to recent applications
in land-mine detection, and mechanisms involving evaporation and coupled processes
are presented. The impact of heterogeneities and scaling on gas and vapor transport
processing in porous and fractured media is also discussed. Two-phase processes
and characteristics are also described, and various models of gas and vapor transport
processes using continuum and Lattice Boltzmann models are presented.
In Part 2, Measurement and Monitoring, various methods are described that have
been used to measure gas and vapor transport processes and parameters at the labo-
ratory and field scales. Measurement of the diffusion coefficient, permeability, flow
rate, constituent concentration, and mass flux of gas and vapors are described. New
technologies and microelectronic sensors that measure gas-phase volatile organic
compounds are also introduced.
Finally, in Part 3, Applications of gas and vapor transport in porous and frac-
tured media are presented. Applications include radon transport, landmine detection,
environmental remediation, geologic waste disposal, oil and gas exploration, carbon
sequestration, and industrial processes.
This book provides a broad and interdisciplinary view of the different processes,
models, experimental methods, and applications associated with gas and vapor trans-
port in porous media. We hope that the reader develops an understanding of the many
diverse topics and an appreciation for the important applications covered in this book.