This thesis describes work on the development of new integrated methods for the
characterisation of porous media. Porous media are of wide importance in a variety of
applications including oil and gas production, tissue engineering, filtration and separation
and ground water hydrology. Such porous media are characterised by the fraction of their
volume occupied by pores (the porosity) and by parameters characterising the ease of flow
and diffusion through the medium (the permeability and the diffusivity). However, the flow
processes are very complex, reflecting the complex nature of the pore structure.
The objective of the work described in this thesis was to develop and apply two new
integrated pieces of apparatus which were aimed at elucidating several aspects of the
complex flow processes. The first integrated apparatus was aimed at the study of gaseous
transport and the second at the study of mercury penetration, flow and electrical conduction,
in the pores of selected media. Thin-section imaging was also applied to obtain
supplementary information.
The integrated gaseous transport apparatus was designed not only to measure permeability
(by the pressure rise technique), but also to study both steady state and (importantly)
transient diffusion of oxygen in nitrogen in the pores of the selected media. The system was
capable of operating with media with a wide range of permeabilities and yielded accurate
values of the viscous permeability and the slip flow coefficient. In addition, experiments were carried out in the partially turbulent flow region. The diffusion measurements yielded
information on the ratio (rD) of the diffusion coefficient in the media to that in free space; this
ratio is also a specific property of the medium. Combining the steady state and transient
diffusion measurements, it was possible to deduce the effective porosity and the pore length.
The second integrated apparatus was for the study of porous media subjected to mercury
penetration under pressure. This apparatus allowed conventional mercury porosimetry
measurements to be performed (i.e. measurements of the pore volume occupied as a function
of pore size penetrated) but, crucially, it also allowed measurements of the permeability to
mercury and of the conductivity with mercury to be made simultaneously. The permeability
to mercury approaches the gaseous value when complete saturation of the medium is
achieved; however the manner in which mercury permeability varies with pore size gives a
striking indication of the role of the various pores in the flow process. In the conductivity
experiments, the ratio (rCp) of the conductivity of the medium penetrated with mercury at
pressure p to the conductivity of pure mercury is determined as a function of p. At high
penetration pressures, the value of rCp approaches that of rD reflecting the analogy between
conduction and diffusion when the medium is saturated with mercury. However, the variation
of rCp with pore size penetrated gives a remarkable indication of the significance of the pores
in given size ranges in the diffusion process (analogous to the information yielded by the
mercury permeability measurements relating to the overall permeability).