EXPERIMENTAL ASSESSMENT OF GAS-TRANSPORT MECHANISMS IN NATURAL POROUS-MEDIA - PARAMETER EVALUATION

An understanding of vapor transport in natural porous media is critica l to the assessment of a wide range of environmental problems. In this work a comprehensive experimental program was undertaken to evaluate the relative importance of different gaseous transport mechanisms in n atural porous media. The dusty gas model was used as a framework for t his evaluation. The experimental program was divided into two parts: t he first emphasizes the measurement of porous media transport paramete rs, and the second explores flux mechanisms in organic vapor transport . Results of the first part are presented in this paper. Single and bi nary gas experiments were conducted to obtain governing transport para meters (coefficients of permeability, Knudsen diffusion, and diffusibi lity) in dry porous media. To conduct these experiments, a special exp erimental apparatus was built that incorporates a diffusion cell that represents an open system where the pressure gradient and absolute pre ssures can be regulated by controlling the flow rates of the component gases at both ends of the soil sample. Soils tested included three un iform materials, a sea sand, an Ottawa sand, and kaolinite clay, and f ive graded mixtures of these uniform soils, Results of the single-gas experiments illustrate the importance of Knudsen diffusion in permeabi lity measurements. Two new transport parameter correlations are develo ped from the presented data and compared with available literature cor relations. The correlation for the Knudsen diffusion radius has a func tional dependence upon the square root of intrinsic permeability, sele cted as a characteristic length of the porous medium. Binary diffusion experiments, using an equimolar pair of gases, are employed to develo p a correlation for a composition independent diffusibility.