Experimental assessment of gas transport mechanisms in natural porous media: Parameter evaluation

Abstract

Abstract. An understanding of vapor transport in natural porous media is critical 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 natural porous media. The dusty gas model was used as a framework for this evaluation. The experimental program was divided into two parts: the first emphasizes the measurement of porous media transport parameters, and the second explores flux mechanisms in organic vapor transport. Results of the first part are presented in this paper. Single and binary gas experiments were conducted to obtain governing transport parameters (coefficients of permeability, Knudsen diffusion, and diffusibility) in dry porous media. To conduct these experiments, a special experimental apparatus was built that incorporates a diffusion cell that represents an open system where the pressure gradient and absolute pressures can be regulated by controlling the flow rates

Valuation of Parameters for the Migration of Components in the Gas System Obtained by Using Column Experiments

“…． 一方，Dusty Gas モデルでは，多成分，非等モル流およ びKnudsen拡散を考慮することができ，ほぼすべての土 壌ガス中の物質移動の解析に適用可能である 8) ． Abu-Ei-Sha'r and Abriola 13) は，ガスの流れのない状態で 行われたカラム実験結果から，Dusty Gasモデルを用いて 分子拡散に関する屈曲度，Knudsen拡散係数とKnudsen拡 散に関する屈曲度を求めた．また，Hibi et al 14) は，Dusty Gasモデルの順解析結果を一次元移流分散方程式の理論 解にフィッテイングさせることにより非等モル流と …”

Development of a Method to Estimate the Dispersion and Knudsen Diffusion Coefficients in Soil by Using the Dusty Gas Model

“…Knudsen拡散係数を算出する方法をReinecke and Sleep 14) は 開発した．なお，Klinkenbergパラメーターbは，土粒子 表面または水とガスとの境界においてガスの速度が0と はならないガス滑り現象の影響の程度を示すパラメータ である．この場合の透過度はk=k 0 (1+b/P)と表される．こ こで，k 0 を有効透過度，Pをガス圧とする．一方，Abu-Ei-Sha'r and Ab-riola 15) は，ガスの流れのない状態のカラム 実験結果から，Dusty Gasモデルを用いて分子拡散係数， Knudsen拡散係数，分子拡散に関係する屈曲度とKnudsen 拡散に関する屈曲度を求めた．また，Hibi et al 16)…”

Effective gas-phase diffusion coefficient in soils

“…Seldom has considered the coupling effect of molecular and Knudsen diffusions in low permeability soil systems and the nonequimolar effect due to unequal molecular masses of the diffusing and ambient gases on gas diffusion. For the application of Fick's law to the interpretation of laboratory data for gas diffusion in soil columns, two questions need to be clarified: (1) what is the specific soil condition under which Knudsen diffusion is substantial and should be considered in the effective diffusion coefficient? (2) How significant is the nonequimolar effect on gas diffusion in soil systems?…”

“…A correction factor, called the obstruction factor, is defined in the DGM, to account for the obstruction of soil particles to molecular diffusion. Brugeman [6], Neale and Nader [21] and AbuEl-Sha'r and Abriola [1] applied the DGM theory and conducted equimolar countercurrent diffusion experiments in porous systems to determine this factor as functions of air-filled porosity. Abu-El-Sha'r and Abriola [1] also determined the Knudsen diffusion coefficient for single gas flow systems with the same soil samples as the ones used for determining the obstruction factor in twocomponent gas diffusion experiments.…”

“…Brugeman [6], Neale and Nader [21] and AbuEl-Sha'r and Abriola [1] applied the DGM theory and conducted equimolar countercurrent diffusion experiments in porous systems to determine this factor as functions of air-filled porosity. Abu-El-Sha'r and Abriola [1] also determined the Knudsen diffusion coefficient for single gas flow systems with the same soil samples as the ones used for determining the obstruction factor in twocomponent gas diffusion experiments. However, the Knudsen effect is not pronounced in their diffusion experiments, as a result that the diffusibility factor is equivalent to the obstruction factor.…”