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Measuring effective diffusivity in porous media with a gasket-free, radial arrangement

机译：无垫圈径向布置可测量多孔介质中的有效扩散率

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摘要

A simple technique for measuring the effective diffusivity, and ultimately tortuosity, in porous media is presented. The method uses a custom-built apparatus, based on a radial geometry, which eliminates the need for any gaskets to seal the edge of the sample. This makes it particularly well suited for thin media such as films and layers. The experiment is based on the transient response of the oxygen concentration at the center of the sample as oxygen diffuses into an initially nitrogen filled domain from the sample perimeter. The analytical solution of Fick's law for transient diffusion in cylindrical coordinates is fitted to the measured oxygen concentration profile to obtain the effective diffusivity. To validate the method, binary diffusion coefficients of N-2-Air system were measured and the results show a close match and are consistent for a range of experimental parameters like flow rate and domain thickness. The classical study of diffusion in porous media based on sphere packing is revisited for further validation of the technique. The results show good agreement to the well-known Bruggeman correlation as well as to the experimental values reported in the literature. The new technique is further applied to other types of thin porous materials and the results indicate that the Bruggeman correlation generally underestimates the effective diffusivity of non -sphere packing. (C) 2018 Elsevier Ltd. All rights reserved.
机译：提出了一种用于测量多孔介质中有效扩散率以及最终曲折度的简单技术。该方法使用基于径向几何形状的定制设备，从而无需使用任何垫圈来密封样品的边缘。这使其特别适合于薄膜和层等薄介质。该实验基于氧气从样品周边扩散到最初充氮区域时样品中心氧浓度的瞬态响应。将菲克定律在圆柱坐标系中的瞬态扩散的解析解拟合到测得的氧气浓度曲线，以获得有效的扩散率。为了验证该方法，对N-2-Air系统的二元扩散系数进行了测量，结果显示出非常接近的结果，并且与一系列实验参数（例如流速和畴壁厚度）一致。再次对基于球体堆积的多孔介质中扩散的经典研究进行了重新验证，以进一步验证该技术。结果表明与众所周知的布鲁格曼相关性以及文献报道的实验值具有良好的一致性。将该新技术进一步应用于其他类型的薄多孔材料，结果表明，布鲁格曼相关性通常低估了非球形填料的有效扩散率。 （C）2018 Elsevier Ltd.保留所有权利。

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