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A Closed Tube Method for Measuring Gas Diffusion Coefficients

Lawrence Berkeley Laboratory, Earth Sciences Division, Building 50 E, Berkeley, CA 94720

L. J. Waldron and J. Nemson

Dep. of Plant and Soil Biology, Univ. of California, Berkeley, CA 94720

ABSTRACT

A transient, closed tube method for measuring both ordinary gas diffusivities and porous media effective diffusivities is presented. The current method is suitable for measuring gas diffusivities in air-dry systems over a range of temperatures. Gas concentrations are continuously monitored in a well-stirred volume of a single end chamber, which is connected to a closed sample chamber during experiments. An analytic solution for this diffusion process is available in which, after a sufficient time, the diffusivity of the sample is obtained from the slope of the logarithm of dimensionless concentration excess versus time. The method was checked by comparing measurements of N₂-O₂ gas diffusivities at 0, 30, and 60 °C to various previously reported values in the literature. The measured diffusivities fall within the uncertainties of these earlier works.

^* For correspondence and reprints.

Contribution of Dep. of Plant and Soil Biology, Univ. of California, Berkeley.

Received for publication July 30, 1987.