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Water Vapor Diffusion in Relatively Dry Soil: IV. Temperature and Pressure Effects on Sorption Diffusion Coefficients¹

ABSTRACT

The temperature and pressure dependence of water transfer coefficients in two relatively dry soil materials were measured. The relative magnitudes of liquid and vapor transfer were obtained from the pressure experiments. The liquid diffusion coefficient for Adelanto loam was 20 to 40% of the total diffusion coefficient, whereas for Pachappa loam the liquid diffusion coefficient was negligible. The temperature dependence of the vapor diffusion coefficient for Adelanto and the total diffusion coefficient in Pachappa can be calculated from published data on the temperature dependence of the water vapor diffusion coefficient in air and the saturated vapor density. The activation energy for the liquid component in Adelanto was calculated by combining the temperature and pressure diffusion data and was found to be about 4.2 kcal mole^-1 for water contents above a monolayer.

¹ Contribution from the Soil and Water Conservation Research Division, ARS, USDA, Tempe, Ariz.

² Research Physicist, U. S. Water Conservation Laboratory, Tempe, Arizona.

Received for publication August 6, 1964. Accepted for publication December 17, 1964.