Water Vapor Diffusion in Relatively Dry Soil: I. Theoretical Considerations and Sorption Experiments

Water transfer was measured in three soil materials at water content ranges corresponding to a relative pressure range of 0.97 to about 0.05. At these water contents vapor flow is probably the predominant transfer mechanism. The data were obtained from a transient sorption experiment and diffusion coefficients were calculated from analyses of water content distribution curves. The evaporation‐condensation reaction between the liquid and vapor phases was treated by using simultaneous diffusion‐reaction theory. Within the water content ranges used the diffusion coefficients increase and then decrease with increasing water content.