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This article in SSSAJ

  1. Vol. 48 No. 1, p. 25-32
    Received: Mar 8, 1983
    Accepted: Sept 10, 1983

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Enhancement of Thermal Water Vapor Diffusion in Soil1

  1. A. Cass,
  2. G. S. Campbell and
  3. T. L. Jones2



The enhancement of water vapor diffusion in soil resulting from a temperature gradient was determined using a transient state thermal conductivity measurement. The method of Parikh et al. (1979) was adapted for this study to allow measurement of the thermal conductivity as a function of temperature, water content, and pressure. The data allowed separation of thermal conductivity from thermally induced latent heat transport. Both the mechanistic enhancement factor η of Philip and de Vries and the phenomenological enhancement factor β of Cary are calculated from the slope of the relationship between thermal conductivity and reciprocal relative pressure. The enhancement factor, η approaches 1 for dry soil and increases rapidly to values around 10 for a sand and a silt loam at water contents above half saturation and temperatures above 22°C. At high water content and 3.5°C, η increased to 15. The inflection point water content for the η vs. saturation curve was about twice as high in silt loam as in sand. Measurements conform well to the pattern predicted by a theoretical examination of enhancement factor behavior. Experimental results were also compared with two recent quantitative models of β from Jury and Letey (1979) and Cary (1979). These model predictions did not agree with measured values, nor did they conform to the theoretical limits of β derived in this paper except at intermediate saturation and temperature values.

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