DIFFUSION OF WATER UNDER SUBFREEZING TEMPERATURE

Details are briefly outlined of an experiment involving a 24 in. long Plexiglas cell with a 1-ft. square cross section and copper end plates. One copper and plate was cooled to a subfreezing temperature while the other was maintained at the initial temperature. Samples of sand were collected from different lateral positions and the moisture content was determined by drying the samples to a constant weight in an oven. The results show that in intially unsaturated sand, the unfrozen zone continuously lost water to the frozen zone, and that a dynamic steady state was never attained. Also, the moisture content registered a step increase above the initial value at the freezing front. The lower the cold end temperature the smaller was the step increase in the moisture content across the freezing front. In the case of a semi-infinite region, the step in the moisture content at the interface would be expected to attain asymptomatic value. The transient portion of the moisture profile is due to the time required for the moisture and thermal energy diffusional processes to reach a dynamic equilibrium. In the case of saturated sand, no moisture diffusion occurred. Evaporation of the liquid to maintain vapor-liquid equilibrium at the local temperature produces a gradient in the liquid water content which then results in liquid diffusion. Mathematical models using both linear and exponential dependence of the water vapor pressure in temperature yield results in agreement with experimental observations.

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  • Accession Number: 00134053
  • Record Type: Publication
  • Report/Paper Numbers: ASCE #11893
  • Files: TRIS
  • Created Date: Jun 23 1976 12:00AM