Thermal gradients in moist soil cause water to move and water redistribution influences temperature. A series of thermal gradients was imposed on sealed laboratory soil columns. Thermo-TDR (heat-pulse technique combined with time domain reflectometry) probes were positioned in the columns to provide automated, co-located measurements of soil temperature, thermal properties, and volumetric water content. Use of the probes enabled repeated measurements on the same soil columns for a series of boundary conditions. This is a clear advantage over earlier investigations, in which one set of boundary and/or soil conditions was applied per column before column disassembly.
Each experimental apparatus consisted of a small soil column within a larger one. The smaller column, 10-cm (length) and 10-cm (diameter), was a PVC-cylinder uniformly packed with soil and instrumented with thermo-TDR sensors at seven depths. The smaller column was placed inside a 20-cm diameter PVC-column of the same length. The space between the two columns was packed with identical soil material, to provide radial insulation and facilitate a 1-D temperature distribution. Boundary temperatures were controlled by a heat exchanger and a temperature-controlled water bath at either end of the columns. A preliminary step in the study was an examination of the radial temperature distribution within the inner and outer columns under the designated boundary conditions. Data revealed that a satisfactory 1-D internal temperature distribution was achieved within the inner columns.
The first set of experiments included two soils (sand and silt loam), each with two uniform initial water contents, for a total of four columns. Columns were first exposed to nine sets of temperature boundary conditions: three constant temperature gradients around three mean temperatures. The columns were then exposed to oscillating temperature boundary conditions with several amplitudes. Transient soil temperature and water content for the various columns and boundary conditions will be reported.
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