STEADY-STATE TEMPERATURE DISTRIBUTION IN NONISOTHERMAL, UNSATURATED CLOSED SOIL CELLS

Ambient temperature interference (ATI) is a concern that has not been adequately addressed in studies of coupled water and heat transport in unsaturated soil. Our objectives were to detect ATI, minimize it, and obtain nonisothermal, steady-state temperature and moisture profiles with minimum ATI. Two soils, a sand and a silty clay loam (sicl), were packed into cylindrical cells with uniform moisture. Temperature gradients were imposed by making one end warmer (40, 23, or 19 degrees C) than the other end (1 or 9 degrees C). Steady-state temperature profile data were obtained for various cell configurations and ambient temperatures. The configuration showing least ATI was a 2.5-cm-diam., 5-cm-long cell, with 8 cm radial insulation. Longer cells of the same basic design or with less insulation had greater ATI, as did a larger diameter cell (4 cm diam. and 14 cm long). All tests (sand at 0.049 m(3) m(-3) moisture; sicl at 0.049 and 0.146 m(3) m(-3)) using lowest ATI cells produced concave upward temperature profiles. In contrast, the larger diameter cell (sicl, high ATI) had concave downward profiles. Water redistribution into the cooler half of cells was more pronounced with sand (>90%) than sicl. Cells exhibiting low ATI appear to provide more consistent and meaningful soil temperature and moisture profiles than had previously been obtainable.