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Method for Maintaining One-Dimensional Temperature Gradients in Unsaturated, Closed Soil Cells

^a Dep. of Agronomy, Iowa State Univ., Ames, IA 50011
^b College of Resources and Environment, China Agricultural Univ., Beijing, China 100094
^c USDA-ARS, St. Paul, MN 55108
^d Dep. of Soil Science, North Dakota State Univ., Fargo, ND 58105
^e USDA-ARS National Soil Tilth Lab. Ames, IA 50011

View larger version (28K): [in a new window]   Fig. 1. Cross-section of the cell tested in the experiments, shown without soil, insulation, and thermocouples. Heat exchangers positioned at the top and bottom of the cell are identical except for orientation. The diagram is not drawn to scale.

View larger version (41K): [in a new window]   Fig. 2. Components of the heat exchanger as arranged on the top of the soil cell. Identical heat exchangers were placed on the top and bottom of each cell. The diagram is not drawn to scale.

View larger version (26K): [in a new window]   Fig. 3. Steady-state temperature (T) profiles as affected by insulation thickness for 30°C ambient temperature: (A) the long, narrow cell, (B) the long, wide cell, (C) the short, narrow cell, and (D) the short, wide cell. Insulation methods included fiberglass insulation at 3.8 cm (F38) and Reflectix insulation at 1.6 (R16) and 4.8 (R48) cm (Table 2).

View larger version (13K): [in a new window]   Fig. 4. Steady-state temperature (T) profiles at two radial positions for 30°C ambient temperature in (A) the long and wide cell with 3.8 cm of fiberglass plus 4.8 cm of Reflectix, and (B) the short and wide cell with 3.8 cm of fiberglass insulation.

View larger version (26K): [in a new window]   Fig. 5. Steady-state temperature (T) profiles as affected by ambient temperatures of 10 to 40°C: (A) the long, narrow cell with 3.8 cm of fiberglass plus 4.8 cm of Reflectix; (B) the short, narrow cell with 3.8 cm of fiberglass and 1.6 cm of Reflectix; (c) the long, wide cell with 3.8 cm of fiberglass and 4.8 cm of Reflectix; and the short, wide cell with 3.8 cm of fiberglass insulation, respectively.

View larger version (15K): [in a new window]   Fig. 6. Final water content () distributions within the long and wide (LW), long and narrow (LN), short and wide (SW), and short and narrow (SN) cells.