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Soil Physics Note

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

^* Corresponding author (rhorton{at}iastate.edu)

One-dimensional temperature gradients are difficult to achieve in nonisothermal laboratory studies because, in addition to desired axial temperature gradients, ambient temperature interference (ATI) creates a radial temperature distribution. Our objective was to develop a closed soil cell with limited ATI. The cell consists of a smaller soil column, the control volume, surrounded by a larger soil column, which provides radial insulation. End boundary temperatures are controlled by a new spiral-circulation heat exchanger. Four cell size configurations were tested for ATI under varying ambient temperatures. Results indicate that cells with a 9-cm inner column diameter, 5-cm concentric soil buffer, and either 10- or 20-cm length effectively achieved one-dimensional temperature conditions. At 30°C ambient temperature, and with axial temperature gradients as large as 1°C cm^–1, average steady-state radial temperature gradients in the inner soil columns were <0.02°C cm^–1. Thus, these cell configurations meet the goal of maintaining a one-dimensional temperature distribution. These cells provide new opportunities for improving the study of coupled heat and water movement in soil.

Abbreviations: ATI, ambient temperature interference • F38, 3.8-cm fiberglass insulation • L, long • N, narrow • R16, 1.6-cm Reflectix insulation • R48, 4.8-cm Reflectix insulation • S, short • TC, thermocouple • W, wide

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