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United States Department of Agriculture

Agricultural Research Service

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

Authors
item Zhou, Jian - IOWA STATE UNIVERSITY
item Heitman, Joshua - IOWA STATE UNIVERSITY
item Horton, Robert - IOWA STATE UNIVERSITY
item Ren, Tusheng - CHINA AGRI UNIV BEIJING
item Ochsner, Tyson
item Prunty, Lyle - NORTH DAKOTA STATE UNIV
item Ewing, Robert - IOWA STATE UNIVERSITY
item Sauer, Thomas

Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 25, 2006
Publication Date: June 21, 2006
Citation: Zhou, J., Heitman, J.L., Horton, R., Ren, T., Ochsner, T.E., Prunty, L., Ewing, R.P., Sauer, T.J. 2006. Method for maintaining one-dimensional temperature gradients in unsaturated, closed soil cells. Soil Science Society of America Journal. 70:1303-1309.

Interpretive Summary: Soil water moves in response to temperature gradients. This linkage between soil temperature and water movement influences springtime seed zone temperature and moisture conditions. Current theories describing the coupling between soil heat and water transfer are inadequate. Careful laboratory studies of these phenomena are needed so that theories can be tested and refined. However, the necessary conditions for such laboratory studies, especially one-dimensional temperature gradients, can be difficult to achieve. A key problem is that ambient temperature interference (ATI) creates an unwanted radial temperature distribution. We developed 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. 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. These findings will benefit researchers who study coupled heat and water movement in soil.

Technical Abstract: One-dimensional temperature gradients are difficult to achieve in non-isothermal laboratory studies because, in addition to desired axial temperature gradients, ambient temperature interference (ATI) creates a radial temperature distribution. Our objective is 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 are 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 degrees C ambient temperature, and with axial temperature gradients as large as 1 degree C cm–1, average steady-state radial temperature gradients in the inner soil columns are < 0.02 degrees 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.

Last Modified: 11/23/2014
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