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SOIL PHYSICS

An Improved Approach for Measurement of Coupled Heat and Water Transfer in Soil Cells

^a Dep. of Agronomy, Iowa State Univ., Ames, IA 50011
^b Dep. of Soil and Water, China Agricultural Univ., Beijing 100094 China
^c USDA-ARS, Univ. of Minnesota, 1991 Buford Cir., St. Paul, MN 55108

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

Laboratory experiments on coupled heat and water transfer in soil have been limited in their measurement approaches. Inadequate temperature control creates undesired two-dimensional distributions of both temperature and moisture. Destructive sampling to determine soil volumetric water content () prevents measurement of transient distributions and provides no direct information on soil thermal properties. The objectives of this work were to: (i) develop an instrumented closed soil cell that provides one-dimensional conditions and permits in situ measurement of temperature, , and thermal conductivity () under transient boundary conditions, and (ii) test this cell in a series of experiments using four soil type–initial combinations and 10 transient boundary conditions. Experiments were conducted using soil-insulated cells instrumented with thermo-time domain reflectometry (T-TDR) sensors. Temperature distributions measured in the experiments show nonlinearity, which is consistent with nonuniform thermal properties provided by thermal moisture distribution but differs from previous studies lacking one-dimensional temperature control. The T-TDR measurements of based on dielectric permittivity, volumetric heat capacity, and change in volumetric heat capacity agreed well with post-experiment sampling, providing r² values of 0.87, 0.93, and 0.95, respectively. Measurements of and were also consistent with the shapes of the observed temperature distributions. Techniques implemented in these experiments allowed observation of transient temperature, , and distributions on the same soil sample for 10 sequentially imposed boundary conditions, including periods of rapid redistribution. This work demonstrates that, through improved measurement techniques, the study of heat and water transfer processes can be expanded in ways previously unavailable.

Abbreviations: TDR, time domain reflectometry • T-TDR, thermo-time domain reflectometry

This article has been cited by other articles:

				J. L. Heitman, R. Horton, T. Ren, I. N. Nassar, and D. D. Davis A Test of Coupled Soil Heat and Water Transfer Prediction under Transient Boundary Temperatures Soil Sci. Soc. Am. J., September 1, 2008; 72(5): 1197 - 1207. [Abstract] [Full Text] [PDF]