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United States Department of Agriculture

Agricultural Research Service

Title: The Heat Pulse Ratio Method for Measuring Soil Water Flow: Reconciling Measurements and Predictions

item Ochsner, Tyson
item Horton, Robert - IOWA STATE UNIVERSITY
item Kluitenberg, Gerald - KANSAS STATE UNIV

Submitted to: ASA-CSSA-SSSA Annual Meeting Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: July 26, 2004
Publication Date: November 1, 2004
Citation: Ochsner, T.E., Horton, R., Kluitenberg, G.J. 2004. The heat pulse ratio method for measuring soil water flow: reconciling measurements and predictions [abstract]. ASA-CSSA-SSSA Annual Meeting Abstracts. p. 32.

Technical Abstract: The ratio of temperature increases at equal distances downstream and upstream from a pulsed line heat source (Td/Tu) is an indicator of soil water flux (J). In theory, a linear relationship exists between the natural logarithm of Td/Tu and J. This relationship is the basis for the heat pulse ratio method for measuring J. Our experiments on saturated soil columns show that the relationship is linear as predicted, but the slope of the relationship is less than predicted; that is the ratios are smaller than expected for a given flow rate. The difference between the measured and predicted slopes is dependent on the soil type. Sand yielded the smallest difference (23%), sandy loam yielded the largest difference (77%), and silt loam was intermediate (60%). Similar discrepancies have been found in earlier attempts to measure fluid flow in porous media using heat transfer measurements. Two possibilities for reconciling the measurements and theoretical predictions are to increase the conduction term in the governing equation or to decrease the convection term. We found that decreasing the convection term completely reconciles the measurements and predictions, but increasing the conduction term allows only partial reconciliation. The physical causes for this reduced convection await explanation.

Last Modified: 4/22/2015
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