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Soil Physics

Correcting Wall Flow Effect Improves the Heat-Pulse Technique for Determining Water Flux in Saturated Soils

College of Resource and Environmental Sciences, China Agricultural Univ., Beijing, China 100094

^* Corresponding author (gongys{at}cau.edu.cn)

Heat-pulse sensors are promising tools that can provide rapid measurements of soil water fluxes. The main objective of this study was to determine whether wall flow could be a main reason for discrepancies between measured and heat-pulse water flux densities. Heat-pulse measurements were obtained with a range of water flux densities imposed on packed soil columns of three saturated media: glass beads, a sandy loam soil, and a sandy clay loam soil. Water flux density was calculated from the thermal properties of the media and the ratio of temperature changes at downstream and upstream positions. A novel finding from this study was that in packed columns, wall flow was responsible for the deviations between water flux estimates from heat-pulse data and water flux measured from outflow, and the magnitude of wall flow was largely determined by soil texture. An amplification factor, 1.12 for the sandy loam and 1.24 for the sandy clay loam, was introduced to correct the influence of wall flow, which reduced the errors of the heat-pulse measurements to within 5%. We demonstrated that wall flow was able to explain quantitatively the "reduced convection" theory proposed by earlier researchers. Under the experimental conditions, heat transfer by dispersion was of minor importance.

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