101831 A PerfectConductor Approach for Estimating Water Flux Density with the HeatPulse Method.
Poster Number 179302
See more from this Division: SSSA Division: Soil Physics and Hydrology
See more from this Session: Advances in Soil Sensing and Model Integration with Instrumentation Poster
Monday, November 7, 2016
Phoenix Convention Center North, Exhibit Hall CDE
Abstract:
The heatpulse method is one of the few methods available for measuring water flux density insitu. The method involves measuring the temperature rise at known distances upstream and downstream from a pulsed heat source. The measurement is accompanied by a heat transfer model for analyzing the temperature data. The fitting of modeled to measured temperature data allows for estimation of the soil thermal properties (i.e. thermal conductivity, heat capacity, and thermal diffusivity) and heatpulse velocity. Volumetric water content can be obtained from the estimated volumetric heat capacity, provided that specific heat of the solids and the soil bulk density are known. Furthermore, water flux density is obtained via the heat pulse velocity.
We present preliminary work that advances the method by using cylindrical probes that have relatively large diameter and high thermal conductivity, so they can be approximated as perfect conductors. This approximation is particularly appropriate for heatpulse sensors with probes constructed from thickwalled stainlesssteel tubing and whose diameter is large relative to the distance between the heater and temperature probes. A perfect conductor model accounts for the finite radius and heat capacity of the probe, but approximates its thermal conductivity as infinite, assuming that the thermal conductivity of the probe is significantly higher than that of the soil.
In this work we analyze the errors that arise from neglecting the thermal conductivity of the probes and the nonuniformity of the Darcy flux that is caused by these largediameter probes. We demonstrate that these errors are relatively small. These small errors allow us to approximate the probes as perfect conductors and the flow as one dimensional, with minimal loss of accuracy, such that relatively simple semianalytical expressions can be used for inverse modeling of the data.
We present preliminary work that advances the method by using cylindrical probes that have relatively large diameter and high thermal conductivity, so they can be approximated as perfect conductors. This approximation is particularly appropriate for heatpulse sensors with probes constructed from thickwalled stainlesssteel tubing and whose diameter is large relative to the distance between the heater and temperature probes. A perfect conductor model accounts for the finite radius and heat capacity of the probe, but approximates its thermal conductivity as infinite, assuming that the thermal conductivity of the probe is significantly higher than that of the soil.
In this work we analyze the errors that arise from neglecting the thermal conductivity of the probes and the nonuniformity of the Darcy flux that is caused by these largediameter probes. We demonstrate that these errors are relatively small. These small errors allow us to approximate the probes as perfect conductors and the flow as one dimensional, with minimal loss of accuracy, such that relatively simple semianalytical expressions can be used for inverse modeling of the data.
See more from this Division: SSSA Division: Soil Physics and Hydrology
See more from this Session: Advances in Soil Sensing and Model Integration with Instrumentation Poster
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