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Transient Plane and Line Source Methods for Soil Thermal Conductivity
Experiments were conducted to compare two sensing techniques for measuring thermal conductivity of unsaturated soils: (i) a modified transient plane source (MTPS) method for non-destructive measurements using a planar, interfacial heat reflectance sensor, and (ii) a transient line source (TLS-SP) method utilizing an embedded single-probe heat source. Measurement protocols for coarse-grained and fine-grained soils were developed. Thermal conductivity dry-out curves (TCDCs) were measured for five soil types, including poorly graded sand, well-graded sand with silt, silty sand, silt, and clay. The MTPS sensor consistently produced higher thermal conductivity for degrees of saturation greater than about 50 % but lower thermal conductivity for saturations less than 50 %. Saturated thermal conductivity measured using the MTPS sensor ranged from 8 % to 26 % greater than values measured using the TLS-SP sensor. Dry thermal conductivity measurements were comparable (<5 % difference) for fine-grained soils but were consistently and appreciably greater using the TLS-SP for coarse-grained soils. Mechanisms responsible for these differences include thermally induced water migration, latent heat transfer, sensor-soil contact resistance, gravity-induced water migration, and specimen heterogeneity. Secondary experiments indicated that the effects of gravity-induced water migration were insignificant within the short (<5 min) time frame elapsed between sample preparation and measurement.
Transient Plane and Line Source Methods for Soil Thermal Conductivity
Experiments were conducted to compare two sensing techniques for measuring thermal conductivity of unsaturated soils: (i) a modified transient plane source (MTPS) method for non-destructive measurements using a planar, interfacial heat reflectance sensor, and (ii) a transient line source (TLS-SP) method utilizing an embedded single-probe heat source. Measurement protocols for coarse-grained and fine-grained soils were developed. Thermal conductivity dry-out curves (TCDCs) were measured for five soil types, including poorly graded sand, well-graded sand with silt, silty sand, silt, and clay. The MTPS sensor consistently produced higher thermal conductivity for degrees of saturation greater than about 50 % but lower thermal conductivity for saturations less than 50 %. Saturated thermal conductivity measured using the MTPS sensor ranged from 8 % to 26 % greater than values measured using the TLS-SP sensor. Dry thermal conductivity measurements were comparable (<5 % difference) for fine-grained soils but were consistently and appreciably greater using the TLS-SP for coarse-grained soils. Mechanisms responsible for these differences include thermally induced water migration, latent heat transfer, sensor-soil contact resistance, gravity-induced water migration, and specimen heterogeneity. Secondary experiments indicated that the effects of gravity-induced water migration were insignificant within the short (<5 min) time frame elapsed between sample preparation and measurement.
Transient Plane and Line Source Methods for Soil Thermal Conductivity
Yao, Jun (author) / Likos, William J
2017
Article (Journal)
English
BKL:
38.58
Geomechanik
/
56.20
Ingenieurgeologie, Bodenmechanik
Local classification TIB:
770/4815/6545
Transient Plane and Line Source Methods for Soil Thermal Conductivity
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