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Thermal Conductivity of Unsaturated ...

Yao, Jun.

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Thermal Conductivity of Unsaturated Soils.

紀錄類型:	書目-電子資源 : Monograph/item
正題名/作者:	Thermal Conductivity of Unsaturated Soils./
作者:	Yao, Jun.
出版者:	Ann Arbor : ProQuest Dissertations & Theses, : 2018,
面頁冊數:	157 p.
附註:	Source: Dissertation Abstracts International, Volume: 79-09(E), Section: B.
Contained By:	Dissertation Abstracts International79-09B(E).
標題:	Geological engineering. -
電子資源:	http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=10817299
ISBN:	9780355943627

Thermal Conductivity of Unsaturated Soils.
Yao, Jun.

Thermal Conductivity of Unsaturated Soils. - Ann Arbor : ProQuest Dissertations & Theses, 2018 - 157 p.

Source: Dissertation Abstracts International, Volume: 79-09(E), Section: B.

Thesis (Ph.D.)--The University of Wisconsin - Madison, 2018.

Heat transfer through soils is a fundamental process in many energy geosystems such as shallow geothermal heat exchangers, energy piles, buried high-voltage power cables in wind or solar energy applications, and subsurface thermal energy storage systems. In these and other applications in the growing field of energy geotechnics, thermal conductivity of unsaturated soils is critical for the performance of these energy geosystems involving coupled heat and moisture transport phenomena. There is considerable basic research need to more effectively link the fundamental soil thermal behavior to the soil (e.g., soil types and water content), environmental (e.g., temperature), and construction (e.g., stress) factors.

ISBN: 9780355943627Subjects--Topical Terms:

2122713
Geological engineering.

Thermal Conductivity of Unsaturated Soils.
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500 $a Source: Dissertation Abstracts International, Volume: 79-09(E), Section: B.
500 $a Adviser: William J. Likos.
502 $a Thesis (Ph.D.)--The University of Wisconsin - Madison, 2018.
520 $a Heat transfer through soils is a fundamental process in many energy geosystems such as shallow geothermal heat exchangers, energy piles, buried high-voltage power cables in wind or solar energy applications, and subsurface thermal energy storage systems. In these and other applications in the growing field of energy geotechnics, thermal conductivity of unsaturated soils is critical for the performance of these energy geosystems involving coupled heat and moisture transport phenomena. There is considerable basic research need to more effectively link the fundamental soil thermal behavior to the soil (e.g., soil types and water content), environmental (e.g., temperature), and construction (e.g., stress) factors.
520 $a The first objective of this study is to explore appropriate experimental techniques and procedures to measure the thermal conductivity of unsaturated soils. 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.
520 $a The second objective of this study is to investigate the effects of elevated temperature on thermal conductivity of unsaturated soils using an evaporative technique in a temperature-controlled oven at temperatures up to 75°C. Thermal conductivity of both sands at low to intermediate saturations ( S &sim; 0.1 to 0.5) increased appreciably at elevated temperature. Maximum thermal conductivity occurred at 75°C and around the point of critical saturation (Sc &sim; 0.1 - 0.13), where thermal conductivity was about twice that at room temperature (&sim;23°C). This was attributed to the influence of latent heat transfer from vapor diffusion at air-water interfaces, which have a maximum surface area within this saturation regime. A new empirical model was proposed for predicting thermal conductivity dry out curves at elevated temperatures. Modeled TCDCs show good agreement with experimental results.
520 $a The third objective of this study is to investigate the coupled effects of temperature and stress level on thermal conductivity of unsaturated sands. A suction-controlled thermo-mechanical (SCTM) method has been developed to measure thermal conductivity of unsaturated soils at different temperatures (5.5 °C to 75.5 °C), isotropic net normal stresses (35 kPa to 400 kPa), and wetting conditions (hysteretic drying and wetting paths). This method permits quantification of thermal conductivity of soils under the influence of stress level and temperature (i.e. construction and environmental conditions). A poorly-graded sand is used to investigate the coupled effects of temperature and stress level on thermal conductivity of unsaturated sands. For saturated sand, thermal conductivity from the initial loading cycle increases with increasing isotropic net normal stress (loading) and decreases along a different path with decreasing normal stress (unloading) due to the irreversible plastic strain. Thermal conductivity of saturated sand also shows a decreasing trend as temperature increases and is potentially due to increasing void space caused by thermal expansion of solid particles during heating. The thermal conductivity increases appreciably as both isotropic net normal stress and temperature increase at intermediate saturations (S &sim; 0.3 to 0.75). Maximum thermal conductivity occurs at 75.5 °C and 400 kPa when S = 0.54, where the value of thermal conductivity is 4.59 W/m-K. The potential mechanisms responsible for increasing thermal conductivity in this saturation range are pore water redistribution and larger effective solid-solid contact area for heat transfer due to increased contact area and water meniscus between solid particles (particle deformation). Hysteresis in thermal conductivity with respect to wetting-drying direction is also observed due to the dilative pattern of soil specimen in the wetting direction.
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