Thermal Conductivity of Standard Sands. Part I. Dry-State Conditions

Abstract

A comprehensive thermal conductivity (λ) database of three dry standard sands and Toyoura) was developed using a transient line heat source technique. The database contains λ data representing a variety of soil compactions and temperatures (T ) ranging from 25 • C to 70 • C. The tested standard sands, due to their repeatable physical characteristics, can be used as reference materials for validation of thermal probes applied to similar dry granular materials. The measured data show an increasing trend of thermal conductivity at dryness (λ dry ) against T in spite of declining quartz λ with T . The air content (porosity) controls the λ of dry sands by acting as a very effective thermal insulator around solid soil particles. As a result, a diminutive increase of λ dry with T is driven by increasing λ of air. The experimental λ data of dry sands were exceptionally well predicted by de Vries and Woodside-Messmer models, and also by a thermal conductance model, a product of λ of solids and the thermal conductance factor. 123 950 Int J Thermophys (2009) 30:949-968

Characterisation of Ground Thermal and Thermo-Mechanical Behaviour for Shallow Geothermal Energy Applications

“…However, there is a trend to utilise steadystate methods for rocks (solid mineral matter) and transient methods for soils (e.g., see Reference [40]). [20,33,34,47,66,[70][71][72][73][74]; Sr: degree of saturation, n: porosity.…”

“…In general, transient techniques can be applied to any type of soil under any water content condition [33], although it is important to make sure the size of any heating needles used are appropriate for the soil grain size. Jackson and Taylor [75], upon assessing transient methods, [20,33,34,47,66,[70][71][72][73][74]; Sr: degree of saturation, n: porosity.…”

“…In general, transient techniques can be applied to any type of soil under any water content condition [33], although it is important to make sure the size of any heating needles used are appropriate for the soil grain size. Jackson and Taylor [75], upon assessing transient methods, concluded that their main advantages are: (i) moisture migration in response to temperature gradients was minimised, and (ii) a long wait for thermal gradients to equilibrate was not required.…”

“…Tarnawski and collaborators [33,71,72], who used the thermal needle probe, and Nikolaev et al [34], who employed the guarded hot plate, constitute the most recent and complete studies on the dependency of the thermal conductivity of standard sands at different degrees of saturation over a temperature range. For dry sands, in Reference [34] agreement was demonstrated, with a maximum discrepancy of 5.7%, between the measurements performed with the guarded hot plate and the thermal needle probe, as reported by References [33,73,77,78] (see Figure 8).…”

“…While not explicitly designed with soils in mind, the guarded hot plate has been used for this application. In References [33,34] the thermal conductivity of sands was measured using this apparatus, while in Reference [35] the method was applied to clay soils. Similar approaches to the guarded hot plate are reported in the literature, such as the thermal cell that has been used for the measurement of clayey samples in Reference [36] and a wider range of soils in [37].…”