Thermal conductivity of standard sands. Part I. dry-state conditions

A comprehensive thermal conductivity (lambda) database of three dry standard sands (Ottawa C-109, Ottawa C-190, and Toyoura) was developed using a transient line heat source technique. The database contains lambda data representing a variety of soil compactions and temperatures (T) ranging from 25 A degrees C to 70 A degrees 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 (lambda(dry)) against T in spite of declining quartz lambda with T. The air content (porosity) controls the lambda of dry sands by acting as a very effective thermal insulator around solid soil particles. As a result, a diminutive increase of lambda(dry) with T is driven by increasing lambda of air. The experimental lambda 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 lambda of solids and the thermal conductance factor.