Instrumentation for Determination of Thermal Conductivity for Geomaterials-Paper

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The study evaluates the thermal conductivity of fine, medium, and coarse sand, fly ash, and moorum at varying water contents using a fabricated thermal probe. The probe was calibrated with glycerin, whose known conductivity is 0.285 W/m·K; testing was then conducted at 1.8 V. Conductivity was calculated from the slope of temperature-versus-logarithmic-time measurements using a transient heat-source method.<br /><br />Results show that thermal conductivity generally increased with water content and dry density. Across the tested moisture levels, values ranged from 0.107 to 0.269 W/m·K for fine sand, 0.151 to 0.379 for medium sand, 0.301 to 0.487 for coarse sand, 0.178 to 0.225 for fly ash, and 0.128 to 0.349 for moorum. Coarse sand had the highest measured conductivity, while fine sand had the lowest dry-state value.<br /><br />The authors attribute the trends to water conducting heat more effectively than air-filled pores and to increased grain-to-grain contact at higher density. Sands also generally outperformed fly ash and moorum, which the study links to quartz content. Overall, the findings indicate that soil texture, moisture, density, and porosity are important factors when estimating heat transfer through ground materials—an important consideration for applications such as buried cables, pipelines, foundations, and ground heat exchangers.

Keywords

thermal conductivity

fine sand

medium sand

coarse sand

fly ash

moorum

water content

dry density

transient heat source

ground heat transfer