A Finite Element Calculation for Determining Thermal Conductivity

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Abstract
A new simple method for in situ measurement of thermal conductivity of porous materials was developed. A heated or cooled Al or glass probe was placed in soil, and its temperature was monitored over time. Thermal conductivity was determined using a finite element method to solve the radial heat flow equation for the temperature of the heated or cooled probe. The probe temperature, as a function of time, was modeled, and model thermal conductivity was adjusted until predicted probe temperatures agreed with measured values. Conductivities for sand, silt loam, and forest litter were measured over a range of water contents. Values obtained using a glass probe were not significantly different from those obtained using an Al probe. Conductivities were in good agreement with those obtained using a water bath method or computed from the deVries equation. There were significant differences between values obtained with heated and cooled probes in sand at intermediate water content.