Volume 28, Issue 5 (September 2000)
Measurement of Apparent Thermal Conductivity by the Thermal Probe Method
Three thermal probes were constructed in accordance with ASTM D 5334 and calibrated using heat-flow metre data. The temperature-time response of the thermal probes for determining apparent thermal conductivity λ under transient state conditions was logged at 1 s intervals. The instrumentation used reduced the determinate error associated with voltage and current measurements to a negligibly small value that made the uncertainty in λ dependent on the uncertainty of the slope dT/dlnt. A test method was run in 1000 s, in which a criterion of 2.5% spread among three consecutive slope values was used to determine the extent of the linear segment of the T–ln t curve.
The probes demonstrated repeatability within ±3.5% but had definite individual bias indicating a need for individual calibration. Using individual probe calibration factors, the experimentally de termined λs for all-purpose sand, sifted sand, and soil were deter mined to be 0.520, 0.445, and 2.11 W/moK, respectively.