Measurement of apparent thermal conductivity by the thermal probe method

Three thermal probes were constructed in accordance with ASTM D 5334 and ca librated using heat-flow metre data. The temperature-time response of the t hermal probes for determining apparent thermal conductivity lambda under tr ansient state conditions was logged at 1 s intervals. The instrumentation u sed reduced the determinate error associated with voltage and current measu rements to a negligibly small value that made the uncertainty in lambda dep endent on the uncertainty of the slope dT/dlnt. A test method was run in 10 00 s, in which a criterion of 2.5% spread among three consecutive slope val ues was used to determine the extent of the linear segment of the T-ln t cu rve. The probes demonstrated repeatability within +/- 3.5% but had definite indi vidual bias indicating a need for individual calibration. Using individual probe calibration factors, the experimentally determined lambda s for all-p urpose sand, sifted sand, and soil were determined to be 0.520, 0.445, and 2.11 W/m.K, respectively.