ISSN: 0090-3973
Page Count: 7

Measurement of Apparent Thermal Conductivity by the Thermal Probe Method

Manohar, K
Lecturer,The University of the West Indies,

Yarbrough, DW
Professorchairman,Tennessee Technological University,TN,

Booth, JR
Adjunct professor,Tennessee Technological University,TN,

(Received 22 September 1999; accepted 7 June 2000)

Abstract

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.

Keywords:
thermal probe, thermal conductivity, line source method

Paper ID: JTE12123J
DOI: 10.1520/JTE12123J
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