Tj. Lewis et al., THERMAL-CONDUCTIVITY MEASUREMENT OF ROCK FRAGMENTS USING A PULSED NEEDLE PROBE, Canadian journal of earth sciences, 30(3), 1993, pp. 480-485
A heat pulse generated inside a needle probe can be used to measure th
e thermal conductivity of surrounding rock fragments or drill cuttings
. As the pulse of heat is conducted outwards into the surrounding aggr
egate of rock fragments and water, the decrease in temperature inside
the probe is recorded as a function of time. An asymptotic relation be
tween probe temperature, conductivity, and inverse time since the heat
pulse is shown to be accurate for the range of times used. The relati
vely slow thermal response of the probe in samples with higher conduct
ivities is accommodated by a delay in the origin time of the pulse. Th
e combined correction for finite pulse length and slow probe response
is shown to be small and predictable. The thermal conductivity of rock
fragments is calculated from a model that is dependent on the water c
ontent of the sample, as in other methods. Results using this method a
nd a divided bar apparatus are equivalent, given the expected accuracy
of a divided bar. The measured thermal conductivities of water, fused
quartz, and crystalline quartz compare closely with their accepted va
lues.