Use of a Pre-Drilled Hole for Implementing Thermal Needle Probe Method for Soils and Rocks

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The thermal needle probe method, which is widely used for measuring the thermal conductivity lambda of soils, deploys a long and thin metallic probe that houses a line heater and a temperature sensor. However, inserting such probes into consolidated or densely compacted soils or rocks is difficult, frequently causing buckling of the probe and severe disturbance to the surrounding ground, leading to unreliable measurements. We found that the use of a pre-drilled hole filled with thermally conductive grease for installing a thermal needle probe was feasible to overcome such challenges, and still yielded reliable measurements of thermal conductivity. The proposed method, i.e., the pre-drilling thermal needle probe method, was verified by finite element calculations and laboratory experiments by varying various parameters, such as the pre-drilled hole diameter, probe diameter, and thermal conductivity of thermal grease. It was observed that increases in the pre-drilled hole diameter and probe diameter and a decrease in the thermal conductivity of the thermal grease caused delays in temperature increase owing to the slowed heat transfer. Nevertheless, all the estimated lambda values agreed well with the reference lambda values with acceptable errors. Thus, the proposed method yields reliable measurements and can be applied for a wide range of soils from compacted soils to hard rocks.
Publisher
MDPI AG
Issue Date
2016-10
Language
English
Article Type
Article
Keywords

CONDUCTIVITY PROBE; SANDS; LINE

Citation

ENERGIES, v.9, no.10

ISSN
1996-1073
DOI
10.3390/en9100846
URI
http://hdl.handle.net/10203/218324
Appears in Collection
CE-Journal Papers(저널논문)
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