Performance of thermal conductivity probes for planetary applications

Hütter, Erika S.; Kömle, Norbert I.

doi:10.5194/gi-1-53-2012

Cited by 9 publications

(22 citation statements)

References 15 publications

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“…Either a much more complicated formalism is used, applying the theory of "short and thick" sensors, or the same simple theory is used with an additional calibration function valid over the desired range of conductivities. The first method has been described in much detail in a recent paper by Hütter and Kömle (2012), in Hütter (2011) and most recently in Macher et al (2013). The second method is the topic of the current paper.…”

Section: Introductionmentioning

confidence: 99%

Calibration of non-ideal thermal conductivity sensors

Kömle

Macher

Kargl

et al. 2013

Geosci. Instrum. Method. Data Syst.

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Abstract.A popular method for measuring the thermal conductivity of solid materials is the transient hot needle method. It allows the thermal conductivity of a solid or granular material to be evaluated simply by combining a temperature measurement with a well-defined electrical current flowing through a resistance wire enclosed in a long and thin needle. Standard laboratory sensors that are typically used in laboratory work consist of very thin steel needles with a large length-to-diameter ratio. This type of needle is convenient since it is mathematically easy to derive the thermal conductivity of a soft granular material from a simple temperature measurement. However, such a geometry often results in a mechanically weak sensor, which can bend or fail when inserted into a material that is harder than expected. For deploying such a sensor on a planetary surface, with often unknown soil properties, it is necessary to construct more rugged sensors. These requirements can lead to a design which differs substantially from the ideal geometry, and additional care must be taken in the calibration and data analysis.In this paper we present the performance of a prototype thermal conductivity sensor designed for planetary missions. The thermal conductivity of a suite of solid and granular materials was measured both by a standard needle sensor and by several customized sensors with non-ideal geometry. We thus obtained a calibration curve for the non-ideal sensors. The theory describing the temperature response of a sensor with such unfavorable length-to-diameter ratio is complicated and highly nonlinear. However, our measurements reveal that over a wide range of thermal conductivities there is an almost linear relationship between the result obtained by the standard sensor and the result derived from the customized, non-ideal sensors. This allows for the measurement of thermal conductivity values for harder soils, which are not easily accessible when using standard needle sensors.

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Section: Introductionmentioning

confidence: 99%

Calibration of non-ideal thermal conductivity sensors

Kömle

Macher

Kargl

et al. 2013

Geosci. Instrum. Method. Data Syst.

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“…Substitution of (16) and (18) into (10) or (8) yields e T 2 , which can be used in (9) to obtain e T 1 . Thus,…”

Section: Solution For Laplace Transformsmentioning

confidence: 99%

“…In certain applications, such as conductivity measurements with cylindrical probes, this resistance may play a significant role if the contact to the surrounding medium is poor. Such a situation can occur, for instance, when measuring the thermal conductivities of surface material on the Moon or comets [13,14,9]. The first application of this kind was made in the framework of the lunar conductivity measurements (Apollo 15 and 17), as described in [15][16][17][18].…”

Section: Introductionmentioning

confidence: 99%

The heated infinite cylinder with sheath and two thermal surface resistance layers

Macher

Kömle

Bentley

et al. 2013

International Journal of Heat and Mass Transfer

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“…-Reasonably large-sized samples were prepared, which were big enough in diameter and height that all three sensors could be inserted without disturbing each other during a measurement and making sure that no influence from the sample boundaries could disturb the measurements. For estimating minimum sample sizes, refer to the formulae given in Hütter and Kömle (2012).…”

Section: Calibration Of the Ruggedized Sensorsmentioning

confidence: 99%

Calibration of non-ideal thermal conductivity sensors

Kömle¹,

Macher²,

Kargl³

et al. 2012

Preprint

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A popular method for measuring the thermal conductivity of solid materials is the transient heated needle method. It allows to evaluate the thermal conductivity of a solid or granular material to be evaluated simply by combining a temperature measurement with a well-defined electrical current flowing through a resistance wire enclosed in a long and thin needle. Standard laboratory sensors that are typically used in laboratory work consist of very thin steel needles with a large length-to-diameter ratio. This type of needles is convenient since it is mathematically easy to derive the thermal conductivity of a soft granular material from a simple temperature measurement. However, such a geometry often results in a mechanically weak sensor, which can bend or fail when inserted into a material that is harder than expected. For deploying such a sensor on a planetary surface, with often unknown soil properties, it is necessary to construct more rugged sensors. These requirements can lead to a design which differs substantially from the ideal geometry, and additional care must be taken in the calibration and data analysis.

In this paper we present the performance of a prototype thermal conductivity sensor designed for planetary missions. The thermal conductivity of a suite of solid and granular materials was measured both by a standard needle sensor and by several customized sensors with non-ideal geometry. We thus obtained a calibration curve for the non-ideal sensors. The theory describing the temperature response of a sensor with such unfavorable length-to-diameter ratio is complicated and highly nonlinear. However, our measurements reveal that over a wide range of thermal conductivities there is an almost linear relationship between the result obtained by the standard sensor and the result derived from the customized, non-ideal sensors. This allows to measure thermal conductivity values for harder soils, which are not easily accessible when using standard needle sensors

show abstract

Performance of thermal conductivity probes for planetary applications

Cited by 9 publications

References 15 publications

Calibration of non-ideal thermal conductivity sensors

Calibration of non-ideal thermal conductivity sensors

The heated infinite cylinder with sheath and two thermal surface resistance layers

Calibration of non-ideal thermal conductivity sensors

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