scholarly journals Calibration of non-ideal thermal conductivity sensors

2012 ◽  
Vol 2 (2) ◽  
pp. 685-701
Author(s):  
N. I. Kömle ◽  
W. Macher ◽  
G. Kargl ◽  
M. S. Bentley
Keyword(s):  
Thermal Conductivity ◽  
Granular Material ◽  
Temperature Measurement ◽  
Temperature Response ◽  
Electrical Current ◽  
Diameter Ratio ◽  
Conductivity Sensor ◽  
Highly Nonlinear ◽  
Wide Range ◽  
Length To Diameter Ratio

Abstract. 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.

scholarly journals Calibration of non-ideal thermal conductivity sensors

2013 ◽  
Vol 2 (1) ◽  
pp. 151-156 ◽  
Author(s):  
N. I. Kömle ◽  
W. Macher ◽  
G. Kargl ◽  
M. S. Bentley
Keyword(s):  
Thermal Conductivity ◽  
Granular Material ◽  
Temperature Measurement ◽  
Temperature Response ◽  
Electrical Current ◽  
Diameter Ratio ◽  
Conductivity Sensor ◽  
Highly Nonlinear ◽  
Wide Range ◽  
Length To Diameter Ratio

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.

scholarly journals Influence of probe geometry on measurement results of non-ideal thermal conductivity sensors

2016 ◽  
Author(s):  
P. Tiefenbacher ◽  
N. I. Kömle ◽  
W. Macher ◽  
G. Kargl
Keyword(s):  
Thermal Conductivity ◽  
Thermal Evolution ◽  
Temperature Response ◽  
Electrical Current ◽  
Diameter Ratio ◽  
The Body ◽  
Ir Radiation ◽  
Contact Points ◽  
Planetary Bodies ◽  
Length To Diameter Ratio

Abstract. The thermal properties of the surface and subsurface layers of planets and planetary objects yield important information that allows us to better understand the thermal evolution of the body itself and its interactions with the environment. Various planetary bodies of our Solar System are covered by so-called regolith, a granular and porous material. On such planetary bodies the dominant heat transfer mechanism is heat conduction via IR radiation and contact points between particles. In this case the energy balance is mainly controlled by the effective thermal conductivity of the top surface layers, that can be directly measured by thermal conductivity probes. A traditionally used method for measuring the thermal conductivity of solid materials is the needle-probe method. Such probes consist of thin steel needles with an embedded heating wire and temperature sensors. For the evaluation of the thermal conductivity of a specific material the temperature change with time is determined by heating a resistance wire with a well-defined electrical current flowing through it and simultaneously measuring the temperature increase inside the probe over a certain time. For thin needle probes with a large length-to-diameter ratio it is mathematically easy to derive the thermal conductivity, while this is not so straightforward for more rugged probes with a larger diameter and thus a smaller length-to-diameter ratio. Due to the geometry of the standard thin needle probes they are mechanically weak and subject to bending when driven into a soil. Therefore, using them for planetary missions can be problematic. In this paper the thermal conductivity values determined by measurements with two non-ideal, ruggedized thermal conductivity sensors, which only differ in length, are compared to each other. Since the theory describing the temperature response of non-ideal sensors is highly complicated, those sensors were calibrated with an ideal reference sensor in various solid and granular materials. The calibration procedure and the results are described in this work.

scholarly journals Influence of probe geometry on measurement results of non-ideal thermal conductivity sensors

2016 ◽  
Vol 5 (2) ◽  
pp. 383-401 ◽  
Author(s):  
Patrick Tiefenbacher ◽  
Norbert I. Kömle ◽  
Wolfgang Macher ◽  
Günter Kargl
Keyword(s):  
Thermal Conductivity ◽  
Thermal Evolution ◽  
Temperature Response ◽  
Electrical Current ◽  
Diameter Ratio ◽  
The Body ◽  
Ir Radiation ◽  
Contact Points ◽  
Planetary Bodies ◽  
Length To Diameter Ratio

Abstract. The thermal properties of the surface and subsurface layers of planets and planetary objects yield important information that allows us to better understand the thermal evolution of the body itself and its interactions with the environment. Various planetary bodies of our Solar System are covered by so-called regolith, a granular and porous material. On such planetary bodies the dominant heat transfer mechanism is heat conduction via IR radiation and contact points between particles. In this case the energy balance is mainly controlled by the effective thermal conductivity of the top surface layers, which can be directly measured by thermal conductivity probes. A traditionally used method for measuring the thermal conductivity of solid materials is the needle-probe method. Such probes consist of thin steel needles with an embedded heating wire and temperature sensors. For the evaluation of the thermal conductivity of a specific material the temperature change with time is determined by heating a resistance wire with a well-defined electrical current flowing through it and simultaneously measuring the temperature increase inside the probe over a certain time. For thin needle probes with a large length-to-diameter ratio it is mathematically easy to derive the thermal conductivity, while this is not so straightforward for more rugged probes with a larger diameter and thus a smaller length-to-diameter ratio. Due to the geometry of the standard thin needle probes they are mechanically weak and subject to bending when driven into a soil. Therefore, using them for planetary missions can be problematic. In this paper the thermal conductivity values determined by measurements with two non-ideal, ruggedized thermal conductivity sensors, which only differ in length, are compared to each other. Since the theory describing the temperature response of non-ideal sensors is highly complicated, those sensors were calibrated with an ideal reference sensor in various solid and granular materials. The calibration procedure and the results are described in this work.

Adaptive Thermal Conductivity Metamaterials: Enabling Active and Passive Thermal Control

2018 ◽  
Vol 10 (5) ◽  
Author(s):  
Austin A. Phoenix ◽  
Evan Wilson
Keyword(s):  
Thermal Conductivity ◽  
Thermal Management ◽  
Passive Control ◽  
Coefficient Of Thermal Expansion ◽  
Thermal Strain ◽  
Thermal Control ◽  
Variable Thermal Conductivity ◽  
Highly Nonlinear ◽  
Wide Range ◽  
Nonlinear Thermal Conductivity

The novel adaptive thermal metamaterial developed in this paper provides a unique thermal management capability that can address the needs of future spacecraft. While advances in metamaterials have provided the ability to generate materials with a broad range of material properties, relatively little advancement has been made in the development of adaptive metamaterials. This metamaterial concept enables the development of materials with a highly nonlinear thermal conductivity as a function of temperature. Through enabling active or passive control of the metamaterials bulk effective thermal conductivity, this metamaterial that can improve the spacecraft's thermal management systems performance. This variable thermal conductivity is achieved through induced contact that results in changes in the F path length and the conductive path area. The contact can be generated internally using thermal strain from shape memory alloys, bimetal springs, and mismatches in coefficient of thermal expansion (CTE) or it can be generated externally using applied mechanical loading. The metamaterial can actively control the temperature of an interface by dynamically changing the bulk thermal conductivity controlling the instantaneous heat flux through the metamaterial. The design of thermal stability regions (regions of constant thermal conductivity versus temperature) into the nonlinear thermal conductivity as a function of temperature can provide passive thermal control. While this concept can be used in a wide range of applications, this paper focuses on the development of a metamaterial that achieves highly nonlinear thermal conductivity as a function of temperature to enable passive thermal control of spacecraft systems on orbit.

The relationship between thermal conductivity and matric suction of soils

2021 ◽  
Author(s):  
Sen Lu
Keyword(s):  
Thermal Conductivity ◽  
Soil Water ◽  
Land Surface ◽  
Matric Suction ◽  
Dew Point ◽  
Pulse Technique ◽  
Highly Nonlinear ◽  
Wide Range ◽  
Mean Square Errors ◽  
The Relationship

<p>The soil thermal conductivity (λ) and matric suction of soil water (h, the negative of matric potential) relationship has been widely used in land surface models for estimating soil temperature and heat flux following the McCumber and Pielke (1981, MP81) λ-h model. However, few datasets are available for evaluating the accuracy and feasibility of the MP81 λ-h model under various soil and moisture conditions. In this study, we developed a new λ-h model and compared its performance with that of the MP81 model using measurements on 18 soils with a wide range of textures, water contents and bulk densities. The heat pulse technique was used to measure λ, and the suction table, micro-tensiometers, pressure plate device, and the dew point potentiometer were applied to obtain soil water retention curves at the appropriate suction ranges. In the range of pF (the common logarithm of h in cm)≤3, the λ-h relationships were highly nonlinear and varied strongly with soil texture and bulk density. In the dry range (i.e., pF > 3), there existed a universal λ-h relationship for all soil textures and bulk densities, and an exponential function was established to describe the relationship. Independent evaluations using λ-h data on five intact soil samples showed that the new model produced accurate λ data from pF values with root mean square errors (RMSE) with the range of 0.03–0.18W m<sup>−1</sup> K<sup>−1</sup>. While, large errors (RMSEs within 0.17–0.36W m<sup>−1</sup> K<sup>−1</sup>) were observed with λ estimates from the MP81 model. </p>

scholarly journals Numerical Characterization of Pressure Drop Across the Manifold of Turbine Casing Cooling System

2012 ◽  
Author(s):  
Riccardo Da Soghe ◽  
Antonio Andreini
Keyword(s):  
Discharge Coefficient ◽  
Cooling System ◽  
Pressure Ratio ◽  
Turbine Blades ◽  
Diameter Ratio ◽  
Data Set ◽  
Wide Range ◽  
Depth Analysis ◽  
Length To Diameter Ratio

Array of jets is an arrangement typically used to cool several gas turbine parts. Some examples of such applications can be found in the impingement cooling systems of turbine blades and vanes or in the turbine blade tip clearances control of large aeroengines. In order to correctly evaluate the impinging jet mass flow rate, the characterization of holes discharge coefficient is a compulsory activity. In a previous work the authors have performed an aerodynamic analysis of different arrays of jets for active clearance control; the aim was the definition of a correlation for the discharge coefficient (Cd) of a generic hole of the array. The developed empirical correlation expresses the Cd of each hole as a function of the ratio between the hole and the manifold mass velocity and the local value of the pressure ratio. In its original form, the correlation does not take in to account the effect of the hole length to diameter ratio (t/d) so, in the present contribution, the authors report a study with the aim of evaluating the influence of such parameter on the discharge coefficient distribution. The data were taken from a set of CFD RANS simulations, in which the behaviour of the cooling system was investigated over a wide range of fluid-dynamics conditions (Pressure-Ratio = 1.01–1.6, t/d = 0.25–3). To point out the reliability of the CFD analysis, some comparisons with experimental data were drawn. An in depth analysis of the numerical data set has led to an improved correlation with a new term function of the hole length to diameter ratio.

scholarly journals A generalized model between thermal conductivity and matric suction of soils

2021 ◽  
Author(s):  
Sen Lu
Keyword(s):  
Thermal Conductivity ◽  
Soil Water ◽  
Land Surface ◽  
Matric Suction ◽  
Dew Point ◽  
Soil Thermal Conductivity ◽  
Pulse Technique ◽  
Highly Nonlinear ◽  
Wide Range ◽  
Mean Square Errors

<p>Soil thermal conductivity (λ) is an important physical property in land surface parameterization. The soil thermal conductivity (λ) and matric suction of soil water (h, the negative of matric potential) relationship has been widely used in land surface models for estimating soil temperature and heat flux following the McCumber and Pielke (1981, MP81) λ-h model. However, few datasets are available for evaluating the accuracy and feasibility of the MP81 λ-h model under various soil and moisture conditions. In this study, we developed a new λ-h model and compared its performance with that of the MP81 model using measurements on 18 soils with a wide range of textures, water contents and bulk densities. The heat pulse technique was used to measure λ, and the suction table, micro-tensiometers, pressure plate device, and the dew point potentiometer were applied to obtain soil water retention curves at the appropriate suction ranges. In the range of pF (the common logarithm of h in cm)≤3, the λ-h relationships were highly nonlinear and varied strongly with soil texture and bulk density. In the dry range (i.e., pF > 3), there existed a universal λ-h relationship for all soil textures and bulk densities, and an exponential function was established to describe the relationship. Independent evaluations using λ-h data on five intact soil samples showed that the new model produced accurate λ data from pF values with root mean square errors (RMSE) with the range of 0.03–0.18Wm−1 K−1. While, large errors (RMSEs within 0.17–0.36Wm−1 K−1) were observed with λ estimates from the MP81 model. </p>

scholarly journals Numerical Characterization of Pressure Drop Across the Manifold of Turbine Casing Cooling System

2013 ◽  
Vol 135 (3) ◽  
Author(s):  
Riccardo Da Soghe ◽  
Antonio Andreini
Keyword(s):  
Discharge Coefficient ◽  
Cooling System ◽  
Pressure Ratio ◽  
Turbine Blades ◽  
Diameter Ratio ◽  
Data Set ◽  
Wide Range ◽  
Depth Analysis ◽  
Length To Diameter Ratio

An array of jets is an arrangement typically used to cool several gas turbine parts. Some examples of such applications can be found in the impingement cooling systems of turbine blades and vanes or in the turbine blade tip clearances control of large aero-engines. In order to correctly evaluate the impinging jet mass flow rate, the characterization of holes discharge coefficient is a compulsory activity. In a previous work, the authors have performed an aerodynamic analysis of different arrays of jets for active clearance control; the aim was the definition of a correlation for the discharge coefficient (Cd) of a generic hole of the array. The developed empirical correlation expresses the (Cd) of each hole as a function of the ratio between the hole and the manifold mass velocity and the local value of the pressure ratio. In its original form, the correlation does not take in to account the effect of the hole length to diameter ratio (t/d) so, in the present contribution, the authors report a study with the aim of evaluating the influence of such parameter on the discharge coefficient distribution. The data were taken from a set of CFD RANS simulations, in which the behavior of the cooling system was investigated over a wide range of fluid-dynamics conditions (pressure-ratio = 1.01–1.6, t/d = 0.25–3). To point out the reliability of the CFD analysis, some comparisons with experimental data were drawn. An in depth analysis of the numerical data set has led to an improved correlation with a new term function of the hole length to diameter ratio.

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