Technique For Measurement Of Thermal Conductivity Research Articles

Simultaneous measurement of thermal conductivity and heat capacity of bulk and thin film materials using frequency-dependent transient thermoreflectance method

The increasing interest in the extraordinary thermal properties of nanostructures has led to the development of various measurement techniques. Transient thermoreflectance method has emerged as a reliable measurement technique for thermal conductivity of thin films. In this method, the determination of thermal conductivity usually relies much on the accuracy of heat capacity input. For new nanoscale materials with unknown or less-understood thermal properties, it is either questionable to assume bulk heat capacity for nanostructures or difficult to obtain the bulk form of those materials for a conventional heat capacity measurement. In this paper, we describe a technique for simultaneous measurement of thermal conductivity κ and volumetric heat capacity C of both bulk and thin film materials using frequency-dependent time-domain thermoreflectance (TDTR) signals. The heat transfer model is analyzed first to find how different combinations of κ and C determine the frequency-dependent TDTR signals. Simultaneous measurement of thermal conductivity and volumetric heat capacity is then demonstrated with bulk Si and thin film SiO2 samples using frequency-dependent TDTR measurement. This method is further testified by measuring both thermal conductivity and volumetric heat capacity of novel hybrid organic-inorganic thin films fabricated using the atomic∕molecular layer deposition. Simultaneous measurement of thermal conductivity and heat capacity can significantly shorten the development∕discovery cycle of novel materials.

Direct Evaluation of the Figure of Merit of Thermoelectric Devices by Guarded Hot Plate Method

An apparatus for the evaluation of the figure of merit (ZT) of thermoelectric devices has been developed and ZT values have been estimated for a thermoelectric device. The most challenging problem in ZT value evaluation in this apparatus was measuring the thermal conductivity of the devices precisely. We have solved the problem by introducing a primary thermal conductivity measurement technique, a guarded hot plate method, which makes it possible to obtain directly and simultaneously four physical parameters related to the ZT, namely the thermal conductivity, electrical conductivity, Seebeck coefficient, and absolute temperature. The ZT evaluation was performed by a single scan of the temperature difference between the top and bottom surfaces of the device. We also addressed the thermoelectric properties and the power generation efficiency of a commercial thermoelectric device. The evaluation uncertainty of the ZT value was assessed to secure reliability of the apparatus and was found to be 3.59%.

Measurement and model on thermal properties of sintered diamond composites

A prelude to the thermal management of grinding processes is measurement of the thermal properties of working materials. Indeed, tool materials must be chosen not only for their mechanical properties (abrasion performance, lifetime…) but also for thermal concerns (thermal conductivity) for efficient cooling that avoids excessive temperatures in the tool and workpiece. Sintered diamond is currently used for grinding tools since it yields higher performances and longer lifetimes than conventional materials (mineral or silicon carbide abrasives), but its thermal properties are not yet well known. Here the thermal conductivity, heat capacity and density of sintered diamond are measured as functions of the diamond content in composites and for two types of metallic binders: hard tungsten-based and soft cobalt-based binders. The measurement technique for thermal conductivity is derived from the flash method. After pulse heating, the temperature of the rear of the sample is measured with a noncontact method (infrared camera). A parameter estimation method associated with a three-layer nonstationary thermal model is used to obtain sample thermal conductivity, heat transfer coefficient and absorbed energy. With the hard metallic binder, the thermal conductivity of sintered diamond increased by up to 64% for a diamond content increasing from 0 to 25%. The increase is much less for the soft binder: 35% for diamond volumes up to 25%. In addition, experimental data were found that were far below the value predicted by conventional analytical models for effective thermal conductivity. A possible explanation is poor heat transfer at the diamond-binder interface. Indeed, better agreement between measurements and model was found by taking into account a thermal contact resistance between matrix and diamond particles equal to 0.75 and 1.25×10−6m2KW−1 for respectively the cobalt- and tungsten-based composites.

Hot Wire Needle Probe for In-Reactor Thermal Conductivity Measurement

Thermal conductivity is a key property that must be known for proper design, test, and application of new fuels and structural materials in nuclear reactors. Thermal conductivity is highly dependent on the physical structure, chemical composition, and the state of the material. Typically, thermal conductivity changes that occur during irradiation are measured out-of-pile using a “cook and look” approach. Repeatedly removing samples from a test reactor to measurements is expensive, has the potential to disturb phenomena of interest, and only provides understanding of the sample's end state when each measurement is made. There are also limited thermophysical property data for advanced fuels. Such data are needed for simulation design codes, the development of next generation reactors, and advanced fuels for existing nuclear plants. Being able to quickly characterize fuel thermal conductivity during irradiation can improve the fidelity of data, reduce costs of post-irradiation examinations, increase understanding of how fuels behave under irradiation, and confirm or improve existing thermal conductivity measurement techniques. This paper discusses efforts to develop and evaluate an in-pile thermal conductivity sensor based on a hot wire needle probe. Testing has been performed on samples with thermal conductivities ranging from 0.2 to 22 W/m·K at temperatures ranging from 20 °C to 600 °C. Thermal conductivity values measured using the needle probe match data found in the literature to within 5% for samples tested at room temperature, 6% for low thermal conductivity samples tested at high temperatures, and 10% for high thermal conductivity samples tested at high temperatures.

Particle agglomeration and properties of nanofluids

The present study demonstrates the importance of actual agglomerated particle size in the nanofluid and its effect on the fluid properties. The current work deals with 5 to 100 nm nanoparticles dispersed in fluids that resulted in 200 to 800 nm agglomerates. Particle size distributions for a range of nanofluids are measured by dynamic light scattering (DLS). Wet scanning electron microscopy method is used to visualize agglomerated particles in the dispersed state and to confirm particle size measurements by DLS. Our results show that a combination of base fluid chemistry and nanoparticle type is very important to create stable nanofluids. Several nanofluids resulted in stable state without any stabilizers, but in the long term had agglomerations of 250 % over a 2 month period. The effects of agglomeration on the thermal and rheological properties are presented for several types of nanoparticle and base fluid chemistries. Despite using nanodiamond particles with high thermal conductivity and a very sensitive laser flash thermal conductivity measurement technique, no anomalous increases of thermal conductivity was measured. The thermal conductivity increases of nanofluid with the particle concentration are as those predicted by Maxwell and Bruggeman models. The level of agglomeration of nanoparticles hardly influenced the thermal conductivity of the nanofluid. The viscosity of nanofluids increased strongly as the concentration of particle is increased; it displays shear thinning and is a strong function of the level of agglomeration. The viscosity increase is significantly above of that predicted by the Einstein model even for very small concentration of nanoparticles.

Design and Application of a Freestanding Sensor Based on 3ω Technique for Thermal-Conductivity Measurement of Solids, Liquids, and Nanopowders

A practical and reusable freestanding sensor based on the 3ω technique is fabricated by encapsulating a nano-thick nickel detector between two pieces of Kapton film. Because of the protection of the Kapton layer, the mechanical strength and applicability of the sensor are greatly improved compared with the traditional 3ω sensor. Furthermore, the nondestructive thermal-conductivity characterization for solids, liquids, and nanopowder specimens based on the 3ω technique is first realized. However, the introduction of the additional protective film also induces an undesirable decrease in accuracy for the thermal-conductivity measurement. This article discusses the underlying reason for this decreased accuracy and accordingly proposes an error correction scheme for accurate determination of the thermal conductivity.

Insights into the reliability of different thermal conductivity measurement techniques: a thermo-geological study in Mære (Norway)

Thermal response tests (TRTs) are used to measure the effective thermal conductivity in boreholes. The results serve as a basis for the dimensioning of commercial ground-source heat pump installations with closed loop systems. The study evaluated the reliability of TRTs performed in winter by comparing two TRTs carried out under very different winter weather conditions. A third TRT elucidated the influence of convection in wells with a higher heat input. Rock cores were analysed for quartz content and these results and the laboratory-measured thermal conductivity data were compared with the TRT results. This highlighted the importance of the distribution and orientation of minerals in the rock, and that a high quartz content does not necessarily give high thermal conductivity values. It is concluded that winter TRTs give useful results if additional temperature loggers are installed in anticipated fracture zones to detect groundwater flow and to survey the effect of infiltrating water.

Improved 3-omega measurement of thermal conductivity in liquid, gases, and powders using a metal-coated optical fiber

A novel 3ω thermal conductivity measurement technique called metal-coated 3ω is introduced for use with liquids, gases, powders, and aerogels. This technique employs a micron-scale metal-coated glass fiber as a heater/thermometer that is suspended within the sample. Metal-coated 3ω exceeds alternate 3ω based fluid sensing techniques in a number of key metrics enabling rapid measurements of small samples of materials with very low thermal effusivity (gases), using smaller temperature oscillations with lower parasitic conduction losses. Its advantages relative to existing fluid measurement techniques, including transient hot-wire, steady-state methods, and solid-wire 3ω are discussed. A generalized n-layer concentric cylindrical periodic heating solution that accounts for thermal boundary resistance is presented. Improved sensitivity to boundary conductance is recognized through this model. Metal-coated 3ω was successfully validated through a benchmark study of gases and liquids spanning two-orders of magnitude in thermal conductivity.

Thermal Transport Properties of Functionally Graded Carbon Aerogels

Novel graded carbon aerogels were synthesized to study the impact of different synthesis parameters on the material properties on a single sample and to test a new, locally resolved thermal-conductivity measurement technique. Two identical cylindrical aerogels with a graded structure along the main cylindrical axis were synthesized. Along the gradient with an extension of about 20 mm the densities range from 240 kg·m−3 to 370 kg·m−3 and the effective pore diameter determined via small angle X-ray scattering and SEM increase systematically from 70 nm up to 11,000 nm. One specimen was cut perpendicular to the cylinder axis into disc-shaped samples; their thermal conductivities in an argon atmosphere, as determined via a standard laser-flash technique, range from 0.06W·m−1·K−1 to 0.12W·m−1·K−1 at 600 °C. The second specimen, cut to obtain a sample with the gradient in-plane, was investigated with a spatially resolved laser-flash technique at ambient conditions. The results of the two different techniques are compared and discussed in detail.

周期加熱サーモリフレクタンス法による Cu-Pt 合金薄膜の熱伝導率測定

A novel thermal conductivity measurement technique combining a periodically modulated thermoreflectance method with numerical simulation has been developed to precisely estimate the thermal conductivity of sub-micrometer thickness metal films. Numerical simulation about the surface temperature response was carried out assuming that the sample surface is irradiated by variable heating area in micrometer order using an amplitude modulated laser beam. Analyzed results show that the phase lag of the reflectance signal depends on not only the thermal effusivity but also on the thermal diffusivity of the film in local heating. Hence, the thermal conductivity determined by the thermal effusivity and the thermal diffusivity can be evaluated by the dependence of the phase lags on the heating area. This technique was applied for Cu(1-X)PtX (0≦X≦1.63 at%) films with 300 nm thickness deposited on glass substrates. The evaluated thermal conductivity varies from 340 W/(mK) to 97 W/(mK) with increasing Pt concentration. We found that the thermal conductivity of the Cu thin film becomes less than 90% of that of the bulk value (~400 W/(mK)). Moreover, the evaluated thermal conductivity was confirmed to correspond well to the electric conductivity with the Wiedemann-Franz law.

Modelling for the thermal characterization of solid materials by dc scanning thermal microscopy

The thermal investigation of matter by use of a very localized heat source, scanning thermal microscopy (SThM), permits materials to be probed at the level of very small subsurface volumes. Therefore, the technique appears to be a promising method to study the thermal properties of thin films of submicrometric thickness. In order to estimate this possibility, we propose a new prediction modelling of the measurement with a SThM based on a hot anemometer wire probe used in a dc regime. From this modelling, a study of the sensitivity of measurement to various parameters operating in the thermal interaction between the probe and a mono-layered sample is presented. It gives new data allowing a better understanding of measurements. A new method to calibrate the technique for thermal conductivity measurement with more accuracy is deduced from this study. New data about the different physical mechanisms governing the probe–sample thermal interaction are given. The proposed approach also supplies a method for the determination of the depth resolution of a thermal probe. This last parameter is essential in the framework of thin film study with a given probe. Its dependence on sample thermal conductivity and thermal coupling area are discussed. Our results specify the possibilities of the technique and should contribute to a more accurate determination of thin film thermal conductivity in its dc regime.

Measurement technique for thermal conductivity of thin polymer films

We present a modified steady-state heat flow technique, which allows measuring the thermal conductivity of films applied on a substrate. The measurement technique with the here presented setup provides an accuracy (overestimation) of 5–10% for film thickness up to 100 μm. For thicker films a correction factor based on finite-element simulations has to be used or the geometry has to be adapted. The technique is validated with thin glass plates of known thermal conductivity. To demonstrate the application of the technique the thermal conductivity of a thin polymer film of fluorinated acrylate is determined as 0.19±0.02 W/mK.

Thermal conductivity studies on wool fabrics with conductive coatings

Methods of improving the thermal conductivity of wool fabrics have been investigated. Thermal conductivity measurement techniques, influence of synthesis parameters on the thermal conductivity of polypyrrole (PPy)-coated wool fabrics, and the relationship between electrical conductivity and thermal conductivity of PPy-coated wool fabrics are presented. An improvement in thermal conductivity was observed when fabrics were coated with the PPy. The thermal conductivity increased with the increase of pyrrole concentration and synthesis time. Anthraquinone-2-sulfonic acid and ferric chloride showed an optimal concentration for their influence on the thermal conductivity of the coated fabric. The improvement of thermal conductivity of wool fabrics is also investigated by Physical Vapor Deposition technique.

Rapid thermal conductivity measurement with a hot disk sensor: Part 2. Characterization of thermal greases

Thermal transport properties of several thermal greases with applications in electronic packaging have been characterized at room temperature using the hot disk technique, which is a transient plane source technique for rapid thermal conductivity and thermal diffusivity measurement. In this technique, the hot disk sensor serves as a heat source and a thermometer. During the measurement, the sensor is sandwiched between two halves of a sample, and a constant current is supplied to the sensor. The temperature increase at the sensor surface is strongly dependent on the thermal transport properties of the surrounding material. By monitoring the temperature increase as a function of time, one can determine the thermal conductivity and the thermal diffusivity of the surrounding material with high accuracy. The results on thermal greases are in good agreement with supplier data, which were obtained by another method.

Technique for thermal conductivity measurements for organic materials over a wide temperature range

We have developed a technique to measure the thermal conductivity, which enables us to measure for organic samples over a wide temperature range between 4K and room temperature. In our technique, two heaters and three thermometers are installed unlike the conventional one-heater-two-thermometer configuration. We describe the detailed design of our cell and the procedure for measurements. We have succeeded in measuring the thermal transport of organic molecular crystals with the conductivity of the order of ∼1W∕Km, by employing our method.

Contactless technique for thermal conductivity measurement at very low temperature

We present a low-temperature thermal conductivity measurement, which requires no electrical wire in contact with the sample. The temperature gradient in the sample is generated via optical heating and detected by two magnetization thermometers with inductively coupled dc-SQUID readouts. The parasitic heat leak and power dissipation of the setup can be arranged to be below 10−15 W. Therefore this contact-free method is well-suited for measuring samples with very small thermal conductiviy at low temperature. We present results for BK7 glass and a-SiO2 down to 5.3 mK.

Heat capacity, thermal conductivity, and thermal expansion of barium titanate-based ceramics

Barium titanate (BaTiO 3)-based ceramics have been used widely as dielectric layers in manufacturing multilayer ceramic capacitors (MLCCs) in the electronics industry. In this study, the heat capacities of two different BaTiO 3-based ceramic materials were determined as a function of temperature using differential scanning calorimetry (DSC). The densities of these materials were measured at room temperature using Archimedes’ principle. Using these experimental values, the thermal diffusivity and thermal conductivity of each material were determined at room temperature with a hot disk sensor, which is a transient technique for rapid thermal conductivity measurement. Finally, the linear coefficients of thermal expansion of these materials were determined using thermomechanical analysis (TMA) from −50 to 250 °C. All these data are useful in modeling the stress and the reliability performance of these chip capacitors under various conditions.

Application of the Transient Hot-Wire Technique to the Measurement of the Thermal Conductivity of Solids

A novel application of the transient hot-wire technique for thermal conductivity measurements is described. The new application is intended to provide an accurate means of implementation of the method to the determination of the thermal conductivity of solids exemplified by a standard reference ceramic material. The methodology makes use of a soft-solid material between the hot wires of the technique and the solid of interest. Measurements of the transient temperature rise of the wires in response to an electrical heating step in the wires over a period of 20 μs to 10 s allows an absolute determination of the thermal conductivity of the solid. The method is based on a full theoretical model with equations solved by finite-element method applied to the exact geometry. The uncertainty achieved for the thermal conductivity is better than ±1%, and for the product (ρCp) about ±3%. The whole measurement involves a temperature rise less than 4 K.

Dynamic measurement access, a new technique for fast thermal conductivity measurement

A new technique called dynamic measurement access (DMA) is presented in this article which was developed for relatively easy, fast, and accurate thermal conductivity measurements. Utilizing a commercial cryocooler adapted for this experiment, the DMA technique allows the measurement of typically 400 data points in a temperature range between 300 and 10 K, during an elapsed time of approximately 90 min. This technique provides very good precision and requires a very simple experimental setup, which is described in this article.

A new periodic technique for thermal conductivity measurement

A new measurement technique for thermal conductivity which does not require knowledge of the sample heat capacity and which involves a weak temperature gradient inside the sample is presented. The apparatus is simple: the strip-shaped'sample is stuck between two metallic plates, the temperature of one of which is multifrequency modulated. The temperatures of both plates are measured. The ratio of these temperatures is called the transfer function of the sample. The phase of this function is sensitive to the diffusivity and the modulus is sensitive to the conductivity. These parameters can thus be identified by comparison between the measured and the calculated transfer functions. Experiments have been carried out at room temperature on a PVC sample. An exhaustive study of the causes of error has been carried out. The evaluated relative uncertainty on the thermal conductivity is less than 4%. The measured value is consistent with the values found in the literature.