Conductivité thermique de mousses cellulaires de carbone: Mesures par méthode flash et interprétation

This paper deals with the thermal diffusivity measurement of cellular carbon foams by the flash method. The thermal conductivity is obtained from the thermal diffusivity by using specific heat and density of carbon foam. These materials constitute non-homogeneous porous semitransparent media, hence the classic experimental set-up of the flash method must be adapted. A study is carried out in order to show the influence of the sample thickness, of the temperature, of the enclosed gas pressure and of the gas composition on the effective thermal conductivity. Identification functions are established in the monodimensional and bidimensional cases. Results indicate the dependence of the equivalent thermal conductivity upon the sample thickness. This result, attributed to radiative transfer, is confirmed by modelling. Radiative thermal conductivities are obtained with a Monte-Carlo code. Experimental and theoretical results are compared. It is demonstrated that the concept of effective conductivity is not relevant to these materials.     

Thermal properties of compressed expanded graphite: photothermal measurements

The thermal diffusivity and the thermal conductivity of compressed expanded graphite (CEG) samples were investigated by photothermal measurements in two geometries differing by a place of temperature disturbance detection. This disturbance can be detected on a surface opposite to the one at which the disturbance was generated (rear detection) or on the same surface (front detection). A measurement based on the rear detection allowed us to determine the effective thermal diffusivity of the sample, while the method with front detection gives the possibility of analysis of homogeneity of the sample. It is shown that the thermal diffusivity of CEG strongly depends on its apparent density. Moreover, CEG samples reveal anisotropy of the thermal properties. The thermal diffusivity in the direction parallel to the compacting axis is lower than the one in the direction perpendicular to it. The parallel thermal diffusivity decreases with growing apparent density, while the perpendicular thermal diffusivity significantly grows when the apparent density grows. The perpendicular thermal conductivity exhibits the same behavior as the perpendicular thermal diffusivity. The parallel thermal conductivity slightly grows with growing density and then reaches a plateau. The anisotropy of CEG samples grows with growing apparent density and vanishes for low-density samples. The photothermal measurement with front signal detection revealed that the CEG samples are non-homogeneous in the direction of the compacting axis and can be modeled by a two-layer system.     

Photothermal methods for determination of thermal properties of bulk materials and thin films

Information on the thermal properties of materials is very important both in fundamental physical research and in engineering applications. The development of materials with desirable heat transport properties requires methods for their experimental determination. In this paper basic concepts of the measurement of parameters describing the heat transport in solids are discussed. Attention is paid to methods utilizing nonstationary temperature fields, especially to photothermal methods in which the temperature disturbance in the investigated sample is generated through light absorption. Exemplary photothermal measuring techniques, which can be realized using common experimental equipment, are described in detail. It is shown that using these techniques it is possible to determine the thermal diffusivity of bulk transparent samples, opaque and semi-transparent plate-form samples, and the thermal conductivity of thin films deposited on thick substrates. Results of the investigation of thermal diffusivity of the ground in the polar region, which is based on the analysis of the propagation of the thermal wave generated by sun-light, are also presented. Based on chosen examples one can state that photothermal techniques can be used for determination of the thermal properties of very different materials.     

Radiative properties of extruded polystyrene foams: Predictive model and experimental results

The radiative properties of extruded polystyrene foams (XPS) were predicted using morphological data and optical properties of bulk medium. A particular attention was paid on the modelling of the radiative properties of struts, which are located at the junctions between cell walls. The radiative properties of XPS foams were determined by adding the contributions of each particle (walls and struts) using the independent scattering hypothesis. Hemispherical reflectance and transmittance measurements were made in addition to total thermal conductivity measurements. Comparisons were made between theoretical and experimental results and some improvements were suggested to better improve modelling of foam radiative properties.     

The effects of experimental parameters in the thermal diffusivity measurements of oriented polymer films using mirage effect: Computer simulation

Computer simulations have been carried out to study the effects of the experimental parameters when the mirage method has been applied to thermal diffusivity measurements of oriented polymer films. The parameters under study are the thermal diffusivity of the fluid surrounding the sample, the modulation frequency and the radius of the heating beam, the height and the radius of the probe beam, and the sample thickness and thermal diffusivity. Proposals for the optimum parameter values to maximize the measurement sensitivity for the sample diffusivity are made and the difficulties arising from the low diffusivity of the samples are described. It is also concluded that because the thermal properties of the fluid surrounding the sample have a strong contribution to the mirage signals, the signals do not include any simple feature corresponding to the sample diffusivity. Therefore it should be determined from the entire measurement data using regression methods.     

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Thermal diffusivity of reduced activation ferritic/martensitic (RAFM) steel CLF-1 has been determined by the modified photoacoustic piezoelectric (PAPE) technique. Firstly, the modified PAPE theoretical model is introduced and the experimental condition with high measurement precision are identified; Secondly, the experimental system is set up and calibrated by investigating the thermal diffusivity of nickel; Finally, the thermal diffusivity of RAFM steel CLF-1 is measured by the modified PAPE method. The results show that the RAFM steel CLF-1 has good thermal diffusion properties and is a fusion reactor structural material with excellent heat conductivity. The modified PAPE technique can determine the thermal diffusivity of RAFM steel CLF-1effectively, and provides an effective way to investigate the thermal-physical property of fusion reactor structural material.     

制备低密度聚-4-甲基-1-戊烯泡沫中的热性能研究

 在聚-4-甲基-1-戊烯(pmp)低密度泡沫的制备中,利用示差扫描量热（DSC）分析仪对pmp聚合物在均四甲苯/萘所组成的溶剂/非溶剂二元体系中的凝胶化过程进行在线测量。测定了它的凝胶化范围以及凝胶化温度与冷却速率和pmp在溶剂/非溶剂体系中所占比例的关系。利用热重-示差扫描量热（TG-DSC）系统对所制备的低密度pmp泡沫的热性能进行了分析,得到了泡沫密度变化对热稳定性等的影响。     

Experimental investigation on the thermophysical properties of moist porous materials

A method has been developed for the combined measurement of thermal conductivity and diffusivity. The proposed method is based on an extension of the transient probe theory. The developed technique, the differential sensor method, is then used here for the measurement of thermal conductivity and diffusivity of glycerin, dry and moist porous materials in the temperature range of –20 to 80°C. Calculations have been doneby IBM PC/XT using a data fitting program. The effect of water content and temperature on the thermophysical properties has been elucidated in frozen as well as unfrozen states. The experimental results of thermal conductivity and diffusivity obtained by the differential sensor method have been compared with the results of other methods.     

制备低密度pmp泡沫中的热性能研究

在聚－4－甲基－1－戊烯（pmp）低密度泡沫的制备中,利用示差扫描量热分析仪对pmp聚合物在均四甲苯／萘所组成的溶剂／非溶剂二元体系中的凝胶化过程进行在线测量,测定了它的凝胶化范围以及凝胶化温度与冷却速率和pmp在溶剂;非溶剂体系中所占比例的关系。利用热重－示差扫描量热系统对所制备的低密度pmp泡沫的热性能进行了分析,得到了泡沫密度变化对热稳定性等的影响。     

Thermal radiative properties of phenolic foam insulation

Thermal insulation has long been an important subject in engineering. Foam insulations have become the most widely used insulations due to their low cost and ease of procesing. In recent years, phenolic foams find increasing applications because of their fire retardation. This paper presents experimental results of thermal radiative properties of phenolic foams, with or without activated carbon. Transmittance spectra were first taken using FTIR for samples of various densities. Extinction coefficient spectra were then obtained by applying Beer's law. Finally, by using the diffusion approximation, the Rosseland mean extinction coefficients and radiative thermal conductivities were obtained for various temperatures. Results show that the extinction coefficient increases with sample density. The addition of activated carbon increases the extinction coefficient slightly.     

Thermal conductivity and thermal diffusivity of samarium in the temperature range of 293–1773 K

The thermal conductivity and the thermal diffusivity coefficients of samarium have been measured by the laser flash method in the temperature interval of 293–1773 K in solid and liquid states including the regions of phase transitions. The measurement errors of the heat transfer coefficients were ±(3–6)%. The approximation equations and the tables of reference data for the temperature dependence of properties have been obtained. The obtained results have been compared with the available literature data.     

Measurements and empirical model of the acoustic properties of reticulated vitreous carbon

Reticulated vitreous carbon (RVC) is a highly porous, rigid, open cell carbon foam structure with a high melting point, good chemical inertness, and low bulk thermal conductivity. For the proper design of acoustic devices such as acoustic absorbers and thermoacoustic stacks and regenerators utilizing RVC, the acoustic properties of RVC must be known. From knowledge of the complex characteristic impedance and wave number most other acoustic properties can be computed. In this investigation, the four-microphone transfer matrix measurement method is used to measure the complex characteristic impedance and wave number for 60 to 300 pore-per-inch RVC foams with flow resistivities from 1759 to 10,782 Pa s m(-2) in the frequency range of 330 Hz-2 kHz. The data are found to be poorly predicted by the fibrous material empirical model developed by Delany and Bazley, the open cell plastic foam empirical model developed by Qunli, or the Johnson-Allard microstructural model. A new empirical power law model is developed and is shown to provide good predictions of the acoustic properties over the frequency range of measurement. Uncertainty estimates for the constants of the model are also computed.     

Off-axis Thermal Properties of Carbon Nanotube Films

Theoretical calculations have predicted that individual Single-Walled Carbon Nanotubes (SWNT) have extremely high thermal conductivity (around 6.6 × 10⁴ W/m-K). The feasibility of constructing practical devices using the above mentioned properties, is critically dependent on the ability to synthesize high-thermal-conducting films. Highly conducting films would be of great use as heat sinks for the next generation of integrated chips. Excessive heating is currently a very serious problem in the endeavor for achieving faster and smaller chips. Since it is still not possible to perfectly align SWNT in the macroscopic scale, the thermal properties of the nano-films are therefore expected to have a statistical effect and thus lower than the intrinsic thermal conductivity of a single nanotube. Also the thermal conductivity perpendicular to the tube direction is more significant from a practical point of view. Multi-Walled Carbon Nanotubes (MWNT) were synthesized by Chemical Vapor Deposition (CVD) technique and subsequently characterized. The thin MWNT films were deposited by a solution casting technique over a metallic substrate. The off-axis thermal properties of these nano-films were studied by AC-calorimetry studies. In this method, the sample is heated by an AC source and the measurement of the relaxation rate is used to determine the thermal properties. This technique is well established for studying the thermal properties of complex fluids. Our results are contrasted with other thermal conductivity measurements intrinsic and bulk carbon nanotube samples. We have also measured off-axis thermal properties of nano-films synthesized from more crystalline SWNT samples and have compared this result with that of the MWNT-film. A model to explain the thermal conduction for our system is proposed. George Muench: Presently at the Department of Physics, University of New Haven, West Haven, CT-06516, USA     

软质聚氨酯泡沫塑料的低温热导率

讨论了软质聚氨酯泡沫塑料对流判据的低温传热机理.根据软质聚氨酯泡沫塑料结构简图,将各种参数和低温数据带入对流判据公式,得到对流判据L的计算结果.计算了软质聚氨酯泡沫塑料的低温热导率.为了与计算的低温热导率比较,采用测试硬质泡沫塑料热导率的稳态热流双试样保护热板装置,测试了软质聚氨酯泡沫塑料的低温热导率,最后给出了低温热导率与温度关系曲线.根据试验,讨论了低温热导率的影响因素如温度、密度、吸水率等.     

Thermal conductivity and thermal diffusivity of the R134a refrigerant in the liquid state

Thermal conductivity and thermal diffusivity of “ozone-safe” refrigerant R134a in liquid state within the range of temperatures 295.9–354.9 K and pressures from the liquid — vapor equilibrium line up to 4.08 MPa have been studied by high-frequency thermal-wave method. The experimental uncertainties of the temperature, pressure, thermal conductivity and thermal diffusivity measurement errors were estimated to be 0.1 K, 3 kPa, 1.5 and 2.5 %, respectively. Values of thermal conductivity and thermal diffusivity of liquid R134a on saturated line have been calculated. Approximation dependences for thermal conductivity and thermal diffusivity within the whole studied range of temperatures and pressures as well as on the saturated line have been obtained. The work was financially supported by the Russian Foundation for Basic Research (grant No. 07-08-00295-a).     

Relating phase transition heat capacity to thermal conductivity and effusivity in Cu2Se

Accurate measurement of thermal conductivity is essential to determine the thermoelectric figure‐of‐merit, zT. Near the phase transition of Cu₂Se at 410 K, the transport properties change rapidly with temperature, and there is a concurrent peak in measured heat capacity from differential scanning calorimetry (DSC). Interpreting the origin as a broad increase in heat capacity or as a transient resulted in a three‐fold difference in the reported zT in two recent publications. To resolve this discrepancy, thermal effusivity was deduced from thermal conductivity and diffusivity measurements via the transient plane source (TPS) method and compared with that calculated from thermal diffusivity and the two interpretations of the DSC data for heat capacity. The comparison shows that the DSC measurement gave the heat capacity relevant for calculation of the thermal conductivity of Cu₂Se. The thermal conductivity calculated this way follows the electronic contribution to thermal conductivity closely, and hence the main cause of the zT peak is concluded to be the enhanced Seebeck coefficient. (© 2016 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Heat transfer coefficients of liquid indium in the temperature range 470–1275 K

Thermal conductivity and thermal diffusivity coefficients of liquid indium have been determined in the range of temperatures from 470 to 1275 K by the laser flash method. Errors of heat transfer coefficients are ±(3.5–5) %. Approximating equations and tables of reference data have been developed for temperature dependence of properties. Measurement results have been compared with the data available in the literature. Temperature dependence of Lorentz number has been calculated up to 1000 K.     

Coefficient of thermal diffusivity of ChS-139 steel in wide temperature range

Laser flash method with 2–4% accuracy was used to determine the coefficient of thermal diffusivity of ferrite-martensite steel ChS-139 in temperature range 296–1274 K. Temperatures of Curie and martensite-austenite-martensite phase changes have been determined.     

Laser flash method for measurement of liquid metals heat transfer coefficients

New laser flash technique for the measurement of heat transfer coefficients of liquid metals is presented. The thermal diffusivity of the liquid mercury has been studied experimentally over the room temperature range. The thermal conductivity coefficient has been calculated with the use of the reference data on density and heat capacity. Analysis of systematic errors of the measurements has shown that the data error is about 3%. Comparison of the obtained results with data available in publications has proved their reliability.     

SiNx薄膜热物性参数实验测量与分析研究

采用一种新的实验测量方案，将金属加热单元与温度探测单元合二为一，间接获得了在半导体和微电子学MEMS领域内有重要用途的SiN_x薄膜的导热系数、发射率、比热容和热扩散系数，并对实验结果进行了不确定度分析，为微电子电路设计和掩模成型工艺等提供了可靠的热物性数据. 实验结果表明，薄膜的导热系数、发射率、热扩散系数远比相应体材质低，而且还与温度、厚度有关，尺寸效应显著，而比热容则与体材质相差不大. 关键词： 微尺度传热 热物性参数 x薄膜')" href="#">SiN_x薄膜 测量技术