共查询到20条相似文献,搜索用时 15 毫秒
1.
J. Wu J. Hameury G. Failleau A. Blahut T. Vachova R. Strnad M. Krause E. Rafeld U. Hammerschmidt 《International Journal of Thermophysics》2018,39(2):23
This paper complements the existing measurement standards and literature for high-temperature guarded hot plates (HTGHPs) by addressing specific issues relating to thermal conductivity measurement of technical insulation at high temperatures. The examples given are focused on the designs of HTGHPs for measuring thin thermal insulation. The sensitivity studies have been carried out on major influencing factors that affect the thermal conductivity measurements using HTGHPs, e.g., the uncertainty of temperature measurements, plate flatness and center-guard gap design and imbalance. A new configuration of center-guard gap with triangular shape cross section has been optimized to obtain the same thermal resistance as a 2 mm wide gap with rectangular shape cross section that has been used in the HTGHPs at NPL and LNE. Recommendations have been made on the selections of heater plate materials, high-temperature high-emissivity coatings and miniature temperature sensors. For the first time, thermal stress analysis method has been applied to the field of HTGHPs, in order to estimate the effect of differential thermal expansion on the flatness of thin rigid specimens during thermal conductivity tests in a GHP. 相似文献
2.
An alternative calibration procedure has been applied using apparatus built in-house, created to optimize thermal conductivity measurements. The new approach compared to those of usual measurement procedures of thermal conductivity by guarded hot plate (GHP) consists of modified design of the apparatus, modified position of the temperature sensors and new conception in the calculation method, applying the temperature at the inlet section of the specimen instead of the temperature difference across the specimen. This alternative technique is suitable for eliminating the effect of thermal contact resistance arising between a rigid specimen and the heated plate, as well as accurate determination of the specimen temperature and of the heat loss at the lateral edge of the specimen. This paper presents an overview of the specific characteristics of the newly developed “high-temperature thermal conductivity measurement apparatus” based on the GHP method, as well as how the major difficulties are handled in the case of this apparatus, as compared to the common GHP method that conforms to current international standards. 相似文献
3.
4.
《纳米技术与精密工程》2016,(1)
在防护热板法装置中,沿整个隔缝的温度分布是不均匀的,导致热板与护板间的功率损失,影响导热系数测量的准确度.针对该问题提出一种补偿方法,通过计算热板功率损失修正热板功率,使修正后热板的功率准确反映理想一维条件下流过试件的热流量,从而提高导热系数测量准确度.实验结果显示,通过提出的补偿方法测得的导热系数准确度达到±2!,有效地解决了由于隔缝温度不平衡而造成的测量导热系数不准确的问题. 相似文献
5.
7.
Thin-Film Characterization for High-Temperature Applications 总被引:1,自引:0,他引:1
M. J. Lourenço J. M. Serra M. R. Nunes A. M. Vallêra C. A. Nieto de Castro 《International Journal of Thermophysics》1998,19(4):1253-1265
Most thin films produced by a wide variety of methods, either physical or chemical (PVD, CVD, sputtering, etc.) for temperature sensor applications, can be used only in very narrow ranges of temperatures, where their components are not subjected to differential thermal expansions, recrystallizations, and grain size modifications. This paper reports the production and characterization of thin films of platinum and titanium in ceramic substrates by one of the physical vapor deposition techniques, the e-gun evaporation. The choice of materials and the determination of film thickness, density, electrical resistivity, surface roughness, and structural characterization (X-ray, SEM, and AES) are studied. Special emphasis is given to the thermal and electrical behavior of these films between room temperature and 1000°C. 相似文献
8.
A High-Temperature Viscometer for Molten Materials 总被引:1,自引:0,他引:1
V. M. B. Nunes F. J. V. Santos C. A. Nieto de Castro 《International Journal of Thermophysics》1998,19(2):427-435
An oscillating-cup viscometer for the measurement of the viscosity of molten materials from room temperature to 1400 K was developed. The instrument is described in detail and the working equations are presented. The operational behavior was tested with water at room temperature. Preliminary measurements show that the new viscometer is capable of measuring the viscosity of water at room temperature to within 0.2%. As the primary objective of this work is the establishment of standard reference data for high-temperature viscosity measurements in molten salts, molten metals, and molten semiconductors, references of earlier viscosity measurements of molten KNO3 are given. 相似文献
9.
10.
The anticipation of recently published European product standards for industrial thermal insulation has driven improvements
in high-temperature thermal conductivity measurements in an attempt to obtain overall measurement uncertainties better than
5 % (k = 2). The two measurement issues that are focused on in this article are the effect of thermal expansion on in situ thickness measurement and on determining the metering area at high temperatures. When implementing in situ thickness measurements, it is vital to correct the thermal expansion of components in a high-temperature guarded hot plate
(HTGHP). For example, in the NPL HTGHP this could cause 3.2 % measurement error for a 50 mm thick specimen at 800 °C. The
thermal expansion data for nickel 201 measured by NPL are presented, and the effect of this on the metering area of NPL’s
heater plate (nickel 201) is discussed. 相似文献
11.
We propose to regard investigations in the field of high-temperature strength of structural metals and alloys interacting with corrosive media as high-temperature physicochemical mechanics of materials (HTPCMM). The most important feature of HTPCMM is the principle of correlation between deformation processes and physicochemical phenomena, which allows one to describe the features and regularities of changes in the properties of materials under service conditions most completely and correctly. We emphasize the most important role of diffusion as a controlling factor in a metal–medium system at high temperatures. Results of analytical investigations aimed at the development and investigation of physicomathematical models of elastic and elastoviscous multicomponent solid solutions with inherent degradation processes (accumulation of damage) are presented. The fact that, as a rule, these models are constructed within the framework of continuum mechanics on the basis of principles of nonequilibrium mechanics is noted Experimental data obtained, in particular, on refractory metals and titanium interacting actively with components of a vacuum or an inert atmosphere testify to the intensification of saturation of metals by interstitial impurities under conditions of long-term loading and to significant changes in the character of their creep, namely, under the influence of oxygen diffusion the creep rate decreases as stresses increase. 相似文献
12.
Spectral and Total Emissivity of High-Temperature Materials 总被引:3,自引:0,他引:3
A number of various high emissivity coatings has been investigated in detail. Oxide ceramic coatings for rotating x-ray anodes must have a total emissivity greater than 0.8 in order to ensure efficient cooling in vacuum. Only one of the investigated coatings showed sufficient long-term stability. For thermal protection of reusable space transportation systems during atmospheric reentry, in addition to high emissivity, oxidation resistance is required. SiC coatings and special polysilazane-based coatings have been tested. Results of emissivity measurements before and after flight experiments on the Russian FOTON capsule are also available. In order to improve the reliability of (high-temperature) emissivity measurements Pt–Rh alloys, SiC, Al2O3 doped with Cr2O3, and graphite have been tested to assess applicability as reference materials for comparative emissivity measurements by various facilities. 相似文献
13.
Sibiath O. G. Osséni Clément Ahouannou Emile A. Sanya Yves Jannot 《International Journal of Thermophysics》2017,38(6):81
This paper presents a study of the hot plate method with two simultaneous temperature measurements, on the heated and unheated faces of a sample to characterize. The thermal properties of polyvinyl chloride, plaster and laterite were considered to be a representative range of building materials. A 1D quadrupolar model was developed to represent the temperature evolution on the two faces over time. Three-dimensional numerical modeling of a quarter of the testing device with COMSOL software allowed defining the domain of the 1D hypothesis validity. The analysis of estimation possibilities of materials’ thermal characteristics, with the developed method, revealed that thermal effusivity can be accurately estimated by using the temperature of the heated face at the beginning of heating. We showed that the simultaneous use of two temperatures enables the estimation of the thermal conductivity with a greater accuracy and over a shorter time interval than using the temperature of the heated face alone. We also demonstrated that under certain conditions (samples with a high ratio of thickness to width) the method with two temperature measurements enabled the estimation of the thermal effusivity and conductivity, while the method with one temperature allowed only the thermal effusivity to be estimated, because of 3D effects. This conclusion was confirmed by experimental results obtained with a mortar sample. 相似文献
14.
Joonsoo Kim 《International Journal of Thermophysics》2018,39(3):42
The thermal property of a porous hollow clay brick was determined by measuring the thermal transmittance of the wall made of porous hollow clay bricks. Prior to the production of porous hollow clay bricks, nonporous and porous tiny clay bricks were prepared to determine the physico-mechanical properties by modifying the amount of wood flour and firing temperature. The bricks were produced by uniaxial pressing and then fired in an electric furnace. Their physico-mechanical properties were measured by water absorption, apparent porosity, bulk density, and compressive strength. The porous tiny clay bricks were produced with three types of wood flour: coarse wood flour (1–0.36 mm), medium-sized wood flour (0.36–0.15 mm), and fine wood flour (< 0.08 mm). The thermal transmittance of porous hollow clay bricks was determined through the guarded hot box method, which measures the wall made of porous hollow clay bricks and nonporous cement bricks. The two walls had a thermal transmittance of 1.42 and 2.72 \(\hbox {W}\cdot \hbox {m}^{-2}\cdot \hbox {K}^{-1}\), respectively. The difference in thermal transmittance was due to the pores created with fine wood flour (< 0.08 mm) as a pore-forming agent. 相似文献
15.
双极板是质子交换膜燃料电池的关键部件,具有多种功能,如传导电流、配反应气与空气、协调电池内部的水、热管理。此外双极板不论是在体积、重量还是费用上都占整个燃料电池很大比重。寻找合适双极板材料方面的研究颇多,主要有石墨、金属及复合材料等。详尽论述了各种已被应用或正处于研究之中的双极板材料,并考察了它们的相关物理化学性能。 相似文献
16.
Bingnan Han Yuxuan Lin Yafang Yang Nannan Mao Wenyue Li Haozhe Wang Kenji Yasuda Xirui Wang Valla Fatemi Lin Zhou Joel I.-Jan Wang Qiong Ma Yuan Cao Daniel Rodan-Legrain Ya-Qing Bie Efrén Navarro-Moratalla Dahlia Klein David MacNeill Sanfeng Wu Hikari Kitadai Xi Ling Pablo Jarillo-Herrero Jing Kong Jihao Yin Tomás Palacios 《Advanced materials (Deerfield Beach, Fla.)》2020,32(29):2000953
Advanced microscopy and/or spectroscopy tools play indispensable roles in nanoscience and nanotechnology research, as they provide rich information about material processes and properties. However, the interpretation of imaging data heavily relies on the “intuition” of experienced researchers. As a result, many of the deep graphical features obtained through these tools are often unused because of difficulties in processing the data and finding the correlations. Such challenges can be well addressed by deep learning. In this work, the optical characterization of 2D materials is used as a case study, and a neural-network-based algorithm is demonstrated for the material and thickness identification of 2D materials with high prediction accuracy and real-time processing capability. Further analysis shows that the trained network can extract deep graphical features such as contrast, color, edges, shapes, flake sizes, and their distributions, based on which an ensemble approach is developed to predict the most relevant physical properties of 2D materials. Finally, a transfer learning technique is applied to adapt the pretrained network to other optical identification applications. This artificial-intelligence-based material characterization approach is a powerful tool that would speed up the preparation, initial characterization of 2D materials and other nanomaterials, and potentially accelerate new material discoveries. 相似文献
17.
18.
Strength of Materials - The temperature dependences of Vickers microhardness, ultimate strength, and offset yield point in the temperature range between 290 and 1070 K were determined for the... 相似文献
19.
Journal of Engineering Physics and Thermophysics - On the basis of investigations into the high-temperature steam thermolysis of organic raw materials in the form of mixtures of wood, agricultural,... 相似文献
20.
The spectral radiant characteristics of plume particles of a solid rocket engine are important in the design of the engine
specific impulse, ablative material, and plume flame hiding. These parameters are measured from tests of the engine. Some
equipment has been established to realize particle heating, uniform particle distribution, and measurements based on an FTIR
spectral instrument. The equipment is based on SiC heating and is divided into a warm-up chamber and a measurement chamber
to improve the particle temperature stability. A special design of uniform particle distribution combined with an acoustic
levitation device is used to determine the particle falling speed. The spectral characteristics and the transmission rate
of the particles have been measured by using the system including a standard blackbody, an assembled optical system, and an
FTIR spectrometer. The measurements of particle concentration and temperature are given in detail. The instrument specifications
are as follows: temperature range – 60–1500 °C; spectral range – 0.60–25 μm; and particle dimension range – 10–500 μm.
Paper presented at the Seventh International Workshop on Subsecond Thermophysics, October 6–8, 2004, Orléans, France. 相似文献