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1.
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). 相似文献
2.
Numerical computations of the free recovery of arc columns in air and nitrogen are presented. In addition to thermal conduction radiation losses are taken into account and the influence of a temperature dependent thermal diffusivity is considered. At short times after interruption a high thermal diffusivity in the core accelerates the conductance decay while at later times the rate of recovery is reduced due to a small diffusivity in the outer regions of the column. For high current arcs radiation is an important loss mechanism immediately after an interruption. 相似文献
3.
对La2CuO4掺锌样品在不同降温速率下(330K保温30min后,分别以6Kh和02Ks的速率冷却至42K)电阻率(42—330K)和热导率(80—300K)随温度的变化关系进行了研究.实验结果表明,在不同降温速率下,热导率和电阻率都受到很大影响.快速降温过程使得130K以上的热导率减小,而热导率最小值出现在130K,且与降温速率无关.而低温下的热导率不受降温速率变化的影响.样品在高温区(T高于125K)电阻率随降温速率的增大而增大,低温区电阻率的非线性行为可用变程跳跃行为来描述.所有样品的热导率和电阻率在反铁磁相变温度都没有出现反常,这与能带理论框架下预期的结果和Anderson电荷自旋分离理论发生了矛盾,对此进行了讨论,并用极化子理论进行了自洽解释.
关键词:
La2CuO4
热导率
电阻率 相似文献
4.
为了能对红外热成像系统的性能进行准确的评价,必须对其MTF进行准确测试。利用高精度双黑体反射靶标评估系统,并依据刀口靶测试原理,首先在计算机中进行微分运算,获得线扩展函数,然后再进行傅里叶变换,最终获得MTF。通过对CEDIT ⅡA型热像仪MTF的测试和分析,发现MTF的测试主要受输入差分信号强度,脉冲电平的去除与否,以及采集到的信号是否滤波等因素的影响。该测试评估系统能保证背景辐射的均匀性和稳定性,且受环境温度变化的影响极小,因此可大大提高测量的准确性和可靠性。 相似文献
5.
为了测试碳/碳复合材料的热扩散系数,本文提出了非线性拟合用于透射式脉冲红外检测的数据处理方法.非线性拟合通过循环迭代的方法持续调整拟合参数,让理论值不断逼近实验值,直至获得最佳结果.传统的透射式脉冲红外成像技术利用半高时间法测试材料的热扩散系数,但通常会受到采集时间不足和信噪比差的限制.本文提出的非线性拟合方法可以有效消除或减弱这两种影响.在使用该方法之前,首先选用常见的304不锈钢评估了该方法的测量精度及拟合长度对测试结果的影响.结果显示304不锈钢的测量精度达到0.3%,且当拟合长度不小于半高时间法采集时间的1/5时,拟合长度对非线性拟合结果影响很小.随后使用该拟合方法测试了不同厚度的碳/碳复合材料试件,并通过热扩散系数测量结果分析了试件之间的热参数差异性和材料自身的均匀性. 相似文献
6.
Jerzy?Bodzenta Anna?Ka?mierczak-Ba?ata Jacek?Mazur 《Central European Journal of Physics》2010,8(2):207-220
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. 相似文献
7.
Generation of four-atom cluster states in thermal cavity and implementing remote controlled not gate 总被引:2,自引:0,他引:2 下载免费PDF全文
We propose an experimentally feasible scheme for preparing a four-atom cluster state
in a thermal cavity. In the scheme, the cavity field is only virtually excited and
the photon-number-dependent part in the effective Hamiltonian is cancelled so that
the system is insensitive to the cavity decay and the thermal field. At the same
time, the scheme can be generalized to prepare n-atom cluster states with the
success probability 100\%. In addition, using the four-atom cluster state, we also
propose a simpler scheme for implementing a remote--controlled not gate (CNOT)
without the Bell states measurement. 相似文献
8.
9.
Summary Thermal diffusivity is obtained with an accuracy of ∼ 1% by means of a new simple method, in which two parallel disks (of
chromel and alumel, respectively) surround the middle section of a cylindrical specimen of conducting material. The disks
act in the clamped zone as the hot juction of a thermocouple and, at the same time, as a heat source for the specimen, subjected
to a laminar air flow. A second thermocouple placed at the base of the cylinder accomplishes acquisition of another set of
experimental data from which the thermal diffusivity and the surface heat loss coefficient can be determined. Preliminary
measurements on aluminium 99.999% consistent with literature data have been reported.
Work supported by the Ministero della Pubblica Istruzione of the Italian Goverment. 相似文献
10.
Laser-induced thermal lens study of the role of morphology and hydroxyl group in the evolution of thermal diffusivity of copper oxide 下载免费PDF全文
The paper explores the evolution of thermal behavior of the material by studying the variations in thermal diffusivity using the single beam thermal lens (TL) technique. For this purpose, the decomposition of Cu(OH)2 into CuO is studied in a time range up to 120 h, by subjecting the sample to morphological, structural, and spectroscopic characterizations. The time evolution of thermal diffusivity can be divided into three regions for demonstrating the dynamics of the reaction. When the reaction is complete, the thermal diffusivity is also found to be saturated. In addition to the morphological modifications, from rods to flakes, the variations in the amount of hydroxyl group are attributed to be responsible for the enhancement of base fluid's thermal diffusivity by 165%. Thus the study unveils the role of hydroxyl groups in the thermal behavior of CuO. 相似文献
11.
An acoustical technique is proposed for determining the thermal diffusivity in solids and the relative difference between
the molar heat capacities at constant pressure and at constant volume. The method, which consists essentially of measuring
the damping of freely vibrating bars, allows determination of the thermal diffusivity with an accuracy better than ±5% and
has the advantage of not requiring a heat source. It also largely eliminates the complications of precise temperature measurements
and insulation of specimen holders. Results are given for tantalum and vanadium over the temperature range 60–300 K. 相似文献
12.
A new technique is developed to measure the longitudinal thermal expansion coefficient of C/C composite material at high temperature. The measuring principle and components of the apparatus are described in detail. The calculation method is derived from the temperature dependence of the thermal expansion coefficient. The apparatus mainly consists of a high temperature environmental chamber, a power circuit of heating, two high-speed pyrometers, and a laser scanning system. A long solid specimen is resistively heated to a steady high-temperature state by a steady electrical current. The temperature profile of the specimen surface is not uniform because of the thermal conduction and radiation. The temperature profile and the total expansion are measured with a high-speed scanning pyrometer and a laser slit scanning measuring system, respectively. The thermal expansion coefficient in a wide temperature range (1000 - 3800 K) of the specimen can therefore be obtained. The perfect consistency between the present and previous results justifies the validity of this technique. 相似文献
13.
David R. Brown Richard Heijl Kasper A. Borup Bo B. Iversen Anders Palmqvist G. J. Snyder 《固体物理学:研究快报》2016,10(8):618-621
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) 相似文献
14.
15.
An attempt has been made to minimize the sources of error involved in the transient probe method for thermal conductivity
determination. Two sensors (thermocouples) are mounted parallel to the needle probe at known distances. This modification
makes it a device for simultaneous conductivity and diffusivity determination. Thermal conductivity and diffusivity for glycerine,
dune sand and mustard seed are determined by this method. Results obtained are compared with those obtained by a calibrated
transient probe for conductivity and by a parallel wire method for diffusivity. Analysis of the results prove it to be a better
instrument over the traditional ones. The technique can also be used as a direct reading device for conductivity and diffusivity
measurements. 相似文献
16.
高精度非致冷长波红外热像仪的辐射标定 总被引:2,自引:0,他引:2
为使非致冷长波红外热像仪在不同温度下保持较高的测温精度,建立了考虑探测器工作温度效应的非致冷长波红外热像仪的辐射标定模型。对非致冷长波红外热像仪进行辐射标定实验,在不同黑体温度和不同亮度增益值条件下,获得了16组图像灰度与探测器工作温度之间的函数关系,建立了目标温度的数学计算模型,并对定标结果进行了实验验证。结果表明:在25~40℃,探测器的工作温度效应可做线性化处理,且与目标温度无关。通过设定合适的亮度增益值可使红外热像仪的测温误差〈0.5℃,极大地提高了非致冷长波红外热像仪在不同温度环境下的测温精度。 相似文献
17.
报道了激光诱导热光栅光谱测温技术的研究. 通过两束相干交叉的脉冲抽运光, 在NO2/N2混合气中诱导出热光栅, 一束满足布拉格散射条件的连续探测光在交叉区域激励出相干的热光栅信号, 经过空间和光谱滤波的信号光由光电倍增管探测, 并由数字示波器显示和存储. 该信号携带了丰富的流场信息, 通过频域分析, 对气体的温度进行了测量, 热光栅光谱技术测量的温度与热电偶温度符合得很好. 同时还利用热光栅光谱技术进行了气体声速的直接测量, 在一定的温度范围内, 测量结果与理论曲线基本一致, 显示了该技术具有较高的测量精度与多参数同时测量的能力. 对影响信号波形的因素进行了分析, 结果表明, 热光栅光谱测温技术在高压强环境下应用具有独特的优势, 是一种应用前景广阔的激光燃烧诊断技术. 相似文献
18.
Study on thermal diffusivity of materials by laser photothermal reflection technique 总被引:1,自引:0,他引:1
A method of measuring thermal diffusivity of materials at room temperature by photothermal reflection technique is described. An intensity-modulated Ar+ laser beam is used as incident light. The beam is focused to about 1 mm diameter spot and illuminates the sample surface. HgCdTe infrared detector is used to receive photothermal signal. Using this technique, the photothermal signals are experimentally measured as the function of different frequencies. The thermal diffusivities can be obtained by fitting the experimental data. On the other hand, the thermal diffusivities of one-way composite and orthogonal symmetric arranged composites Al2O3/Al are measured in transverse, longitudinal and arbitrary directions. The results show that the diffusivity of one-way material decreases with the increase of the measurement angle; the diffusivity of orthogonally arranged material almost keeps the same when measurement angle changes. 相似文献
19.
20.
Jiaqi Guo Xinwei Wang Lijun Zhang Tao Wang 《Applied Physics A: Materials Science & Processing》2007,89(1):153-156
In this work, the thermal diffusivity of single polyacrylonitrile (PAN) wires with diameters from 4.62 μm down to 324 nm is
measured by using our recently developed transient electro-thermal technique. The wires span from 23 μm to 126.2 μm in our
measurement. Since PAN wires are dielectric, a thin Au film is coated on the surface of the wires to make them conductive.
In the experiment, a step current (with ∼2 μs rising time) is fed to the sample. The sample is heated and takes a certain
time to reach its steady thermal state. The temperature rising response of the sample is sensed by measuring the resistance
change of the thin Au coating. From the average temperature evolution of the sample, the thermal diffusivity can be extracted.
Three PAN wires with different diameters are synthesized using the electro-spinning technique and are measured to obtain their
thermal diffusivities (around 1.53×10-7 m2/s), which are slightly smaller than the bulk value.
PACS 65.80.+n; 66.30.Xj; 44.10.+i 相似文献