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1.
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
2.
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
3.
The Einstein model to consider thermal effect in universal equations of state (UEOS) is modified. It is proposed that the zero-point vibration term should be deleted in a thermal UEOS, and the parameters cannot be directly taken as experimental data at a reference temperature, VR, BR, and , but their values at absolute zero temperature, V0, B0, and . An approach is proposed to solve V0, B0, and from VR, BR, and . The approaches are applied to three typical universal EOSs, including the Baonza, mGLJ and Morse EOSs. The numerical results show that the solved values of parameters are almost identical for different EOSs. And the thermo-physical properties predicted through different EOSs are almost identical at zero- and low-pressure conditions, once the same approach and input experimental data are used to solve the parameters. It is concluded that the prediction of thermo-physical properties at zero- and low-pressure conditions cannot be taken as the criteria to judge the applicability of a universal EOS. 相似文献
4.
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
5.
PTR技术测量材料的热扩散系数的线性化方法 总被引:2,自引:0,他引:2
报道了一种用光热辐射 (PTR)技术测量不透明材料热扩散系数的优化方法。从光热辐射理论出发 ,在一定条件下 ,推导出位相信号和调制频率的关系表现为线性关系 ,分析实验数据得出材料的热扩散系数。 相似文献
6.
An optically pumped far infrared laser provides fixed photon energies near the superconducting gap, making it possible to carry out experiments where the temperature is swept through Tc. Such thermal measurements in thin films of V3Si show both known and unexplained features, with some of the latter perhaps due to a second gap. The thermal technique shows potential for the study of superconductors.Work supported by the U.S. Department of Energy under Contract No. DE-AS05-79ER10436. 相似文献
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本文采用基于速率理论的模拟方法研究钨材料中氢同位素氘的热脱附谱. 热脱附数据来源于520 K下受等离子体辐照的多晶钨, 入射离子能量为40 eV, 剂量为1× 1026 D/m2. 通过调节速率理论中的俘获能、俘获率等参数, 最终获得与实验相符合的热脱附拟合谱. 拟合结果表明, 钨中俘获的氘存在于三种俘获态, 俘获能分别为1.14 eV, 1.40 eV和1.70 eV, 相应脱附温度峰值为500 K, 600 K和730 K. 这三个俘获能分别应对应于第一原理计算得到的空位俘获第3–5个氢原子的俘获能(含零点振动能修正)、空位俘获第1–2个氢原子的俘获能, 空位团簇对氢原子的俘获能. 模拟结果表明, 在本辐照实验条件下, 钨中空位及空位团簇是氘在钨中的主要俘获态. 相似文献
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A dilatometer, using the three terminal capacitance technique, suitable for measurement of linear thermal expansion of solids
in the temperature range 1.3–300 K is described. The dialtometer is designed such that the mounting system for the specimen
does not undergo any significant changes in dimensions when the specimen is heated. The apparatus, therefore, yields in principle
absolute values of α, the coefficient of linear thermal expansion. The performance of the apparatus has been checked by measurements
on copper in the temperature range of 77–300 K. Some preliminary results on the behaviour of α for Y1Ba2Cu3O6.9 compound in the vicinity of superconducting transition temperature,T
c are also described. The system can detect relative changes in length Δl/l
0 of about 10−8. Attempts are being made to improve the sensitivity. 相似文献
11.
Thermal conductivity and thermal diffusivity of tantalum in the temperature range from 293 to 1800 K
Thermal diffusivity of polycrystalline tantalum at the temperature range from 293 to 1800 K has been measured by the laser
flash method with the error of 2–4 %. Thermal conductivity has been calculated with the use of reference data on density and
heat capacity. Approximating equations and tables of reference data for the temperature dependence of heat transfer coefficients
have been obtained; comparison with the published data has been carried out.
The work was financially supported by the Russian Foundation for Basic Research (Grant No. 07-08-00071). 相似文献
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In this Letter, the homotopy perturbation method (HPM) has been used to evaluate the efficiency of straight fins with temperature-dependent thermal conductivity and to determine the temperature distribution within the fin. The fin efficiency of the straight fins with temperature-dependent thermal conductivity has been obtained as a function of thermo-geometric fin parameter and the thermal conductivity parameter describing the variation of the thermal conductivity. The results reveal that homotopy perturbation method is very effective and simple. The resulting correlation equations can assist thermal design engineers for designing of straight fins with temperature-dependent thermal conductivity. 相似文献
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Thermal gelation of methylcellulose in water was studied using FTIR-ATR spectroscopy. It is found that the formation of a
three-dimensional network of physical cross-links between macromolecules of methylcellulose on gelation occurs not only as
the result of hydrophobic association of methoxyl substituents but also due to the formation of inter-chain hydrogen bonds
involving unsubstituted primary hydroxyl groups accompanied by a conformational change in the polymer backbone.
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Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 75, No. 4, pp. 490–494, July–August, 2008. 相似文献
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基于不规则波导模式匹配法以及缓变波导中电磁波模式耦合理论,研究了一种W波段圆波导TE62模式激励器. 该波导模式激励器采用矩形波导TE10模式通过侧壁耦合馈入同轴波导,利用同轴波导的选模特性激励TE61模式;随后利用轴向半径周期微扰的圆波导实现TE61–TE62模式变换. 文中推导了矩形-同轴波导模式匹配理论,系统研究了波导结构缓变参数对模式变换效率的影响,完成了模式变换器的优化仿真设计,数值计算结果表明:中心频率处TE62模式的转换效率为94.5%,纯度为98.16%,效率85%以上带宽达到1 GHz,能够满足回旋管冷测的要求.
关键词:
同轴波导
模式变换
耦合模理论
半径微扰 相似文献
18.
This paper describes equilibrium ensembles of thermally excited electromagnetic fields in layered media. The obtained results complement Planck's law of thermal radiation that determines the spectrum of the radiation but supplies little information about the ensemble of eigenfields (normal modes) excited in the medium. The developments regarding these ensembles presented in this paper make it possible to apply perturbation techniques for the analysis of the ensembles of radiated fields in layered media with a steady heat flux. 相似文献
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《Current Applied Physics》2019,19(11):1145-1149
We demonstrate a method for examining the effects of thermal aging of cellulose pressboard using terahertz time-domain spectroscopy. The change of refractive indexes at the frequencies of pulsed terahertz waves while applying heat reveals that the degree of thermal aging and the condition of thermal breakdown can be clearly analyzed by performing terahertz measurements. The visual examination method only allows evaluation of the degree of blackness on the external surfaces of cellulose pressboard. However, using terahertz techniques for non-destructive inspection enables determination of the dielectric integrity to check the strength of the electrical insulation inside the cellulose pressboard. The results indicate that the terahertz techniques could be very useful, especially in the electric power industry, which requires a variety of methods for internal non-destructive testing to ensure the safety and reliability of insulation materials in electric power facilities and components. 相似文献