液体导热系数的双线式瞬态热线测试技术

为了消除端部效应,采用双线式结构设计,研制了测量液体导热系数的瞬态热线装置,详细分析了系统测量误差。样品测试结果表明,测量装置具有较高的精确度,可以用来测量液体的导热系数。     

Determination of the thermal conductivity of composted material

The objective of this study was to develop a reliable method for the determination of the thermal conductivity of composted material using the TP08 probe. Study was set out to determine whether the selection of a signal fragment used to establish thermal conductivity (λ), has a significant influence on the results. Also minimum number of measurements was determined for every phase of the composting process. No significant differences were reported between results, but certain changes in the value of λ were noted. In successive stages of the process, thermal conductivity of composted material were: 0.31 ± 0.09, 0.45 ± 0.14, 0.27 ± 0.03 and 0.37 ± 0.17 W m⁻¹ K⁻¹.     

平板式稳态导热仪的设计及实现

基于一维无限大平板稳态传热模型开发改进平板式稳态导热仪,采用K级热电偶和数字温度仪表进行温度数据采集,数据控制系统与数字温度表通过RS232串口进行数据通讯,读取温度数据,在输入加热电压、加热板电阻、试件面积、厚度等数据后可直接获得并显示试件的导热系数.利用设备进行试验,测定了方形橡胶试样和圆形橡胶试样的导热系数,方形橡胶试样比圆形橡胶试样更适合于设备.与LFA447导热仪测定的标准数据相比,在正常操作下利用设备测定的数据误差小于(5～10)%,基本可满足高等学校实验室和实际工程测量的需要.     

The mapping of vortex fields around single and dual bluff bodies

The development and use of a system to measure important parameters of the vortex field in a coordinate grid around several single bluff bodies and dual bluff body combinations are described. Two hot wire sensors were used: a reference sensor at a fixed position and a moving sensor with position coordinates adjusted by using computer control. The strength, frequency and regularity of the vortex shedding are found from the auto-power spectral density of the moving sensor signal. The phase difference between moving and reference sensor signals is found from the cross-power spectral density function between the signals. The results are presented as maps of vortex parameters plotted as a function of sensor position coordinates. The main features of these maps, including the enhancement of vortex shedding from certain dual bluff body combinations, is then discussed.     

New device and method for measuring thermal conductivity of thin-films

Thermal sensitive paints (TSPs) are used for global nonintrusive detection of boundary layer transition in flow over the surface of wind tunnel research models. Since the transition is a transient process, the TSP should have a fast response characteristic. A low paint thermal conductivity is required for fast response. A thin-film thermal conductivity meter (TFTCM) was designed and built to measure thermal conductivity of the TSPs, which are typically between 50 and 150 microm thick. In this paper, the design and operating features of the TFTCM are described. Measurement of the thermal conductivity with this TFTCM of three standard thin-film low conductivity specimens, Kapton, Teflon, and Borofloat glass, showed good agreement with the manufacturer quoted values, thus validating the instrument and the procedure. Consistently repeatable values for thermal conductivity (k=0.41 +/- 0.02 W/m K) were also obtained for the TSP specimen (TSB-B, 75 microm) tested.     

The measurement of thermal conductivity variation with temperature for solid materials

An apparatus was designed to routinely measure the thermal conductivity variation with temperature for solid materials. The apparatus was calibrated by measuring the thermal conductivity variations with temperature for aluminum, zinc, tin and indium metals. The variations of thermal conductivity with temperature for the Zn-[x] wt.% Sb alloys (x = 10, 20, 30 and 40) were then measured by using the linear heat flow apparatus designed in present work. From experimental results it can be concluded that the linear heat flow apparatus can be used to measure thermal conductivity variation with temperature for multi component metallic alloys as well as pure metallic materials and for any kind of alloys. Variations of electrical conductivity with temperature for the Zn-[x] wt.% Sb alloys were determined from the Wiedemann–Franz (W–F) equation by using the measured values of thermal conductivity. Dependencies of the thermal and electrical conductivities on composition of Sb in the Zn–Sb alloys were also investigated. According to present experimental results, the thermal conductivity and electrical conductivity for the Zn-[x] wt.% Sb alloys decrease with increasing the temperature and the composition of Sb.     

大型回转零件有限元热与瞬态动力学耦合分析

以一种屏压机的关键部件大盘为研究对象。其结构在高速、高温工作情况下能否满足性能要求将直接影响产品的质量。为了预测大盘的工作性能，我们首先建立了大盘转台的实体建模，然后采用有限元方法进行热与瞬态动力学耦合分析，从而获得大盘转台的动态特性参数．这些分析不仅为优化设计提供必要的参考数据，而且为进一步提高产品设计水平打下坚实的基础。     

气相色谱热导检测器的信号测量与电源电路研究

在气相色谱仪中,采用热导检测器检测物质成分的浓度变化,具有构造简单、测定范围广、稳定性好、线性范围宽等优点。针对气相色谱热导检测器的弱信号失真和电源不稳定问题,研究与设计热导检测器的弱信号测量电路、信号放大电路以及电源电路。实践表明,该方法有效提高气相色谱热导检测系统的可靠性。     

Useful polynomials for the transient response of solids under mechanical and thermal excitations

Integral- and fractional-order polynomials capable of describing the transient response of mechanical and thermal systems to a generalized excitation of displacement or temperature were derived using convolution theory. Excellent agreement between the derived polynomials and an existing closed-form solution was then seen for the mechanical case where a single-degree of freedom system without damping was subjected to an asymptotic-exponential and half-sine displacement excitations. Excellent agreement was also seen with the thermal case of a slab subjected to an asymptotic-exponential temperature rise on the exposed surface. However, in order to avoid the use of functions involving complex arguments that arise during a portion of the integration, the Laplace Transform identity of the convolution integral and a ten-term Gaver–Stehfest inversion formula were used. The use of polynomials in the solution was intended to allow the incorporation of empirical date not easily represented by standard functions. The resulting relationships are easily programmed and can be used to solve a variety of problems in engineering, as well as verify numerical calculations involving more sophisticated methods such as finite-element analysis.     

用标准样法测量材料的导热系数

在对导热系数的稳态测量方法的综述与讨论的基础上,提出了测量材料导热系数的标准样比较方法。分析了该方法的简单性、经济性及可行性。     

红外/热导法检测C-103中氧氮含量

使用LECO ON736氧氮分析仪,采用红外和热导法,对C-103铌铪合金中氧、氮含量进行检测。通过助熔剂处理、坩埚选择、定量下限、分析功率、试样质量、精密度和加标回收实验,建立了C-103中氧、氮含量的检测方法。该方法氧和氮的RSD分别为3.36%和6.86%,加标回收率分别为95.5%~106.0%和92.5%~107.5%,精密度和加标回收实验结果良好,满足分析需要。     

Thermal transient rough EHL line contact simulations by aid of computational fluid dynamics

Reynolds equation is the pre-dominantly used PDE for modelling the fluid flow or more accurately the fluid pressure in an elastohydrodynamic lubrication (EHL) contact. The equation is derived by combining the two conservation equations of momentum and continuity into a single equation for the fluid pressure. The numerical approach for theoretical investigations performed on EHL contacts in this work is somewhat different. The modelling of the fluid flow is based on a computational fluid dynamic (CFD) technique. The fluid flow is simulated by aid of the equations of momentum and continuity in a more complete form and when the thermodynamics is incorporated, the equation of energy. The aim of the investigation was to examine whether the CFD technique could be used to handle thermal transient rough EHL line contacts. It is shown that commercial CFD software can be modified to meet such requirements. The influence of thermal effects on the flow under sliding motion was investigated. The non-Newtonian model used in this work is the Ree-Eyring model. It is shown that the choice of the Eyring stress in the model influences flow in the contacts. If the thermal properties of the surrounding solids differ, it has been shown experimentally and theoretically that a dimple or increased central film thickness may appear in the EHL contacts. This work shows that the governing mechanisms that result in the dimple are also present in thermal transient rough EHL line contacts.     

Leak detection in pipe using transient flow and genetic algorithm

An inverse transient method with genetic algorithm (GA) was applied to leak detection in pipeline. Transient flow caused by valve operation was calculated using the characteristics method. The location and discharge of leak were determined so that the difference of the calculated pressure may be minimized from the reference pressure calculated under a given leak condition. Calculations were done for the leak at one and two locations in pipeline. Furthermore, the effect of noise in pressure data was discussed, and the leak locations and leak discharges can be predicted precisely even in the case of noisy data. This paper was presented at the 9^th Asian International Conference on Fluid Machinery (AICFM9), Jeju Korea, October 16–19, 2007.     

Enhancing electrical conductivity and electrical thermal characteristics of a PEDOT:PSS thin layer by using solvent treatment and adding Ag nanoparticle solution

A method of enhancing the electrical conductivity of 3,4-ethylenedioxythiophene:poly styrene sulfonate (PEDOT:PSS) by combining solvent treatment (adding high polar solvent: 5 wt% ethylene glycol) and adding a small amount of silver (Ag) nanoparticles in a solution was investigated. The main purpose of this was to apply a PEDOT:PSS conductive layer to micro-thermal devices driven by electricity and, for this, to reduce the layer thickness (for low stiffness) while maintaining necessary high electrical conductivity. Layers with thicknesses of less than about 10 μm were examined for electrical conductivity and temperature when electricity was applied. The solvent treated PEDOT:PSS had suitable electrical resistance to generate appropriate temperature properties. The added Ag nanoparticles reduced the electrical resistance by 30–70% over the measured thickness range. The electric conductivity applied with this method was 200–260 Ω⁻¹ cm⁻¹ for thicknesses of 1–2 μm (conductive area: 12 mm × 10 mm) and the generated temperature increase was 20–50 °C at applied voltages of 3–5 V. These characteristics are considered to be suitable to use the conductive layer as a heating element. In addition, the method we used scarcely degraded the transparency of the layer. Measurements of the conductive area in a layer with conductive atomic force microscope (AFM) indicated that the added Ag nanoparticles contributed to increasing the conductive areas and distributing them more uniformly.     

网状静电传感器弯管处颗粒速度与浓度的测量

为了对气力输送管道进行实时监控,并且提高炉膛内的燃烧效率,需要对气力输送管道中颗粒的速度与浓度分布进行测量。采用一种网状结构的静电传感器测量气力输送管道弯管处的颗粒速度与浓度分布。为了研究传感器的特性,首先建立了网状静电传感器的有限元模型。根据有限元仿真结果,优化网状静电传感器的设计,使其拥有更高更均匀的灵敏度分布,在实验室规模颗粒流实验平台上进行了实验研究。通过对上下游平面对应位置网状电极所得静电信号进行互相关运算,可以估测颗粒的轴向速度分布;通过对同一平面网状电极静电信号的均方根值进行重建,可以得到固体颗粒的相对浓度分布。实验研究表明,该网状静电传感器可以用来测量气力输送管道弯管处颗粒速度与浓度分布。     

Measurement of thermal diffusivity using deformation gradient and phase in the photothermal displacement technique

As technology advances with development of new materials, it is important to measure the thermal diffusivity of material and to predict the heat transfer in the solid subject to thermal processes. The measurement of thermal properties can be done in a non-contact way using photothermal displacement spectroscopy. In this work, the thermal diffusivity was measured by analyzing the magnitude and phase of deformation gradient. We proposed a new data analysis method based on the real part of deformation gradient as the pump-probe offset value. As the result, compared with the literature value, the measured thermal diffusivities of materials showed about 3% error.     

Elasto-plastic contact problem of laying wire rope using FE analysis

The three-dimensional elasto-plastic contact model, formulated with variational equalities, has been described for laying wire rope in this paper. The augmented Lagrangian multiplier method has been applied to calculate both the normal contact force and friction contact force, and the radial return mapping algorithm has been employed to handle stick/slip phases of friction. With a graphical user interface (GUI), a program for calculating boundary conditions of a three-dimensional finite element modelling is developed to create external files, which are in the format of the ANSYS parametric design language (APDL) and the external files can be accessed by ANSYS for nonlinear analysis. FE simulation of a simple wire strand has been given and the effects of friction coefficient and self-rotating ratio on the contact stress have been analysed. Also the effects of them on the forming stress and strain have been discussed.     

The effects of particle size and volume fraction of Al2O3 on electronic thermal conductivity of α-Al2O3 particulate reinforced aluminum composites (Al/Al2O3MMC)

The effects of particle size and volume fraction of Al₂O₃ on the thermal conductivity properties of α-Al₂O₃ particulate reinforced aluminum composites (Al/Al₂O₃MMC) are investigated herein. It is found that the thermal conductivity of composites is higher with an Al₂O₃ particle size of 15 μm than with a particle size of 30 μm. The increase in the thermal conductivity could be due to the greater stability of thermal conductive paths with smaller Al₂O₃ particles.     

Experimental study on response of hot wire and cylindrical hot film anemometers operating under varying fluid temperatures

The working principle of constant temperature anemometer (CTA), used for fluid velocity and/or turbulence measurements, is based on convective heat transfer from a sensor (a hot wire or a hot film) to the fluid being measured. Response of a CTA, working in temperatures other than its calibration temperature, involves errors which must be corrected for reliable measurement data. We have experimentally studied the effect of variations in fluid temperature on the response of hot wire and cylindrical hot film anemometers, and have discussed the application of different correction factors. Effects of overheat ratio (sensor temperature) and fluid velocity on the CTA output voltage correction factor have been discussed. The results show that the error in the CTA response depends on the sensor temperature, and it shows a decrease with increasing sensor temperature (increasing overheat ratio). The results also show that the error correction factor depends on the overheat ratio and fluid velocity. The required error correction factor also depends on whether the fluid temperature decreases or increases with respect to the calibration temperature of the CTA. In spite of differences in sensor characteristics, our work on cylindrical hot film sensors shows that the correction factors for hot wire and hot film sensors are similar and close in magnitude.     

A study of the method of the thermal conductivity measurement for VIPs with improved RBF neural networks

Thermal conductivity is an important physical quantity which is the token of the heat-conducting property of VIPs. The measurement of thermal conductivity is invaluable for VIPs can be widely used. This paper presented a fast and high precision measuring method of VIP’s thermal conductivity, and proved its feasibility by simulation. New methods use improved neutral networks to fit the relationship between VIP’s thermal conductivity and characteristic value of frequency change, and verified the superiority of this method by experiment compared with the least squares. The presented methods are very valuable for the widespread use of vacuum insulation panels.