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。     

Measurement of thermal conductivity of fluid using single and dual wire transient techniques

A modified measurement device to measure thermal conductivity of fluids using transient hot-wire technique has been designed, developed, tested and presented in this paper. The equipment is designed such that the thermal conductivity could be measured using both single wire sensor of different length and dual wire sensor. The sensor, which is also a heater, is a platinum micro-wire of 50 μm diameter. The influence of wire length on the measurement of thermal conductivity of fluids is tested using two single wires of length 50 mm and 100 mm. The thermal conductivity is also measured using a dual hot wire arrangement; which is achieved by placing the 100 mm and 50 mm wires in a Wheatstone bridge with the 100 mm wire as the sensor and 50 mm wire as a compensation wire. The apparatus requires a 100 ml of test fluid to perform the experiment. The testing temperature of the test fluid during the experimentation can be suitably varied by the choice of heat exchange fluid used in the apparatus. Water is chosen as testing fluids for primary standards. When compared to single wires, the thermal conductivity of the fluids measured is consistent with dual-wire method with an uncertainty of ±0.25%.     

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.     

单片机控制的气相色谱热导检测器研究

针对气相色谱热导检测器的弱信号失真问题,研究与设计热导检测器的弱信号测量电路及其单片机控制系统,进一步提高气相色谱热导检测系统的灵敏度和可靠性。     

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.     

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.     

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。     

颗粒弥散强化金属陶瓷材料传热特性研究

为解决现代工业制造中,颗粒弥散强化金属陶瓷复合材料有效导热系数测量困难、传统模型理论模型有缺陷,测不准等问题,将平均积分法和热阻串并联法应用到新模型之中。开展了界面热阻、颗粒性状和孔隙对复合材料有效导热系数影响的分析,建立了复合材料等效导热系数的通用表达式,在模型预测复合材料导热系数上提出了新的方法。然后对界面热阻、孔隙、颗粒形状等因素对复合材料导热系数的影响进行了评价。研究结果表明,在颗粒弥散强化陶瓷复合材料中,复合材料的有效导热系数随着填充颗粒的体积分数增大而增大,随着气孔率的增加而减小,随着填充颗粒的形状因子增大而增大;计算值与实验数据相吻合,误差小、模型适用范围广,证明了公式的正确性。     

Radiative heat losses in thermal conductivity measurements: a correction for linear temperature gradients

A method for the quantification of the radiative heat losses in a steady-state thermal conductivity measurement set-up is developed based on the Stefan–Boltzmann radiation law with the assumption of a linear temperature distribution along the specimen. The resulting expression can be applied to any regular-shaped sample with well-defined side surfaces and cross-section. Owing to the quantification of the radiative heat losses the accuracy of the steady-state thermal conductivity measurement method is improved and the measurement range can be extended to higher temperatures. An exemplary application in a commercial device is presented. The results are in an excellent agreement with the independently measured high temperature thermal conductivity.     

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.     

On the thermal characterization of solids by the relaxation photothermal technique

The photothermal relaxation method is widely used for determining the volume thermal capacity of solids. The complete mathematical treatment necessary for obtaining the analytical solution of the heat diffusion equation considering the experimental setup usually used is presented. The conditions of applicability of the method are discussed.     

Development of a device for the measurement of thermal and fluid flow properties of heat exchanger materials

As yet, no standard equipment exists for the measurement of heat transfer through porous materials, such as metal foams (metals with a high volume fraction of porosity). Most research in this area has been carried out using bespoke test rigs. Here the creation of a test rig specifically developed for the measurement of the heat transfer of metal foams is reported. This method has been applied to laboratory made samples processed by replication and examples of commercially available aluminium foams (Duocel and Corevo), and should be suitable for the testing of all materials with comparable permeability. As this equipment is new and unique, the design will be discussed in detail, along with the various tests that were performed to ensure reliability and consistency with other methods and published data.     

Equivalent thermal conductivity of heat pipes

In precision machining, the machining error from thermal distortion carries a high proportion of the total errors. If a precision machining tool can transfer heat fast, the thermal distortion will be reduced and the machining precision will be improved. A heat pipe working based on phase transitions of the inner working liquid transfers heat with high efficiency and is widely applied in spaceflight and chemical industries. In mechanics, applications of heat pipes are correspondingly less. When a heat pipe is applied to a hydrostatic motorized spindle, the thermal distortion cannot be solved during the heat transfer process because thermal conductivity or equivalent thermal conductivity should be provided first for special application in mechanics. An equivalent thermal conductivity model based on equivalent thermal resistances is established. Performance tests for a screen wick pipe, gravity pipe, and rotation heat pipe are done to validate the efficiency of the equivalent thermal conductivity model. The proposed model provides a calculation method for the thermal distortion analysis of heat pipes applied in the motorized spindle.     

A non-steady-state probe measurement method to determine heat conductivity, heat capacity as well as moisture in solids and bulk materials

It is important to know the heat conductivity coefficent for an effective use of energy, for quality control of many products or numerical simulation of heat transfer problems. Measurement of heat conductivity should be realized with high reliability and accuracy, in a short time and with low expenditure both in the laboratory and in situ at the production process, to be able to influence the current process. A non-stationary probe and measurement method developed at Dresden University (Institute of Thermodynamics and Human Engineering) allows the determination of heat conductivity, heat capacity as well as water content of solid and bulk materials. Comparative measurements on standard materials and expert opinions of various institutions confirm the high accuracy and the reliability of the non-steady-state probe measurement device also in so called “problematic” materials.     

松散物料导热系数便携式测试系统

本文设计了一套测定松散物料导热系数的便携式测试装置。利用平行热线法,采用新型便携式装置,方便程度大大增加,成本却大幅降低。测定时对松散物料恒功率加热,将其实时温度送入单片机,处理结果经串口通讯传入笔记本电脑。通过特定的算法,将所测松散物料的导热率计算出来。实测结果与相关文献参照值相符。     

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.     

EDM effects on the thermal properties of 36NiCrMo16 steel

In this paper we have studied the effects of the electrical discharge machining (EDM) process on the evolution of thermal properties from the surface towards the core of the 36NiCrMo16 steel using the photothermal deflection (PTD) technique. We have shown that the PTD technique is able to detect the depth of the affected zone, which is characterized by a heterogeneous structure, and allows us to deduce that both the thermal conductivity and the diffusivity would increase from the surface to the core of the sample.     

毛细管气相色谱法测定环丁砜纯度

介绍一个新开发的毛细管气相色谱测定环丁砜纯度的试验方法。该方法载气为氦气,样品径ＣＢＰ２０或ＨＰ－１石英毛细管柱分离,采用 ＴＣＤ检测,归一化法定量。环丁砜纯度分析数据 ＲＳＤ ０.０１％;样品单次分析时间１５ｍｉｎ,方法操作简单、快速,数据精密、准确,适用于环丁砜纯度的质控分析。     

A new thermal property measurement technique by modified pattern search method

The high temperature thermal properties of materials are critical in industrial production and theoretic simulation. However, these properties are not always readily available. In this paper, a new technique was developed to obtain the temperature dependent thermal conductivity and specific heat through only one experiment. More importantly, this experiment was very convenient, since only thermal cycle recording was necessary. In addition, the finite element method and pattern search method were applied to optimize the supposed thermal property values. In order to avoid the convergence difficulty of the classical pattern search method, the step size adjusting function was rewritten. A solid sample and a particle like sample were selected to verify the measurement technique. The verification experiment showed that the thermal property results were accurate to some extent.     

微型涡喷发动机辐板热变形故障分析

研究了某微型涡喷发动机在研制中出现的辐板热变形故障,应用湍流换热计算公式 计算了辐板上的换热系数等有关参数,应用有限元素法计算了辐板的稳态温度场、机械 应力和热应力。基于上述的计算,分析了辐板热变形,并对辐板结构的改进提出了建议。