Étude expérimentale de la résistance thermique de contact entre l'étain en cours de fusion et un creuset refroidi

This paper deals with the analysis of the thermal contact conditions during the melting of tin on different cooled walls, for different heat situations and for different cooling flows. Two experimental set ups are studied. A polished nickel substrate covers the melting-pot of the first one. Semi intrinsic thermocouples are implemented to measure the temperature of the substrate. This will allow a better study of the thermal contact resistance distribution on the wall. The second melting-pot is made of copper. Its surface roughness is variable. The heat system is stronger. The results obtained with the first experimental set-up show that the thermal contact resistance is time-dependent and non-uniformly spread. However, the heat evacuation is relatively uniformly spread while the heat power increases. Tests carried out with the second experimental set-up point out huge temperature oscillations which are attributed to unstable thermal contact conditions. This thermal behaviour can be explained by the buckling of the tin crust. The apparition of buckling seems to be favoured by a higher dissipated power and by a higher thermal conductivity of the melting pot.     

Thermal characterization of dielectric thin films using an improved genetic algorithm

This paper presents theoretical and experimental investigations of the thermal conductivity and the contact resistance of dielectric materials deposited as thin films. Silicon dioxide and poly(p-phenylene) films deposited on alumina substrates are studied in order to determine simultaneously the thermal conductivity of the film and the resistance of the contact between the film and the substrate. Measurements are obtained by using a photothermal technique, and an improved genetic algorithm (GA), especially suitable for thermal characterizations of thin film structures in the sub-micron range. A theoretical study for evaluating the optimal conditions for the photothermal measurements is presented. This is done by studying the sensitivity of the unknown parameters to the thin film thickness and to the properties of the materials. As the photothermal analysis is basically performed in unsteady state conditions, this study highlights the relation between the intrinsic and effective conductivity of the materials.     

高温超导直接冷却的氮化铝与无氧铜接触界面热阻的实验研究

氮化铝(AlN)具有高热导性、高电绝缘性,是超导二元电流引线热截流结构中常用的材料之一。根据稳态导热法建立低温真空实验装置,实验研究了超导冷却系统热截流结构中,界面温度和接触压力对AlN块材与无氧铜(OFHC-Cu)块材间接触界面热阻的影响。在实验温度(90K-210K)和压力(0.273MPa-0.985MPa)条件下,AlN/OFHC-Cu接触界面热阻随接触压力的提高而降低,而当界面温度上升时界面热阻由于热载子热运动的强化而降低,温度较高时,接触界面热阻随压力变化的速率趋缓。低温下AlN/OFHC-Cu间的接触界面热阻是直接冷却超导系统的设计和超导系统的热稳定性方面必需解决的问题。     

考虑界面接触热阻的一维复合结构的热整流机理

建立了考虑变截面、变热导率及界面接触热阻效应的组合热整流结构的温度场及热整流系数的理论模型和有限元解.数值算例证明了本文模型及算法的可靠性,进而通过参数影响研究确定了若干几何及材料参数对结构热整流系数的影响规律,揭示界面接触热阻对热整流效果的影响机理.研究结果表明长度比、截面半径变化率、热导率、边界条件温差和界面接触热阻等因素必须通过优化设计才能得到最大的热整流系数,同时界面接触热阻的引入也为调控热整流系数提供了一条新的途径.     

Premiers instants du refroidissement d'une goutte métallique après son impact sur une paroi

This paper presents an experimental study of the evolution of thermal contact conditions (temperature jump at the interface, heat flux and transient thermal contact resistance) during the first stages of solidification of a liquid metal drop on a water-cooled wall. Two complementary approaches were developed. The first method, valid for times longer than 10⁻³ s, is based on the use of one temperature measurement inside the solidifiying drop, using a usual thermocouple, and several temperature measurements in the wall using very fine semi-intrinsic thermocouples installed near the active surface. By solving an inverse heat conduction problem in both regions (drop, wall), this method allows a local thermal characterization. The second approach uses an intrinsic method, based on the use of metal drop and wall as two thermocouple elements, to measure the mean micro-contact temperature of drop and wall. This kind of sensor, without inertia, has approximatively the time delay of fast data acquisition (t_c < 10⁻⁶s). The measured temperature represents the mean surface temperature of all the contact areas of drop and wall. The physical interpretation of this kind of measurement is difficult and needs the development of a new theoretical model. We can already observe that at t = 0⁺, the measured temperature is close to the theoretical one, ie, the interface temperature contact of two semi-infinite media, the liquid metal drop and the wall (effusivity ratio). This means that solidification has not yet taken place.     

空间相机接触热阻的计算

为了解决空间相机接触热阻难以确定的问题,从接触面传导和辐射换热的角度考虑,给出了其接触热阻的计算方法。根据空间相机的材料、加工、装配及其特殊运行环境,得到一个合理的接触系数范围。以空间相机的正视相机为例,对其结构进行合理的简化,利用I-DEAS/TMG热分析模块建立有限元模型,仿真计算了低温稳态平衡工况,考查了热阻波动对温度分布的影响。正视相机热分析计算结果和热环境模拟试验数据较为吻合,最大偏差为0.45℃。研究结果表明,该接触热阻计算方法合理,可以预测太空环境中干接触的精密加工表面间的接触热阻。     

An inverse problem of estimating the Biot number in deep X-ray lithography

In this study, an inverse algorithm based on the conjugate gradient method and the discrepancy principle is applied to estimate the unknown space- and time-dependent Biot number in deep X-ray lithography using temperature measurements. It is assumed that no prior information is available on the functional form of the unknown Biot number; hence, the procedure is classified as the function estimation in the inverse calculation. The accuracy of the inverse analysis is examined by using simulated exact and inexact temperature measurements. Results show that an excellent estimation of the space- and time-dependent Biot number can be obtained for the test case considered in this study. PACS 85.40.Hp; 44.05.+e; 46.15.Cc     

Transient thermal loading induced optical effects in tightly jacketed double-coated optical fibers with interlayer thermal contact resistance

This article investigates the transient microbending loss and refractive index changes in a tightly jacketed double-coated optical fiber subjected to thermal loading with stress-dependent interlayer thermal contact resistance. The effects of interlayer thermal resistance on the transient microbending loss and refractive index changes of the optical fiber are analyzed and discussed. Results show that the stress-dependent interlayer thermal contact resistance increases the lateral pressure induced by the transient thermal loading in the tightly jacketed double-coated optical fiber and, thus, the microbending loss. Similarly, the interlayer thermal contact resistance increases the thermal loading induced refractive index changes in the transient state of the loading.     

玻璃钢低温下导热及接触热阻的实验研究

利用稳态法测试了固体复合材料在不同温度下的导热系数及复合材料与铜之间的接触热租。在90K~300K的温度范围内,固体复合材料导热系数随温度的提高而增大,而当温度上升时,接触热阻降低,温度大于100K时,热阻变化较小。     

ESTIMATION OF THERMAL CONTACT CONDUCTANCE DURING RESISTANCE SPOT WELDING

This article describes an experimental procedure conducted to estimate and investigate the transient thermal contact conductance (or thermal contact resistance) between the electrodes and workpieces during resistance spot welding. A fine thermal metrology was developed to collect thermal histories near the welding region. Indeed, the electrode tip was instrumented with several interior microthermocouples for measuring the transient temperature response during the welding process. A simple mathematical model, using an inverse heat transfer method, was built for the estimation of the transient heat transfer coefficient from interior transient temperature measurements. A simple resistance welding case of two steel sheets was investigated. The initial transient values of thermal contact conductance were found to be in agreement with those observed in the dry copper–steel solid contact case. At the end of the process, the transient heat transfer coefficient reaches a high value corresponding to the best heat transfer phenomenon at the interface during the welding process. When the metal is melted, the contact quality increases due to the high-applied electrode force. Higher electrode force and heating temperatures produce lower thermal contact resistance. The results obtained show the capabilities and the power of the coupled thermal metrology and transient inverse technique developed to investigate thermal history of resistance spot welding.     

高效在线测量加速实验中双极晶体管结温方法的研究

针对晶体管在加速寿命实验和老炼实验等实际工程中结温的在线测控问题,本文基于大电流电学测温方法研究了型号为2N3055的双极大功率晶体管在恒定的集电极电压V_(ce)和集电极电流I_(ce)条件下发射结电压V_(be)随着温度T变化的对应关系.研究结果表明,温度在40—140℃范围内时,在集电极加载大功率电流电压的条件下,发射结电压随温度上升而线性减小,基极电流随温度变化不超过4%.通过理论推导恒定功率下发射结电压与温度的数学模型,证明了当基极电流数值随温度变化不超过4%时,V_(be)-T关系曲线呈线性且理论上引起的温度误差不超过0.5℃,以此为基础推导出一种新的在线测量加速实验中结温测试公式.最后利用Phase11进行对比验证实验,证明了该方法的正确性.     

基于CMY模型改进的界面热阻模型及其应用

导热膏填充的接触界面热阻由接触热阻和间隙热阻两部分组成。本文采用截锥体接触的单热流通道模型代替CMY模型中的圆盘接触的单热流通道模型,推导出了改进的接触热阻计算公式。本文还结合间隙热阻的计算公式,得到了一种改进的导热膏填充的接触界面热阻模型。通过分析得出了如下结论:对于使用导热膏填充的接触界面的热阻而言,其主要影响因素为接触表面的粗糙度和导热膏的导热系数,而接触界面间压力对其的影响则相对较小。     

低温真空下固体界面间接触热导实验分析

主要叙述了低温真空下接触热导实验装置的设计 ,通过改进实验装置来扩展研究的温度范围。在 10 0 K～ 30 0 K范围内 ,对铝、不锈钢和铜三种金属材料进行了大量的接触热导的实验研究 ,并分析了接触热导与界面载荷和温度之间的关系     

金属的冲击波温度测量（Ⅳ）——“三层介质模型”及其应用

 重点讨论了非理想界面对利用辐射法测量金属的冲击波温度的影响,建立并给出了“三层介质模型”的热传导方程的普适解析解,分别将该解析解应用于块状金属样品的冲击波温度测量、“热阻模型”以及利用对称夹心装置测量蓝宝石单晶的高压热传导问题;重点研究和讨论了利用块状样品进行金属材料冲击波温度测量的原理和可能性,以及在利用块状样品进行金属材料冲击波温度测量时实验装置设计应该满足的要求。“三层介质模型”的分析表明：只要块状样品与透明窗口之间的间隙尺度小于1.0 μm（最好小于0.5 μm）,则“样品/窗口”界面的温度在大约几十纳秒的时间内即可从尖峰温度衰减到与理想界面温度相当接近的值。根据“样品/窗口”界面的这一热弛豫特性,可以直接利用块状金属样品测量冲击波温度而不必采用镀膜技术。给出了利用块状铁陨石样品和单晶蓝宝石（Al₂O₃）窗口进行冲击波温度测量的初步实验结果,与三层介质模型的预期结果符合得很好。     

纳米尺度点接触的实验研究

由交叉微米线构成了T形结构,并测量了Pt-Pt和Pt-Au节点的接触热阻和接触电阻。分析表明,增大接触点长度与宽度的比值,线接触模型和椭圆接触模型计算得到的接触热阻的差别逐渐减小,当比值超过20时,椭圆接触模型不再适用。测量得到的接触热阻随温度变化不明显,而接触电阻随温度升高而增大。由于存在表面绝缘层,接触热阻将远大于Wiedemann-Franz定律的预测值。考虑Kundsen数的影响以后,由接触电阻计算得到的金属接触点尺寸近似与温度无关。     

A Technique for Obtaining Thermal Resistance of the Dielectric-Substrate Contact under High-Intensity Irradiation

Heating of dielectric materials is investigated under irradiation of specimens by periodically pulsed ion-beams. The solution to the equation of thermal conductivity yields constrained variations of the specimen's temperature around its average value, with the repetition rate being that of the radiation-pulse frequency. Initially, the average variation-period temperature is found to grow, while after saturation it approaches a quasi-stationary value controlled entirely by the thermal resistance of the specimen-substrate contact under the same irradiation conditions. A method for the time-averaged dielectric temperature under saturation is proposed. Using this method, an express-technique for calculating thermal resistance of the dielectric-substrate contact is offered. It is based on periodically pulsed heating of the dielectric specimen by a moderate-density ion beam and precision measurements of the its average temperature. The error of the express technique is evaluated and so is its applicability range. A hypothesis is put forward that proceeding form this new method for thermal resistance one may determine the energy lost in ion sputtering.     

The thermal contact problem in nano- and micro-scale photothermal measurements

Thermal contact resistance between two solids is discussed with regard to its influence on the measurements of temperature and thermo-physical parameters in micro- and nano-structures. Two important applications are considered: thin film coatings on substrates and local measurements with a nano-probe in scanning thermal microscopy. The mechanical contact of a copper layer on carbon is measured by adhesion strength experiments and correlated to the thermal transport across the interface deduced from infrared radiometric measurements. A novel quantity the thermal wave contrast is introduced which takes into account the interface resistance and modifications of the coating and substrates at the interface. With regard to scanning thermal microscopy the contact resistance problem is discussed for 3ω-measurements in the active mode and for temperature measurements in the passive mode. It is shown that the thermo-elastic response can offer a means to avoid the influence of the thermal contact resistance on local temperature measurements.     

低温下用3ω法测量热导率的研究

3ω法是测量体材料和薄膜材料热导率的主要方法之一。低温真空条件下测量热物性往往受接触热阻以及加热器自热效应的影响比较大。文中针对低温下体材料热导率的测量,通过总结国内外近年来用3ω法测量热导率的主要研究成果,对如何选择合适的加热频率以减小这两方面所带来的影响做了一些研究,并指出了低温下用3ω法测量体材料热导率的进一步研究工作。     

A compact optical heterodyne interferometer by optical integration and its application

A compact high-resolution optical heterodyne interferometer combining a two-frequency light module and a minute optical system is described. The light module, which generates two independent frequencies of light, is fabricated by proton exchange method on LiNbO₃ substrate. We report an experiment evaluating measurement accuracy using a micro-displacement measurement system which incorporates this interferometer. Results of the experiment with a standard thickness sample show high thermal stability with maximum measurement error of 1.8 nm at a temperature from 19°C to 33°C. The system was used to measure the hysteresis of a piezoelectric element for displacements of several nm, thereby making it possible to analyze the system quantitatively in practice.     

一种测量功率型LED热阻的方法

叙述了正向电压法测量功率型LED温度系数K和热阻的原理,介绍了测试装置及具体测试过程,对蓝宝石衬底正装LED和硅衬底倒装LED的温度系数和热阻进行了测量.选用热阻已知的LED样品,对其实际值与测量值进行了比较,误差在5% 左右,证实了这种热阻测量方法是可行的.