二极管端面抽运固体激光器晶体棒与热沉接触热导研究

二极管端面抽运固体激光器中,圆棒晶体采用金属热沉夹持并散热,晶体侧面受到的压力呈非轴对称分布.建立了此状态下晶体棒与热沉间无热界面物质、采用厚度为平均间隙厚度和远大于平均间隙厚度的热界面物质三种情况下接触热导模型.针对前两种模型,采用截断高斯模型和塑性形变模型,讨论了接触热导与装配压力、等效均方根粗糙度的关系.建立了晶体棒与热沉的接触散热模型,对高斯型热耗分布,采用有限元法得到了无热界面物质和采用铟箔作为热界面物质时晶体棒温度的空间分布.结果表明:无热界面物质时,晶体棒与热沉间接触热导随圆心角变化较大,其 关键词： 激光二极管端面抽运固体激光器 热效应 有限元法 接触热导     

Studies of the magnetic and reversal properties for thin CoCrTa films

The effects of magnetic layer thickness on film structural and magnetic properties were studied systematically with emphasis on the thermal effects on thin recording media films. X-ray diffraction measurements reveal structural changes as thickness decreases, and the existence of a “Cr enriched phase” associated with the interface. The saturation magnetization M_s decreases with thickness and the thickness of the “dead layer” was found to be ∼23 Å. Systematic measurements of effective anisotropy, coercivity and saturation magnetization as functions of temperature have been carried out. Magnetic viscosity measurements reveal that thermal stability is affected not only by grain sizes but also by anisotropy reduction associated with nanostructure evolution, as the film thickness decreases.     

The effect of silicon substrate on thickness of SiO2 thin film analysed by spectral reflectometry and interferometry

Techniques of spectral reflectometry and interferometry are used for measuring small changes in thickness of SiO₂ thin film grown by thermal oxidation on different silicon substrates. A slightly dispersive Michelson interferometer with one of its mirrors replaced by a thin-film structure is used to measure the reflectance and interferometric phase of the thin-film structure at the same time. The experimental data are used to determine precisely the thickness of the SiO₂ thin film on silicon wafers of two crystallographic orientations and different dopant concentrations. We confirmed very good agreement between the experimental data and theory and revealed that the thin-film thickness, which varies with the type of silicon substrate, depends linearly on the wavelength at which minimum in the spectral reflectance occurs. Similar behaviour was revealed for the interferometric phase.     

超光谱成像仪中棱镜的热光谱特性

为了确定超光谱成像仪热控指标和开展热设计,研究了超光谱成像仪中棱镜的热光谱特性。介绍了超光谱成像仪的工作原理以及热光谱特性的含义,分析了棱镜的环境热效应,论述了棱镜热光谱特性研究内容及技术路线,推导了温度变化时棱镜偏转角以及角色散的函数关系,进一步得到光谱中心平移及光谱带宽随温度变化规律。借助有限元分析,比较了K9、熔石英两种材料的棱镜的入射角、顶角、材料色散、光谱中心平移及光谱带宽随温度变化规律,确定了棱镜的热控指标,并设计了热光谱试验。理论分析和试验结果表明由于热变形引起的光谱带宽和光谱分辨率改变可以忽略不计,光谱平移主要由材料折射率温度系数决定;棱镜材料色散(dn/dλ)对温度变化不敏感,因此温度变化对其光谱带宽影响不明显; 本文研究方法合理,结果可信,对确定棱镜的热控指标和优化热设计具有指导意义。     

Thermally driven sensitive surface phonon polariton modes in thin-film SiC

The results of this work show that significant changes to the spectral properties of thermal emission may be accomplished by taking advantage of surface phonon polariton (SPP) modes that are very sensitive to small refractive index changes. Surface phonon polaritons are interface restricted wave modes that do not usually participate in thermal radiative energy exchange. In this work, the possibility of varying the spectral properties by using a thin-film surface active material, layered between dielectrics, is explored. Unlike surface gratings, the multilayered structure discussed in this work couples the surface modes into radiative modes using subtle changes in refractive index. The proposed multilayer effect is studied by first developing the SPP mode dispersion relation to identify the spectral location of the surface modes. The relationship between SPP coupling and refractive index change is then developed. The fluctuation-dissipation theorem and an impedance boundary condition is used to theoretically show how thermal radiation can excite SPP modes. Results are then presented that show how film thickness and substrate properties act to support SPP modes that are particularly sensitive to changes in refractive index and therefore offers opportunities for dramatic changes to the spectral properties.     

Size-dependent thermal buckling of heated nanowires with ends axially restrained

Nanowires (NWs) are being actively explored for applications as nanoscale building blocks of sensors, actuators and nanoelectromechanical systems (NEMS). Temperature changes can induce an axial force within NWs due to the thermal expansion and may lead to buckling. The thermal buckling behaviors of ends-axially-restrained nanowires, subjected to a uniform temperature rise, are studied based on Bernoulli–Euler beam theory including the surface thermoelastic effects. Besides the surface elastic modulus, the influences of surface thermal expansion coefficient are incorporated into the model presented herein to describe size-dependent thermoelastic behaviors of nanowires. The results show that the critical buckling temperature and postbuckling deflection are significantly affected by surface thermoelastic effects and the influences become more prominent as the thickness of nanowire decreases. The corresponding influences of the slenderness ratio are also discussed. This research is helpful not only in understanding the thermal buckling properties of nanowires but also in designing the nanowire-based sensor and thermal actuator.     

Thermally stimulated electromagnetic-field spectra in planar structures of complex composition: II. Radiative fields

It is demonstrated that the spectral composition of the radiative thermal fields of a Cd _x Zn_{1 ? x}Te solid solution film on a metallic substrate is sensitive to small changes in the impurity concentration and film thickness. The calculated spectral densities of the p- and s-polarized states of the radiative component of thermal fields in a plane-layered system are compared using the refraction additivity principle. The spectral densities are calculated at different values of the impurity concentration and film thickness.     

管内高温介质层流入口段中的热辐射作用

数值研究了高温介质密度随温度变化时,管内层流入口段耦合换热中的热辐射作用。采用离散坐标法、控制容积法耦合求解辐射传递方程、能量方程及N-S方程。考察了中等大小光学厚度下,热辐射作用对介质内速度分布、温度分布以及换热的影响。结果表明,即使在不大的光学厚度下,热辐射作用对管内高温介质层流入口段耦合换热的速度场与换热强度都有明显影响。     

Thickness alterations of CR-39 plastic detectors due to the heating influence: Basic theory and experimental results

Heating experiments were conducted on CR-39 polymer/plastic detector samples at temperatures between 50 and 175 °C for various time intervals from 5 to 210 min to investigate the thermal behavior of detector material. Mass and thickness of un-heated and heated polymer samples were measured. Three distinct regimes have been observed showing different degrees of changes in thickness and mass of annealed samples. The percent change of thickness was considerably higher than the mass change during heating. Thermodynamic concepts are used to explain the experimentally observed heating regimes. Role of the difference between free energies of lateral and fold surfaces in detector thickening during heating is discussed. Scanning electron microscopy (SEM) was carried out on un-heated and heated CR-39 samples to examine the surface alterations due to heating. Results are useful for researchers who employ track detectors for radiation measurements in nuclear reactors and cosmic rays. They are also interesting for researchers in related fields, like fission track dating, which consider the thermal history of track recording materials. Our quantitative data and SEM imaging suggests that structural changes, especially surface changes in CR-39 polymer are very important and need to be explored carefully through joint SEM and the Atomic Force Microscopy (AFM).     

基于有限元的平面光波导粘接热应力分析

基于有限元理论对阵列光纤和波导芯片粘接情况进行了建模与仿真,分析了在温度变化下不同粘接区域厚度的热应力和微位移的产生和分布,结果表明粘接界面的边缘区域对温度变化最敏感.根据光弹效应定性分析了粘接区域的应力双折射,并利用光束传播法计算了由此微位移所导致的光功率损耗,结果表明若以附加损耗小于0.15 dB的标准考察,则必须要求粘胶厚度的理论值在16 μm以内.总结了温度变化和在相同条件下不同粘胶厚度对平面光波导封装性能的影响规律.     

The study of ceramic-like oxide coatings on zirconium produced by plasma treatment in electrolytes

Ceramic-like oxide coatings on zirconium with a thickness of up to 300 μm produced by plasma treatment in an electrolyte demonstrate high thermal resistivity and low thermal conductivity during high-temperature testing in a plasmatron in a plasma flow. Data on the structure of coatings and its changes during thermal testing obtained using the methods of scanning electron microscopy, X-ray diffraction analysis, and nuclear backscattering spectrometry are discussed.     

Conductivité thermique de mousses cellulaires de carbone: Mesures par méthode flash et interprétation

This paper deals with the thermal diffusivity measurement of cellular carbon foams by the flash method. The thermal conductivity is obtained from the thermal diffusivity by using specific heat and density of carbon foam. These materials constitute non-homogeneous porous semitransparent media, hence the classic experimental set-up of the flash method must be adapted. A study is carried out in order to show the influence of the sample thickness, of the temperature, of the enclosed gas pressure and of the gas composition on the effective thermal conductivity. Identification functions are established in the monodimensional and bidimensional cases. Results indicate the dependence of the equivalent thermal conductivity upon the sample thickness. This result, attributed to radiative transfer, is confirmed by modelling. Radiative thermal conductivities are obtained with a Monte-Carlo code. Experimental and theoretical results are compared. It is demonstrated that the concept of effective conductivity is not relevant to these materials.     

Hydrophobic switching nature of methylcellulose ultra-thin films: thickness and annealing effects

We have studied the thermosensitive property of methylcellulose (MC) thin films supported on Si substrate by static sessile drop contact angle measurements, and their surface properties and thin film structure by x-ray reflectivity (XRR) and atomic force microscopy (AFM) techniques. From the static sessile drop contact angle measurements, the MC thin films showed the characteristic hydrophilic-to-hydrophobic transition at ～70?°C, which is the lower critical solution temperature of the bulk solution volume phase separation transition. For films with thickness d ≤ R(g), the onset of such a transition is affected by the film thickness while very thick films, d ? R(g), yielded higher contact angles. Annealing the MC thin films with thicknesses ～200 ? (near the radius of gyration, R(g), of the polymer) below the bulk glass transition temperature (T(g) ～ 195?° C) would not change the hydrophobic switch nature of the film but annealing 'at' and above the bulk T(g) would change its surface property. From surface topography images by AFM, there were no significant changes in either the roughness or the film texture before and after annealing. With XRR data, we were able to determine that such changes in the surface properties are highly correlated to the film thickness changes after the annealing process. This study, we believe, is the first to examine the thermal annealing affects on the thermal response function of a thermoresponsive polymer and is important for researching how to tailor the hydrophobic switching property of MC thin films for future sensing applications.     

Thermal conductivity of hydrogenated amorphous silicon

The thermal conductivity of amorphous silicon thin films is measured in one dimension steady state condition. The experimental method is based on heating the sample front surface and monitoring the temperatures at its two sides. The experiments were carried out in conditions ensuring one-direction heat flow from top to bottom throughout the sample thickness. Sputtered a-Si:H films prepared with different conditions are used in order to investigate the dependence of thermal conductivity on material properties (i.e. hydrogen content and microstructure). The results show that, firstly, amorphous silicon is a very bad thermal conductor material. Secondly, the disorder in the film network plays an important role in thermal conduction. The highly disordered film exhibits the lowest thermal conductivity.     

Thermal characterization of TiC<Subscript>x</Subscript>O<Subscript>y</Subscript> thin films

Thermal wave characterization of thin films used in industrial applications can be a useful tool, not just to get information on the films' thermal properties, but to get information on structural-physical parameters, e.g. crystalline structure and surface roughness, and on the film deposition conditions, since the thermal film properties are directly related to the structural-physical parameters and to the deposition conditions. Different sets of TiC_XO_Y thin films, deposited by reactive magnetron sputtering on steel, have been prepared, changing only one deposition parameter at a time. Here, the effect of the oxygen flow on the thermal film properties is studied. The thermal waves have been measured by modulated IR radiometry, and the phase lag data have been interpreted using an Extremum method by which the thermal coating parameters are directly related to the values and modulation frequencies of the relative extrema of the inverse calibrated thermal wave phases. Structural/morphological characterization has been done using X-ray diffraction (XRD) and atomic force microscopy (AFM). The characterization of the films also includes thickness, hardness, and electric resistivity measurements. The results obtained so far indicate strong correlations between the thermal diffusivity and conductivity, on the one hand, and the oxygen flow on the other hand.     

混合磁体超导线圈低温传输线冷屏的设计与分析

对于低温传输线,冷屏是其重要的结构。文中在低温传输线冷屏结构初步设计的基础上,对冷屏屏体材料进行比选,计算分析了低温传输线在80K温区的漏热量,并采用Solidworks软件,对不同厚度的低温传输线冷屏的温度分布进行模拟分析,完成冷屏的工程设计。     

Opposed-flow flame spread in microgravity-theoretical prediction of spread rate and flammability map

The spread rate formulas of de Ris in the thermal regime of opposed-flow flame spread are inarguably the most well-known formulas in the flame spread literature. Similar easy-to-use formulas are lacking in all other regimes of flame spread. This paper presents a simplified analysis leading to the development of closed-form expressions for spread rate for both thin and thick fuels in the microgravity regime of opposed-flow flame spread. The resulting formulas, expressed in terms of the thermal limit of spread rate and a radiation number that can be evaluated from the known parameters of the problem, are shown to reproduce the experimentally and numerically observed trends quite well at both limits of fuel thickness. These formulas are utilized to develop quantitative criterion to delineate thin and thick fuels in the microgravity and thermal regimes. The transition between the microgravity and thermal regimes is also explored. The flammability maps, derived from the spread rate expressions, are the first of their kind, establishing fuel thickness as one of the critical parameters.     

Amélioration du transfert thermique par un dépôt poreux sur la paroi d'un échangeur tubulaire

A study of flow regime and heat transfer in an annular heat exchanger partially filled with a porous medium is presented in this work. Constant heat flux and constant wall temperature boundary conditions on the inner cylinder are considered, while the outer cylinder is assumed adiabatic. The study is for both the thermal entry region and the thermally fully developed region. The flow in the porous region is modelled either by the Darcy-Brinkman equation for which an exact solution is developed or by the Darcy-Brinkman-Forchheimer equation in order to take into account inertial effects. For this case a numerical solution based on a control volume method is discussed. The results emphasize the effect of the porous layer attached to the inner cylinder on the thermal development length and heat transfer rate. It is shown that the porous substrate reduces the thermal entry length. When the effective thermal conductivity of the saturated porous medium is of the order of the fluid thermal conductivity, the local Nusselt does not vary monotonically with the thickness of the substrate. However, the use of a porous matrix always leads to an increase in the heat transfer rate provided its thermophysical properties and thickness are well chosen.     

Accurate determination of anisotropic thermal conductivity for ultrathin composite film

Highly anisotropic thermal conductive materials are of significance in thermal management applications. However, accurate determination of ultrathin composite thermal properties is a daunting task due to the tiny thermal conductance, severely hindering the further exploration of novel efficient thermal management materials, especially for size-confined environments. In this work, by utilizing a hybrid measuring method, we demonstrate an accurate determination of thermal properties for montmorillonite/reduced graphene oxide (MMT/rGO) composite film with a thickness range from 0.2 μ m to 2 μ m. The in-plane thermal conductivity measurement is realized by one-dimensional (1D) steady-state heat conduction approach while the cross-plane one is achieved via a modified 3ω method. As-measured thermal conductivity results are cross-checked with different methods and known materials, revealing the high measurement accuracy. A high anisotropic ratio of 60.5, independent of composite thickness, is observed in our measurements, further ensuring the negligible measurement error. Notably, our work develops an effective approach to the determination of ultrathin composite thermal conductivity, which may promote the development of ultrathin composites for potential thermal-related applications.     

Thermal experiment of silicon PIN detector

The experiment of this paper is the thermal test of the leakage current of silicon PIN detector.Raising temperature may cause the detector to increase leakage current,decrease depletion and increase noise.Three samples are used in the experiment.One (called △E) is the sample of 100 tan in thickness.The other two (called E1 and E2) are stacks of five detectors of 1000 μm in thickness.All of them are 12 mm in diameter.The experiment has been done for 21 hours and with power on continuously.The samples have undergone more than 60 ℃ for about one hour.They are not degenerated when back to the room temperature.The depletion rate is temperature and bias voltage related.With the circuit of the experiment and temperature at 35 ℃,△E is still depleted while E1 and E2 are 94.9% and 99.7% depleted respectively.The noises of the samples can be derived from the values at room temperature and the thermal dependence of the leakage currents.With the addition of the noise of the pre-amplifier,the noises of E1,E2 and AE at 24 ℃ are 16.4,16.3,and 10.5 keV (FWHM) respectively while at 35 ℃ are about 33.6,33.1,and 20.6 keV (FWHM) respectively.