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     

Correlations of Thermal Contact Conductance for Nominally Flat Metallic Contact in Vacuum

Heat transfer experiments were performed in a vacuum environment (0.045 torr) to find out solid spot contact conductance for nominally flat surfaces of copper, brass, and stainless steel with different surface roughnesses (1–5 μm) for each specimen under several load conditions (0.6–15 MPa). A precise estimation of thermal contact conductance for the interface of sets of similar materials has been carried out employing a steady-state approach. Results have been compared with the theoretical models based on plastic and elastic deformation based theories for nominally flat metallic contacts. It has been demonstrated that a dire need exists to develop an experimentally based generalized correlation of thermal contact conductance for nominally flat metallic contacts that can be used by design engineers as well as for research purposes in different fields. Along with the generalized correlation, a specific correlation for thermal contact conductance has been proposed for three sets of materials. The thermal contact conductance of each set of materials presented in the form of specific correlations for different roughness parameters is one of the most important outcomes of the present research.     

Experimental Study of Thermal Contact Resistance in Hardened Bearing Surfaces

The significance of thermal contact resistance on a bearing steel surface and its application in the analysis of heat flow through layers has been discussed. In the present study, it is considered that the surface roughness and the interface temperature vary to estimate effective thermal conductivity of the bearing model under steady-state and insulated conditions. Surface roughness was considered in the range of 2.37–7.16 μm, and thermal contact properties of the hardened steels were studied under dry and lubricated conditions. These results help to predict temperature distributions of the bearing using SolidWorks2011 (Dassault Systèmes SolidWorks Concord, MA, USA).     

接触角与液固界面热阻关系的分子动力学模拟

本文利用分子动力学方法模拟了液体在固体表面的 接触角及液固界面热阻, 并探讨了二者之间的关系. 通过分别改变液固结合强度和固体的原子性质来分析接触角和界面热阻的关系及变化趋势. 模拟结果显示增强液固间相互作用时, 接触角减小的同时界面热阻也随之单调减小; 而改变固体原子间结合强度和原子质量时, 接触角几乎保持不变, 但界面热阻显著改变. 固体原子间结合强度和原子质量影响界面热阻的原因是其改变了固体的振动频率分布, 导致液固原子间的振动耦合程度发生变化. 本文的结果表明界面热阻不仅与由接触角所表征的液固结合强度有关, 还与液固原子间的振动耦合程度有关. 接触角与界面热阻间不存在单值的对应关系, 不能单一地将接触角作为液固界面热阻的评价标准. 关键词： 液固界面 接触角 界面热阻 分子动力学模拟     

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.     

表面粗糙度对薄膜面向热导率的影响研究

通过求解声子辐射输运方程(EPRT)计算得到了薄膜的面向晶格热导率.在薄膜界面采用与声子波长相关的镜反射率模型,考虑了薄膜的厚度、温度和表面粗糙度等对其热导率的影响.结果表明,界面粗糙度对薄膜热导率的影响很大.减小界面粗糙度,会使得薄膜热导率大大增加.另外,薄膜厚度减小使得热导率峰值对应的温度增加.     

气凝胶单元体模型结构参数与等效热导率研究

本文基于二氧化硅气凝胶的微观结构特点,运用小球构成的立方阵列单元体纳米孔隙模型,结合固相导热和气相传热的尺度效应,计算得到了一定尺寸范围内材料的等效热导率,分析了材料密度、颗粒接触面积、材料比表面积等因素对材料等效热导率的影响。结果表明:存在使气凝胶等效热导率取最小值的最佳密度;在一定的密度范围内,孔隙率一定时,材料的等效热导率随比表面积的增大而减小;颗粒间接触界面直径与固相颗粒直径的比值越大,等效热导率越低,在该比值一定时,气孔的尺寸和分布成为影响模型等效热导率的关键因素。     

Experimental analysis of interface contact behavior using a novel image processing method

The spatial and temporal evolution of real contact area of contact interface with loads is a challenge. It is generally believed that there is a positive linear correlation between real contact area and normal load. However, with the development of measuring instruments and methods, some scholars have found that the growth rate of real contact area will slow down with the increase of normal load under certain conditions, such as large-scale interface contact with small roughness surface,which is called the nonlinear phenomenon of real contact area. At present, there is no unified conclusion on the explanation of this phenomenon. We set up an experimental apparatus based on the total reflection principle to verify this phenomenon and analyze its mechanism. An image processing method is proposed, which can be used to quantitative analysis micro contact behaviors on macro contact phenomenon. The weighted superposition method is used to identify micro contact spots, to calculate the real contact area, and the color superimposed image is used to identify micro contact behaviors.Based on this method, the spatiotemporal evolution mechanism of real contact area nonlinear phenomena is quantitatively analyzed. Furthermore, the influence of nonlinear phenomenon of real contact area on the whole loading and unloading process is analyzed experimentally. It is found that the effects of fluid between contact interface, normal load amplitude and initial contact state on contact behavior cannot be ignored in large-scale interface contact with small roughness surface.     

测定双层组合介质接触热阻

 当激光辐照双层固体组合介质的外表面时，在变物性及界面接触热阻不变的条件下，数值计算了介质内部温度场时空分布。实验测定该双层介质背面对应点的温度曲线，与数值计算的结果进行比较，从而确定介质界面间的接触热阻。     

A review on the effects of different parameters on contact heat transfer

In this paper, a complete literature review for thermal contact between fixed and periodic contacting surfaces and also thermal contact between exhaust valve and its seat in internal combustion engines is presented. Furthermore, the effects of some parameters such as contact pressure, contact frequency, the contacting surfaces topography and roughness, curvature radius of surfaces, loading–unloading cycles, gas gap conductance and properties, interface interstitial material properties, surfaces coatings and surfaces temperature on thermal contact conductance are investigated according to the papers presented in this field. The reviewed papers and studies included theoretical/ analytical/experimental and numerical studies on thermal contact conductance. In studying the thermal contact between exhaust valve and its seat, most of the experimental studies include two axial rods as the exhaust valve, and seat and the one ends of both rods are considered at constant and different temperatures. In the experimental methods, the temperatures of multi-points on rods are measured in different conditions, and thermal contact conductance is estimated using them.     

接触热阻理论模型的简化

本文分析了机械加工表面的粗糙度曲线形貌参数的统计特征.基于单点接触热导理论模型和弹性形变理论模型,建立了总的接触热阻与总的压力之间的一般关系,简化了接触热导的计算模型,并与现有的计算方法进行了对比.研究结果表明,简化模型具有很好的精度.     

固-固接触界面热传输研究

提出了固-固接触热传导接触界面层的概念并进行了解释。接触界面层的建立,把微结构的散射和辐射热传导机制统一于界面层内,通过对接触界面层、接触界面层的厚度和界面层热导率等的讨论,初步揭示了接触界面层热传导的机制。在界面层微观传热的机制上,建立了接触界面层热阻预测模型,并把模型预测接触热阻值与扩散失陪模型(DMM)以及实验值进行了比较。结果显示该模型克服了DMM模型预测值偏低的缺陷,这些将对接触界面层的微尺度热分析有一定的帮助。     

纳米结构影响沸腾换热特性的分子动力学模拟

采用分子动力学方法模拟液体在纳米结构表面的快速沸腾过程.主要研究了纳米结构表面粗糙度以及栏栅形和棋盘形两种排列方式对液体快速沸腾过程以及换热特性的影响.研究结果表明,随着纳米结构表面粗糙度的增加,栏栅形和棋盘形纳米结构表面液体沸腾起始时间均提前.当栏栅形和棋盘形纳米结构表面粗糙度相同时,棋盘形纳米结构表面会进一步缩短液体沸腾起始时间.形成这种现象的原因是纳米结构表面粗糙度的增加,增加了固液接触面积,提高了初始时刻热通量,减小了固液界面热阻,导致表面附近液体动能增大,增大了液体高度方向的温度梯度,有利于液体发生沸腾.当纳米结构表面粗糙度相同时,棋盘形纳米结构表面具有较小的界面热阻,从而缩短了沸腾所需要的时间.     

固-固接触热传导的声子传递系数

声子传递系数是影响低温接触界面热传导的重要因素,文中对中间低温(20K~200K)接触传导模型的声子传递系数进行了讨论,分析了接触界面温差、弹性镜面传递和散射传递下的声子传递系数;还讨论了热流方向对声子传递系数的影响;指出了声失配理论预测值与实验值间存在差别的可能原因。该讨论对分析接触热传导有一定意义。     

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。     

用分形理论研究低温条件下Al-Al界面间的接触导热现象

界面形貌是固体界面间接触导热的最主要影响因素 ,传统的形貌表征参数与仪器的分辨率和取样长度密切相关 ,因而基于这些参数的常规接触导热模型显然是尺度相关的。分形网络模型利用粗糙表面处处连续却不可微的分形特征 ,采用与尺度无关的分形参数 ,揭示了接触导热的本质 ,为准确预测接触热导开辟了一条新的途径。实验测定了粗糙表面的分形参数和低温条件下 Al50 52 - Al50 52界面间的接触热导 ,将接触热导的实验值与分形网络模型的预测结果进行了比较 ,并就接触热导与压力、分形参数和温度之间的关系进行了分析 ,指出分形网络模型的预测精度与分形参数相关联。     

低温下粗糙表面接触间隙气体热导的研究

对低温非真空环境下粗糙接触界面间隙中介质气体的传热进行了理论分析．依据克努森数的大小,建立了不同传热区域的间隙气体热导理论模型．并对影响接触界面间隙热导的克努森数、普朗特数、热导率、适应系数、压力等参数进行了分析,为实际情况下接触界面的传热提供了理论基础．而且通过实验证明了在界面接触压力较小的情况下,即使对于硬度较小导热性能好的接触固体,间隙气体的导热量仍大于通过实际接触点的导热量．     

Effect of phonon scattering by surface roughness on the universal thermal conductance

The effect of phonon scattering by surface roughness on the thermal conductance in mesoscopic systems at low temperatures is calculated using full elasticity theory. The low frequency behavior of the scattering shows novel power law dependences arising from the unusual properties of the elastic modes. This leads to new predictions for the low temperature depression of the thermal conductance below the ideal universal value. Comparison with the data of Schwab et al. [Nature (London) 404, 974 (2000)] suggests that surface roughness on a scale of the width of the thermal pathway is important in the experiment.     

Modelling of thermal conductance during microthermal machining with scanning thermal microscope using an inverse methodology

In this study, a general methodology for determining the thermal conductance between the probe tip and the workpiece during microthermal machining using Scanning Thermal Microscopy (SThM) has been proposed. The processing system was considered as an inverse heat conduction problem with an unknown thermal conductance. Temperature dependence for the material properties and thermal conductance in the analysis of heat conduction is taken into account. The conjugate gradient method is used to solve the inverse problem. Furthermore, this methodology can also be applied to estimate the thermal contact conductance in other transient heat conduction problems, like metal casting process, injection molding process, and electronic circuit systems.     

表面黏附导致的接触行为转变

应用大规模分子动力学方法, 模拟了具有不同原子级粗糙形貌的两种刚性球形探头与弹性平面基体的黏附接触行为. 研究了载荷与真实接触面积、接触界面排斥力与真实接触面积, 以及黏附力与真实接触面积之间的关系. 分子模拟得到的载荷与真实接触面积的关系, 与连续力学接触理论预测很好地定性一致. 无论是原子级光滑探头还是粗糙探头, 黏附接触下的排斥力与真实接触面积的关系, 都与无黏附接触时的规律相一致, 即黏附力对接触行为的影响作用, 可以等效为附加在真实外载荷基础上的虚拟载荷, 将对黏附接触行为的分析转变为无黏附接触分析. 两种探头的黏附力随真实接触面积都呈幂函数形式的增长, 但是, 原子级光滑探头的幂指数大于1, 而原子级粗糙探头的幂指数小于1. 关键词： 接触行为 表面黏附 分子动力学模拟