松散煤体导热系数测量及影响因素分析研究

导热系数是物体本身的属性,在研究物体传热方面发挥着重要作用。为了得到特定煤种的导热系数及其影响因素,通过建立导热系数测量系统,并搭建相关的试验模型,使用热线法测量松散煤体导热系数,对导热系数测量结果进行了分析,并对导热系数的影响因素具体分析。结果表明:条件不同的松散煤体导热系数各不相同,导热系数随温度、含水量的升高而增大,随粒径、孔隙率以及热值的升高而减小。     

保温材料导热系数测定

各种保温材料及其制品,经常要测其耐火保温的热物理系数,其中最常用的就是导热系数。导热系数随材料配比、制造工艺、容重等因素而变。一般资料所载导热系数范围都较宽,不符合实际情况。所以,测定实际应用中材料的导热系数非常重要。导热系数不易准确测定的原因是单向导热热流难以控制,现介绍两种简易测定导热系数的方法。     

蒸汽发生器传热管导热系数的测量研究

蒸汽发生器传热管的导热系数是热工分析的重要输入参数之一,该导热系数很难通过理论计算或常规的试验装置直接获得。运用一维稳态导热的原理,针对传热管导热系数的测量,设计了一种圆管法导热系数测量装置。误差分析表明,该测量装置的精度控制在0.5%以内,满足工程的要求。利用该测量装置对4种蒸汽发生器用管进行测试,形成每种传热管导热系数随温度变化的拟合公式,通过该公式可求得每种合金管在使用温度范围的任意温度点的导热系数,为蒸汽发生器传热计算提供可靠的参数。     

国产690TT合金传热管导热系数的测定及其不确定度评定

导热系数是蒸汽发生器及传热管设计分析中的重要参数。应用激光闪射法对国产690TT合金的热扩散系数、比热容进行了测试,根据测试结果,得到导热系数,并对导热系数测试结果进行了不确定度评定,包括测量热扩散系数和比热容引入的不确定度分量的评定、由数值修约引入的不确定度分量的评定,以及合成不确定度和扩展不确定度的评定,最终得到不确定度评定报告。测试结果表明,100～350℃范围内,国产690TT合金传热管导热系数比ASME规范给出的N06690对应温度导热系数低约3%～10%,导热系数随温度变化满足线性关系λ=0.014T+11.54。     

线圈径向导热系数的实验测定和数值模拟

研究线圈的导热系数,对于线圈的浇注、固化等过程有着重要的指导作用.基于稳态传热法基本原理,通过自设实验装置对模拟线圈径向导热系数进行了测定和计算,得出线圈(不含导线)的导热系数λ为0.3W/(m·K),并用数值模拟验证了其正确性.     

基于饱和水恒温加热的平板导热系数测试装置性能分析北大核心CSCD

针对目前广泛使用的防护热板恒功率加热导热系数测试方法测试速度慢、难以满足高精度测量的不足,研制了一种基于饱和水恒温加热的导热系数测试装置,并用该测试装置及国内某型高精度中高温防护热板法导热系数测定仪对标准参比板的导热系数进行了对比测量,实验结果表明:在测试温度100~300℃范围内,该测试装置测得的导热系数精度1.5%,优于某型高精度中高温防护热板法导热系数测定仪测量精度3%,测试时间缩短60%以上,测试性能得到明显提升,此新型导热系数测试装置具有较好的推广应用前景。     

基于单片机的导热系数测试仪的系统设计浅谈

当今,计算机尤其是单片微型计算机(单片机)的飞速发展,为生产和科研带来了重大飞跃和巨大财富。单片机以其体积小、功能强大、价格便宜、应用广泛、市场占有率高等特点在计算机领域占有越来越重要的地位。我们根据国标的有关规定,研制导热系数测试仪的仪表部分,要求能够对绝缘材料的导热系数进行自动测试,包括高精度温度自动检测,护板温度控制,导热系数的计算等。本文涉及到的具体内容是:(1)根据导热系数的测定原理,实现热量的一维传递。(2)实现高精度的温度检测,要求达到GB要求,分辨出0.1℃。包括硬件选型的论证,硬件的连接及精度保证。     

自润滑活塞环导热特性研究

针对自润滑活塞环的摩擦热失效问题,通过建立二元填充体系导热系数计算有限元模型,研究了18组不同配方填充材料对自润滑活塞环导热系数的影响。研究结果表明复合材料导热系数与填料相含量成正比;填充颗粒形状及取向对复合材料导热系数影响较大,沿热流方向的颗粒特征长度越大,复合材料导热系数就越高。     

热管导热板当量导热系数研究

对用于高热流密度分布式点热源的散热的预埋热管铝基导热板进行了传热性能试验研究,结合模拟仿真,通过求解导热反问题的方法求得热管导热板的当量导热系数。研究结果表明,采用的热管导热板具有优良的热传导能力,当量导热系数随传输功率的增大而降低,当量导热系数范围为1 100～7 600 W/(m.K)。     

锂/二氧化硫电池稳态法导热系数试验研究

导热系数是描述物体热物理性能的主要指标。文中介绍了锂/二氧化硫电池的导热系数测试方法,在前期测试工作的基础上加入了热补偿部件、水冷散热系统等改进措施。对锂/二氧化硫电池进行了未放电和完全放电后电池的测试。测试结果表明：文中介绍的导热系数测试仪器测量结果可靠,精度较高;与未放电电池相比,完全放电后电池的导热系数明显减小。     

固体吸附制冷吸附床数值分析及强化传热技术

建立了固体吸附制冷吸附床的物理模型和数学模型,通过数值分析得到床层温度分布及其各点温度随时间的变化情况,并分析吸附剂的物性参数、换热流体流速、温度和床层初始温度参数变化对床层温度分布的影响.结果表明,吸附剂的物性参数对床层温度分布影响显著;换热流体流速、温度和床层初始温度对床层温度影响不大,但影响换热效率和传热速率.在径向上床层温度存在着较大的温度梯度,但在轴向上温度分布比较均匀.在吸附剂的物性参数中,导热系数影响最大,其次是密度和比热容.因此为了提高传热效率,应增大吸附剂的导热系数,选取具有较小密度和比热容的吸附剂.     

闭孔泡沫纯铝的导热性能

采用隔热测试仪研究了闭孔泡沫纯铝的孔隙率和孔径对其导热性能(导热系数)的影响.结果表明:闭孔泡沫纯铝的导热性能受传导、对流、辐射三者的综合影响;孔隙率为83.2%～91.0%的闭孔泡沫纯铝的导热系数随孔隙率的增大而减小,而孔径对导热系数的影响没有一定规律;在孔隙率为83.2%～91.0%、孔径为2.5～5.3 mm时,闭孔泡沫纯铝的导热系数在常温下为0.297～0.752 W/(m·K).     

Performance of synthetic oils in the hydrodynamic regime ‐ II. Generalisation

In Parti I the results of an extensive experimental investigation of the performance of environmentally adapted oils in the hydrodynamic regime were reported. Four oils were tested in a tilting‐pad thrust bearing for different combinations of load, shaft speed, and supply oil temperature. In this second part, details of a generalisation procedure are described. A number of parameters representing the physical properties of an oil, such as viscosity and viscosity‐temperature coefficient, are adopted. The influence of each of these parameters on minimum oil film thickness, maximum temperature rise, and bearing power loss is then analysed. It is shown that viscosity measured at the supply oil temperature is the most important parameter. The effects of the viscosity‐temperature coefficient and oil thermal conductivity are less pronounced and yet significant. It is also shown that it is not possible to select an optimum oil that yields maximised oil film thickness, minimised temperature rise, and minimised power loss at the same time.     

电子设备热设计中高效导热垫的选型方法

文中针对电子设备热设计中高效导热垫选型缺乏理论计算的现状,提出了基于导热垫厚度和导热系数计算的导热垫选型方法。该方法以热源与散热板的间隙尺寸链为基础,通过尺寸链公差和导热垫压缩量的关系,推导出导热垫厚度计算方法;通过自然对流散热理论,计算散热板的温度,再以单层平壁导热理论给出的导热系数与温差公式为基础,提出导热系数的计算方法,进而确定导热垫的型号。最后用实例详细介绍了电子设备热设计中导热垫的选型方法,并通过仿真验证了该方法的合理性。     

Determination of deposit thickness in natural gas cooler based on the measurements of gas cooling degree

An original method for estimating fouled deposit thickness on the inside surfaces of natural gas cooler tubes is presented. This method does not require opening and inspecting a cooler as it is based on the measurement of gas cooling degree, i.e. the gas temperature difference between the cooler inlet and discharge. The deposit layer on the internal heat transfer surfaces is of semi-liquid consistency and its thermal conductivity coefficient has not been investigated until now. This paper describes the experimental determination of the deposit thermal conductivity coefficient. This parameter enables determination of a cooler’s performance as a function of current deposit thickness. Practical application of the method is illustrated in the case of CH_R cooler working in the KS01 compressor station in Vel’ké Kapušany, Slovakia. For this type of cooler, a diagram for deposit thickness as a function of the gas cooling degree is presented.     

基于不平衡系数对地埋管热短路的评价与分析

在热响应试验的基础上,通过FLUENT建立单U型竖直地埋管系统的三维非稳态数值模型。引入热短路不平衡系数作为评价热短路现象强弱的指标,分析了回填土导热系数、管内流速、系统井深和运行方式对地埋管热短路现象的影响。模拟结果表明,回填材料导热系数和系统井深与热短路不平衡系数成正比;流速与热短路不平衡系数成反比,而且对热短路现象强弱影响最大;采用间歇运行可以提升系统换热效率,但不能缓解热短路现象。     

The effect of thermal conductivity and friction coefficient on the contact temperature of polyimide composites: Experimental and finite element simulation

In this work, the Finite Element Method is used to simulate and visualize the maximum contact temperature of polymer composites under ring-on-block tribolgical test. The simulated temperatures are in good agreement with the experimental results under all testing conditions. The error values between the experimental and simulated temperature are less than 10%. The contact temperature is decreased to nearly 72 °C just by reduction of the friction coefficient by 40%, which is about 18 times higher than the 40% increase of thermal conductivity. The results indicate that the friction coefficient plays a more important role in the contact temperature than the thermal conductivity.     

SiO2包裹纳米Cu粒子/环氧树脂复合材料及其在芯片封装领域的应用

为提高微电子封装材料的散热性能并保留其良好的电绝缘性能,以环氧树脂为基体,二氧化硅包裹纳米铜粒子(SiO2-Cu)为填料,采用机械混炼法制备了芯片封装用SiO2-Cu环氧树脂复合材料。采用SEM和TEM研究了SiO2-Cu纳米粒子在环氧树脂中的分散情况;研究了填料对复合材料导热系数、热膨胀系数(CTE)和力学性能的影响。结果表明:SiO2-Cu纳米粒子在环氧树脂中分散性良好;复合材料的导热系数随SiO2-Cu纳米粒子填充量的增加而增大,填充量(体积分数)超过25%时导热系数开始下降,SiO2-Cu纳米粒子适宜用量为总体积的25%;随着填料的增加,复合材料的CTE减小;当SiO2-Cu纳米粒子填充量为25%时,用于芯片封装材料时具有良好的抗冲击性能和较长的电迁移失效时间。     

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。     

Effect of functionally graded material on frictionally excited thermoelastic instability

Thermoelastic instability (TEI) is investigated focusing on the effect of functionally graded materials (FGM) where the FGM half plane slides against a homogeneous conducting or rigid non-conducting body at speed V. Results confirm analytically that there is maximum critical speeds occurring at a certain value of non-homogeneous parameter of FGM within a range of thermal conductivity, which was reported previously in the simulation model [Y.H. Jang, S.-H. Ahn, Frictionally-excited thermoelastic instability on functionally graded material, Wear 262 (2007) 1102–1112]. The effect of non-homogeneous parameters for FGM on thermoelastic instability shows that the non-homogeneous parameters of the elastic modulus and thermal expansion coefficient are strong influential factors. It is also found that when the non-homogeneous parameters of FGM range between two positive bounded values, unconditionally stable behavior is shown for a range of thermal conductivity.