温差发电器件导热系数

建立了半导体温差发电器件的基本模型，推导出器件等效导热系数的数学表达式，发现其与N型、P型半导体材料及两端陶瓷片的导热系数紧密相关，对半导体材料和陶瓷片的导热系数随温度的变化关系进行了实验研究并进行了数值拟合，绘制了器件等效导热系数与温度的曲线，得到的计算值与实验结果基本吻合。     

基于红外测温的内部缺陷尺寸、方位的计算方法研究

对具有内部缺陷的平板试件的传热建立了三维物理和数学模型,提出了通过表面红外测温确定内部缺陷尺寸、方位的计算方法。同时,分析了测量误差和缺陷导热系数对计算结果的影响。通过计算分析可以得到结论：本方法可以精确地确定内部缺陷的尺寸和方位,测量误差对内部缺陷估计的影响较小;在试件的导热系数远大于缺陷的导热系数时,缺陷导热系数的微小变化对缺陷尺寸和位置的计算没有明显的影响;适用于任何尺寸、方位可用有限个参数描述的内部缺陷的检测。     

TPS法测定泡沫铜/石蜡复合相变材料热物性

运用瞬态平面热源法(Transient Plane Source-TPS)对4种孔隙率的泡沫铜/石蜡复合材料热物性进行了测量。以10μm厚的镍金属按双螺旋线布置作为测量探头。泡沫铜材料孔隙率分别为ε=97.79%、ε=96.17%、ε=94.94%和ε=93.26%,经线切割加工后向内灌入液态石蜡,凝固后作为测试样品。在室温(25±1℃)和常压下对复合材料的等效导热系数、热容及热扩散率进行了测量。测试结果表明:复合材料导热系数和热扩散率因泡沫铜的加入而大幅提高,在孔隙率ε=93.26%时,等效导热系数已达到单纯石蜡的25倍,而复合材料等效热容则由于铜金属加入的绝对量较少相对原石蜡热容变化较小。以比例加成的方法对泡沫铜/石蜡复合材料的等效热容进行了计算,并利用实验数据拟合了其等效导热系数的计算公式,运用这些公式对复合材料物性的计算结果与实验结果非常吻合。     

新浇筑混凝土热学参数现场试验与分析

寒冷地区自然入仓情况下混凝土浇筑温度难以得到保障,高拱坝需要较好的完整性才能保障结构的安全,不建议长间歇,由此需要准确地计算分析寒冷地区极端条件下的浇筑温度保障措施。由于新鲜混凝土自由水分含量与老混凝土存在较大区别,因此新浇筑混凝土表面等效热交换系数、导热系数、导温系数与老混凝土也可能存在较大差别,需要进行试验确定。因此,针对新浇筑混凝土布置试验,对距离坯层表面不同位置混凝土温度进行监测,提出相应的参数反演方法,对混凝土导热系数、导温系数和表面等效热交换系数进行反演分析。结果表明,新浇筑混凝土表面等效热交换系数、导热系数、导温系数与老混凝土存在较大差别,导热系数和导温系数为老混凝土的1.67倍,裸露时新浇筑混凝土表面等效热交换系数则为老混凝土的7.78倍。这些差异造成的计算误差足以影响施工措施的制定。该试验结果可以为坯层浇筑期间混凝土温度变化计算提供参考。     

微孔硅酸钙的有效导热系数和最佳使用密度

利用等效热阻模型,考虑辐射传热影响,对硬硅钙石型微孔硅酸钙绝热材料的有效导热系数进行了预测,给出了计算公式,探讨了不同使用温度下微孔硅酸钙绝热材料的最佳使用密度.分析表明,模型计算值与实验值吻合好,有效导热系数预测模型可精确预测其绝热性能并指导绝热设计施工.     

Review on effective thermal conductivity of bubble type porous media

多孔介质内部结构中发生的质量,动量,能量的传递是众多自然现象和生产,生活领域中发生的基本过程.有关多孔介质中的传热问题涉及许多科学领域,早就引起人们的广泛关注,研究人员也对其进行了长期的研究.等效导热系数方法即将多孔介质视为一种连续介质,将实际多孔介质中固体骨架与各种流体的传热模式(导热,对流,辐射)折合成一个综合的传热问题.此方法已成为研究多孔介质内部传热问题最常用的方法.最近一二十年,泡沫型多孔介质(如泡沫金属,泡沫碳等)的出现引起人们广泛的关注.本文针对此种新型多孔介质等效导热系数的研究做了综述,介绍了3种常用的研究方法,分别是实验测试法,理论推导法及数值模拟法,探讨了各种研究方法存在的问题.实验测试法准确性高,但每种传热模式对等效导热系数的影响很难确定,且成本高;理论推导法虽然物理意义明确,适用性广,但与实测结果有较大的偏差,且有些方法还需与实验相结合;数值模拟法建模较复杂,但模拟结果与实验数据较接近.     

大型燃气轮机透平第一级静叶表面温度分布的计算方法

利用附加源项法计算叶片外表面换热系数及温度分布,编制叶片内部冷却计算程序及壁面导热程序,应用该程序计算了某大型燃气轮机第一级静叶表面温度分布,对燃气涡轮叶片先进的内外部冷却系统设计方法的消化吸收奠定了基础。     

纳米流体稳定性及其导热性能研究

为了探究影响纳米流体稳定性和导热系数的因素,采用一步法和两步法分别制备了SiO_2-EG/DW(50∶50)纳米流体和SiO_2-EG纳米流体,探讨团聚体等效直径对纳米流体稳定性的影响。基于瞬态热线法的原理,测量一步法纳米流体的导热系数,分析温度和纳米颗粒质量分数对其导热系数的影响。结果表明:相比一步法制备的纳米流体,两步法纳米流体内团聚体的沉降速度增加了10~3倍,团聚体等效直径对纳米流体稳定性具有关键性的影响。纳米流体导热系数与温度和纳米颗粒质量分数呈线性正相关,纳米流体质量分数为15%时,80℃的样品导热系数相比40℃时提高了5.2%;60℃时,质量分数6%的纳米流体导热系数相比基液提高了6.4%;质量分数增加到15%时,导热系数相比基液提高了15.8%。     

ISP工艺中卷取箱内板卷导热数学模型的研究

依据ISP工艺中卷取箱内板带的表面特性、板带厚度和板间接触压力对板卷径向热量的传递有较大影响,建立了能真实反映该影响因素的板带间径向等效导热系数计算模型,并建立了适用于求解为非连续介质的板卷导热数学模型。通过对模型的模拟求解,计算分析了板卷热过程,板卷最大温差为12℃,满足轧制工艺的要求,并为计算分析箱内热过程提供理论依据。     

孔隙率与含水率对砂质土样导热系数的影响

鉴于研究岩土体导热系数的变化规律及影响因素,对岩土的导热理论和工程实践的现实意义,利用热探针测定了不同孔隙率和含水率条件下的砂质土样导热系数,分析其变化规律,并用1stOpt软件得到孔隙率、含水率与导热系数的拟合公式。计算结果与试验结果表明,导热系数随孔隙率的增加而减小,随含水率的增加而增大,且在一定含水率下,导热系数随孔隙率的增加呈线性减小,孔隙率为0.468~0.511时,导热系数降幅为20.19%;在一定孔隙率下,导热系数随含水率的增加呈非线性增长,含水率0~10%时,导热系数增幅为338.38%,含水率10%~15%时,导热系数的增幅为8.83%。     

Radiative properties and heat transfer characteristics of fiber-loaded silica aerogel composites for thermal insulation

The radiative properties and heat transfer in fiber-loaded silica aerogel composites were investigated using modified anomalous diffraction theory in a combined heat conduction and radiation model. The randomly parameterized 2-D fiber distribution was generated to simulate a very realistic material structure. The finite volume method was then used to solve a two flux radiation model and the steady-state energy equation to calculate the effective thermal conductivity of the composite. The numerical results provide theoretic guidelines for material designs with optimum parameters, such as the inclination angle, diameter and length-to-diameter ratio of the fibers. The results show that the fiber extinction coefficient increases as the fiber length-to-diameter ratio is reduced or the fiber inclination angle is increased. The effective thermal conductivity of the fiber-loaded aerogel can be reduced by reducing the fiber length-to-diameter ratio and the inclination angle and by moderately increasing the fiber volume fraction. The 4–6 μm diameter silicon fibers are optimum for high-temperature thermal insulation.     

管道保温计算数学模型研究

采用有限差分法和焓降法相结合的方法数值模拟三维方管保温温度场,研究提高保温计算精度的途径和方法。研究结果表明：管内空气出口温度测试结果与考虑保温层热导率随温度变化及管内壁传热热阻时的数值模拟结果误差〈2．1％;保温材料热导率随温度变化和管内壁传热热阻对短管管内介质出口温度的影响可以忽略;管长〉2．35km时管内介质出口温度计算要考虑保温层热导率随温度变化;忽略保温层热导率随温度变化的管外壁散热损失误差〉11％,表明管外壁散热损失和长管管内介质出口温度计算必须考虑保温层热导率随温度变化,但可忽略管内壁综合表面传热热阻。     

Insulation System Using High-Temperature Fibrous Insulation Materials

ABSTRACT

In this study, we performed a preliminary research on an insulated sandwich structure using high-temperature fibrous insulation materials. Two types of fibrous materials, Saffil alumina and KCC cerakwool insulation materials, were selected. A sandwich specimen was invented to test the heat-shielding performance of the fibrous materials which were sandwiched by an Inconel plate and a titanium plate. The insulated sandwich structure was heated to 800°C for 2,000 seconds. The temperature profiles of the back side of the titanium plate were measured to compare the heat-shielding performance of the fibrous insulation materials. The microstructure of insulation materials, such as the fiber diameter, fiber orientation, and the parent materials of the fiber, was studied to understand how those characteristics influence the radiative properties of the fiber. The difference in microstructural parameters caused a difference in thermal resistance in the fibrous materials. The Saffil alumina insulation had a better performance than KCC cerakwool insulation because of its small fiber diameter and in-plane fiber orientation. The experimental results confirmed the heat transfer simulation results for fibrous materials done by other researchers. In addition, the reusability of high-temperature fibrous insulation, one of the important issues in real applications, was tested.     

变导热系数时保温层经济厚度的计算

在变导热系数条件下,分别对平壁和管道保温层的经济厚度进行了分析和计算,给出了有关计算式．并把结果与常导热系数时保温层经济厚度的计算结果进行了比较,得到了有关结论,从而为工程上保温层的设计提供参考。     

Numerical prediction of effective thermal conductivity of ceramic fiber board using lattice Boltzmann method

Abstract

Application of the lattice Boltzmann method has been extended for the analysis of combined transient conduction and radiation heat transfer through highly porous fibrous insulation media. Firstly, LBM has been employed for the analysis of combined mode of transient conduction radiation heat transfer in a 2?D rectangular enclosure containing an absorbing, emitting and scattering medium and results are compared with already published ones. The results have been found in good accord for different values of radiation-conduction parameter, scattering albedo and south (hot) wall emissivity. Furthermore, the proposed LBM for the calculation of effective thermal conductivity of ceramic fiber board has been employed. A random-generation growth method for generating micro morphology of natural ceramic fiber board has been selected. The conductive, radiative and effective thermal conductivity has been numerically estimated using the present LBM. It is found that the predicted effective thermal conductivity for different values of fibrous bulk density is in good agreement with the experimental data.     

一种新型多层反射型保温结构材料

作者对多层反射型保温结构材料应用于不同场合时的保温性能进行了深入分析计算,并将此结构的技术经济性能与常规保温材料进行了比较,结果表明,此新型保温结构具有更优的综合技术经济性能。     

基于改进K-means算法的坝体保温效果时空聚类分区评价方法

在高寒地区修建混凝土拱坝,超低极端气温和超大年内温差等环境温度荷载是影响混凝土结构拉裂破坏的关键因素,因此分析结构内部温度变化规律,开展长期保温防裂措施的效果评价意义重大。为解决传统保温效果评价过程中温度场蕴含规律和模式复杂,难以量化对比的问题,提出了一种基于时空聚类数据挖掘的混凝土坝保温效果分区评价方法,即以多测点时空监测数据为输入,以改进的K-means聚类算法为分区手段,通过有效性函数自动确定聚类数,降低聚类分析结果对参数的依赖性,解决了保温效果评价分区时聚类数目难以确定的问题。实例应用表明,该方法可对大体积混凝土内部温度测值和规律进行有效分区,能充分反映合理实施保温措施和维护保温材料完好对结构运行的重要性。     

Thermal Insulation for a Pipe Using Phase Change Material

This research studies the effectiveness of phase change material (PCM) as a thermal insulation for a pipe. The proposed PCM insulation can be used for a pipe when the operating time is limited. The objective of using PCM is to utilize its latent heat from fusion to minimize heat loss from the pipe by absorbing and storing it to be discharged later to the pipe. The finite element method is employed to solve the problem, and both conduction and natural convection of liquid PCM are considered modes of heat transfer. The effectiveness of the PCM insulation is evaluated by comparing its thermal performance with insulation without phase change. Both time-dependent and time-independent boundary conditions are examined. For the time-independent case, the PCM insulation reduces the heat loss from the pipe for a significant amount of time if the Rayleigh number is low. For the time-dependent case, heat loss is effectively reduced with the PCM insulation for a significant amount of time. The high resolution capturing of the solid/liquid moving boundary and the details of flow structure are also presented.     

真空隔热油管传热性能研究

真空隔热油管是稠油注蒸汽开采的主要设施之一,其隔热性能直接影响热采效果,因此,分析隔热油管隔热层内部的传热过程,研究隔热层各种结构参数对隔热油管隔热性能的影响,对改善隔热油管隔热性能有重要的指导作用。本文在测试隔热油管视导热系数的实验模型基础上,建立了隔热层传热的物理及数学模型,计算得到不同结构参数下隔热油管的视导热系数;研究了玻璃丝布孔隙比、隔热层层数、支撑材料导热系数以及铝箔发射率对隔热油管隔热性能的影响,研究表明:隔热层层数宜选为4~6层之间;选用的铝箔发射率应在0.01~0.05之间;在缠绕玻璃丝布工艺中,尽量不要让玻璃丝布对角线方向受力,以确保较大的孔隙比;在隔热油管加工过程中,应尽量使玻璃丝布和铝箔保持干燥。     

Design of a Smart Thermal Insulation System

The present work aims to design a smart thermal insulation system. The smart system allows the passing of heat transfer in one direction while preventing its passing in the other direction. This system consists of two gaps separated by a thin movable partition. The two gaps have the same area and width. The partition has radiation emissivity very close to zero to exclude radiation heat transfer. The partition is free to move to either side depending on the driving force causing the motion. The first gap is filled with a fluid that has both high thermal conductivity and high thermal expansion properties, while the second gap is filled with a fluid that has very low thermal conductivity and very high thermal expansion properties. Each gap is connected by a tiny tube to its own small storage tank. Temperature and pressure sensors are used to provide signals to the programmable microcontroller in order to select and activate the desired insulation or conduction mode of the system.