瞬态热线法测量复合材料导热系数的方法

通过比较导热系数测试方法,结合非平面式薄片状复合材料试样结构特点,确定采用瞬态热线法测量复合材料的纵向和横向导热系数。简要介绍瞬态热线法测量原理,探讨复合材料试样与传感器的放置方式、试样外表面粗糙状况、测试重复性对导热系数测量结果的影响,得到复合材料纵向和横向导热系数。     

耐火浇注料的干燥机理

通过测定试样在干燥过程中的导热系数，有助于阐明试样干燥机理，圆柱形试样在恒速加热时所获得的数据表明，试样的表面和中心的温差ΔT与热扩散系数的倒数和试样直径的平方成正比。测定的导热系数受到试样的化学成分，强度和气孔率的影响。当试样的长度与直径之比小时，测定值和计算值之间的温差ΔT会因水蒸汽的散逸而趋于增大。如果试样的长度是试样直径的2．88倍，ΔT的计算值与由实验数据获得的ΔT值一致。但是，如果考虑到水蒸汽的扩散，ΔT的计算值和测定值的一致性就会变差。     

超薄玻璃导热系数测量方法及影响因素

针对超薄玻璃导热系数测量所面临的温度梯度小、易热击穿、透光性强等难题,根据热流法原理,创新性地提出了多层叠片法测量超薄玻璃导热系数,并探讨了试样叠加厚度、加载压力、冷热极温差及导热硅脂对导热系数测量结果的影响.结果表明,当多层叠片试样厚度大于2.0 mm,加载压力在200～300 N之间,冷热极温差大于40℃,导热硅脂的导热系数大于1.5 W/(m·K)时,超薄玻璃导热系数的测量结果具有重复性和准确性.     

PE-XC材料导热系数的测量

文章采用瞬态热线法测试PE材料的导热系数,介绍了瞬态热线法的优势,并使用TC3000导热系数仪更加快捷、精确、高效的测试PE材料的导热系数。     

发射药导热系数测定的影响因素

利用热流法导热系数测定仪测量了不同实验条件下双基发射药的导热系数。分析了试样高度、真空度及硝化甘油含量对测量结果的影响。结果表明,发射药试样的高度较低时,或测试过程中的真空度越高,导热系数测定值较接近其真空值。硝化甘油含量对发射药的导热系数有明显影响。     

高炉炭砖的导热系数及其影响因素

对微孔、半石墨质和普通等级炭砖试样的导热系数与温度的关系做了回归分析,得到了导热系数和温度的关系表达式,由此,可以从室温导热系数预测高温导热系数。另外,还计算了导热系数与体积密度、显气孔率、透气度和原料等级之间的相关系数。结果表明,导热系数与透气度和原料等级有一定的相关关系,而与体积密度和显气孔率无关。     

测定材料高温导热系数的非稳态热线法

本文介绍材料高温导热系数的新型测定方法——非稳态热线法的原理,并研究使用国产仪器实现这种方法。结果表明,与国外仪器测定结果比较,符合良好。自行设计的加热炉设备为全耐火纤维炉衬、升降式结构、具有快速升温优良性能的节能电炉。用Mittenbuhler热线方法测定了四种低导热材料(聚胺酯硬质泡沫塑料、加气混凝土、轻质耐火浇注料以及轻质粘土砖),并且探索了测定高导热材料的平行热线法,测定了镁砖的导热系数,结果是令人满意的。     

碳酸二乙酯液相导热系数实验研究

为了给可替代清洁燃料的研究提供急需的基础物性数据,利用瞬态单热线法对温度区间为250～390K、压力区间为0.1～30MPa的碳酸二乙酯（DEC）的导热系数进行了实验研究。将实验数据拟合成关于温度和压力的导热系数方程,并分析了碳酸二乙酯导热系数与温度和压力的关系,方程采用完全三次多项式形式。结果表明,碳酸二乙酯的导热系数随温度升高而减小,随压力的升高而增大。实验数据与拟合方程计算值的最大偏差为-1.94%,绝对平均偏差为0.84%。另外,文中对改进的瞬态单热线测量导热系数实验装置以及所采用的测量系统进行了说明。     

非金属材料高温试样与热电偶的粘接

在铸造领域中,应用激光技术测量造型材料的热物理参数(比热、热扩散、导热系数)。测量时,温度信号靠粘接在试样背表面的热电偶直接输入到测量电路中。由于造型材料多数为强度较低、粒度较大的混合材料制成,且测试温度较高,因而给热电偶的粘接带来很大困难。在高温测试时,往往由     

甲基叔丁基醚饱和液相导热系数的实验研究

利用瞬态双热线法测量了243—403 K温度范围内饱和液相甲基叔丁基醚的导热系数,并将实验数据拟合为温度的关联式。实验数据与导热系数关联式计算结果的标准偏差和最大偏差分别为0.30%和0.89%,导热系数的合成标准不确定度小于±1.0%。甲基叔丁基醚导热系数的实验研究为正在进行的甲基叔丁基醚替代物筛选提供急需的基础热物性数据,对改进汽油、柴油质量,提高油品的环境友好性及推广使用清洁燃料方面有重要价值。     

Verification of Use of Peak Area for Quantitative Differential Thermal Analysis

The amount of reacting material in a sample investigated by differential thermal analysis can be determined from the peak area according to the Boersma equation, which accounts for heat flow through sample and thermocouple wires. This relation has been checked by experiment and it has been found that the use of different thermocouples for the calibrations may lead to variations of about 30%. The values obtained for heat transfer through a sample and thermocouple have been checked by comparison of computations and observation of base-line offset at the beginning of a run and exponential decay of the amount of heat dissipating out of a sample. It is shown that according to the equation it is not the total amount of reacting material that determines the peak area but merely the density of the material near the thermocouple. The sensitivity of the method for quantitative analysis is discussed in relation to the possible variations in the factors involved, namely, density and heat conductivity of the sample and heat transfer through the thermocouple.     

Numerical simulation of the effect of moisture on the thermal conductivity of porous ceramic materials

A simulation model to analyze the influence of moisture content on the thermal conductivity of porous ceramic materials is developed based on the numerical integration of the energy equation. The experimental technique employed for thermal conductivity measurements is the hot wire parallel technique. The numerical model proposed is checked by evaluating the thermal conductivity of a hypothetical porous ceramic material containing different concentrations of water in its structure. The behaviour of the thermal conductivity as a function of temperature, as predicted by the model proposed in this work was experimentally verified by the authors for an unfired refractory concrete. ©     

周期性边界条件下埋地热油管道传热影响因素的分析

建立土壤多孔介质模型,采用有限容积法对地表温度周期性波动条件下埋地热油管道非稳态传热过程进行数值计算。考虑了土壤中水相、气相迁移对管道传热的影响,对比分析了有、无保温层及保温层厚度、保温层导热系数、土壤导热系数、土壤含水率、管径、埋深等因素对埋地管道非稳态传热规律的影响。研究表明：保温层厚度、导热系数、土壤导热系数对埋地热油管道非稳态传热的影响相对较大。管径、埋深对管道传热的影响相对次之,且埋深对管道的影响冬季远要大于夏季,而土壤含水率对管道传热的影响相对较小。     

Thermal conductivity of high density polyethylene filled with graphite

The effect of the grade, the content, and the particle diameter on the thermal conductivity of high‐density polyethylene (HDPE) filled with graphite were studied. The results show an increase of thermal conductivity of the HDPE/graphite composite with increase of graphite content. The thermal conductivity of the HDPE filled with the expanded graphite was larger than that of the HDPE filled with the colloid graphite system. At the same volume content (7%), the thermal conductivity of the former was twice that of the latter one. The particle diameter of the graphite also affected the thermal conductivity of HDPE composites. With increase of the particle diameter of the colloid graphite, the thermal conductivity of the HDPE/graphite increased. However, when the particle diameter of colloid graphite was larger than 15 μm, the increase of thermal conductivity of HDPE/graphite changed by inches. Some models proposed to predict thermal conductivity of a composite in a two‐phase system could not be applied to HDPE filled graphite powder composites, such as Maxwell‐Eucken, Cheng and Vachon, Zieblend, Lewis and Nielsen, Agari and Uno equations. But, according to the increase of thermal conductivity of HDPE composites filled with the colloid graphite, we find that Ziebland equation is suitable except of some constant. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 3806–3810, 2006     

Thermal conductivity of glass fiber reinforced polypropylene under high pressure

The thermal conductivities of molten polypropylene and its glass fiber composites were measured by the compensating hot wire method. The testing apparatus empolyed was designed and tested in our laboratory. The measurements were carried out with temperatures ranging from 170 to 230°C and pressures from 1 to 2000 kg/cm². The results show that the thermal conductivity increases with increasing pressure and glass fiber content, but is almost independent of temperature. The thermal conductivity data were fitted satisfactorily with a proposed empirical equation for polypropylene and Lewies-Nielsen equation for the composites, respectively.     

Thermal properties of silicate esters

Fourteen dimethyldialkoxysilanes are prepared by reacting dimethyldichlorosilane with corresponding alcohols in the liquid phase. Their physicochemical properties are determined by standard methods and their tentative empirical formulae are elucidated. The thermal conductivity values of dimethyldialkoxysilanes are determined using a two slab guarded hot plate apparatus over a temperature range of 30–190°C. The thermal conductivity values of dimethyldialkoxysilanes calculated from empirical equations are found to vary from -14% to +19%. Because thermal conductivity is an important parameter in heat transfer calculations, and to minimise the deviation of the values, new equations involving easily measurable ultrasonic parameters have been formulated. The proposed equations have been tested for the series of dimethyldialkoxysilanes, tetraalkoxysilanes and polydimethylsiloxanes. The thermal conductivity values computed from the proposed equations are comparable with experimental thermal conductivity values. Further, an equation involving the calculation of thermal conductivity values at varying temperatures is also proposed.     

镀锡用赫尔槽试验装置

介绍了一种具有制冷功能的镀锡用赫尔槽装置,用该装置进行酸性镀锡试验时,可保持镀液温度恒定。该装置主要由镀槽、温度控制器、冷却水箱和冷却水泵组成。镀槽侧壁内设有热电制冷片,镀槽侧壁外环绕有冷却水管,冷却水管与冷却水箱连接。镀槽内还设有热电偶,热电偶先感知镀液温度,随后通过温度控制器控制冷却水箱和热电制冷片的通断来调节镀液的温度,使镀液温度恒定。     

Design of dedicated instrumentation for temperature distribution measurements in solid oxide fuel cells

A thermocouple was designed for temperature distribution measurements in solid oxide fuel cells. A theoretical model, based on mixed convective–radiative heat transfer was used to predict the thermocouple response. The proposed flat type thermocouple was shown to be a high sensitive, low error temperature sensor, capable of satisfying the requirements for solid oxide fuel cell thermal behaviour research. Thereafter, a purpose-built, thin, flat-type thermocouple has been used for temperature distribution measurements at the cathode side of a planar solid oxide fuel cell. High temperature conditions of 1223K have been tested. Beside temperature mapping, local hot spots have been easily located.     

TEMPERATURE MEASUREMENT ERROR BY RADIAL INSERTION OF THERMOCOUPLE IN THERMAL CONDUCTIVITY MEASURING DEVICE

To measure the temperature of the inner part of a material, an axially inserted thermocouple is often used. But, when the measurement by an axially inserted thermocouple is difficult, we must insert the thermocouple radially. In the case of radial insertion, a measuring error usually exists. To know the true temperature by the method of radial insertion of a thermocouple, we must conduct numerical calculations.

In this report, numerical calculations have been conducted for the temperature measuring error by radial insertion of thermocouple in a gas thermal conductivity measuring device.^2-5