热针法瞬态测量热物性研究

该文从一维圆柱面传热模型的定解问题出发,分析热线法测量材料热导率的局限性,推证热针法瞬态测量材料热物性的基本原理、热扩散系数和热导率的计算公式,设计和开发针式热物性瞬态测量的软硬件,试制SHT-C针式热物性瞬态测量仪,实现对材料热物性的瞬态测量,并实测证明该测量仪有很好的重复性和实用价值.     

具有线性反馈的热导气体分析仪电桥电路

人们常用热导气体分析仪(即热导率检测器)来测量二元或准二元混合气的浓度(Daynes，1933年；jessop，1966年；Warncke，1980年)。此法的依据是气体具有导热的能力和混合气热导率是其成份浓度的函数。     

供应信息

<正>贝克曼库尔特商贸(中国)有限公司产品名称:贝克曼库尔特SA3100比表面积及孔径分析仪产品简介:SA3100比表面积及孔径分析仪采用当今被公认为最准确的气体吸附技术测量固体的比表面积与多孔特性,利用固体表面对气体分子产生吸附作用的原理,结合BET、LANGMUIR等模拟理论,对多孔材料的比表面积、孔径分布进行高精度分析。SA3100比表面积及孔径分析仪是当今功能齐全、分析精确高而     

石蜡/纳米铝在蓄能换热器中的热性能研究

选用螺旋管换热器作为蓄能装置,研究了石蜡类相变材料RT6在螺旋盘管中的蓄能过程,针对其导热系数低,蓄能时间长的缺点,采用纳米铝粉制备复合材料强化换热,利用计算流体动力学数值模拟软件(Fluent)对传热过程进行数值模拟,分析了RT6在自然对流条件下以及强化后的相变过程、纳米流体石蜡/纳米铝的热物性,与实验值进行对比,优化设计方案。     

磁场中磁性纳米流体热导率的研究

进行了提高磁场中含四氧化三铁(Fe3O4)纳米磁性颗粒机油(磁性纳米流体)热导率的研究。在有或无超声波辅助的条件下,采用共沉淀法合成了不同粒度的Fe3O4磁性纳米颗粒,采用一种热常数分析仪对该磁性纳米流体的热导率进行了测定,探讨了纳米磁性颗粒粒度、体积分数以及背景磁场对磁性纳米流体导热性能的影响。实验结果表明,在外磁场中,磁性纳米流体所含Fe3O4纳米颗粒的体积分数越大,磁性颗粒粒度越小,磁性纳米流体的热导率越高;当磁场方向平行于温度梯度时更有利于提高磁性纳米流体的热导率。     

水基碳管纳米流体制备及其热物性实验研究

采用添加表面活性剂阿拉伯胶(GA)的方法制备碳管纳米流体,并对不同长径比以及经球磨、酸化处理的碳管纳米流体热物性进行了研究。通过透射电子显微镜和扫描电子显微镜观察表明,所制备的碳管纳米流体具有很好的分散性和稳定性。碳管纳米流体热物性实验结果表明,碳管的比表面积和直线度是碳管长径比影响纳米流体热导率的主要因素。碳管经球磨处理时,随球磨时间延长,碳管长径比和直线度先后对纳米流体热导率提升起主导作用,碳管酸化处理后,改善了其分散性并降低了接触热阻,这是纳米流体热导率提高的主要因素。但随着碳管酸化时间的延长,碳管长径比起主导作用。碳管纳米流体的粘度主要受碳管分散性和直线度的影响。     

磁性回热材料低温热导率测量及Matlab数据库建模

为了建立磁性回热材料低温热物性参数数据库,准确分析深低温高频脉冲管制冷机的工作机理,以液氦温区GM制冷机为冷源,采用稳态轴向热流法测量了Er3Ni、Er0.5Pr0.5、Gd2O2S(GOS)、Ho Cu2等磁性回热材料在低温下的热导率,并利用液氦温区脉冲管制冷机对测量结果进行分析和验证。基于Matlab建模,创建了一套应用于深低温系统磁性回热材料的热物性数据库,对于深低温的获取及系统效能优化具有理论意义。     

一种测量低温导热系数 电阻率和热电势的装置

低温下固体材料的导热系数、电阻率和热电势是三个重要的物性参数。精确而快速测量上述参数一直是人们所关心的问题。本文介绍一种能测量低温下固体材料(特别是金属材料)的导热系数、电阻率和热电势的装置。该装置主要由低温量热器和电子测量控制系统两大部分组成,包括试样、测温夹具、热汇和试样加热器、可控温热补偿屏、真空腔、内杜瓦及计算机数据采集与打印系统等。试样的长度可变化(30～80mm),截面积也可变化(0.1～6cm~2)。它可以测量零点几到数千W/m·K不同导热系数的材料。只要在内杜瓦中充装LN_2、LH_2、LHe,就可以测量从这些液化气体温度到室温范围的上述三个物性     

TPS法导热系数测量的仿真分析

通过对Hot Disk热物性分析仪的探头建立完善的二维仿真模型,将三维实体简化,数值模拟测量TPS(瞬态平面热源)法导热系数,再使用模拟温升进行计算。将模拟计算值与Hot Disk不锈钢标样导热系数测量值进行对比,证明模拟计算结果符合TPS法原理准确度要求。并对铜及气凝胶的导热系数测量进行模拟分析,考察实际测量过程中可能存在的各种因素如空气间隙、空气对流及样品微小形变对测量结果的影响。结果表明:实际测量时应保证样品与探头紧密接触以减小空气间隙,维持测试环境稳定以降低空气对流,而样品的微小形变对测量影响可忽略不计。     

柔性基底喷墨打印墨滴数值模拟与实验

目的研究喷墨过程中流体物性参数对喷墨质量的影响。方法采用数值模拟方法,基于流体体积法建立仿真模型,以不同粘度和表面张力的流体为研究对象,通过分析墨滴形成及铺展过程的形态变化,探索流体的物性参数(粘度、表面张力)对于墨滴成形过程的影响,得出高质量喷墨印刷的流体物性参数范围,并在柔性基底上印刷UHF(超高频)天线来验证模拟结果的可靠性。结果使用无量纲常数Z表征流体的可喷印性能,数值模拟结果表明表面张力为40 m N/m,粘度为10 Pa·s的墨水能达到良好的喷印状态。结论通过实验观测墨水的喷射过程,与模拟结果对比具有较高的重合度,数值模拟结果可以较准确地预测墨水印刷质量,经测量可知印制天线满足使用要求。     

Estimation of Parameters of Universal Distribution of Moments of Failure of Products

A method is proposed for estimating the parameters of a mixture of exponential and Weibull distributions for which the accuracy of preliminary estimates obtained by graphical analysis is refined in accordance with the criterion of maximum likelihood. The efficiency of the proposed method is supported by the results of statistical modeling.     

Evaluation of optical properties of highly scattering media by moments of distributions of times of flight of photons

A novel method for the determination of the optical properties of tissue from time-domain measurements is presented. The data analysis is based on the evaluation of the first moment and the second centralized moment, i.e., the mean time of flight and the variance of the measured distribution of times of flight (DTOF) of photons injected by short (picosecond) laser pulses. Analytical expressions are derived for calculation of absorption and of reduced scattering coefficients from these moments by application of diffusion theory for infinite and semi-infinite homogeneous media. The proposed method was tested on experimental data obtained with phantoms, and results for absorption and reduced scattering coefficients obtained by the proposed method are compared with those obtained by fitting of the same data with analytical solutions of the diffusion equation. Furthermore, the accuracy of the moment analysis was investigated for a range of integration limits of the DTOF. The moment analysis may serve as a comparatively fast method for evaluating optical properties with sufficient accuracy and can be used, e.g., for on-line monitoring of optical properties of biological tissue.     

Estimation of potentialities of methods of summation of direct measurement errors

Conventional methods for summation of direct measurement errors are considered. Conditions under which these methods provide consistent results are stated. It is proposed to utilize for characteristic of the total error, its interval estimator or the half-sum of the value obtained by adding up its arithmetic and geometric random errors.Translated from Izmeritel'naya Tekhnika, No. 4, pp. 10–12, April, 1995.     

空压机轴承箱蜗壳温度探头油封改造

由于空压机进气侧轴承箱蜗壳温度探头密封效果不好,使空压机及其后续管道受到油污染。后将温度探头的O形圈密封改为骨架油封,杜绝了轴承箱漏油问题。文章简介空压机的结构和技术参数,详细介绍了骨架油封的制作和优点。     

Characteristics of mechanical properties of materials in studies of conditions of attainment of marginal states

It is shown that conditions of attainment of marginal states in the material of structural components are formulated on the basis of analysis of force and deformation criteria of formation and development of destruction. The parameters of these criteria are data on types of structural materials, standard and special characteristics of their mechanical properties, structural forms of considered elements of the equipment, and their operating stress loading. In this case, the construction of a system of state equations for describing interrelation of current damage, external actions, and responses to them is based on the concept of calculating variations in properties of materials at all stages of the design life cycle.     

Determination of parameters of microstructural inhomogeneity of deformation of metals by the method of modeling

The article suggests a method of evaluating the microstructural inhomogeneity of deformation of metals by modeling. The method includes the measurement of deformations of metal according to meshes of a dividing grid with small base and the calculation of the distribution parameters of microdeformations in model representation. It is shown that the modeling method makes it possible objectively to evaluate the microinhomogeneity of deformation of metals independently of the chosen mesh size of the dividing grid. New structural characteristics are introduced: the base and wave of variation expressing the degree of crumbling or amalgamation of metal grains by inhomogeneity of deformation.Translated from Problemy Prochnosti, No. 7, pp. 40–44, July, 1991.     

Analysis of the rate of propagation of the wave of change of boiling modes

An approximate analytical expression is derived for the velocity of the front of the wave of change of boiling modes on a rod and on a plate. The impact of the Thomson effect and of the heater orientation in the gravity field is included. Adequate agreement is demonstrated between the derived relations and experimental data.     

水三相点复现的不确定度评定

水三相点是开尔文热力学温度的唯一基准点，也是ITS-90国际温标重要的定义固定点。因此，水三相点不确定度分析对整个温标的建立、温度量值传递起着至关重要的作用。近3年来，中国计量科学研究院研制出一系列高质量的水三相点容器，加强了水三相点的研究，为不确定度的分析提供了更为可靠的实验依据。同时，不确定度的分析也是客观评价新研制容器性能的一个重要指标。因此，根据实验结果对新研制容器所复现的水三相点进行了不确定度评定。评定结果表明，其扩展不确定度为0．16mK(k=2．69，P=0．99)。