多层纳米薄膜结构热物性重构

基于谐波探测技术测量材料导热系数和热扩散系数的基本原理,给出3ω法用于多层纳米薄膜结构热物性实验表征的方法.考虑了层间接触热阻的作用,在频域内定义了热阻抗的概念.理论分析了各层纳米薄膜的导热系数、热扩散系数等热参数对加热膜温度波动影响的敏感性.将敏感系数与实验数据处理相结合,利用三次谐波的实部和虚部分量测量了ZrO2/SiO2增透膜多层膜结构中各层的导热系数和热扩散系数.该方法可用来有效表征其他微纳米结构的热性能.     

3ω法测量单根碳纤维导热系数和热容

考虑环境热损失,建立了单根碳纤维沿轴向的导热方程,得到了碳纤维热参数与交流加热信号的频域特性之间的关系.建立了适用于微细导电线或丝的3ω测试系统.利用3ω方法同时测量了单根碳纤维沿轴向的导热系数和热容.在室温下测量了Pt丝的导热系数和热容,验证了建立的实验系统的合理性,利用该方法测量的直径为7 μm单根碳纤维沿轴向的导热系数和热容分别为84.35 W·m-1·K-1和1.19 MJ·m-3·K-1.给出了实验测量的不确定度分析.建立的实验系统可用于单根碳纳米管或导电纳米线热参数的表征.     

3ω法加热/测温膜中温度波解析及其在微/纳米薄膜导热系数测量中的应用

给出了3ω法测试系统中描述薄膜表面加热/测温膜中温度波动的级数形式解，并将复数温度波动的实部和虚部分开表示.利用该解分析了交流加热频率、加热膜宽度和材料热物性的组合参数对加热膜温度波动幅度的影响.并根据此解对测量原理的数学模型进行了修正，建立了相应的3ω测试系统，首先测定了厚度为500 nm SiO₂薄膜的导热系数，验证了实验系统的合理性.加大了测试频率，利用级数模型在高频段直接得到SiO₂薄膜的导热系数，结合低频段的数据同时确定了Si基体的导热系数.利用级数解分析测试了激光晶体Nd:YAG〈111〉面上多层ZrO₂/SiO₂增透膜的导热系数，测试的ZrO₂薄膜的导热系数比体材料小.进行了不确定度分析.结果表明，提出的分析方法可以有效研究微器件表面薄膜结构的导热性能. 关键词： ω法')" href="#">3ω法 微/纳米薄膜 导热系数 微尺度加热膜     

温度依变性对纳米颗粒悬浮液导热系数测量影响

本文报告了50 nm氧化铜(体积百分比φ≤0.6%)与去离子水的悬浮液有效导热系数测量结果,讨论了温度依变性对导热系数的影响,运用适用于低浓度悬浮液的能量和质量方程进行分析表明,颗粒空间分布和温度场间相互影响,进而影响导热系数测量结果.考虑低浓度悬浮液中颗粒布朗扩散和热泳作用,讨论了运用准稳态方法测量纳米颗粒悬浮液导热系数的有效性,即需同时保证合适的加热热流密度和液体试样两侧的温差.     

液体导热系数的测量

液体导热系数的测量李成仁，吕翎，曲业民，尹海滨（辽宁师范大学物理系大连１１６０２２）一、引言导热系数是表征材料导热性能的一个参数，其数值不仅与材料的种类有关，对同一种材料还取决于温度．目前，各高校测量导热系数的实验多以金属铜棒为样品．对于液体，由于导...     

液相饱和度对多孔介质稳态导热系数的影响

在非饱和含湿多孔介质传热传质的过程中,由于湿分迁移的存在,使得真实导热系数的测量和处理存在争议。为此,运用有限元方法,求解了二维稳态条件下非饱和含湿多孔体特征单元的温度和热流密度,给出了不同液相饱和度时的有效导热系数。结果表明,对于通常的导热能力固体远大于液体、液体远大于气体的情形,随着液相饱和度的增加,多孔介质的导热系数先迅速增加,然后逐渐趋于平稳。     

3ω法研究微尺度下铂丝自然对流换热

建立了测量微细丝表面空气自然对流换热系数3ω法模型。利用3ω法测量了直径为10.6μm水平和垂直方向铂丝表面室温下的空气换热系数。水平和垂直铂丝产生的三次谐波比较接近,结果说明,微尺度下空气的自然对流换热以导热为主,自然对流作用可以忽略。基于3ω线法原理,引入形状因子并提出了微尺度下铂丝表面换热系数的理论计算模型。空气自然对流换热系数远大于大尺度下的值,主要原因是铂丝的面积体积比值大。     

稳态法测量冰的导热系数

基于保护热板法原型,使用干冰-乙醇和乙二醇混合浴制造不同温度稳定低温环境之间的传热代替传统的加热传热,设计了冰的导热系数测量装置,在较大的温度范围(-70～-30℃)内实现了冰的导热系数稳定可靠的测量.同时充分借助电子式温度计高效测量数据,测得了冰在不同温度下和含有不同杂质情况下的导热系数变化规律,实验结果与参考值符合较好.利用杂质对冰的导热系数的影响规律,可以按需求调节冰的导热系数.     

基于准稳态实验方法研究橡胶材料的热传导性质

采用准稳态方法探讨测量橡胶材料导热系数的最佳实验条件,当在加热电压为18V,测量时间间隔为60s时,橡胶导热系数的测量值λ=(0.64±0.030)W/(m·K),与相关文献给出的参考值误差非常小.在满足测量精度的前提下,准稳态法具有操作简便、耗时少、实验条件容易达到,得出的结果更加准确.     

三氟碘甲烷的新气相状态方程和输运物性

提出了三氟碘甲烷（ＣＦ３Ｉ）的新蒸气压方程和新状态方程；给出了ＣＦ３Ｉ的偏心因子、正常沸点等物性参数，并与文献值进行了比较．使用毛细管粘度计测量了ＣＦ３Ｉ的２５３～３３８Ｋ的饱和液粘度，采用以钽丝为热线的双线瞬态热线法测量了ＣＦ３Ｉ的气相导热系数，并分别给出了关联式．     

THERMAL CONDUCTIVITY OF METALLIC WIRES

The effect of radial thickness on the thermal conductivity of a free standing wire is investigated. The thermal conductivity is evaluated using the Boltzmann equation. A simple expression for the reduction in conductivity due to the increase of boundary scattering is presented. A comparison is made between the experimental results of indium wires and the theoretical calculations. It is shown that this decrease of conductivity in wires is smaller than that in film where heat flux is perpendicular to the surface.     

用变长度“T”形法测量单根纤维热导率

为了解决"T"形法中的接触热阻问题,本文在不改变纤维与热线之间的接触节点的前提下,通过测量同一根纤维不同长度对应的表观热阻,同时得到了纤维热导率以及节点的接触热阻.用变长度"T"形法测量得到 Pt 丝以及两根沥青基碳纤维的热导率分别为 73,480 和 500 W m-1 K-1.     

Thermal Instability of Non-Ideal Current-Carrying Plasmas of Metal Vapors

As a result of Ohmic heating the transition proceeds from the liquid metal state to the state of the gaseous plasma. The conductivity drops rapidly. This paper reports on the thermal instability of such a discharge. The instability results in the plasma stratification across the current direction. The discussion is given of the experiment by DIKHTER and ZEIGARNIK. The discharge is layered under the isobaric heating of cesium wire in the argon atmosphere.     

粒径均匀散体导热系数的分形描述

本文以分形理论为工具,采用填充率、散体颗粒直径等宏观易等测参数较准确地描述了颗粒散体的几何结构;运用导热与逾渗的类比,建立了均匀散体导热系数的逾渗模型,模型的预测值与实验测量结果基本一致。     

自激振荡流热管脉冲加热强化传热实验研究

自激振荡流热管也称为脉动热管,是一种新型高效的传热元件。本文提出了采用脉冲加热代替常规连续热源加热强化自激振荡流热管传热的方法,并对其进行了实验研究。实验结果显示,脉冲加热时热管冷、热端壁面温度的振荡频率明显大于连续加热热管的壁面温度振荡频率。在相同的加热功率下,当脉冲宽度在200-1000 ms时,脉冲加热热管的传输热流量与当量导热系数均大于连续加热热管的传输功率和当量导热系数．这表明脉冲加热强化自激振荡流热管传热的方法是可行的．     

Thermal transport in multiwall carbon nanotube buckypapers

A steady-state electro-Raman-thermal (SERT) technique is developed to characterize the thermal transport in multiwall carbon nanotube (MWCNT) buckypapers. This SERT technique involves steady-state joule heating of a suspended sample and measuring its middle point temperature based on Raman shift intensity. The thermal conductivity is determined from linear fitting of the temperature against heating power. Combined with the transient-electro-thermal technique, the thermophysical properties of two MWCNT buckypapers are characterized as 1.19 and 2.92 W/(m K) for thermal conductivity, 3.65×¹⁰−6 and 7.58×¹⁰−6 m²/s for thermal diffusivity, 459 and 543 kg/m³ for density. Detailed discussion and analysis are provided about the uncertainty of the SERT technique and its capacity for measuring wires down to sub-μm length. The low thermal conductivity of the buckypaper indicates its thermal transport is determined by the thermal contact resistance between MWCNTs. These contact points feature low thermal conductance. The mean distance between two adjacent contact points is estimated in the order 45-450 μm and 93-933 μm for the two samples, indicating low-density contacts within the buckypaper.     

纳米悬浮液热导率测量及其预测模型的探讨

纳米颗粒悬浮液具有广泛应用于强化传热的潜在优势。本文采用加入表面活性剂的方法提高纳米悬浮液的悬浮稳定性,并用瞬态热线法测量了热导率。在分析现有理论模型和纳米悬浮液热导率影响因素研究的基础上,从弹性传动和非弹性传动两方面分析了纳米尺度效应导致纳米悬浮液热导率提高的机理。发现已有的理论公式仍然存在一定欠缺,预测值比实验值偏低,有关机理尚有待于深入探讨。     

Characterization of thermal diffusivity of micro/nanoscale wires by transient photo-electro-thermal technique

In this work, a transient photon-electro-thermal (TPET) technique based on step laser heating and electrical thermal sensing is developed to characterize the thermophysical properties of one-dimensional micro/nanoscale conductive and nonconductive wires. In this method, the to-be-measured thin wire/tube is suspended over two electrodes and is irradiated with a step cw laser beam. The laser beam induces a transient temperature rise in the wire/tube, which will lead to a transient change of its electrical resistance. A dc current is applied to the sample, and the resulting transient voltage variation over the wire is measured and used to extract the thermophysical properties of the sample. A 25.4-μm thick Pt wire is used as the reference sample to verify this technique. Sound agreement is obtained between the measured thermal diffusivity and the reference value. Applying the TPET technique, one can measure the thermal diffusivity of conductive single-wall carbon nanotube (SWCNT) bundles and nonconductive cloth fibers. For nonconductive wires, a thin (∼ nm) metallic film is coated on the outside of the wire for electrical thermal sensing. The measured thermal diffusivity for the SWCNT bundle is 2.53×10^-5 m²/s, much less than the thermal diffusivity of graphite in the layer direction. For microscale cloth fibers, our experiment shows its thermal diffusivity is at the level of 10^-7 m²/s. PACS 78.20.Nv; 42.62.-b; 65.80+n; 66.30.Xj     

Characterization of thermal transport in micro/nanoscale wires by steady-state electro-Raman-thermal technique

In this work, a novel steady-state electro-Raman-thermal (SERT) technique is developed to characterize the thermal transport in one-dimensional micro/nanoscale materials. The SERT technique involves steady-state joule heating of a suspended sample and measuring its middle point temperature based on the temperature dependence of the Raman shift peak intensity. The thermal conductivity is determined from a linear fitting of the temperature against heating power. Multi-wall carbon nanotube bundles are characterized using the SERT technique to verify its measurement capacity. As it does not need to track the transient process of heat transfer, the SERT technique has the great potential for measuring short materials down to nm long.     

Measurement of thermal conductivity in laser-heated diamond anvil cell using radial temperature distribution

ABSTRACT

Thermal conductivities of planetary materials under extreme conditions are important input parameters for modeling planetary dynamics such as accretion, geodynamo and magnetic field evolution, plate tectonics, volcanism-related processes etc. However, direct experimental measurements of thermal conductivity at extreme conditions remain challenging and controversial. Here we propose a new technique of thermal conductivity measurement in laser-heated diamond anvil cell (LH-DAC) based on radial temperature distribution around laser focal spot, mapped by imaging tandem acousto-optical tunable filter (TAOTF). The new technique provides much more information about heat fluxes in the laser-heated sample than existing static heating setups, and does not require dynamic numerical modeling using heat capacities in contrast to dynamic pulsed heating setups. In the test experiment, thermal conductivity of γ-Fe at conditions relevant to cores of terrestrial planets was measured.