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。     

新型无机非金属材料相变的热物性研究

本文系统地研究了新型无机非金属材料的各类相变、极化处理和晶体取向对其热物理性质的影响。用各种测试技术测定了六种新型无机材料在较大温度范围内的导热系数、导温系数、比热和热膨胀系数。实验结果显示出这些材料发生相变时,在热物性曲线上都将出现突变。由突变点所确定的相变温度(居里点)与用电学方法测定的结果相吻合,据此,热物性的测试研究可作为研究材料相变的一个新的判据和手段。     

添加纳米颗粒和分散剂的相变流体性能测试研究

结合太阳能低温集热蓄热,基于前期选定的烃类相变流体,通过热物性和稳定性测试对比,选取了适合的纳米颗粒(TiO_2)和分散剂(SDBS),分析了纳米颗粒质量分数、粒径以及分散剂质量分数对相变流体的热物性及稳定性的影响。结果表明,纳米颗粒质量分数越大,颗粒粒径越大,相变流体的热物性及动态稳定性越差,而分散剂质量分数对相变流体的动态稳定性影响不大。烃类相变流体中分别添加质量分数为0.1%的20 nm TiO_2纳米颗粒和质量分数为0.1%的SDBS分散剂,其热物性及稳定性最佳。     

纳米流体的分散性研究及其热物性测量

采用"两步法"制备了稳定性良好的γ-Al2O3-DW和CNTs-DW纳米流体,研究了分散剂对纳米流体悬浮稳定性的影响,测试了溶液的热扩散系数和比定压热容,并根据测试数据计算出导热系数.结果表明,分散剂种类和用量对纳米流体的分散有重要影响,相对于基础液体(DW),纳米流体的导热系数和热扩散系数有一定的提高,但比定压热容减小.     

点热源热脉冲法测算生物流体的热物性参数

采用微珠状热敏电阻作为点热源和测温元件，在一维点源脉冲传热模型的基础上建立一种同时测量生物流体热扩散系数、导热系数和热容的瞬态方法。运用非线性参数拟合，直接从感温热敏电阻对热脉冲温度响应中同时获取待测的热物性参数。实验中设计了一个高灵敏度的温度测量电路，测试结果表明，本方法测量误差小于4％。此外，还讨论了测量数据的处理和影响测量的因素。     

低温流体热物性数据库的国内外概况

综述了国外低温流体热物性数据库工作进展情况、氦热物性数据库的研究概况。并综述了国内一些学者研完低温流体物性数据的概况。     

瞬态热丝法测量纳米流体的导热系数

推导了用双铂丝测量流体导热系数的瞬态热丝法的实验关联式,并据此设计实验装置,分析误差因素,给出了系统误差修正系数.用该装置测量了几种纳米流体的导热系数并作了相关分析.     

金属及合金熔点热物性动态测试新方法研究

利用物质熔化与凝固过程中导热逆(或反)问题原理，在建立了相界面移动与两相热物理性质关系的基础上，提出了一种新颖的热物性动态测试方法，即由相变速率动态测试热物性参数。由于是对熔点高的金属进行测试，故不能采用解析求解，而是运用数值求解；并用铅、锌、铝等已知热物性的金属对此方法进行了评定，测试结果与参照值误差不超过3％；还对相变导热系数未知的铅锑、铅锡、铋锡、铝硅、铝铜5种共晶合金进行了测试，其结果具有较高的参考价值。该方法的优点在于测试过程中所求热物性参数与相界面位置是由精确的传热方程所约束，故测量较简便，结果准确、可靠、误差小，并可测得多个热物性数据。     

关于测试材料热物性热脉冲法的新探讨

建立起热脉冲法的新理论模型，分析了相应的测试技术问题。利用研制的微机测试系统 种材料的热扩散系数和导热系数进行了测定，得到了满意的结果，表明本文所提出的测试广阔进可信的。     

国外低温流体热物性数据库的引进消化

介绍了从美国、日本引进的气体热物性数据库、氦热物性数据库、流体热物性数据库、混合物热物性数据库的内容、性能、特点、计算范围和可求解的物性参数等,并给以消化、改进。     

Simultaneous measurement of thermal conductivity and thermal diffusivity of solids by the parallel-wire method

An improved parallel-wire technique for simultaneous measurement of thermal conductivity and thermal diffusivity is presented. The deviation between experimental results and recommended (or another author's) values is less than 5% for fused quartz and refractory brick.     

Thermal Conductivity,Thermal Diffusivity,and Heat Capacity of Gaseous Argon and Nitrogen

Low-pressure thermal conductivity and thermal diffusivity measurements are reported for argon and nitrogen in the temperature range from 295 to 350 K at pressures from 0.34 to 6.9 MPa using an absolute transient hot-wire instrument. Thermal conductivity measurements were also made with the same instrument in its steady-state mode of operation. The measurements are estimated to have an uncertainty of 1% for the transient thermal conductivity, 3% for the steady-state thermal conductivity, and 4% for thermal diffusivity. The values of isobaric specific heat, derived from the measured thermal conductivity and thermal diffusivity, are considered accurate to 5% although this is dependent upon the uncertainty of the equation of state utilized.Paper presented at the Sixteenth European Conference on Thermophysical Properties, September 1–4, 2002, London, United Kingdom     

Thermal conductivity of air in the range 312 to 373 K and 0.1 to 24 MPa

We have used the transient hot-wire technique to make absolute measurements of the thermal conductivity of dry, CO₂-free air in the temperature range from 312 to 373 K and at pressures of up to 24 MPa. The precision of the data is typically ±0.1%, and the overall absolute uncertainty is thought to be less than 0.5%. The data may be expressed, within their uncertainty, by polynomials of second degree in the density. The values at zero-density agree with other reported data to within their combined uncertainties. The excess thermal conductivity as a function of density is found to be independent of the temperature in the experimental range. The excess values at the higher densities are lower than those reported in earlier work.Nomenclature Thermal conductivity, mW · m^–1 · K^–1 - Density, kg · m^–3 - C _p Specific heat capacity at constant pressure, J · kg^–1 · K^–1 - T Absolute temperature, K - q Heat input per unit wire length, W · m^–1 - t Time, s - K(=/C _p) Thermal diffusivity, m² · s^–1 - a Wire radius, m - Euler's constant (=0.5772 ) - p _c Critical pressure, MPa - T _c Critical temperature, K - _c Critical density, kg · m^–3 - R Gas constant (=8.314 J · mol^–1 · K^–1) - V _c Critical volume, m³ · mol^–1 - Z _c(=p _c V _c/RT _c) Critical compressibility factor     

The thermal conductivity of the molten NaNO3-KNO3 eutectic between 525 and 590 K

Molten salts are one of the few remaining classes of fluids for which standardquality (±1% accuracy) data on thermal conductivity have not hitherto been available. We have therefore developed a new apparatus based on the transient hot-wire technique to obtain reference-quality measurements of the thermal conductivity of molten salts at high temperatures. Liquid metal-filled quartz capillaries served as insulated hot wires in our method, and in addition, a two-wire technique was used in order to obtain absolute values of the thermal conductivity. New data for the NaNO₃-KNO₃ eutectic between 525 and 590 K are reported in this paper and comparisons with other recent measurements are shown.     

瞬态热线法液体导热系数测试系统的研制

根据瞬态热线法测量导热系数的原理,研制了测量装置和数据采集系统.利用阳极氧化的方式,在热线表面进行绝缘处理,使其能够适用于导电性或者极性物质的导热系数的研究.为了检验该系统的性能,在常温常压下对蒸馏水的导热系数进行了测量.测试结果表明,该系统能够满足导热系数测试的需要.     

The thermal conductivity and viscosity of benzene

New absolute measurements of the thermal conductivity of liquid benzene are reported. The measurements have been carried out in the temperature range 295–340 K, at atmospheric pressure, in a transient hot-wire instrument. The accuracy of the measurements is estimated to be ±0.5%. The measurements presented in this paper have been used, in conjunction with other high-pressure measurements of thermal conductivity and viscosity, to develop a consistent theoretically based correlation for the prediction of these properties. The proposed scheme permits the density dependence of the thermal conductivity and viscosity of benzene, for temperatures between 295 and 375 K and pressures up to 400 MPa, to be represented successfully by two equations containing just two parameters characteristic of the fluid at each temperature.     

Absolute measurements of the thermal conductivity of alcohols by the transient hot-wire technique

New absolute measurements of the thermal conductivity of methanol, ethanol, propanol, butanol, pentanol, and hexanol at atmospheric pressure and in the temperature range 290–350 K are reported. The overall uncertainty in the reported thermal conductivity data is estimated to be better than ±0.5%, an estimate confirmed by the measurement of the thermal conductivity of water. The measurements presented in this paper have been used to develop a consistent theoretically based correlation for the prediction of the thermal conductivity of alcohols. The proposed scheme, based on an extention of the rigid-sphere model, permits the density dependence of the thermal conductivity of alcohols, for temperatures between 290 and 350 K and atmospheric pressure, to be represented successfully by an equation containing just one parameter characteristic of the fluid at each temperature.Paper presented at the Tenth Symposium on Thermophysical Properties, June 20–23, 1988, Gaithersburg, Maryland, U.S.A.     

Thermal properties of aqueous solutions of polyvinylpyrrolidone in the temperature range 20–80°C

The thermal properties (thermal diffusivity a, thermal conductivity , and volumetric heat capacity C _p) of aqueous solutions of polyvinylpyrrolidone (PVP) were measured in the temperature range 20–80°C. The measurements were carried out using the hot-wire (strip) technique. Three different average molecular weights of PVP were used [M = 10,000 (PVP-10), M = 24,500 (PVP-24.5), and M = 40,000 (PVP-40)], i.e., the average degrees of polymerization are 90, 220, and 360, respectively. The results show that the values of the thermal properties depend on the temperature and the concentration of PVP in the medium. The mechanism of heat transfer was discussed. The role of convection and radiation were taken into consideration.     

Absolute measurement of the thermal conductivity of propylene carbonate by the AC transient hot-wire technique

The paper describes a new apparatus for measuring the thermal conductivity of liquids based on a transient hot-wire method. The apparatus has been used to measure the thermal conductivity of propylene carbonate (C₄H₆O₃). The measurements have been carried out in the temperature range 284–313 K and at saturation pressure. The accuracy of the data is within ±1.5%.     

Thermal Conductivity of Molten Lead-Free Solders

The paper reports measurements of the thermal conductivity of a number of molten solders for the electronics industry that are part of a group of materials designed to be free of the toxic problems associated with lead-based solders. The measurements have been carried out with a transient hot-wire instrument originally designed for the measurement of the thermal conductivity of pure molten metals. In the application reported here the instrument has been used largely unchanged but an improved finite-element code has been used for the analysis of the raw data so as to yield the thermal conductivity of the molten solders. The measurements extend from the melting point of the solder up to 625 K. The uncertainty in the thermal conductivity measurements is estimated to be no larger than 3%.Paper presented at the Seventh Asian Thermophysical Properties Conference, August 23–28, 2004, Hefei and Huangshan, Anhui, P. R. China