稳态平板法测导热系数的补充实验研究

以建陶坯体为研究对象,针对目前平板法测量圆饼状固体材料导热系数的常见问题,采用蜡封方法避免水分沿圆周方向的逸出,分析湿度对导热系数的影响。试验结果表明:坯体导热系数随温度和含水率的升高而升高,并首次针对不符合尺寸要求的实验样品采用简化的实验方法,推导出其导热系数的计算公式。     

THE EFFECTS OF VARIABLE FLUID PROPERTIES ON MHD MAXWELL FLUIDS OVER A STRETCHING SURFACE IN THE PRESENCE OF HEAT GENERATION/ABSORPTION

An analysis is performed to investigate the effects of variable viscosity and thermal conductivity on the two-dimensional steady flow of an electrically conducting, incompressible, upper-convected Maxwell fluid in the presence of a transverse magnetic field and heat generation or absorption. The governing system of partial differential equations is transformed into a system of coupled nonlinear ordinary differential equations, and is solved numerically. Velocity and temperature fields have been computed and shown graphically for various values of the physical parameters. The local skin-friction coefficient and the local Nusselt number have been tabulated. It is found that fluid velocity decreases with an increase in the viscosity parameter and the Deborah number. It is also observed that increasing the magnetic parameter leads to a fall in the velocity and a rise in the temperature. Furthermore, it is shown that the temperature increases due to increasing the values of the thermal conductivity parameter and the heat generation parameter, while it decreases with an increase of both the absolute value of the heat absorption parameter and the Prandtl number.     

AlN陶瓷的烧结致密化与导热性能

氮化铝陶瓷具有高热导率、低介电常数、与硅相匹配的热膨胀系数等优良特性,应用领域非常广泛。对A l N粉体的合成、烧结工艺、助烧结剂及其应用等方面进行了介绍,并对A l N未来的发展趋势进行了展望。     

THE EFFECT OF THERMAL RADIATION ON THE HEAT AND MASS TRANSFER FLOW OF A VARIABLE VISCOSITY FLUID PAST A VERTICAL POROUS PLATE PERMEATED BY A TRANSVERSE MAGNETIC FIELD

The effect of temperature-dependent viscosity on free convective flow past a vertical porous plate is studied in the presence of a magnetic field, thermal radiation, and a first-order homogeneous chemical reaction. Boundary layer equations are derived and the resulting approximate nonlinear ordinary differential equations are solved numerically by the shooting method. A parametric study of all parameters involved is conducted, and a representative set of numerical results for the velocity and temperature profiles as well as the skin-friction parameter and the Nusselt and Sherwood numbers is illustrated graphically to show typical trends of the solutions. The dynamic viscosity in this study is taken as a function of the temperature although the Prandtl number is considered constant.     

高导热石墨材料微观结构与其导热性能的关系研究

考察了以膨胀石墨为原料制备的高导热炭材料（高导热石墨块、高导热石墨片）与以中间相沥青为原料制备的高导热炭材料（高导热石墨膜）在微观结构及导热性能上的差异。研究表明：由中间相沥青为原料制备的高导热石墨膜的石墨化度较高、La和Lc更大。高结晶石墨块、高导热石墨片、高导热石墨膜的热导率由高到低的顺序为：高导热石墨膜〉高导热石墨块〉高导热石墨片。     

测定多孔性固体催化剂颗粒有效导热系数的新方法

提出了一种测定空气中催化剂有效导热系数的方法。该方法简便、易行,实验误差小于5％.在此基础之上用woodside随机分布模型计算了反应条件下催化剂有效导热系数。误差分析表明：该模型误差较小,完全可以用于工程计算。     

热解炭结构对C/C复合材料热物理性能影响

炭布叠层为预制体，采用等温CVI工艺制备出炭/炭（C/C）复合材料。通过调节丙烯与氢气的比例得到热解炭结构分别为粗糙层（RL），光滑层（SL），各向同性（ISO）的三种C/C复合材料，研究了热解炭组织结构对C/C复合材料热导率的影响，讨论了C/C复合材料的导热机理。结果表明：RL织构C/C复合材料的热导率无论是在平行方向还是在垂直方向上都明显高于SL和ISO织构C/C复合材料，在两个方向上，RL织构C/C复合材料的最大热导率比SL织构C/C复合材料分别大41.0%和31.7%，是ISO织构C/C复合材料的2倍多，且3种C/C复合材料的热导率随温度的升高呈现不同的变化趋势。     

一种能同时提高固体吸附制冷吸附剂传热传质性能的方法

通过在沸石分子筛中添加膨胀石墨和发泡剂并固结成型进行处理,使吸附剂的导热系数和渗透性有了显著提高,并测定了几种吸附剂的导热系数,采用SEM观察了发泡前后的沸石分子筛的晶体结构和微观形貌的变化,分析了膨胀石墨所具有的特性是使其成为合适的添加剂的原因。通过TGA测试表明吸附剂的传质性能有提高。     

影响硬质聚氨酯泡沫塑料导热系数因素的研究及配方优化

详细研究了密度、催化剂、水分、F_(11)用量和聚醚对硬质聚氨酯泡沫导热系数的影响。实验结果表明,密度对导热系数的影响有一峰值,即最佳点,聚醚、催化剂、匀泡剂、F_(11)用量对导热系数都有明显的影响,水分对导热系数影响十分敏感。同时进行了配方优化,得到了最优配方。     

YSZ薄膜的溶胶—凝胶法制备及其电导性能

应用溶胶－凝胶方法制备了ＹＳＺ薄膜，通过ＸＲＤ，ＳＥＭ和低频阻抗分析仪等分析手段，研究了ＹＳＺ薄膜的相结构，形貌特征及其电导性能，结果表明，应用溶胶－凝胶方法制备的ＹＳＺ薄膜经８００℃以上热处理后形成完整的立方相结构，随着烧结温度的升高，薄膜表面变得致密，气孔明显减少，至１０５０℃时，薄膜表面光滑，无裂纹，无针孔，圆球形的小颗粒均匀分布，薄膜与衬底的结合紧密，薄膜厚度均匀，膜厚约为１．０μｍ，阻抗     

液体的导热系数与蒸发潜热及温度间的关系

提出了流体导热系数的自由体积模型,用方阱流体的分子动力学模拟结果验证了模型,获得满意的结果.将所得模型结合统计力学理论,导出了液体的导热系数与蒸发潜热间的关系,对40种有代表性的物质(569个点)的关联,误差仅为1.78%,最后得到关联导热系数与温度的两参数模型,对40种物质的关联结果表明,所得模型适用于直到临界点附近的宽广的温度范围,优于被认为较成功的Jamieson的两参数经验式.     

EXPERIMENTAL INVESTIGATION OF PARAMETERS AFFECTING NANOFLUID EFFECTIVE THERMAL CONDUCTIVITY

The present research reports nanofluid effective thermal conductivity enhancements (ETCE) using an accurate transient short hot wire method system. Preparation of nanofluids was carried out through a two-step method with highly powered pulses similar to that for nanoparticle dispersion in base fluids. Parameters affecting nanofluid heat conductivity such as concentration, sizes, and material of nanoparticle? type of base fluid, temperature, ultrasonic mixing time, and elapsed time after preparation were studied. In the present study, nanoparticles of Al, Al₂O₃, CuO, SnO₂, TiO₂, and SiO₂ with base fluids of water and ethylene glycol were used. Parameters like concentration, size, temperature, and the type of base fluid showed more noticeable effect on the effective thermal conductivity than the others, and mixing time had the least effect. The results showed that any increase in concentration and temperature, and also any decrease in size of nanoparticles and time elapsed after nanofluid preparation, leads to the ETCE of the nanofluid. However, the effects of nanoparticle material, base fluid, and mixing time on thermal conductivity of the nanofluid showed varying trends. Last, a number of mathematical models for prediction of thermal conductivity of nanofluids were applied.     

EFFECT OF MAGNETIC FIELD-DEPENDENT VISCOSITY ON THERMAL CONVECTION IN A FERROMAGNETIC FLUID

This article deals with the theoretical investigation of the effect of magnetic field-dependent (MFD) viscosity on a layer of ferromagnetic fluid heated from below subject to a transverse uniform magnetic field. For a flat fluid layer contained between two free boundaries, an exact solution is obtained using a linear stability analysis and normal mode analysis method. For the case of stationary convection, the MFD viscosity has a stabilizing effect, whereas the departure of linearity in the magnetic equation of state has a destabilizing (or stabilizing) effect on the system under certain conditions. The critical wave number and critical magnetic thermal Rayleigh number for the onset of instability are also determined numerically for large values of buoyancy magnetization, and results are depicted graphically. The principle of exchange of stabilities is valid for the ferromagnetic fluid heated from below.     

AN APPARATUS FOR MEASURING THERMAL CONDUCTIVITY OF LIQUIDS UNDER HIGH PRESSURE

We have reported a method for measuring the thermal conductivity of liguids un-der high pressure previously [1,2].Such data are necessary for improving thetechnologies such like processing as acidity,pressure cracking,thermal exploitation ofpetroleum,etc. An apparatus has thus been constructed,as shown schematically in Fig.1,tomeasure the thermal conductivity of liquids under pressure up to 25 MPa and temperatureranging from 150 to 250℃.The thermal conductivity cell is cylindrical in from,35mmin length and 25mm in inner diameter.The sample is poured into the cell through the     

煤孔结构对煤/PAN复合材料导电性能的影响

煤基聚苯胺复合导电材料是利用煤的酸性官能团特征、孔结构特征和芳香层片特征 ,以煤为模板 ,用 APS引发苯胺单体 ,在煤中原位聚合而成的 .其中煤的孔结构是影响煤 / PAN导电性能的重要因素 .选择 HNO3 ,H2 O2 氧化及苯胺抽提的方法改变煤的孔结构 ;通过电导率及孔结构分析表明 ,氧化和抽提使煤的孔结构变得发达 ,因而苯胺能更好地进入已溶胀煤的孔结构中 ,提高了煤基聚苯胺的电导率 .     

喷动流化床流动特性研究

选用密度与尿素相近而粒度不同的三种模拟物料，在内径为１８２ｍｍ的有机玻璃喷动流化床中，对喷动流化床的流体力学行为进行了研究。测定了不同物料最大操作区所对应的静床高及喷动流化气速与床层压降、床层空隙率分布的关系。为喷动流化床尿素造粒热态试验提供了可资借鉴的设计及操作依据     

温度对碳热还原合成SiC晶须的影响

以工业硅溶胶和碳黑为主要原料,用溶胶-凝胶和碳热还原法进行了合成SiC晶须的试验,探讨了合成温度对产物组成微观形貌的影响.结果表明:合成SiC晶须适合的温度为1600℃,在此条件下得到的产物中SiC晶须含量最高(74%以上)、质量最好.     

岩矿棉隔热材料导热系数与密度及温度的关系

用稳态法研究岩矿棉隔热材料热系数与密度及温度的关系，结果表明，在一定的工艺条件下，对于化学组成稳定确定的岩矿棉隔热材料，在一个大气压及确定的温度下，在８０－１００ｋｇ／ｍ＾３的密度范围将出现导热系数最小值；其导热系数随着温度的增加而非线性地增大，并从理论上提高其经济性的途径，这为陶瓷窑炉保温结构的热设计提供了科学依据。     

炭前驱体形态对C/C复合材料导热系数的影响

利用热塑性中间相沥青为黏结剂,短炭纤维.增强体,一步热压成型制备C/C导热复合材料.采用SEM和偏光显微镜观察等分析手段,研究了2∶1,2.5∶1和3∶1三种不同管径比对C/C复合材料的影响.结果表明:通过热压模具空腔结构的改变可以引起炭前驱体挤出形态的变化,使得轴向基体炭有序生长与短炭纤维增强体呈现有序排列,其中间相液晶分子垂直和平行于模压压力方向均排列成纤维状长程有序结构,短切纤维呈现出与压力平行方向排布.当空腔管径比为3:1,轴向导热系数由86.2 W/(m·K)增大至115.5 W/(m· K),各向异性比由1.6减小为1.2.由此所得块体C/C复合材料具有显著的二维取向结构,轴径向导热系数趋于平衡.