金刚石、碳化硅复合热传导材料的发展

金刚石或碳化硅增强的金属基或陶瓷基复合热传导材料理论上具有高的热导率、低的热膨胀系数,然而金刚石或者碳化硅与基体的界面结合问题严重降低了复合热传导材料的热导率。通过改善烧结工艺、添加碳化物形成元素、增强相表面镀铜等方法来解决问题,虽取得一定效果,但并未完全解决界面问题。本文介绍了两种更为有效的解决手段,在金属基复合材料中,通过在增强相表面镀覆碳化物金属镀层的方法改善界面结合问题;在陶瓷基复合材料中,采用添加活性添加剂以及在增强相表面镀覆障碍层的办法解决陶瓷基复合热传导材料中的氧化问题。

热传导聚合物基复合材料的研究进展

本文主要介绍了聚合物基复合材料的导热机理 ,以及预测二相体系复合材料热导率的理论模型方程。同时介绍了聚合物基导热材料的 3种类型及其具体应用 。

电子窑炉热效率提升与节能技术研究

电子窑炉作为工业生产中的重要设备,其热效率和节能技术的提升对降低能源消耗和生产成本具有重要意义。本文首先探讨了通过优化热传导和隔热材料提升热效率的方法,包括新型高效热传导材料和隔热材料的应用。接着,分析了高效热交换器设计和废热回收系统集成的技术,展示了这些技术在实际应用中的效果。然后,研究了先进燃烧控制系统和智能控制系统在燃烧过程监控与优化中的作用,探讨了综合节能管理策略对提升电子窑炉节能效果的协同作用。最终,提出了提高电子窑炉热效率和节能技术的可行性建议。

一维非线性功能梯度材料的热整流反转

采用非平衡分子动力学方法,研究了一维非线性功能梯度材料的不对称热传导性质.通过耦合两段Frenkel-Kontorova链,并引入线性质量梯度,研究平均温度、界面耦合强度及体系大小对热整流的影响.结果表明,当界面耦合强度较小,并在特定的体系中时,通过调节热浴温差来控制系统的热整流方向,无需进行结构重建,在原结构中就能进行热整流方向的控制.讨论了该系统在实验制备及应用方面的可能性.

Numerical study of directional heat transfer in composite materials via controllable carbon fiber distribution

Carbon fiber reinforced polyamide 12(CF/PA12),a new material renowned for its excellent mechanical and thermal properties,has drawn significant industry attention.Using the steady-state research to heat transfer,a series of simulations to investigate the heat transfer properties of CF/PA12 were conducted in this study.Firstly,by building two-and three-dimensional models,the effects of the porosity,carbon fiber content,and arrangement on the heat transfer of CF/PA12 were examined.A validation of the simulation model was carried out and the findings were consistent with those of the experiment.Then,the simulation results using the above models showed that within the volume fraction from 0% to 28%,the thermal conductivity of CF/PA12 increased greatly from 0.0242 W/(m·K)to 10.8848 W/(m·K).The increasing porosity had little influence on heat transfer characteristic of CF/PA12.The direction of the carbon fiber arrangement affects the heat transfer impact,and optimal outcomes were achieved when the heat flow direction was parallel to the carbon fiber.This research contributes to improving the production methods and broadening the application scenarios of composite materials.

烧蚀；C／C复合材料；热传导；非线性

在高压高热流作用下，高马赫数飞行器防热层常用耐高温的C／C复合材料出现烧蚀现象。考虑到C／C复合材料的高温导热系数为温度的函数，基于傅里叶传热定律和高温烧蚀机制，利用FORTRAN语言编程计算分析了C／C复合材料板烧蚀中热传导特性。结果表明：较低热流入射时，物体表面温度变化速率与内部的不同；随时间的推移，受热表面的温度趋于一致，而背面温度相差较大；物体内部温度分布趋势大体相同。较高热流入射时，表面出现烧蚀现象，温度急速升高，并维持在某一温度值保持动态平衡。

热通量传感器的应用及检定

通过对热通量传感器在新材料的研制及热分析仪参量测量领域的研究,分别给出了其在表面安装和热分析仪中的应用方法,并针对应用中出现的问题提出解决方案,同时通过比较法求解检定常数。给出了热通量传感器的检定方法,提出了热通量微观效应的概念,对埋入绝缘材料和表面镀金属层热偶的微观效应进行了分析。结果证明,周围材料的不同是影响检定误差的重要因素。

Microstructure and thermal conductivity of carbon/carbon composites made with different kinds of carbon fibers

The microstructure and surface state of three kinds of polyacrylonitrile-based carbon fibers （T700, T300 and M40） before and after high temperature treatment were investigated. Also, the pyrocarbon and thermal conductivity of carbon/carbon composites with different carbon fibers as preform were studied. The results show that M40 carbon fiber has the largest crystallite size and the least d002, T300 follows, and TT00 the third. With the increase of heat treatment temperature, the surface state and crystal size of carbon fibers change correspondingly. M40 carbon fiber exhibits the best graphitization property, followed by T300 and then T700. The different microstructure and surface state of different carbon fibers lead to the different microstructures of pyrocarbon and then result in the different thermal conductivities of carbon/carbon composites. The carbon/carbon composite with M40 as preform has the best microstructure in pyrocarbon and the highest thermal conductivity.

Optimization of volume to point conduction problem based on a novel thermal conductivity discretization algorithm

A conduction heat transfer process is enhanced by filling prescribed quantity and optimized-shaped high thermal conductivity materials to the substrate. Numerical simulations and analyses are performed on a volume to point conduction problem based on the principle of minimum entropy generation. In the optimization, the arrangement of high thermal conductivity materials is variable, the quantity of high thermal-conductivity material is constrained, and the objective is to obtain the maximum heat conduction rate as the entropy is the minimum.A novel algorithm of thermal conductivity discretization is proposed based on large quantity of calculations.Compared with other algorithms in literature, the average temperature in the substrate by the new algorithm is lower, while the highest temperature in the substrate is in a reasonable range. Thus the new algorithm is feasible. The optimization of volume to point heat conduction is carried out in a rectangular model with radiation boundary condition and constant surface temperature boundary condition. The results demonstrate that the algorithm of thermal conductivity discretization is applicable for volume to point heat conduction problems.

The Moisturein Capillaries of Building Materials

The behavior of building materials in constructions of civil structures is influenced by the surrounding moisture and it is a crucial for intensively examined field of the construction physics. Most standard building materials are characterized by a porous structure, which results in the ability to receive water in a liquid as well as gaseous form in the inner pores. The water fills the storage space of pores under certain conditions; it is transported and transferred back to the surroundings. Many technical studies show that the moisture monitoring is prevailingly based on experiments. Previous calculating methods introduced, e.g., by Glaser, which became the basis for the standard calculations in many European countries in the 1960s, are not always sufficient with respect to the demands of the civil structures. The moisture influences thermo-insulating properties of the material. By a change of the thermo insulation properties of the construction also the thermal and diffusion scheme of the construction is changed and its thermal resistance is decreasing. Faults in the thermo-technical projects occur when thermal conductivity coefficient L values for material in a dry state are substituted.The aim of the research is to determine the capillary conductivity coefficient as a characteristic material moisture parameter of the building materials by the means of a non-destructive method using the experimentally assembled apparatus developed at the Department of Civil Engineering, Brno University of Technology. Keywords： Capillary conductivity coefficient, moisture transfer, EMWR （electromagnetic microwave radiation）, diffusion

Thermal Radiative Properties of Xonotlite Insulation Material

This paper presents experimental results of thermal radiative properties of xonotlite-type calcium silicate insulation material. Transmittance spectra were first taken using Fourier transform infrared spectrometer （FTIR） for the samples with p = 234 kg/m^3. Specific extinction coefficient spectra were then obtained by applying Beer＇s law. Finally, by using the diffusion approximation, the specific Rossland mean extinction coefficients and radiative thermal conductivities were obtained for various temperatures. The results show that the specific spectral extinction coefficient of xonotlite is larger than 7 m^2/kg in the whole measured spectra, and diffusion approximation equation is a reasonable description of radiative heat transfer in xonotlite insulation material. The specific Rossland mean extinction coefficient of xonotlite has a maximum value at 400 K and the radiative thermal conductivity is almost proportional to the cube of temperature.

Inverse Radiation Problem of Boundary IncidentRadiation Heat Flux in Semitransparent Planar Slabwith Semitransparent Boundaries

An inverse method is presented for estimating the unknown boundary incident radiation heat flux onone side of one-dimensional semitransparent planar slab with semitransparent boundaries from theknowledge of the radiation intensities exiting from the other side. The inverse problem is solved usingconjugate gradient method of minimization based on discrete ordinates method (DOM) of radiativetransfer equation. The equations of sensitivity coefficients are derived and easily solved by DOM, withthe result that the complicated numerical differentiation commonly used in solving sensitivity coefficients is avoided. The effects of anisotropic scattering, absorption coefficient, scattering coefficient,boundary reflectivity, fluid temperature outside the boundaries, convection heat transfer coefficients,conduction coefficient of semitransparent media and slab thickness on the accuracy of the inverse analysis are investigated. The results show that the boundary incident radiation heat flux can be estimatedaccurately, even with noisy data.

Controlling Thermal Conduction by Graded Materials

Manipulating thermal conductivities are fundamentally important for controlling the conduction of heat at will. Thermal cloaks and concentrators, which have been extensively studied recently, are actually graded materials designed according to coordinate transformation approaches, and their effective thermal conductivity is equal to that of the host medium outside the cloak or concentrator. Here we attempt to investigate a more general problem: what is the effective thermal conductivity of graded materials? In particular, we perform a first-principles approach to the analytic exact results of effective thermal conductivities of materials possessing either power-law or linear gradation profiles. On the other hand, by solving Laplace's equation, we derive a differential equation for calculating the effective thermal conductivity of a material whose thermal conductivity varies along the radius with arbitrary gradation profiles.The two methods agree with each other for both external and internal heat sources, as confirmed by simulation and experiment. This work provides different methods for designing new thermal metamaterials(including thermal cloaks and concentrators), in order to control or manipulate the transfer of heat.

One-Dimensional Analysis of Supersonic Two-Stage HVOF Process

The one-dimensional calculation of the gas/particle flows of a supersonic two-stage high-velocity oxy-fuel(HVOF) thermal spray process was performed. The internal gas flow was solved by numerically integrating theequations of the quasi-one-dimensional flow including the effects of pipe friction and heat transfer. As for the supersonicjet flow, semi-empirical equations were used to obtain the gas velocity and temperature along the centerline. The velocity and temperature of the particle were obtained by an one-way coupling method. The material ofthe spray particle selected in this study is ultra high molecular weight polyethylene (UHMWPE). The temperaturedistributions in the spherical UHMWPE particles of 50 and 150 m accelerated and heated by the supersonic gasflow was clarified.

Homogenization and Upscaling for Diffusion,Heat Conduction,and Wave Propagation in Heterogeneous Materials

We present a general homogenization method a periodic heterogeneous material with piecewise constants for diffusion, heat conduction, and wave propagation in The method is relevant to the frequently encountered upscaling issues for heterogeneous materials. The dispersion relation for each problem is first expressed in the general form where the frequency co （or wavenumber k） is expanded in terms of the wavenumber k （or frequency ω）. A general homogenization model can be directly obtained with any given dispersion relation. Next step we study the unit cell of the heterogeneous material and derive the exact dispersion relation. The final homogenized equations include both leading order terms （effective properties） and high order contributions that represent the effect of the microscopic heterogeneity on the macroscopic behavior. That effect can be lumped into a single dimensionless heterogeneity parameter β, which is bounded between -1/12≤β≤ 0 and has a universal expression for all three problems. Numerical examples validate the proposed method and demonstrate a significant computational saving.

Thermal Conductivity of Complex Plasmas Using Novel Evan-Gillan Approach

The thermal conductivity of complex fluid materials （dusty plasmas） has been explored through novel Evan-Gillan homogeneous non-equilibrium molecular dynamic （HNEMD） algorithm. The thermal conductivity coefficient obtained from HNEMD is dependent on various plasma parameters （T,k）. The proposed algorithm gives accurate results with fast convergence and small size effect over a wide range of plasma parameters. The cross microscopic heat energy current is discussed in association with variation of temperature （1/Г） and external perturbations （Pz）. The thermal conductivity obtained from HNEMD simulations is found to be very good agreement and more reliable than previously known numerical techniques of equilibrium molecular dynarnic, nonequilibrium molecular dynamic simulations. Our new investigations point to an effective conclusion that the thermal conductivity of complex dusty plasmas is dependent on an extensive range of plasma coupling （P） and screening parameter （k） and it varies by the alteration in these parameters. It is also shown that a different approach is used for computations of thermal conductivity in 2D complex plasmas and can be appropriate method for behaviors of complex systems.