基于热辨识技术的硅基防热材料高温热导率测量

硅基防热材料是高超声速飞行器防热系统用重要材料之一,但由于硅基防热材料在高温条件下存在着复杂的物理化学变化,使得高温热导率的获取变得困难,这已成为飞行器防热系统精细化设计的主要制约瓶颈。基于热导率辨识方法,设计了一种能够实现硅基防热材料高温热导率测量的试验测量装置,对硅基防热材料在常温~800℃热导率进行了测量,并将测得的热导率外推应用到其他试验状态。结果表明,测得的硅基防热材料高温热导率合理可靠,具有很高的工程精度。该试验测量装置可实现不同温度下热导率的同步测量,测量成本低,效率高,这对其他防热材料的高温热导率测量具有重要的参考价值。     

Simultaneous Measurement of Thermal Conductivity,Thermal Diffusivity,and Specific Heat of Nanofluids

Effective thermal conductivity, effective thermal diffusivity, and effective specific heat of nanofluids were simultaneously measured by using a transient double hot-wire technique. Several types of nanofluids were prepared by suspending different volume percentages (1 to 5%) of titanium dioxide (TiO₂), aluminum oxide (Al₂O₃), and aluminum (Al) nanoparticles in ethylene glycol and engine oil. While effective specific heats of these nanofluids decrease substantially with nanoparticle volume fraction, the enhanced effective thermal conductivity and effective thermal diffusivity were found to increase significantly with increasing volumetric loading of these nanoparticles. The increments of the effective thermal diffusivity of nanofluids were slightly larger than their effective thermal conductivity values. Predictions of the effective specific heats of nanofluids by the volume fraction mixture rule-based model showed fairly good agreement (within 7%) with the experimental results. Besides particle volume fraction, particle material, particle shape and the type of base fluid were identified to have influence on these properties of nanofluids. Both the calibration results of the base fluids (system accurate to ≤2.7%) and uncertainty analysis (uncertainty ≤2.1%) indicate high accuracy of using the double hot-wire method to simultaneously measure the effective thermal conductivity, effective thermal diffusivity, and specific heat of nanofluids.     

热薄材料表面火焰传播的三维效应

利用能够限制自然对流的水平窄通道,对薄材料表面逆风传播火焰的三维效应进行了实验研究,参数包括气流速度、氧气浓度、燃料宽度等.结果表明,在足够宽的通道内,火焰传播随燃料宽度的变化,表现出随氧气浓度和气流速度的不同而变化的三维特性.侧面热损失和氧气扩散对火焰传播的影响,在各种氧气浓度和气流速度下,都限于燃料宽度小于10倍扩散长度.     

Dual-Wavelength Laser Flash Raman Spectroscopy Method for In-Situ Measurements of the Thermal Diffusivity: Principle and Experimental Verification

This paper presents an in-situ, non-contact, non-destructive dual-wavelength laser flash Raman spectroscopy method for measuring the thermal diffusivity. In this method, a heating pulse is used to heat the sample and another pulsed laser with a different wavelength and negligible heating effect is used as a probe to measure the sample temperature changes during the heating and cooling periods from the Raman peak shifts. The sample temperature rise and fall curves are measured by changing the delay between the heating pulse and the probing pulse with the thermal diffusivity then characterized by fitting the temperature curves. The time delay between the heating and probing pulses can be precisely controlled with a minimum step of 100 ps. Hence, the temperature variation can be scanned with an ultra-high temporal resolution of up to 100 ps, which significantly improves the measurement accuracy of transient thermal parameters. The measurement accuracy of this method has been verified using a bulk material model and experiments. The measured thermal diffusivity of a silicon sample has been obtained to be 8.8×10~(-5 )m~2/s with a 3% difference between the measured value and the average result for bulk silicon in the literature which verifies the reliability and accuracy of this method.     

循环流化床循环流率冲击法在线测量方法

开发了一种通过测量下落颗粒和靶板碰撞冲击力来确定颗粒流率的流量计,通过试验验证了该流量计的可行性,并研究了颗粒下落速度、颗粒粒度和颗粒密度对流量计的影响.建立了该冲击式流量计的理论模型,利用冷态流化床试验数据对理论模型进行了校验.结果表明：该流量计具有操作简便、测量准确、反应灵敏、易于校准、对提升管内的颗粒流动无干扰的特点;模型计算结果与试验数据较吻合,可利用模型简化流量计的校准程序,增加流量计的应用范围.     

石灰：石煅烧过程等效扩散系数的测量

对大颗粒石灰石煅烧过程中的测量等效扩散系数公式进行推导的基础上,通过测定其失重曲线和煅烧完成时间,获得了煅烧后产物层内的等效扩散系数。对多种石灰石进行了试验,发现在不烧结的情况下,各种石灰石在煅烧过程中其扩散系数间的差别很小。     

一种测量金属表面温度及辐射率的方法

通过在辐射图像测温方法中引入光谱辐射率修正,提出一种非接触式、精确测量高温金属表面温度及辐射率的方法.利用光谱仪根据高温金属表面的光谱信息计算单色辐射率随波长变化的曲线;使用彩色CCD摄像机拍摄高温金属表面的彩色图像,结合单色辐射率修正曲线从红、绿单色辐射强度分布中比色计算金属表面温度和辐射率.以一块出炉钢坯为实验对象验证该方法的准确性.结果表明:测量结果能够真实反映钢坯表面温度分布,给出受热不均匀性信息,可用于指导改进加热工艺.     

Influence of the Window Thermal Diffusivity on the Silicon Wafer Temperature in a Rapid Thermal System

The heating of a silicon wafer in a rapid thermal process is studied by numerical simulation. In the model, the equations of conservation of mass and energy are solved with the finite-volume method and the determination of the solutions of the radiative transfer equation is based on the Monte-Carlo method. The results of numerical simulations, without optimization and in steady state, show a close relationship between the thermal profiles of the silicon wafer and the ones of the quartz window. By introducing a high thermal diffusivity value for the window, the homogeneity of the wafer temperature is improved by 54%. The effect of heat storage by the quartz window on the temperature profile of the silicon substrate is hence well appreciated. Finally, a selection of materials is proposed for the implementation of the high diffusivity infrared window.     

用于现场测量深层岩土导热系数的简化方法

为便于工程上实现应用现场测量确定实际介质的物性,采用一种简化的传热分析方法确定深层岩土导热系数。该方法不需要测量钻孔中埋管的具体位置、上升管和下降管之间的距离以及埋管和回填材料的特性等参数,可消除上述参数测量带来的误差。通过现场测量地下埋管回路的加热热流、回路循环水流量以及回路出入口水温度随时间的变化,利用简化分析和最优化估计方法,确定了某工地地下岩土的导热系数,检验证实了该方法的实用性和可靠性。     

A Constitutive Equation of Thermoelasticity for Solid Materials

A new constitutive equation of thermoelasticity for crystals is presented based on the interatomic potential and solid mechanics at finite temperature. Using the new constitutive equation, the calculations for crystal copper and graphene are carried out under different loading paths at different temperatures. The calculated results are in good agreement with those of the previous thermoelasticity constitutive equation based on quantum mechanics, which clearly indicates that our new constitutive equation of thermoelasticity is correct. A lot of comparisons also show that the present theory is more concise and efficient than the previous thermal stress theory in the practical application.     

Optimization of Thermal Insulation Performance for the Porous Materials

ABSTRACT

Porous materials are widely used in porous media filtration, membrane separation, catalyst substrates, solid fuel cells, insulation, and other fields. When the porous material used in the field of insulation, heat transfer characteristics become its most important performance parameters. The heat transfer characteristics of porous material is a complex issue affected not only by solid elements and porosity, it is also affected by composite structures. Therefore, how to optimize the heat transfer properties of porous materials is a problem to be urgently solved. In this paper, the numerical method is used to study the effects of pore size, pore shape, pore connectivity, porosity and so on. It is found that pore shape, pore connectivity and gas conductivity have great impacts on the heat transfer of porous materials. The effect of pore arrangement is very little. The design optimization of porosity is affected by porous material mechanical property.     

双弯管法固相质量流量测量误差的标定

采用弯管流量传感器测量固相质量流量时,固相质量流量与其影响因素之间存在着复杂的非线性关系,这给固相流量的测量带来困难。在双弯管法基础上对其进行优化,利用小波神经网络对实验数据进行训练,给出了固相质量流量与综合流量系数β的复杂非线性关系,并对实验数据进行预测。预测结果与实验结果吻合较好,最终误差不超过5%,实现了对测量误差的标定。     

Influence of Participating Radiation on Measuring Thermal Conductivity of Translucent Thermal Insulation Materials with Hot Strip Method

The hot strip method, as one typical transient method, is widely used to measure the effective thermal conductivity of thermal insulation materials at various temperatures. Since the test theory is based on solving the energy equation via heat conduction, the test result will be questionable when measuring thermal insulation materials, such as silica aerogel and photovoltaic glazing, in which the participating thermal radiation is a dominant heat transfer mode at high temperature. In this study,...     

城市固体废弃物中氯含量的分析方法比较

低品位固体燃料如固体废弃物和生物质等通常含有氯元素（Cl）。在热化学过程中,燃料中的Cl会对颗粒物的排放和设备的运行造成一定的影响,并造成设备的腐蚀,因此有必要准确地量化燃料中的Cl含量。本文利用已有的Cl测定方法如燃烧法（氧弹燃烧法、艾士卡法）、水萃取法和XRF法对纯NaCl、PVC和固体废弃物模拟组分和厨余沼渣中的Cl含量进行检测和比较,提出一套能准确定量出含多种氯化物的城市固体废弃物中Cl含量的方法。结果表明,单一采用燃烧法、水萃取法和X射线荧光（XRF）法均无法准确量化城市固体废弃物中Cl的含量,而采用水萃取联合艾士卡法可以较准确地检测出城市固体废弃物中的Cl含量。     

活塞热负荷测试及有限元分析

本文对国内外目前对活塞温度场测试的方法进行了具体的阐述，并对各方法的优缺点进行了说明。     

瞬态热线法测量煤层气水合物导热系数的实验研究

煤层气(瓦斯)的储存和运输是实现煤层气能源利用的重要前提,水合物法是将来煤层气等气体固化储运的主要技术之一。煤层气水合固化储运过程受热量传递的控制,而开展瓦斯水合物的热量传递机理研究,其导热系数是必须要知道的热物性参数。基于瞬态热线法原理,建立了一套测试设备对瓦斯水合物的导热系数进行了实验研究,获得该瓦斯水合物样品导热系数及其和温度的关系。从瓦斯水合物的热物性因素方面支持了以NGH(水合物储运)形式对瓦斯进行水合固化储运的可行性。     

活塞热负荷测试及有限元分析

本文对国内外目前对活塞温度场测试的方法进行了具体的阐述,并对各方法的优缺点进行了说明.     

热网络法在发动机舱温度场仿真中的应用

对应用于温度场分析的热网络方法及基于热网络法的软件SINDA/FLUINT进行了介绍.利用热网络法和流体网络法对某发动机舱进行热仿真与热分析.建立了飞行器发动机舱各部件与其内外流体之间的网络关系及仿真模型,并进行耦合求解,得到此发动机舱各部件不同位置的温度分布,并对优化方案进行了仿真.其结果为发动机舱热分析及布局设计提供了参考.     

陶土基高温相变蓄热复合材料的制备

高级陶瓷基高温相变蓄热复合材料具有蓄热密度较高、基体耐腐蚀强等优点,但也存在制作成本高的缺点。本研究采用粉末烧结工艺将陶土分别同性能优良的高温熔融盐复合,成功地制备出蓄热密度高、耐腐蚀性好且成本低廉的相变蓄热复合材料。并对相变蓄热复合材料制备过程的工艺参数进行初步研究。