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.     

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.     

Effects of Diesel Concentration on the Thermal Conductivity,Specific Heat Capacity and Thermal Diffusivity of Diesel-Contaminated Soil

High energy consumption is a serious issue associated with in situ thermal desorption(TD)remediation of sites contaminated by petroleum hydrocarbons(PHs).The knowledge on the thermophysical properties of contaminated soil can help predict accurately the transient temperature distribution in a remediation site,for the purpose of energy conservation.However,such data are rarely reported for PH-contaminated soil.In this study,by taking diesel as a representative example for PHs,soil samples with constant dry bulk density but different diesel mass concentrations ranging from 0％to 20％were prepared,and the variations of their thermal conductivity,specific heat capacity and thermal diffusivity were measured and analyzed over a wide temperature range between 0℃ and 120℃.It was found that the effect of diesel concentration on the thermal conductivity of soil is negligible when it is below 1％.When diesel concentration is below 10％,the thermal conductivity of soil increases with raising the temperature.However,when diesel concentration becomes above 10％,the change of the thermal conductivity of soil with temperature exhibits the opposite trend.This is mainly due to the competition between soil minerals and diesel,because the thermal conductivity of minerals increases with temperature,whereas the thermal conductivity of diesel decreases with temperature.The analysis results showed that,compared with temperature,the diesel concentration has more significant effects on soil thermal conductivity.Regardless of the diesel concentration,with the increase of temperature,the specific heat capacity of soil increases,while the thermal diffusivity of soil decreases.In addition,the results of a control experiment exhibited that the relative differences of the thermal conductivity of the soil samples containing the same concentration of both diesel and a pure alkane are all below 10％,indicating that the results obtained with diesel in this study can be extended to the family of PHs.A theoretical prediction model was proposed based on cubic fractal and thermal resistance analysis,which confirmed that diesel concentration does have a significant effect on soil thermal conductivity.For the sake of practical applications,a regression model with the diesel concentration as a primary parameter was also proposed.     

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.     

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。     

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。     

热网络法概论

对应用于温度场分析的热网络方法进行了系统的介绍。介绍了热网络法的原理及其应用领域,总结了该方法在卫星、航空航天、建筑、油田等更多领域的应用成果,对基于热网络法的软件SINDA/FLUINT也进行了详细介绍。     

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.     

蓄热式加热炉的热平衡测试与分析

随着蓄热式加热炉的逐步推广应用,近10年迅速成为一项值得推广的节能环保新技术,在不同工业炉上得到快速应用。通过对韶钢蓄热式加热炉的热平衡测试与分析来评价蓄热式加热炉的实际使用效果,以及热平衡测试找出设计、施工和使用中的薄弱环节,为发挥蓄热式加热炉的优势提出建议,为同行建设和使用好蓄热式加热炉提供一些参考。     

热箱-热流计法现场检测围护结构热阻

探讨了采用热箱-热流计法检测建筑物围护结构的热阻以实现非采暖季进行检测。由于检测面大量广,因此检测方法必须相对地简便易行。根据这一原则提出对热箱法中由于侧向热流引起的误差采用把在两侧测得的热流值加权平均的方法加以修正,以实现现场测试基本的精度。根据建筑围护结构检测的特定情况,用数值模拟的方法归纳总结出适用于不同保温形式的围护结构的加权平均系数,即修正系数。通过对多种常见的围护结构的形式的修正系数及其相应误差值的分析,表明这种修正方法可以满足对于建筑围护结构热工性能现场检测的要求。     

The Ultrafast Laser Pump-Probe Technique for Thermal Characterization of Materials With Micro/Nanostructures

Advances in nano-electronics, nano-optics, energy harvesting materials, and nanoparticle-based photothermal therapies are motivating studies of the thermal properties of micro/nanostructures. Thus, the demands for highly sensitive and accurate thermal measurement techniques are encouraged for both fundamental studies and industrial applications. The time-domain thermoreflectance (TDTR) method, based on an ultrafast pump-probe technique, enables high-fidelity thermal measurements at the micro/nanoscale and the observation of dynamic processes with sub-picosecond time resolution. TDTR is an optical technique, capable of measuring the thermal properties of micro/nanostructures, including thermal conductivity and interfacial thermal conductance of bulk substrates, thin films, and nanoparticles, among others. Here we review some recent developments in the state-of-the-art ultrafast pump-probe method applied to study the thermal and magnetic properties of materials at the micro- and nanometer scales. We also discuss in detail improvements to this technique by presenting several example extensions to its capabilities.     

改善材料选择性热辐射的方法

从波动力学的观点出发，解析了热辐射波和材料内部的阻尼谐振子之间的相互作用过程，从而揭示了热辐射波在材料内部的发射、吸收、透射和反射机理。基于洛伦兹色散理论，分析了影响材料选择性热辐射的因素，提出了改善材料选择性热辐射复合化和超细化方法。实验研究证实了这些方法的正确性和可靠性。