Thermodynamic properties by levitation calorimetry — V. High-temperature heat content of liquid gallium

The heat content (enthalpy) of liquid gallium relative to the supercooled liquid state at 298.15 K has been measured by levitation calorimetry over the temperature range 1412–1630 K. Thermal energy increments were determined using an aluminum block calorimeter of conventional design. The sharp decrease of C _p with increasing temperature observed just above the melting point does not persist up to the high temperatures of the present work. When combined with recent laser-flash calorimetry results from the literature, the present work indicates that C _p is 26.46 ± 0.71 J · g-atom^–1 · K^–1 over the temperature range 587–1630 K.Paper presented at the Japan-United States Joint Seminar on Thermophysical Properties, October 24–26, 1983, Tokyo, Japan.     

IR Radiative Properties of Solid and Liquid Alumina: Effects of Temperature and Gaseous Environment

An infrared spectrometer (spectral range 2–6 μm), coupled with a 9 μm pyrometer (Christiansen’s wavelength), has been developed to collect time-resolved measurements (32 spectra/s) of the spectral emissivity of alumina droplets (d≈ 3 mm) freely cooling in an aerodynamic levitation system from the liquid-to-solid phases [2800 → 1500 K]. The temperature and nature of the gaseous atmosphere surrounding the droplet (oxidizing/neutral/reducing) are two important parameters affecting the spectral emissivity in the semi-transparent range. Observations are discussed in the framework of the thermal activation and of the chemical interactions of alumina with the environment. Paper presented at the Seventh International Workshop on Subsecond Thermophysics, October 6–8, 2004, Orléans, France.     

Processing Method of Multi-Wavelength Pyrometer Data for Continuous Temperature Measurements

The processing of multi-wavelength pyrometer data is a problem that needs further improvements. The solutions developed in earlier decades generally assumed one particular mathematical relation for emissivity versus wavelength in the wavelength range of the measurements. Sometimes this assumption worked and produced acceptable results, but in many other cases this approach provided erroneous results. Individual results were strongly dependent on the assumed mathematical relation that often needed some prior knowledge of the emissivity behavior in the wavelength range. A new data processing method for a multi-wavelength pyrometer for continuous temperature measurements is presented. A linear relation between emissivity and true temperature at different wavelengths is assumed. Based on this assumption, the true temperatures and spectral emissivities at the two continuous temperature measurement points can be simultaneously calculated. Some experimental results for the practical data processing of measurements performed on a solid propellant rocket engine show that the difference between the calculated true temperature and the theoretical true temperature indicated by the rocket engine designer is within ±20 K. Paper presented at the Seventh International Workshop on Subsecond Thermophysics, October 6–8, 2004, Orléans, France.     

Spectral Emissivities and Emissivity X-Points of Pure Molybdenum and Tungsten

Prediction methods for thermophysical properties of metals and alloys such as emissivity are of great interest not only for science but also for the metal working industry as time-consuming and often expensive measurements may not be required. As recent results have shown, an assumed Hagen–Rubens relation for the prediction of emissivity based on electrical resistivity results was not found in the visible spectra. Within this work normal spectral emissivity results obtained with two complete different techniques are presented. On one hand, a multi-wavelength-pyrometry (MWLP) approach has been used to obtain emissivity as a function of temperature at 684.5, 902, and 1570 nm, and on the other hand, a radiance-comparison method was used to obtain emissivity isotherms as a function of wavelength for a range starting from 1 to 24 μm. From results of the radiance-comparison measurements an intersection of the isotherms, often referred to as the emissivity x-point, was found for both investigated materials, tungsten and molybdenum. According to these results, the x-point wavelengths are given by λ _x = 1.41 μm for tungsten and λ _x = 1.55 μm for molybdenum. Based on these x-points and the MWLP measurements, a new prediction method for the liquid-phase behavior of emissivity is developed and discussed. Paper presented at the Seventh International Workshop on Subsecond Thermophysics, October 6–8, 2004, Orléans, France.     

Measurement of band emissivity of porous spheres at high temperatures

A relatively simple technique has been developed to measure the band emissivity of spherical solids at high temperatures. The technique involves measuring the surface temperature of a sphere when in thermal equilibrium with a furnace enclosure, followed by isolating it from the enclosure by means of a shield. The emissivity is evaluated from the drop in energy flux from the pellet consequent upon changing the enclosure from an effectively black-body to a freely radiating one. The value of the band emissivity is validated by simulating the experimental cooling curve using independently measured values of the effective thermal conductivity and total emissivity of the solid to obtain internal consistency. In this way highly accurate values of band emissivity are obtained. The technique was applied to pellets of both reacted and unreacted mixtures of calcined-dolomite and silicon, as used in the commercial production of magnesium.     

红外发射率调制技术研究

物体红外发射率的调制具有广泛的应用前景.从理论上研究了红外发射率的调制机理,给出了三种调制发射率的技术途径:机械式、半导体载流子调制和电化学式.机械式发射率调制技术是利用不同发射率的材料组合来进行调制,通过调整不同材料在表面所占比例来调整发射率.半导体材料可通过调制PN结中的自由电子浓度实现红外发射率的调节.电化学式调制可通过多层薄膜实现.通过电场控制器件中变发射率薄膜层的离子和电子浓度,实现器件红外发射率的调制.     

基于FGMRES-PBTG算法的介质粗糙面散射特性的模拟

针对具有大介电常数介质粗糙面的电磁散射问题,提出了灵活的广义最小余量法(FGMRES)和基于物理意义的双网格法(PBTG)的混合算法,并对介质粗糙面的电磁散射系数和发射率进行了仿真.在PBTG算法的基础上,应用了FGMRES迭代算法求解矩阵方程.通过PBTG算法加速矩阵向量积和FGMRES算法加快迭代收敛速度,达到减少计算量和加快计算速度的目的.通过计算实例可知,FGMRES相对其他迭代法具有很好的收敛性,耗时较少,在满足精度要求的前提下,较其他迭代法明显加快了计算速度,并有效地模拟了介质粗糙面的电磁散射特性.     

海表面盐度的微波遥感--平静海面的微波辐射机理研究

基于平静海面微波辐射理论和海水相对电容率εr的经验公式,探讨了平静海面在L波段（1．4GHz）的微波辐射特性。依据两个不同的经验公式获得的海水相对电容率εr有较大差异,这种差异也体现在盐度反演结果上。海表面温度Ts越高,海表面盐度Ss对平静海面亮温（Tbv,或Tbh）的影响越大,即｜aTbv,bh／aSs｜越大。因此,在Ts较高的海域,Ss遥感容易达到较高的精度;反之,Ss反演的精度则会降低。采用小角度入射角观测方案进行Ss遥感具有优势。此时,Ss和Ts越高,则前述两种海水相对电容率εr经验公式反演Ss的差异越小。在较小的入射角条件下,对于具有较高Ts和Ss的平静海面,使用现有海水相对电容率εr经验公式反演Ss比较可行。而对于具有较低Ss的近岸海域,则反演的Ss可能产生比较大的误差。     

热处理对氧化铋在8μm～14μm波段内的发射率的影响

本文通过设计正交实验,采用不同的热处理工艺对着色颜料氧化铋粉末进行热处理,随后测量样品在8μm～14μm波段的平均法向发射率,并得出优化的热处理工艺路线;对各个影响因素进行的分析表明,温度是热处理过程中影响样品发射率变化的主要因素,并通过XRD、SEM、EDS等多种表征手段,分析了红外发射率变化的内在机理.结果表明,晶格畸变是引起发射率变化的主要因素,而由气体分子吸附引起的表面成分变化对发射率也有一定的影响.     

非同温对平面混合像元温度发射率分离的影响分析

在热红外光谱区域,假设非同温平面混合像元的发射率为r-emissivity,那么它的辐射温度是随波长变化的.以典型的由土壤和植被组成的非同温平面混合像元为例,分析了非同温对其辐射温度的影响,并给出体现辐射温度变化的可能的方法.利用模拟的热红外高光谱数据对该方法进行了验证,验证结果表明,该方法能够较好地刻画非同温平面混合像元辐射温度随波长的变化,提高了非同温平面混合像元r-emissivity的反演精度.