The surface tension of liquid silicon at high temperature

The measurement of the surface tension of liquid silicon has a long history with many results but no general agreement between them. Two values at the melting temperature are cited in reviews (749 and 827 mN/m [N. Eustathopoulos, E. Ricci, B. Drevet, Note Technique DEM No. 97/58, CEA, 1997]) but there are few arguments to determine the correct one. In the present study, new data for the surface tension obtained with the analysis of characteristic frequencies of a levitating drop are presented. The effect of oxygen and nitrogen are also considered. These data are compared with former data obtained with contactless techniques. The most recent surface tension values obtained with drop weights ranging on two orders of magnitude and environments of different natures (argon, hydrogen and vacuum) show excellent agreement (within a 1.5% margin) at temperatures between 1350 K and 2400 K. The comparison of these data to others obtained with different techniques, reveal a good agreement, except those obtained with the sessile drop technique on some supports like BN, SiO₂ and MgO. However, these special cases may be connected with the reactivity of silicon with these supports.     

Effect of different parameters on the in situ thermal conductance evaluation

In the last years many studies have been carried out on the possible improvements of the in situ thermal conductance measurement; as well known, this has to be derived by recorded values of temperatures and heat fluxes. A big effort has been addressed in the implementation and comparison of different analysis methods. The aim of this paper is to widen the existent literature in the study of the influence of different kinds of input data on the final result. First the problem of analysing input data with significant drift in temperature is considered, adopting both nominal clean and noise affected data. Then the effect due to the presence of the Heat Flux Meter (HFM) on the thermal field of the testing element has been analysed, as well as the possibility of recording HFM surface temperature. These studies are based on Finite Element Method (FEM) simulations; both nominal clean and noise affected data have been considered as input. Finally, a difference in emissivity between the heat flux meter and internal plaster surface has been analysed by means of FEM simulations based on nominal clean data. An overall estimation of the occurred deviations in the different cases is shown.     

Measurement technology for material emissivity under high temperature dynamic heating conditions

The thermal dissipation of radiation is main heat shield mechanism for non-ablative thermal protection materials on hypersonic vehicles withstanding high temperature dynamic heating cycle during endo-atmospheric ascent, cruise and reentry. Therefore, it is necessary to know the thermal radiative properties of the material under the simulated high temperature dynamic heating conditions on the ground. The emissivity depends on the surface state and its temperature. A new simultaneous measurement technology of emissivity and varying surface temperature is proposed under high temperature dynamic heating conditions. This new technology solved synchronous measurement problems by utilizing spectral signal of Fourier transform infrared (FTIR) spectroscopy. The calibration of different temperature ranges, the background disturbances, the influences on temperature measurement by wavelength range and its corresponding fluctuations of measurement signal, were thoroughly investigated. The measured results of steel and graphite as reference materials proved the effectiveness of this simultaneous measurement technology and showed great potential in engineering applications under high temperature dynamic heating conditions.     

Experimental testing of correlations to calculate the atmospheric “transparency window” emissivity coefficient

An experimental verification of the correlations existing in literature for the calculation of the coefficient of emissivity inside the atmospheric transparency window, situated in the wavelength band 8–14 μm, has been performed. In addition, the authors propose a new correlation for the calculation of the coefficient ε_in, easily applicable since it presupposes the knowledge of the global emissivity of the sky, for which there are a lot of correlations in literature.     

Temperature behaviour of the substrate surface during growth of nanocrystalline silicon carbide films by deposition of 120 eV carbon and silicon ions

Changes in the temperature of nanocrystalline SiC film surface were measured during film growth by direct deposition of carbon and silicon ions onto substrates at ∼800 °С. It has been found that the initial stage of the film growth is characterized by uncontrolled variations of the surface temperature, which are observed for constant values of the deposition parameters. The energy components of the temperature balance on the film surface during its growth under conditions of direct ion deposition are analyzed. It is shown that magnitudes of temperature variations depend on the energy and current density of the deposited ions and on the ratio of the emissivity coefficients of the substrate material and silicon carbide. If this ratio is 1:6, the temperature rise at the initial growth stage reaches 160 °С when using 120 eV ion energy. For ion deposition onto silicon carbide substrates these uncontrolled temperature deviations at the initial stage of film growth were not observed.     

Emissivity of substrate supported films

Results of experimental measurements of emissivity carried out on cobalt oxide and nickel sulphide films deposited on aluminum substrates are reported in this paper. Experimental results supported the general behaviour of variation of emissivity with film thickness as reported theoretically. The theoretical model is based on the interaction and attenuation of the emitted wavelengths from the substrate and film materials.     

Silver-based low-emissivity coatings for architectural windows: Optical and structural properties

Spectrally selective coatings are, nowadays, deposited onto architectural windows to be employed in commercial and residential buildings for the purpose of saving energy. In this work, the fundamental optical and structural properties of two types of low-emissivity silver-based coatings deposited onto glass, Ag and SnO₂/Ni-Cr/Ag/Ni-Cr/SnO₂ (Vitrage à couches avec une forte reflexion des rayonnements thermiques, European Patent EP 0 506 507 B1) are analyzed. It has been demonstrated that the silver-based multilayer coatings give an efficient heat isolation due to their low emissivity values, thus not deteriorating the optical properties in the visible range given by the glass substrate. From Atomic Force Microscopy measurements it has been determined that the Ag layer has a more homogeneous grain size when is deposited onto the Ni-Cr layer than when is deposited onto glass.     

抽气热电偶隔热罩黑度变化下陶瓷窑高温烟气测温误差分析

为了研究隔热罩黑度变化下抽气热电偶的测试误差，根据陶瓷窑内高温烟气静态和动态不同情况，对抽气热电偶测试误差进行推导与计算，结果显示，由于隔热罩黑度变化，高温烟气抽气热电偶测试误差较大，必须对输出信号进行修正。     

在红外目标模拟系统中温度及发射率对辐射照度的影响

本文以辐射理论出发,导出了在3～5μm范围内探测面上的辐射照度与目标光源的温度及发射率的关系。讨论了目标光源的温度及发射率的变化对探测面上辐射照度的影响,并给出了△E与△T及△ε的关系曲线。     

基于LRO卫星Diviner热红外发射率的尺度问题研究

尺度问题作为对地观测的主要挑战和遥感科学的核心问题,一直以来备受关注.国内外学者对这一问题进行了大量的基础理论研究和科学验证工作,探讨和解决了许多与遥感尺度相关的核心问题.当然,在遥感探测内容中,发射率和温度遥感中也存在明显的尺度问题.以往混合像元发射率尺度问题的研究往往集中于地球表面,幸运的是,月球为我们研究这一问题提供了绝佳的对象.同时,伴随着Diviner热辐射探测器月表测量数据的不断更新,混合像元中发射率尺度问题的具体研究及其定量描述逐渐变为可能.本文以月表Diviner热红外测量数据为基础,在充分研究和分析Diviner数据特征和发射率计算方法的前提下,以不同尺度下的Apollo 15登月区或者登月点热红外发射率为研究对象,依据混合像元发射率定义,分析和研究了混合像元中发射率的尺度转换和尺度效应两个问题,从发射率数值角度出发讨论和验证了尺度变换和尺度效应的一般规律,并给出定量描述,希望能够为尺度变换和尺度效应等问题的研究提供理论支持和实验依据.