Normal Spectral Emissivity Research Articles

A Measurement Device for the Normal Spectral Emissivity of Materials Under Low-Temperature and Vacuum Conditions

Based on parallel light, a device for measuring sample emissivity under vacuum and low temperature was established. In this paper, a new emissivity measurement formula was designed, which replaces the derivation of Kirchhoff’s law of thermal radiation. The device is designed with a light-weight blackbody, an improved cooling speed, and an improved PID temperature control system to achieve a good temperature stability, close to 1 mK. The device is capable of measuring within a wavelength range of 4 μm to 16 μm. The results of the uncertainty assessment show that the uncertainty of the normal emissivity is better than 1.6% in the range of 4 μm to 7 μm, and better than 0.6% in the range of 7 μm to 14 μm (k = 1) at 0 °C.

Normal spectral emissivity measurement of thermal management materials for electronic components in the 2–14 μm range

Reducing the operating temperature of electronic components is an effective method for enhancing their performance. Selecting suitable thermal management materials is crucial for optimizing cooling efficiency. Normal spectral emissivity, a dimensionless physical quantity, is key in assessing a material’s capability for radiative cooling. This paper outlines the construction of a reflective infrared emissivity measurement apparatus using the IS-50 Fourier Transform Infrared Spectrometer. A gold-coated diffuse integrating sphere was strategically placed in the spectrometer’s sample chamber. By ingeniously leveraging the spectrometer’s original optical path, a dual-sided gold-coated mirror was employed to capture both incident and reflected light, enabling accurate measurements of the normal spectral emissivity of materials used for cooling electronic components. The measurement results for typical materials were consistent with those reported in the literature, satisfyingly so. The uncertainty of the measurement setup was thoroughly evaluated, achieving a combined uncertainty of better than 1 %. This experimental study measured the normal spectral emissivity of various thermal management materials and analyzed the influence of temperature on normal spectral emissivity. These results provide crucial data support for thermal design, simulation analysis, and temperature monitoring in the development of thermal structures for electronic components.

In-situ measurement method for surface temperature and normal spectral emissivity of TC-4 high-temperature alloy based on thin film interference mechanism model

This paper proposes a novel in-situ measurement method for surface temperature and normal spectral emissivity of thermally oxidized TC-4 high-temperature alloy, and establish a model for solving temperature and normal spectral emissivity based on the thin film interference mechanism. The results indicate that the temperature calculations are in good agreement with the measurements from surface thermocouples, with a maximum error of less than 3 K within the temperature range of 473 K to 973 K. The maximum error in the total directional emissivity within the wavelength range of 2 μm to 14 μm is 0.014. The measurement method and apparatus exhibit excellent repeatability, with the standard deviation of multiple measurements of normal spectral emissivity at temperatures of 473 K and 973 K is 0.035, 0.019, respectively. This method provides an effective solution for addressing the issue of fluctuating emissivity on the thermally oxidized surface of TC-4 high-temperature alloys over service time.

Thermophysical properties of Ni-Ti melts measured by electromagnetic levitation method using static magnetic field

The normal spectral emissivity, molar heat capacity at constant pressure, and thermal conductivity of Ni-Ti melts were measured during electromagnetic levitation under a static magnetic field. The emissivity and heat capacity of the Ni-Ti melts were measured under a 3 T static magnetic field. The temperature range for the emissivity measurements was 1240–1839 K, and the temperature range for the heat capacity measurements ranged was 1223–1851 K. The emissivity and heat capacity of the Ni-Ti melts, except for the Ni mole fractions (xNi) of 0 and 0.25, showed without temperature dependence within the experimental temperature range. Furthermore, the heat capacity was larger than the ideal solution over the whole range of compositions. The emissivity of the Ni-Ti melts was discussed based on the Drude model. The temperature dependence of thermodynamic functions, such as enthalpy of mixing, excess entropy, and excess Gibbs energy, were calculated using excess heat capacity. The thermal conductivity of Ni-Ti melts was measured under a static magnetic field of 10 T. The temperature range for the thermal conductivity measurements was 1177–1900 K. The thermal conductivities of the Ni-Ti melts increased with increasing temperature, exhibited a local minimum for xNi = 0.75, and were higher than those calculated using the Wiedemann–Franz laws. This difference in thermal conductivity was discussed by considering the contribution of atomic vibrations.

Normal spectral emissivity measurement study of high-temperature alloy (316L) at 673–1273 K with a thermal oxidation surface

One effective approach to better understanding the performance characteristics of high-temperature alloys is to study their thermal oxidation behavior, and to accurately determine their spectral emissivity is helpful for increasing the accuracy of temperature measurements. Using a self-developed high-temperature emissivity testing system, the normal spectral emissivity across the range 673–1273 K and a spectral band of 1–14 μm was measured relative to this background radiation. The normal spectral emissivity of 316L high-temperature alloy was investigated during the thermal oxidation process. The change in emissivity of 316L high-temperature alloy during thermal oxidation was observed. The emissivity of the 316L high-temperature alloy undergoes great changes during thermal oxidation; for example, at 1273 K it was 0.055 in its un-oxidized state but after 50 h’ thermal oxidation went up to 0.829. Below 1073 K the emissivity of 316L high-temperature alloy in 8–14 μm range showed little change, making it ideal for radiation thermometry. By fitting the measurement data, we derived that the emissivity of 316L high-temperature alloy has an exponential relationship with thermal oxidation temperature, and is a power function relationship with thermal oxidation time.

Melting spectral emissivity measurement of metal during the melting and solidification process

In the field of energy-intensive industrial processes, investigating the spectral emissivity of molten metals is crucial for improving energy utilization and efficiency. However, previous research efforts have not fully explored the measurement of melting emissivity. This study presents an effective method for measuring the spectral emissivity of molten metals. A new experimental apparatus was developed to measure the melting spectral emissivity within a range of 2–8 μm and temperatures ranging from 873 K to 2373 K. The sample was rapidly melted using a specially designed electromagnetic cold crucible, while its spectral radiance was detected using a Fourier transform infrared (FTIR) spectrometer. To enhance energy utilization rate, numerical simulation of the cold crucible improved induction heating performance. Additionally, calculating radiation within the cylindrical chamber enhanced measurement accuracy of emissivity. To validate the reliability of this apparatus, normal spectral emissivity measurements were conducted on liquid nickel. The results demonstrate that comprehensive uncertainty associated with liquid nickel's spectral emissivity does not exceed 1.82 %. Furthermore, verification based on the Drude-Roberts model confirms normal spectral emissivity values for liquid nickel as well.

Thermophysical Properties of Vanadium Melts and Discussion of Thermal Diffusivity in Mott’s Theory

The temperature dependence of density, normal spectral emissivity, heat capacity at constant pressure, and thermal conductivity of the V melt were measured with high accuracy using electromagnetic levitation in a static magnetic field. Surface vibration, translational motion, and convection of the electromagnetically levitated droplet sample were suppressed by the magnetic field. In the measurement of thermal conductivity, convection in the V-melt was sufficiently suppressed by the application of a field of 7 T or higher. In this study, the measured emissivity and thermal conductivity are compared with those evaluated using the free-electron models (Drude model and Wiedemann–Franz rule). Correlations between the density of states and thermal diffusivity at the Fermi energy of transition metals in the liquid state are investigated and the applicability of Mott's s–d scattering model is discussed.

Data reduction and uncertainty assessment of the direct pulse heating technique with both contact and radiance temperature measurements

This work presents a data reduction procedure of the direct pulse heating technique with both contact and radiance temperature measurements. The technique is applied for the measurement of thermophysical properties of electroconductive solids over a wide temperature range, i.e., from room temperature up to about 2300°C. Absolute and radiance temperatures of a tested material are measured by thermocouple and radiation thermometer, respectively and these and other experimental data are then reduced to the values of specific heat, specific electrical resistivity, hemispherical total emissivity and normal spectral emissivity of the tested material. The related data reduction and corresponding uncertainty assessment for each property is described in detail. An example of uncertainty assessment is given for the recent measurement of specific heat, specific electrical resistivity, hemispherical total emissivity and normal spectral emissivity at 900 nm of molybdenum alloy TZM specimens.

Fast Measuring Device for the Normal Spectral Emissivity in a Broad Temperature Range

Fast Measuring Device for the Normal Spectral Emissivity in a Broad Temperature Range

A multispectral radiometry method for measuring the normal spectral emissivity and temperature

A multispectral radiometry method was developed to simultaneously determine normal spectral emissivity of continuum spectra and temperature of materials. Linear dependence assumption would be a constraint to associate the spectral emissivity to the temperature when spectral radiance for various spectrum was measured within small temperature differences. The methodology was evaluated for different parameter constraints, and validated by seven emissivity hypothesis models. To verify the reliability of the experimental device and the multispectral radiometry method, the spectral emissivities of graphite at high temperatures were verified that the deviations between the official experimental data and the results in this work are all less than 5 %. Besides, the spectral emissivity and temperature of the graphite-carbon fiber composite in the spectral range of 0.3–2.5 μm at 1473–1873 K were measured. The temperature uniformity of the sample front surface was evaluated, and the relative error of the temperature distribution is less than 2 %. The uncertainties of the spectral emissivity and temperature in the studied spectrum are less than5.0 % and 6.0 %, respectively. The method is useful for accurately measuring the sample spectral emissivity without direct temperature measurements at high temperatures.

Change in the Normal Spectral Emissivity during Melting of Elements

Change in the Normal Spectral Emissivity during Melting of Elements

Environmental conical nozzle levitator equipped with dual wavelength lasers

AbstractThe environmental conical nozzle levitator (E‐CNL) with dual‐wavelength lasers is an extreme environment materials characterization system that was designed to investigate ultra‐high‐temperature materials: refractory metals, oxides, carbides, and borides above 3000 K in a controlled atmosphere. This article details the characterizations using this system to establish its high‐temperature capabilities and to outline ongoing work on materials under extreme conditions. The system has been used to measure the melting point of several oxide materials (TiO2, Tm = 2091 ± 3 K; Al2O3, Tm = 2310 3 K; ZrO2, Tm = 2984 31 K; and HfO2, Tm = 3199 ± 45 K) and several air‐sensitive refractory metals (Ni, Tm = 1740 K; Ti, Tm = 1983 K; Nb, Tm = 2701 K; and Ta, Tm = 3368 K—note: mean ± standard deviation) during levitation which matched literature values within 0.17–2.43 % demonstrating high accuracy and precision. This containerless measurement approach is critical for probing properties without container‐derived contamination, and dual‐wavelength laser heating is essential to heat both relatively poor electrical conductors (some refractory metals and carbides) and insulators (oxides). The highest temperature achieved utilizing both lasers in these experiments was ∼4250 ± 34 K on a 76.6 mg, molten HfO2 sample using a normal spectral emissivity of 0.91. Stable levitation was demonstrated on spherical samples (yttria‐stabilized zirconia) while adjusting levitation gas composition from pure oxygen to pure argon, verifying atmospheric control up to 3173 K on solid or molten samples. These successes demonstrate the viability of in situ high‐temperature environmentally controlled studies potentially up to 4000 K on all classes of ultra‐high‐temperature materials in one system. These measurements highlight the E‐CNL system will be essential for the development of next‐generation ultra‐high‐temperature materials for hypersonic platforms, nuclear fission and fusion, and space exploration.

Thickness and Roughness Effect of Pr2NiO4+δ Coating on the Normal Spectral Emittance

Thickness and Roughness Effect of Pr2NiO4+δ Coating on the Normal Spectral Emittance

Influence of the oxidation on the optical properties of Mo-Si-Ti, Ta-Mo-Cr-Al and Ta-Mo-Cr-Ti-Al alloys

Three refractory element-based alloys were oxidized for 6 h at 1100 °C in air inside a muffle furnace and the way the oxidation, especially through the evolution of the surface composition and roughness, affects the optical properties of these materials is discussed here. The ternary Mo-20.0Si-52.8Ti (at%) serves as an example of Mo-based alloys, while the equimolar Ta-Mo-Cr-Al (TMCA) and Ta-Mo-Cr-Ti-Al (TMCTA) are typical of the class of oxidation-resistant refractory compositionally complex alloys. The normal spectral emissivity of these three samples was increased due to the oxidation process. Oxidized TMCA and TMCTA exhibit a solar absorptivity higher than that of state-of-the-art Ni-based alloys used for solar receivers in concentrated solar power plants. Thus, the two refractory compositionally complex alloys are considered promising candidates for solar thermal energy conversion application.

Study of the roughness effect on the normal spectral emissivity of GH3044

The normal spectral emissivity is a significant parameter characterizing the radiative capacity of the object's surface. However, the normal spectral emissivity of superalloys varies with the rough state of the surface, causing unacceptable errors in radiation thermometry and heat transfer calculation for aero-engines and gas turbines. A computational method for estimating the effect of roughness on the normal spectral emissivity of superalloys was established based on constructing randomly rough surfaces. Through this method, the effect of roughness on four emissivity models commonly used in multispectral radiometric thermometry (MRT) was computationally evaluated, and the relationship between roughness and spectral emissivity was quantitatively analyzed. In addition, the normal spectral emissivity of GH3044 superalloy with different rough surfaces at 300 K and high temperatures was experimentally measured and compared with the result calculated by this computational method. Their maximum relative error was close to ± 5 % for the rough surface without emissivity oscillation. This study promotes understanding the mechanism of normal spectral emissivity varying with roughness.

Simultaneous measurement of normal spectral emissivity and temperature of materials with low thermal conductivity

This study develops a measurement system and a method for measuring the normal spectral emissivity and temperature of low thermal conductivity materials at high temperatures. A self-design heating device using a synergistic heating treatment including a high-power laser and a radiation heating cavity is introduced, and a Fourier transform infrared spectrometer is utilized to measure the radiation signal of sample. Based on the temperature hypothesis model, which considers normal spectral emissivity keeps constant within small temperature difference less than 10.0 K, a method is proposed for realizing the inversion of normal spectral emissivity and temperature with the multispectral radiation signal. A genetic algorithm-based technique with big mutations is used to estimate the normal spectral emissivity and temperature of sample at high temperatures. The variation of blackbody radiation signals with the blackbody radiance is analyzed to verify the linearity for the detector of FTIR spectrometer. The apparent normal spectral emissivity of an alumina ceramic fiber is determined in the spectral range of 2.5–25.0 μm at 673–1273 K. Furthermore, the uniformity of temperature distribution on the sample surface and inside the sample is numerically evaluated. The standard uncertainty in the experiment at 1273 K is less than 4.0 % in the investigated bands.

Normal spectral emissivity characteristics of tungsten in the mid-infrared region

Tungsten is an important material constituting the first wall of the Experimental Advanced Superconducting Tokamak due to its excellent corrosion resistance. The temperature distribution of the first wall during the discharge process are the key to ensuring the safe and stable operation of the EAST. Therefore, it is necessary to explore the dependence of material emissivity on temperature and wavelength for improving temperature measurement accuracy. This work quantitatively explores the normal spectral emissivity of tungsten within the 3 μm to 5 μm in the temperature range between 100°C and 500°C based on the Fourier transform infrared spectrometer. The dependence of emissivity on wavelength and temperature are experimentally analyzed, and the possible functional relationship between the emissivity of tungsten and the surface temperature and the wavelength are established respectively. This work could lay the foundation for the application of multi-wavelength thermometry on temperature measurement of the first wall of the EAST.

Spectral emissivity measurement of free-falling particle groups

A solar energy receiver is a device that absorbs solar radiation and transfers the generated heat energy to a heat transfer medium. As a heat transfer medium in solar energy receivers, solid particles can safely absorb strong solar radiation flux and achieve a higher operating temperature. Hence, they have attracted considerable research interest. The emissivity of particles is an important parameter in numerical simulation and efficiency analysis of solid particle receivers. However, it is rarely reported, especially for dispersed particles flowing in receivers. In this study, a measurement system for the normal spectral emissivity of free-falling particles is designed and developed. The system is based on the energy method and uses an FTIR spectrometer as a radiation measurement device, which can achieve measurement in the wavelength range of 2.5–16 µm below 800 °C. The emissivity of the sheet SiC material is measured to verify the reliability of the system. The results are in good agreement with the data published in NIST. Furthermore, the effects of the particle material, temperature, and particle group thickness on the particle group emissivity are studied. It is found that the emissivity of gray ceramic sand particles is not sensitive to the temperature, whereas that of alumina ceramic particles is positively correlated with the temperature. The emissivity of the two particles increases rapidly with the release width of the particle group, which is related to the increase in the mass flow rate of the particle group. Finally, uncertainty analysis of the measurement system is performed. The results measured in this paper can provide the original emissivity data for heat transfer simulation and efficiency evaluation in the receiver.

Near-infrared normal spectral emissivity of molten Fe-Ni alloys by electromagnetic heating

The spectral emissivity of molten Fe-Ni alloys is especially critical to analysis the performance and quality of alloy. The near-infrared normal spectral emissivity of molten Fe-Ni alloys was measured at 1000–1600 nm in the temperature range of 1690–1845 K by a self-built measurement apparatus using the electromagnetic heating technology. The measurement apparatus mainly consists of the electromagnetic heating furnace, blackbody, optical fiber spectrometer and colorimetric thermometer. The dependence of near-infrared normal spectral emissivity of Fe-Ni alloys (Ni, Fe10Ni90, Fe30Ni70, Fe50Ni50, Fe70Ni30, Fe90Ni10 and Fe) on wavelength, temperature and composition were systematically investigated. The results show that the emissivity of Fe70Ni30 is higher in the iron-rich area, while the emissivity of Fe30Ni70 is the lowest in the nickel-rich area. Comparison of the measured and simulated results show that the emissivity of molten Fe-Ni alloys is reliable. The emissivity of Fe-Ni alloys provides reliable data for the research of alloys properties.

Normal spectral emissivity and heat capacity of Pd–Fe melts measured at constant pressure under electromagnetic levitation with a static magnetic field

The normal spectral emissivity at 807 and 940 nm and heat capacity at constant pressure of Pd–Fe melts were measured under electromagnetic levitation with a static magnetic field. The samples were made of Fe of mass purity 99.9985%. The present emissivity of Fe melts was relatively low compared with previously reported data using Fe with purity lower than 99.95% mass purity. The spectral emission of the Fe melts was analyzed using their normal spectral emissivity obtained from the Drude model. The excess heat capacity of Pd–Fe melts was evaluated from the measured heat capacity of Pd–Fe melts. Applying the Lupis–Elliot rule, we concluded from the obtained excess heat capacity that the enthalpy of mixing and excess entropy of the Pd–Fe melts should be negative. The composition dependence of the enthalpy of mixing, excess entropy, and excess Gibbs energy of Pd–Fe melts were evaluated using data obtained in this study and the literature.