Emissivity Values Research Articles

An Ultra-Wideband Frequency Selective Rasorber with Low Infrared Emissivity.

The paper proposes an ultra-wideband frequency selective rasorber (FSR) with low infrared emissivity for the composite detection threat of both radars and infrared sensors. Firstly, the equivalent circuit (EC) method based on transmission line (TL) theory is utilized to analyze the absorption/transmission conditions. Then, based on the analysis above, sinusoidal microstrip lines with non-frequency-varying characteristics are adopted in the design, which significantly enhances the transmission bandwidth of FSR. The FSR demonstrates an absorption band ranging from 2.65 GHz to 8.80 GHz and a transmission band ranging from 9.15 GHz to 17.71 GHz. Furthermore, an infrared shielding layer (IRSL) exhibiting low emissivity in the infrared band and high transmittance in the microwave band is applied to the FSR. The simulation and experiment results verify that the IRSL-FSR demonstrates an ultra-wide transmission band ranging from 9.16 GHz to 17.94 GHz and an ultra-wide absorption band ranging from 2.66 GHz to 8.01 GHz. Additionally, it exhibits a low emissivity value (0.23) in 8-14 μm, providing a viable solution to the formidable challenge of radar-infrared bistealth for satellites and other communication-enabled flying platforms.

Radiative heat transfer in H<sub>2</sub>O and CO<sub>2</sub> mixtures

In this work, an approximate solution is presented to evaluate the heat exchange by radiation through a gaseous participating medium composed of and , which is valid for values of the product of the total pressure and the mean beam length (PL) from 0.06 to and temperatures (T) from 300 K to 2100 K. To approximate the exact solutions, the Spence root weighting method is used. For each set of PL; T values, the values of exact spectral emissivity and absorptivity and for the gas mixture are calculated using the analytical solution (AS) and the values of the emissivity and absorptivity of the mixture and , using the Hottel graphical method (HGM) and the proposed approximate solution. The weaker correlation fit corresponds to the HGM, with mean errors of ±15 % and ±20% for 54.2% and 75.3 % of the data evaluated, respectively, while the proposed method provides the best fit, with mean errors of ±10% and ±15% for 79.4% and 98.6 % of the data evaluated, respectively. In all cases, the agreement of the proposed model with the available experimental data is good enough to be considered satisfactory for practical design.

Role of Surface Energy Fluxes in Urban Overheating Under Buoyancy‐Driven Atmospheric Conditions

AbstractUrbanization alters land surface properties in absorbing, reflecting and emitting radiation as well as infiltrating, evaporating and storing water. This consequently modifies surface energy and water fluxes and, thus, urban climates. Weak synoptic flow, clear sky conditions and higher surface temperatures in cities compared to their rural surroundings create a buoyancy‐driven atmospheric circulation, in which surface energy fluxes become the main determinants of urban daytime overheating. Here, we demonstrate the role of surface energy fluxes for warming and cooling processes in the urban canopy layer under buoyancy‐driven atmospheric conditions. We improve and apply an integrated CFD‐GIS modeling approach to provide a detailed analysis of fine‐scale land‐atmosphere interactions and assess the surfaces' profound implications on energy and water exchange. We show that variations in the ratios of the surface energy fluxes to the net radiation can be separated from meteorological conditions (wind speed, air temperature and incoming solar radiation) and emissivity values, varying explicitly with changes in land surface type and water availability for vegetated areas. Based on the energy flux ratios, we introduce an approach to assess the surface‐induced warming and cooling effect and its contribution to urban overheating in the urban canopy layer, under buoyancy‐driven atmospheric conditions, directly applicable to strategic urban planning for climate change adaptation. Independent of meteorological conditions, this approach can be used to evaluate different surface materials (both natural and artificial) and climate adaptation measures, such as urban nature‐based solutions and blue‐green infrastructures, and to monitor changes in the energy and water balance.

A multi-objective design optimization for the exterior wall coatings of residential buildings in hot summer and warm winter regions

In building design and renovation, achieving thermal comfort and enhancing energy saving are two crucial objectives. To obtain trade-off solutions between these two objectives, a multi-objective optimization approach was proposed to optimize the key parameters of exterior wall coatings through the integration of Non-dominated Sorting Genetic Algorithm II with EnergyPlus. Three optimization scenarios (i.e., prioritizing energy saving, prioritizing thermal comfort, and prioritizing energy saving and thermal comfort equally) were investigated to help decision-makers design coatings. The results indicated that under the first scenario, the energy savings account for 21 % of comparison building (cooling energy intensity: 2.83 kWh·m−2·a−1, thermal comfort time: 4195 h), while the thermal comfort time is 4061 h. Under the second scenario, the thermal comfort time is 7 % greater, while the cooling energy intensity is 3.07 kWh·m−2·a−1. Under the third scenario, the energy savings are 8 %, and the thermal comfort time is 4295 h. Moreover, the effects of thermal parameters of coatings on thermal comfort and energy savings were investigated. Low thermal conductivity and longwave emissivity are beneficial for these two objectives. Hence, thermal conductivity and longwave emissivity values of 0.05 and 0.85, respectively, are recommended. However, the effects of solar reflectance on these two objectives are opposite. A high solar reflectance is beneficial for energy savings and unbeneficial for thermal comfort, so its value should be determined according to the objective priority. The investigate results could provide significant guidance for parameter design of exterior wall coatings for residential buildings located in hot summer and warm winter regions.

Experimental Measurement of Emissivity of Polished Steel Strips from a Continuous Annealing Line.

The long-term use of steel strip in various industries makes it an important semi-finished product, which makes it necessary to improve its chemical composition and mechanical properties, reduce its thickness and weight, expand the range of new types of steel strip and increase its production. This entails a large number of technological operations dependent on precise temperature measurement and control. In some industrial plants, the steel strip is in continuous motion, which makes the use of contact measuring devices impossible. When using non-contact measuring devices such as pyrometers or thermal imaging cameras, the emissivity of the materials being measured is a problematic parameter, as setting an incorrect emissivity value to the measuring device results in inaccurate temperature readings. The essence of this research was to establish a measurement method and to perform experimental measurements of the emissivity of a polished steel strip used in a continuous annealing line, the subsequent processing of the data from these measurements and their evaluation. The emissivity measurements were carried out for 5 types of steel strip of different parameters, while the measurement itself was carried out in the long wavelength range of 7.5-14 µm and at strip temperatures of 100-300 °C. Depending on the type of steel strip, the mean emissivity values ranged from 0.0835- to 0.1143. The emissivity of the steel strip increased with increasing strip temperature, and it was not a linear dependence. The emissivity values determined in this research could be applied to measuring equipment in actual production, which could improve the accuracy of temperature measurement in the heat treatment of polished steel strip. Thermal camera measurements in the long wavelength range, taking thermal images and their processing and determining the emissivity value of polished steel strips are the parts of this research that make it different from other already published research.

Nieselektywne powierzchnie referencyjne w teledetekcji hiperspektralnej w zakresie dalekiej podczerwieni

This article focuses on the construction of reference surfaces with the desired spectral characteristics similar to a gray body. Using wooden plywood with a rough surface and coatings of various emissivity values, surfaces with non-selective spectral properties were created. The consistency of laboratory measurement results using a reflectance spectrometer with data obtained from a hyperspectral camera was confirmed. By utilizing multiple reference surfaces with precisely known emissivity characteristics, it will be possible to accurately determine the radiation components of the measured scene’s surroundings. Although the technology of these surfaces still requires improvement, their usefulness in remote sensing measurements is undeniable. Additionally, differences in response to solar radiation between various reference surfaces provide significant information that can be used in remote sensing and material identification. Incorporating the heating dynamics of the studied objects’ surfaces is crucial for accurate measurement modeling.

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.

Analyzing the role of emissivity in stranded conductors for overhead power lines

Emissivity and absorptivity are important parameters in overhead power line conductors that depend on the conductor surface condition, so their values change as the conductors age. They have an important effect on their thermal behavior, so it is important to know their value when designing dynamic line rating (DLR) strategies. DLR methods are becoming increasingly important, especially in areas with congested power lines, as they allow the full capacity of the lines to be utilized by dynamically determining their maximum allowable currents without exceeding the safe temperature limits of the conductors, thus ensuring that they operate within safe limits. However, measuring emissivity and absorptivity is non-trivial and requires complex tests that cannot be performed in the field. Using simulations based on a realistic thermoelectric model and experimental tests performed on three types of transmission line conductors in a high-current laboratory, this paper shows the importance and effect of emissivity on conductor temperature. It also presents a method for measuring the emissivity value based on adjusting the emissivity and absorptivity values in the thermoelectric model to match the experimental values. The results presented show that aged conductors allow an increase in the maximum current carrying capacity compared to new conductors in the order of 5–14 %, depending on the conductor type considered and the operating conditions.

Sustainable chitosan derived 3D hierarchically porous carbon aerogel toward advanced infrared-radar compatibility

Simultaneously achieving infrared-radar compatibility in one material is an important challenge for multi-spectral compatible stealth technology. Chitosan-derived three-dimensional (3D) hierarchically porous carbon aerogel can effectively solve the problem. Inspired by floors-pillars concept, this work elaborately designed and successfully fabricated 3D skeletons consisted of two-dimensional (2D) sheets and one-dimensional (1D) struts. Benefiting from esterification and directional freeze drying method, the entire network could provide sufficient space for reducing thermal conductivity and motivating dipole polarization sites. Thanks to the facile calcination process, conductive components could be obtained, which guarantee low infrared (IR) emissivity and high conduction loss performance. In this work, the as-prepared carbon aerogel with ultra-low density of 0.005 g cm−3 exhibits superb infrared stealth property. It shows a low thermal conductivity coefficient of only 0.0933 W m−1 K−1. In addition, the heating rate of the upper surface is slow when placed on a heating platform of 60 °C. The relevant IR emissivity value is as low as 0.563 in 3–5 μm band and 0.432 in 8–14 μm band. Under relatively thin thicknesses, the prominent radar stealth performance including the optimum reflection loss value of −75.90 dB, the maximum effective bandwidth of 3.93 GHz, and the simulated radar cross section reduction value of 27.66 dB m2, can be obtained. This study not only introduces innovative design ideas but also offers technical approaches, facilitating further development in the realm of infrared-radar compatible stealth.

Development of high‐performance zinc stannate based multifunctional thermoplastic polyurethane nanocomposite films

AbstractA lot of demand exists for multifunctional TPU that can provide enhanced performance to address a variety of inflatable application needs. To develop multifunctional nanocomposite films for such uses, synthesized zinc stannate (ZnSnO3) nanoparticles are integrated for the first time in a thermoplastic polyurethane (TPU) matrix. ZnSnO3 was synthesized using hydrothermal method. The morphological analysis vividly displayed the nanocubic structures. As‐synthesized nano ZnSnO3 was added as a nanofiller at varied concentration from 2 to 10 wt% in TPU and nanocomposite films were prepared by solvent intercalation and casting method. These films were thoroughly examined for their multifunctional properties such as UV protection, helium gas barrier and infrared emissivity. Mean value of UV protection factor was improved by 75% at 10 wt% loading of ZnSnO3 whereas 23% improvement was observed in helium gas barrier. Moreover, a good correlation of experimental data with various theoretical models of gas permeability was obtained at lower volume fraction of ZnSnO3. IR emissivity value also showed improvement from 0.802 to 0.842. Thus, the developed TPU‐ZnSnO3 nanocomposite films exhibited a significant improvement in multiple functional properties with improved tensile strength at optimized loading of 6 wt% of ZnSnO3.Highlights UPF mean value of ZnSnO3 incorporated TPU film has been improved by 67%. Helium gas barrier has been improved by approximately 23% at 6 wt% loading. TPU film exhibited improved properties at optimized loading of 6 wt% of ZnSnO3. Nanocomposite TPU film can be employed in various weathering inflatables.

Satellite Time-Series Analysis for Thermal Anomaly Detection in the Naples Urban Area, Italy

Naples is the most densely populated Italian city (7744 inhabitants per km2). It is located in a particular geological context: the presence of Mt Vesuvius characterizes the eastern part, and the western part is characterized by the presence of the Phlegrean Fields, making Naples a high-geothermal-gradient region. This endogenous heat, combined with the anthropogenic heat due to intense urbanization, has defined Naples as an ideal location for Surface Urban Heat Island (SUHI) analysis. SUHI analysis was effectuated by acquiring the Land Surface Temperature (LST) over Naples municipality by processing Landsat 8 (L8) Thermal Infrared Sensor (TIRS) images in the 2013–2023 time series by employing Google Earth Engine (GEE). In GEE, two different approaches have been followed to analyze thermal images, starting from the Statistical Mono Window (SMW) algorithm, which computes the LST based on the brightness temperature (Tb), the emissivity value, and the atmospheric correction coefficients. The first one is used for the LST retrieval from daytime images; here, the emissivity component is derived using, firstly, the Normalized Difference Vegetation Index (NDVI) and then the Vegetation Cover Method (VCM), defining the Land Surface Emissivity (LSɛ), which considers solar radiation as the main source of energy. The second approach is used for the LST retrieval from nighttime images, where the emissivity is directly estimated from the Advance Spaceborne Thermal Emission Radiometer database (ASTER-GED), as, during nighttime without solar radiation, the main source of energy is the energy emitted by the Earth’s surface. From these two different algorithms, 123 usable daytime and nighttime LST images were downloaded from GEE and analyzed in Quantum GIS (QGIS). The results show that the SUHI is more concentrated in the eastern part, characterized by intense urbanization, as shown by the Corine Land Cover (CLC). At the same time, lower SUHI intensity is detected in the western part, defined by the Land Cover (LC) vegetated class. Also, in the analysis, we highlighted 40 spots (10 hotspots and 10 coldspots, both for daytime and nighttime collection) that present positive or negative temperature peaks for all the time series. Due to the huge amount of data, this work considered only the five representative spots that were most representative for SUHI analysis and determination of thermal anomalies in the urban environment.

Practical approaches for evaluating radiative heat from high pressure hydrogen flame

As the construction of hydrogen stations and other hydrogen-related facilities progresses, it becomes increasingly crucial for safety designs to account for scenarios where leaked hydrogen might ignite. Since a hydrogen flame is usually invisible, detection must rely on radiative heat or temperature. While it is possible to predict accurate radiative heat flux from a high pressure hydrogen jet flame through detailed numerical calculations of hydrogen combustion with its radiation, the objective of this study is to provide a simpler and more accurate prediction method. Previous experimental data of radiative heat flux, Qr from high pressure hydrogen jet flames were compiled, and a simple experimental equation Qr=1463.3(Lo/Lf)−2.32 was derived, where Lf and Lo represent the flame length and the distance perpendicular to the flame axis from the midpoint of the flame length to the observer, respectively. Radiative heat fluxes were computed through detailed numerical simulations using three types of water vapor radiation models: Goody's narrow random band model, the exponential broad band model by Edward and Elsasser's narrow regular band model. The temperature and water vapor partial pressure distributions obtained from numerical simulations were used as input conditions. The results were found to be in good agreement with the experimental equation. Moreover, a simple diagram representing the radiative heat flux from a hydrogen flame was derived using the method of cylinder-like approximation. The results of this study show that if the hydrogen pressure and leakage aperture diameter are given, the radiative heat flux at a certain distance can be predicted with high accuracy. Additionally, the average value of emissivity for the hydrogen diffusion flame was found to be on the order of 0.03.

Vanadium dioxide/aluminum composites for adaptive infrared stealth

Vanadium dioxide (VO2) is assumed as a promising dynamic infrared stealth material owing to its tunable emissivity. However, the relatively high emissivity associated with VO2-based adaptive infrared stealth materials poses a constraint on their practical applications. To address this issue, this study proposed a VO2/Al composite endowed with a smart infrared stealth function. With 50 % VO2, the composite achieved a low emissivity value of 0.54 at 30 °C, while it exhibited a reversible variation to 0.43 at 100 °C, demonstrating a change up to 0.11. When the temperature of the sample remained at 100 °C, the surface temperature detected by an infrared camera was only 53.4 °C, indicating a promising infrared stealth performance. Meanwhile, the metal-insulator transition (MIT) effect and thermal insulation performance were investigated under the framework of the composition effect of composite materials. The design strategy of this metal composite material paves the way for novel approaches in designing dynamic infrared stealth materials with low emissivity.

Elevating thermal comfort with eco-friendly concrete roof tiles crafted from municipal solid waste

Developing eco-friendly construction materials is imperative from an energy and environmental standpoint. This technical study investigates the sustainable utilization of municipal solid waste incinerated fly ash (MSWIFA) as a substitute for M-sand in construction materials. This study primarily focuses on reducing landfill waste and promoting waste reuse in the construction sector. This study evaluates various thermo-physical properties of MSWIFA-based concrete, including solar reflectance index, slip and skid resistance, straightness, flatness, rectangularity, water absorption, wet transfer, and thermal performance metrics such as heat flow values for thermal comfort and solar emissivity. The proposed concrete tiles have suitable thermal emissivity (0.87), solar reflectance (0.8), and solar absorption (0.26), which are appropriate for eco-friendly building techniques. The use of MSWIFA tiles lowered the indoor temperature by 2 °C when compared to conventional roof tiles at similar ambient conditions. MSWIFA-based concrete roof tiles are promising in terms of thermal comfort, energy efficiency, environmental conservation and waste reduction and promote a more sustainable approach in the construction industry. This research emphasizes the potential of waste-to-resource strategies in achieving sustainable development goals and reducing the ecological footprint of construction materials.

Radiant energy exchange through participating media composed of arbitrary concentrations of H2O, CO2, and CO

AbstractIn this work, an approximate analytical solution (AS) is presented to evaluate the radiative thermal exchange through a gaseous participating medium composed of H2O, CO2, and CO, which is valid for the product values of pressure path‐length (PL) from 0.06 to 20 atm m and temperatures (T) from 300 K to 2100 K. The Spence root weighting method is used to approximate the exact solutions. For each set of , the value of exact spectral emissivity and absorptivity and for the gas mixture is calculated using the AS, the Hottel graphical method (HGM) and the proposed approximate solution. The weaker adjustment was achieved in the modeling of the HGM, with a mean deviation obtained of ±15% and ±20% for 43.8% and 56.3% of the data evaluated, respectively, while the best indices were obtained in the estimation of the proposed method, with a mean deviation obtained of ±10% and ±15% for 81.3% and 98.1% of the available data, respectively. In all cases, the agreement of the proposed model with the available experimental data is good enough to be considered satisfactory for practical design.

Magnetron sputtering method for the preparation of Cu-ZrB2 composite film and their optical properties

The exceptional thermal and chemical stability of zirconium diboride (ZrB2) is attributed to its unique combination of ceramic and metallic properties. In this work, copper composited zirconium diboride (Cu-ZrB2) composite film was prepared on Si (100) substrates with dual-target magnetron co-sputtering method. The introduction of metal (Cu) has been observed to adjust the free electron concentration in thin films, thereby optimizing their properties. When copper was sputtered at 3 W, the composite film exhibited superior performance, demonstrating the average reflectance of 90% within the wavelength range of 3–14 μm. Additionally, it showcased remarkably low infrared emissivity values at 3–5 and 8–14 μm, measuring 0.309 and 0.294 respectively. This experiment has demonstrated that ZrB2-based composite films have great potentials in low infrared emissivity applications.

Transverse emittance growth of proton sources from laser-irradiated sub-μm-thin planar targets.

Proton bunches with maximum energies between 12 and 22 MeV were emitted from submicrometer-thin plastic foils upon irradiation by laser pulses with peak intensity of 4×10^{20}W/cm^{2}. The images of the protons by a magnetic quadrupole doublet on a screen remained consistently larger by a factor of 10 compared to expectations drawn from the ultralow transverse emittance values reported for thick foil targets. Analytic estimates and particle-in-cell simulations attribute this drastically increased emittance to formerly excluded Coulomb collisions between charged particles. The presence of carbon ions and significant transparency likely play a decisive role. This observation is highly relevant because such thin, partially transparent foils are considered ideal for optimizing maximum proton energies.

Micro Machining of a Si3N4/SiO2/Ti/Pt Hotplate and Its IR Emissivity Properties

This paper presents the fabrication processes for a Si3N4/SiO2/Ti/Pt membrane based micro hotplate (MHP) using photolithography (PL) micro-machining techniques. The properties of the MHP filament are investigated and overall performance characteristics with regard to infrared (IR) radiation emissivity, resistance, breakdown voltage, and temperature of the fabricated Si3N4/SiO2/Ti/Pt micro heater. During characterization, the results show the device breakdown voltage of 24.24 V corresponding to the optimum operation temperature of ~ 1730.30 K. The device also showed an emissivity value of 5.2% with ~ 7% efficiency of transforming electrical power to IR thermal radiation power. The relationship between temperature and resistance, behaviour of fourth power of temperature and thermal response time constant of IR radiation obtained from direct experimental measurements, analytical calculations and extrapolations are shown to provide practical parameters that are needed for applications of MHP in IR radiation sources.

Line-of-sight gas radiation effects on near-infrared two-color ratio pyrometry measurements during plasma wind tunnel experiments

Two-color ratio pyrometry is commonly used to measure the surface temperature of aerospace materials during plasma wind tunnel experiments. However, the effect of the plasma radiation on the measurement accuracy is often neglected. In this paper, we formulate a model of the instrument response to analyze the systematic error induced by the gas radiation along the optical path. CFD simulations of the plasma flow field, together with a radiation code, allow to compute the gas spectral radiance within the instrument wavelength range. The measurement error is numerically assessed as a function of the true object temperature and emissivity value. Our simulations explain the typical behavior observed in experiments, showing that a significant bias can affect the measured temperature during the material heating phase. For an actual experiment on a ceramic-matrix composite, a correction to the measured data is proposed, while comparative measurements with a spectrometer corroborate the results.

Novel (La0.2Eu0.2Nd0.2Sm0.2Pr0.2)(Al0.6Co0.4)O3-δ and (La0.2Eu0.2Nd0.2Sm0.2Ca0.2)(Al0.6Co0.4)O3-δ high-entropy ceramics with high emissivity and low degradation

Novel (La0.2Eu0.2Nd0.2Sm0.2Pr0.2)(Al0.6Co0.4)O3-δ (HE-1) and (La0.2Eu0.2Nd0.2Sm0.2Ca0.2)(Al0.6Co0.4)O3-δ (HE-2) high-entropy ceramics were synthesized via solid-phase reaction technology. These two ceramics simultaneously own excellent infrared radiation performance and low degradation. The mechanism of emissivity enhancement was investigated, and emissivity decay of ceramics heated at 1500 °C for various holding time was studied. The results verify that the synthesized ceramics have perovskite crystal structure. The emissivity values of HE-1 and HE-2 are 0.78/0.66 and 0.82/0.83 in the near/mid-infrared band, respectively. These IR emissivity values are much higher than that of pure LaAlO3, which is attributed to enhanced impurity absorption, free carrier absorption and lattice vibration absorption. Moreover, after heating at 1500 °C for 10 h, HE-1 and HE-2 ceramics appear extremely slower emissivity decay rate (1.2–4.5 %), in comparison with fast decay rate (25.5–36.8 %) of pure LaAlO3. This phenomenon can be attributed to the hysteresis diffusion effect of high-entropy ceramics, which can inhibit grain growth and emissivity decay. The novel ceramics have important application prospect in long-term energy-saving for high-temperature industry.