Emissivity Values Research Articles

High-temperature thermal imaging to inform the arc-melt synthesis of nuclear materials

The advancement of nuclear energy technology necessitates the development of novel materials and synthesis methods to produce materials which enable new fuel cycles. Alongside the maturation of R&D scale technologies to produce these materials, there is an ongoing effort to develop in situ monitoring capabilities to reduce the time to the discovery and development of these fuels. Monitoring data can be leveraged in artificial intelligence platforms to detect phenomena which lead to varied macro- and microstructural features which impact the application and performance of samples synthesized. The present study presents early-stage findings of the implementation of high-temperature, high-frame-rate infrared thermal imaging to monitor the arc-melt synthesis of novel fuels and compounds relevant to advanced nuclear reactors. The study illustrates both the challenges and opportunities of this methodology, highlighting the importance of internal standards while determining emissivity and transmission values as well as visualizing volatilization during melt synthesis.

Estimation of AMSU-A and MHS Antenna Emission from MetOp-A End-of-Life Deep Space View Test

A unique End-of-Life (EOL) Deep Space View Test (DSVT) was performed on 27 November 2021 for the Advanced Microwave Sounding Unit-A (AMSU-A) and the Microwave Humidity Sounder (MHS) onboard the first EUMETSAT MetOp-A satellite in the deorbiting process. The purpose of this test is to recalibrate the antenna sidelobe, to derive antenna emission, and to quantify the in-orbit asymmetric scan biases of AMSU-A and MHS to, ultimately, improve Near Real-Time (NRT) products for MetOp-B and -C and the entire Fundamental Climate Data Records (FCDR). In this study, MetOp-A AMSU-A and MHS EOL DSVT data on 27 November 2021 have been analyzed. The deep space scene antenna temperatures were first applied for the antenna pattern correction; then, the antenna reflector channel emissivity values were derived from the corrected temperatures. For the MHS, the observed scan-angle-dependent brightness temperatures (BTs) for all channels were well behaved after the antenna pattern correction, except for channel 1. The derived antenna reflector emissivity values from this test are 0.0016, 0.0036, 0.0036, and 0.0019 for channels 1, 3, 4, and 5, respectively. For AMSU-A, the deep space view counts were not homogeneous during the test period, exhibiting large variations in the along-track and cross-track directions, mainly due to the instrument temperature’s rapid change during the test period. The large relative noise in the deep space view observations negatively impacted the data quality and limits the value of this test. The large relative noise may contribute to the different emissivity values derived from the same frequency for channels 9 to 14. We also found unexpected scan-angle-dependent BT after antenna pattern correction for quasi-vertical (QV) channels 1 and 2 when compared to the emission model. Further investigation using a simulation confirmed that channels 1 and 2 are QV channels, as designed.

Fast data processing method for multispectral radiation thermometry based on Euclidean distance optimization.

This study presents a fast and accurate data processing method for multispectral radiation thermometry that can accurately measure the true temperature of steel materials without requiring a priori emissivity model. The method generates a temperature matrix by inputting emissivity values at different wavelengths and selects a reference vector from the matrix. Then, it rearranges the temperature matrices at other wavelengths and calculates the Euclidean distance between each column element of the rearranged matrix and the reference vector. The method uses an unconstrained optimization technique to minimize the Euclidean distance and obtain the true temperature and emissivity of the object simultaneously. We evaluate the performance of the method by simulation and experiment in the response band of 1.4 ∼ 2.5 µm and temperature range of 873 ∼ 1173 K. The simulation results indicate that the relative error of the inverted temperature is within 0.229%, and the average computation time is less than 112.301 ms. The experimental results show that the maximum temperature error during the measurement process is 0.813%. Our method provides a feasible and efficient solution for real-time temperature measurement of steel materials.

An Ideal Molecular Construction Strategy for Ultra-Narrow-Band Deep-Blue Emitters: Balancing Bathochromic-Shift Emission, Spectral Narrowing, and Aggregation Suppression.

Narrowband emissive multiple resonance (MR) emitters promise high efficiency and stability in deep-blue organic light-emitting diodes (OLEDs). However, the construction of ideal ultra-narrow-band deep-blue MR emitters still faces formidable challenges, especially in balancing bathochromic-shift emission, spectral narrowing, and aggregation suppression. Here, DICz is chosen, which possesses the smallest full-width-at-half-maximum (FWHM) in MR structures, as the core and solved the above issue by tuning its peripheral substitution sites. The 1-substituted molecule Cz-DICz is able to show a bright deep-blue emission with a peak at 457nm, an extremely small FWHM of 14nm, and a CIE coordinate of (0.14, 0.08) in solution. The corresponding OLEDs exhibit high maximum external quantum efficiencies of 22.1%-25.6% and identical small FWHMs of 18nm over the practical mass-production concentration range (1-4 wt.%). To the best of the knowledge, 14 and 18nm are currently the smallest FWHM values for deep-blue MR emitters with similar emission maxima under photoluminescence and electroluminescence conditions, respectively. These discoveries will help drive the development of high-performance narrowband deep-blue emitters and bring about a revolution in OLED industry.

All‐Solid‐State Transparent Variable Infrared Emissivity Devices for Multi‐Mode Smart Windows

AbstractSmart windows that incorporate photothermal modulators (PMs) can independently regulate solar transmittance and infrared (IR) emissivity to improve building comfort and reduce energy consumption. Herein, a novel all‐solid‐state variable IR emissivity device (VED) is first designed and fabricated with a high visible irradiation transmittance (T′vis = 0.79) and solar irradiation transmittance (T′sol = 0.75) using an ITO/SiO2/ITO Fabry–Perot cavity structure. The VED exhibits different IR emissivity (ɛ) values at positive (ɛP = 0.80) and negative (ɛN = 0.38) bias, allowing for dynamic regulation of radiation by controlling the electrical conductivity of the indium tin oxide (ITO) layer. Furthermore, an all‐solid‐state PM with a structure of ITO/SiO2/ITO/Glass/ITO/NiO/ZrO2/Li/WO3/ITO, which is capable of independently regulating solar transmittance (ΔT'sol = 0.31) and IR emissivity (Δɛ2.5–25 µm = 0.42), is fabricated. The multi‐mode smart window incorporating PMs can achieve “bright,” “dark,” “warm,” and “cool” modes, making them suitable for deployment in diverse climate zones. The innovative smart window holds a massive potential for use in reducing building energy consumption.

Improving the optical properties of CuCoMnOx spinel absorber using ZnO nanorod arrays for thermal collector and photocatalytic applications

Solar-selective and high entropy materials are one of the key factors for thermal applications. CuCoMnOx (CCMO) spinel compound is also a suitable material for this purpose due to its spin-allowed transitions in partially filled d orbitals. In this study, the CCMO absorber compound was coated on ZnO nanorod-coated aluminum (Al) substrates for the first time by the sol-gel dip-coating method, and its optical, structural, and morphological properties were examined. According to the results obtained, ZnO nanorods increased the active surface area of the Al substrate and accordingly increased the absorptance value of the CCMO material from 87 % to 94 %. Analyzes performed with FT-IR spectrometry showed that the thermal emittance values were 90 % and 67 % for Al/CCMO and Al/ZnO/CCMO samples, respectively. The thermal emittance reduced by around 25 % with the use of ZnO nanorods on the Al substrates in the wavelength range of 2.5 μm–25 μm. The photocatalytic effect of this spinel compound was also investigated. The degradation spectra of organic methylene blue (MB) solution within 120 min were examined with UV–Vis spectroscopy, and the degradation efficiency increased by 23 % in the presence of ZnO nanorods. The obtained results showed that ZnO nanorod structures significantly changed both the solar and photocatalytic properties of the CCMO compound.

Assessment of Thermal Runaway propagation in lithium-ion battery modules with different separator materials

The current work aims to understand and model thermal runaway (TR) events in lithium-ion (LIB) 18650 cells within the context of aircraft battery applications. The primary goal is to comprehend the phenomenon and discuss strategies for mitigating its consequences during aircraft operation. TR is modeled using Arrhenius kinetic equations and is implemented in both lumped parameters (Matlab SimulinkTM), and 3D CFD simulations (Ansys FluentTM) using User Defined Functions. To validate the thermochemical model, cells are initially simulated in an oven test, where a cell is exposed to a temperature-controlled atmosphere, triggering exothermic reactions. With a strong correlation between lumped parameters and 3D models, the latter is simulated under battery module installation conditions. An internal short-circuit is then implemented within the cell to observe how thermal runaway is triggered by an internal heat source. The trigger cell is subsequently placed in a battery module assembly to assess the dominant heat transfer modes and the likelihood of TR induction from one cell to its neighbors. This work’s main objective and innovation are to compare different materials in which cells are immersed while observing the main heat transfer parameters for each material. Three conditions are tested: ceramic paper fiber and G7 as solid separators, and no separator material, where air fills the gaps between cells. The analysis of heat transfer modes reveals radiation’s dominance in the case of air interstice, suggesting the possibility of using a special coating to reduce the cell surface emissivity as an alternative to decrease the likelihood of TR propagation. Thus, two values of surface emissivity were tested in the case of air. Considering a cell triggered by an internal short-circuit, a thermal runaway temperature spike is not observed in any of the four cases. However, the air interstice case with regular emissivity is the most critical one, with the closest cell reaching peak temperatures as high as 136 °C in 490 s. The ceramic paper fiber is considered the best separator material, as it postpones the temperature increase in the closest cell while also being lighter than G7. The results and discussions concerning heat propagation presented herein can serve as guidelines for developing strategies to mitigate thermal runaway in battery modules.

Surface treatment of VO2 films with enhancing the modulation of phase transition and thermochromic performance

As a typical phase transition material, vanadium dioxide (VO2) exhibits a promising candidate in the thermochromic field, while the relatively high critical temperature, low luminous transmittance and poor near-infrared modulation impede its practical application. Herein, we propose a facile strategy to overcome the challenges above. The critical temperature of VO2 films gradually reduced as the phosphating temperature increased and became a metallic state even below 2 kelvin. Combining with the first-principles calculations, the mechanism that P-doping induced the metal-insulator transition of VO2 was ascribed to the increment of itinerant electrons, and the migration of the energy band that moved toward the Fermi level. Optical performances demonstrated that the near-infrared modulation ability reached 19.3 %, while there was a 12.1 % improvement in luminous transmittance after the appropriate phosphating process of VO2 films. Meanwhile, the thermal emissivity value greatly decreased from 0.83 to 0.56. The current findings not only offer a novel strategy to boost the thermochromic characteristics of VO2, but also bring insight into a comprehensive understanding of the mechanism of phase transition in VO2.

Heat Transfer In Automatic Duck Egg Incubator Using A Light Bulb As The Heater

The egg incubator is an egg incubator equipped with a heater with a special construction so that the heat in the box is not wasted. This study aims to determine the heat transfer in an automatic egg incubator with incubator dimensions of 0.38 × 0.35 × 0.45 m. The research was conducted by collecting data directly to obtain heat transfer values in automatic egg incubators with a heat source from a light bulb. A digital thermometer was used to measure the temperature of the egg incubator. The incubator temperature was maintained at a maximum temperature of 39°C. Radiation heat transfer that occured in an egg incubator with a surface area of 0.92 m² which was coated with aluminum foil with a material emissivity value of 0.07 and an egg incubator temperature of 39°C (312 K) was 34.6 Watt. The conduction heat transfer that occured on the wall of the egg incubator with the thermal conductivity value of aluminum foil, namely k = 0.034 W/mK, was 34.78 Watt. The results of the study by setting the temperature of the incubator room to a maximum of 39oC obtained a hatching success rate with a hatchability of 75%.

Influence of Buoyancy and Inter-Surface Radiation on Confined Jet Impingement Cooling of a Semi-Cylindrical Concave Plate

Abstract In this article, the confined jet impingement cooling of a semicylindrical concave plate is analyzed numerically. The finite volume approach is applied to two-dimensional numerical simulations in the transient regime. Air is employed as the working fluid and is regarded as nonparticipant for radiation. The investigation is done for different jet Reynolds numbers (Rej) ranging from 100 to 1000, as the Richardson number (Ri) corresponding to this interval ranges between 0.1 and 10. For any Richardson number, the modified Grashof number (Gr*) is fixed at 105. When analyzing the impact of intersurface radiation between the target plate and confined surfaces on the overall cooling performance, three emissivity values (ε= 0.05, 0.5, and 0.95) are taken into consideration. Additionally, simulations are done for the pure convective heat transfer, ignoring intersurface radiation (ε= 0.0). The influence of surface emissivity and the Richardson number on velocity, temperature, and pressure distribution in the flow domain, local dimensionless temperature (θ) alterations on the target plate and confined walls, alterations in convective (Nuc), radiative (Nur), overall Nusselt numbers (Nuovr), pressure coefficient (Cp), and ratio of radiative Nusselt number to overall Nusselt number (Nur/Nuovr) on the target plate are highlighted. The findings demonstrate that surface emissivity has a significant influence on thermal and hydrodynamic boundary layer formation, buoyancy induced flow and heat transfer, and the proportion of intersurface radiation in overall heat transfer rises as the Richardson number and surface emissivity increase. At low Richardson numbers, the pressure in the stagnation region is greater than the atmospheric pressure. However, as the buoyancy effect increases, the pressure in the stagnation region falls below the atmospheric pressure and rises toward the exit.

Precision black body model at a temperature of 200–450 K:metrological ensurance for optical-electronic equipment for remote sensing of the Earth in the infrared range of the spectrum

The issues of radiometric calibration of optical-electronic equipment for remote sensing of the Earth in a wide range of spectral radiance have been studied. An alternative method for transmitting a spectral radiance unit from a reference source at the phase transition temperature of pure metals to optical-electronic equipment for remote sensing of the Earth in the infrared wavelength range above 2.5 μm is presented. The method is based on the stepwise transfer of a spectral radiance unit from a reference source through a precision model of a black body with a high level of emissivity and a wide temperature range identical to the temperature range of a wide-aperture black body model with a range of spectral radiance required for calibrating optical-electronic equipment for remote sensing of the Earth. A precision black body model PMBB-60m with an output aperture with a diameter of 30 mm was developed, studied and calibrated in the temperature range of 200–450 K. The calculated value of the effective emissivity of PMBB-60m with coating of the cavity by Aeroglaze Z306 paint is 0.9997. The composition and design of PMBB-60m are described. PMBB-60m can operate both in vacuum conditions and in conditions of inert gas or atmospheric pressure. The metrological characteristics of PMBB-60m , obtained by transferring a temperature unit from the State Standard of the zero digit of a temperature unit in the range from 0 to 3000 °C using a comparator, based on a precision pyrometer TRT II (Heitronics Infrarot Messtechnik GmbH, Germany) are presented. The correction to the PMBB-60m temperature readings in the temperature range of 223.15–450.15 K did not exceed 39 mK according to the results of calibration in the temperature range of 223.15–450.15 K. The results of calculating the expanded uncertainty in the temperature range of 223.15–450.15 K did not exceed 1 K. The values of instability of temperature maintenance PMBB-60m, measured in steps of 10 s for 15 minutes, did not exceed 15 mK in the considered temperature range. The results of calculation of the spectral effective emissivity of PMBB-60m, carried out using the STEEP3 program, are presented.

Slit extraction and emittance results of a permanent magnet minimum-B quadrupole electron cyclotron resonance ion source

We present an experimental and simulation study of high charge state ion beams produced with a permanent magnet electron cyclotron resonance ion source (ECRIS) with minimum-B quadrupole magnetic field topology and slit extraction system. The unconventional topology generates fan-shaped plasma flux, favouring a rectangular aperture for beam extraction. We demonstrate successful low-energy transport of the slit beam, achieving up to 25 times higher beam currents compared to a round extraction aperture. Maximum beam intensities are 1.5 and 15 μA for argon 11＋ and 9＋, respectively. The results indicate microwave power-limited beam production. Emittance values are comparable to traditional ECRIS. Unlike in conventional ECRIS, the emittance increases monotonically with increasing charge state due to slit extraction, magnetic topology, and beam transport characteristics. The experimental transport efficiency for helium ranges from 32% to 50%, depending on the total beam current. The losses primarily occur due to the dipole magnet’s insufficient vertical aperture.

LBM simulation for combined thermal radiation and natural convection in 2D enclosure with multiple solid blocks

A numerical investigation of conjugate natural convection in a 2D square enclosure with multiple solid blocks, considering the impact of volumetric thermal radiation, was conducted using the lattice Boltzmann method (LBM). The effect of Planck number wall surface emissivity extinction coefficient solid-to-fluid volume fraction and the number of solid blocks on the fluid-structure and heat transfer within the enclosure were analyzed. The numerical model was validated using benchmark problems from the literature, showing good agreement. The results revealed that at and increasing wall surface emissivity significantly increased the Nusselt number, ranging from approximately 51-116% for different wall emissivity values, as compared to scenarios without surface radiation (). On the other hand, reducing χ, Pl, and β improved the heat transfer rate. The results also demonstrated that subdividing the initial block reduced the heat transfer rate depending on the number of blocks and the value of the Planck number. For instance, when 64 solid blocks were present in the cavity and the Nusselt number decreased by 59.36% compared to the case with a lower solid-to-fluid volume fraction (χ = 15%). The parametric analysis provided useful insights for engineering design in the modern construction industry, with possible applications in building block design and energy efficiency enhancements.

Emissivity measurements conducted on intermetallic γ-TiAl-based alloys for aeronautical applications

The directional spectral emissivity of a Ti–48Al–2Nb–2Cr alloy (in at.%), 4822 alloy, and a Ti-43.5Al–4Nb–1Mo-0.1B alloy (in at.%),TNM alloy, used in the aeronautical industry, are measured between 150 and 850 °C. The differences in the emissivity values between both alloys at the lowest temperatures, indicates that the βo phase, only present in TNM, exhibit higher emissivity values. By numerical integration of the measured data, the total directional and hemispherical emissivity have been calculated. At 850 °C the total hemispherical emissivity in vacuum are nearly identical with 0.274 ± 0.006 for the 4822 alloy and 0.273 ± 0.007 for the TNM alloy. The lower emissivity change with temperature measured in TNM alloys is related with the deconvolution of βo phase by diffusion processes. Afterwards, near-normal spectral emissivity measurements are performed in both alloys during isothermal oxidation treatments at 750 °C and 850 °C for 120 h. The emissivity data reveal that the TNM alloy exhibits higher oxidation resistance especially at 750 °C. In parallel, microstructural characterization has been performed before the measurements, after the directional emissivity measurements prior to oxidation and after isothermal oxidations. The formed oxide scale is composed of four layers that coincide with those reported in the literature: an outer layer of TiO2 contiguous with a layer of Al2O3, followed by a TiO2/Al2O3 mixed layer and finally a thin layer of Nb-rich nitride. This mixed layer governs the interferential part of the alloys’ emissivity spectra, which, in combination with the background, determines the overall radiative behavior of the alloys under service conditions.

Ultrafast laser pulse stretching via dispersive materials including high dispersion orders

Ultrafast laser systems typically employ complicated systems for varying their pulse length (duration) such as an ultrafast IR mode-locked laser used at the Schlesinger Compact Accelerator Center at Ariel University. The laser is an Astrella manufactured by Coherent generating an 800nm pulse. The pulse duration can be varied from 10 ps to 35 fs using a remote-controlled grating-based compressor. In order to measure the time duration of the pulse, an automated compact autocorrelator was designed and developed. The laser is mainly used to extract electrons from a photo-cathode using dual BBO frequency tripling system, providing a UV (266nm) ultra-short pulse. The electrons are formed into a beam, which is used to generate a THz FEL. Using an fs-level UV pulse, the extracted electron beam is unstable, resulting in high space-charge effects, high emittance values, and lowered radiation power dramatically. For this reason, we aim to stretch the UV pulse to a ps level. We study here an applicative method that uses dispersive materials. This method is convenient, compact, and can be easily installed. However, ultrafast lasers can suffer from high dispersion orders. Therefore, we study the contribution of the third and fourth orders of dispersion using analytical and numerical methods. Furthermore, our analysis takes into account the self-phase modulation effect when intense lasers are used. An experimental measurement is executed to confirm our numerical results, and a comparison between the experimental and simulation results is presented.

Transparent Sol-Gel-Based Coatings Reflecting Heat Radiation in the Near Infrared.

Thin, flat textile roofing offers negligible heat insulation. In warm areas, such roofing membranes are therefore equipped with metallized surfaces to reflect solar heat radiation, thus reducing the warming inside a textile building. Heat reflection effects achieved by metallic coatings are always accompanied by shading effects as the metals are non-transparent for visible light (VIS). Transparent conductive oxides (TCOs) are transparent for VIS and are able to reflect heat radiation in the infrared. TCOs are, e.g., widely used in the display industry. To achieve the perfect coatings needed for electronic devices, these are commonly applied using costly vacuum processes at high temperatures. Vacuum processes, on account of the high costs involved and high processing temperatures, are obstructive for an application involving textiles. Accepting that heat-reflecting textile membranes demand less perfect coatings, a wet chemical approach has been followed here when producing transparent heat-reflecting coatings. Commercially available TCOs were employed as colloidal dispersions or nanopowders to prepare sol-gel-based coating systems. Such coatings were applied to textile membranes as used for architectural textiles using simple coating techniques and at moderate curing temperatures not exceeding 130 °C. The coatings achieved about 90% transmission in the VIS spectrum and reduced near-infrared transmission (at about 2.5 µm) to nearly zero while reflecting up to 25% of that radiation. Up to 35% reflection has been realized in the far infrared, and emissivity values down to ε = 0.5777 have been measured.

High vacuum flat plate photovoltaic-thermal (HV PV-T) collectors: Efficiency analysis

Through a numerical model developed in MATLAB, we investigate the performance of a novel hybrid flat plate photovoltaic-thermal collector under high-vacuum (HV PV-T) to optimize the solar-to-thermal energy conversion and efficiently meet the thermal loads of industrial processes up to 150 °C along with additional production of electrical energy. In the proposed design, the photovoltaic (PV) cell is positioned directly above the Selective Solar Absorber (SSA) in a multi-layered PV-SSA structure.The performance analysis of the system has been first carried out by considering the theoretical Shockley-Queisser limit of the electrical efficiency, different values of energy bandgap (0.66 eV ≤Eg≤3.00eV), emittance (0.1≤ɛ≤1), and working temperature (25°C ≤TPV≤175°C) of the PV layer, and secondly by focusing on a wide variety of actual semiconductive materials. We analyzed the specific case of high bandgap materials, such as CdTe, CdS, and GaAs reported in previous publications. The analysis performed shows that full exploitation of the incident solar radiation with HV-PVT collectors can produce about 12.2% of electrical efficiency while 76.4% of the incident power remains available for thermal conversion at 100 °C. Moreover, obtaining the same annual energy using stand-alone solutions (i.e., a combination of the best PV and solar thermal collectors commercially available) would require up to 50% of the collector area more than the proposed HV PV-T collector.

Enhanced infrared radiation of LaAlO3 ceramics via Co2+ doping

Infrared radiation (IR) ceramics are generally recognized as energy-saving materials for thermal equipment. In this work, as novel infrared radiation ceramics, Co2+-doped LaAlO3 ceramics were synthesized via a solid-phase reaction method, and the influence of the Co2+ doping concentration on the infrared emissivity of ceramics was systematically investigated. The original Al element position was replaced by Co in Co2+-doped LaAlO3, leading to lattice distortion, oxygen vacancy generation and the "Co2+→Co3+" transformation. The increase in doped Co content leads to enhanced impurity absorption, free carrier absorption and lattice vibration absorption, which significantly improve infrared emissivity. The average emissivity values in the 0.76–2.5 μm and 2.5–14 μm bands of the LaAl0.6Co0.4O3-δ specimen (40 mol% Co) are 0.89 and 0.86 respectively, which are 324% and 28% higher than those of pure LaAlO3. This novel Co2+-doped LaAlO3 ceramic with high infrared emissivity has significant application prospects for energy-saving applications of thermal equipment.

The development of a novel apparatus to measure the emissivity of high-roughness materials at 82 K

The emissivity of a material changes with temperature. The knowledge of emissivity plays an important role in the estimation of radiation heat load in cryogenic systems. As the emissivity values of different materials at cryogenic temperatures are scarcely available in the literature, room-temperature emissivity values have been extensively used to estimate the radiation heat load in cryogenic systems. This may lead to a significant deviation between the predicted and actual radiation properties at cryogenic temperatures. Therefore, in the present work, an apparatus is developed based on a calorimetric technique for measuring the emissivity of an opaque material around 82 K. The novelties of the apparatus are its compact size, ease of sample handling, shorter time required to reach thermal equilibrium and, most importantly, capacity to measure the emissivity of a sample of high roughness. To understand the effectiveness of low and high emissivity-coated heat radiators for the system, a theoretical and an experimental approach has been followed. It is found that the high-emissivity heat radiator leads to a significant reduction in the time required to reach thermal equilibrium compared to a low-emissivity heat radiator. To verify and validate this setup, the emissivities of Aeroglaze Z306 (high emissivity) and Cu (low emissivity) are measured and compared with the values reported in the literature. Finally, this work has been extended to measure emissivity at cryogenic temperature for the first time for PU1, SG121FD and indigenously developed novel materials, such as black paints, adhesive and activated charcoals of different granule sizes.

An alternative nighttime radiative cooling paint using glass microspheres in water-based acrylic paint

An alternative method for producing radiative cooling paint using sustainable and cost-effective green materials, which can significantly reduce indoor temperatures. Prior research on radiative cooling systems revealed that multilayer metal oxide systems require expensive raw materials and high-end facilities, limiting large-scale production. Therefore, this study aimed to identify optimal conditions for producing radiative cooling paint using commercial spherical glass microspheres and titanium dioxide nanoparticles. The study investigated the effect of glass microsphere size, quantity, and coating thickness on emissivity and light reflectance. Results showed that glass microsphere size did not significantly affect emissivity. However, increasing coating thickness and glass microsphere quantity initially increased emissivity but stabilized at saturation points. The addition of glass microspheres decreased light reflectance, increasing temperatures during the daytime. The radiative cooling efficiency of the paint was tested, and the results showed that the glass microsphere content significantly affected the reduction in daytime temperatures. A mixture content of 45 and 75 wt% reduced the temperature by 2.96 and 3.09 °C, respectively, lower than the ambient temperature during the nighttime. The double layer of titanium dioxide/glass microspheres paint was more effective at cooling than the single layer of 45% glass microspheres, despite similar emissivity values. HIGHLIGHTS Commercial spherical glass microspheres and titanium dioxide nanoparticles are used as raw materials. Glass microsphere quantity and coating thickness are found to affect emissivity and light reflectance. A mixture of 45 and 75wt% glass microsphere content is shown to significantly reduce nighttime temperatures. Double layer paint is more effective at cooling than single layer paint despite similar emissivity values. GRAPHICAL ABSTRACT