Thermal Radiative Properties Research Articles

Incandescent metasurfaces: A tutorial

Incandescence has long been the most popular source of light, despite a number of limitations in terms of efficiency, polarization, and coherence. In the last twenty years, it has been shown that most of these limitations can be overcome by taking advantage of the advances in nanophotonics. In this paper, we provide a tutorial presentation of the field with emphasis on the fundamental principles used to control the properties of thermal radiation in the far field. We introduce several figures of merit and list some directions for future work.

The Role of Two Models of Thermal Radiation and Variable Properties on Thermal Explosion Critical and Transition Conditions of the Optically Thin Droplets

ABSTRACT Determining the criticality and disappearance of optically thin droplets (gas phase) by thermal explosions is crucial for maintaining thermal stability in various industrial and nonindustrial applications. The governing nonlinear ordinary differential equations of this problem make use of two distinct approximation models for thermal radiation loss, which were completed by Cogley et al. and Sohrab et al. Two methods of solving the problem – the Semenov method and the inflection point method – are used to identify the circumstances of criticality and disappearance of criticality (transition conditions). The governing equations utilize the use of the temperature-dependent Arrhenius frequency factor of the reaction and the thermal conductivity of the gas. The analytical solution of the equations yields the transitional values of the distinctive parameters at various initial conditions. Numerical methods are used to determine the equation’s exact solution. At specific initial conditions, the impact of θo, θa, γSh,F, and αSh,F on the temperature-time histories of ignition (supercritical region), non-ignition (subcritical region), and the critical boundary between them is derived. Notable effects on the ignition, non-ignition, and critical temperatures and times include the changing frequency of the reaction, the gas thermal conductivity, and two approximation models of radiation heat loss. The two radiation heat loss approximation models of the analytical and numerical findings are compared.

Development of novel multifunctional phase change microcapsules for improving thermal comfort and radiation properties

Microencapsulated phase change materials (MPCMs) have gained widespread application in energy-efficient buildings, aiming to improve thermal comfort and reduce energy consumption. To enhance the engineering feasibility of MPCMs, researchers are now focusing on developing MPCMs with multifunctional properties, beyond single thermal storage functionality. In this study, we proposed a novel and straightforward approach to fabricate multifunctional MPCMs with BaCO3 as shell and a core composed of binary phase change materials (PCMs) and lipophilic-modified graphite (MG) via self-assembly method. The incorporation of BaCO3 shell provides MPCMs with additional resistance to ionizing radiation pollution due to the high atomic number element Ba. Additionally, the incorporation of MG into PCMs enhances its temperature sensitivity. The thermal analysis indicates that the binary PCMs’ composition in MPCMs results in two phase transition temperatures at 3.3 °C and 26.4 °C, making them capable of thermal storage in line with comfortable residential temperatures across different seasons. Furthermore, MPCMs were introduced into cement paste (CPM) and used to construct cement chambers. Adding 10 wt% MPCMs in the CPM chambers placed outdoors in Wuhan (from June 7th to June 9th) led to a 23.8 % decrease in temperature fluctuations compared to the reference sample. Radiation shielding results indicated that the linear attenuation coefficient (μ) of CPM increased by 58.7 %, due to enhanced incoherent scattering and photoelectric effects between high atomic number elements and photons. Additionally, XCOM simulations predicted a strong correlation between MPCM content and μ values, with particularly high accuracy at low photon energies. Overall, the multifunctional MPCMs developed in this study not only offers a new route for reducing residential energy consumption and shielding ionizing pollution, but also broadens the applicability of traditional PCMs in the building and other fields.

Theory and application of temporal coupling mode for a SiC/CaF2/Ag cell-based grating.

Tailoring spectral thermal radiation properties via multiple resonances excited by micro/nanoscale-patterned structures plays a vital role in designing functional emitters and devices. However, predicting thermal radiation properties of a structure with multiple resonances-via a fast and accurate algorithm-is still challenging because of the complex mode coupling effects of different resonances. Herein, we establish a temporal coupling mode (TCM) model for a SiC/CaF2/Ag cell-based grating by extracting the intrinsic parameters and coupling constants of the resonances. The accuracy and efficiency of the established TCM model for predicting absorption spectra of SiC/CaF2/Ag gratings with multiple resonances in each unit cell is verified. Results indicate that the narrowband absorption of the SiC/CaF2/Ag cell-based grating can be enhanced via the multiple-resonance coupling effects. This work provides an alternative tool for predicting absorption characteristics of complex structures with multiple-resonance coupling effects.

Molecularly and Structurally Designed Polyimide Nanofiber Radiative Cooling Films for Spacecraft Thermal Management

AbstractRadiative cooling films (RCFs) are crucial for spacecraft thermal management, but their optical performance is currently limited by their structures and intrinsic high absorption at short wavelengths. In this study, a novel RCF using electrospun polyimide nanofibers optimized at both the molecular and microscale levels is developed. The newly designed polyimide molecules significantly decrease visible and ultraviolet (UV) light absorption while maintaining excellent thermal radiation properties in the infrared spectrum. By optimizing the diameter and orientation of the nanofibers using Monte Carlo simulations, the resulting film achieves a solar reflectivity of 99.6% and a mid‐infrared emissivity of 0.93. Its physical structures and optical properties remain stable under exposure to UV light, atomic oxygen, and extreme temperature changes. Further vacuum radiative cooling tests reveal that the thermal equilibrium temperature of this film is approximately 28 °C lower than that of Kapton‐based RCFs currently used in spacecraft. These results provide a new approach for creating efficient thermal management materials for space applications, with potential for broader use in architecture, electronic devices, and outdoor equipment.

Enhanced SWIR Absorption in PMMA‐Coated TiN‐Based Metamaterial

AbstractAchieving highly efficient absorption in the short wavelength infrared (SWIR) spectral region is crucial for advancing numerous technologies. SWIR absorption enhances energy harvesting in solar cells, improves the sensitivity of infrared sensors, and enables precise control of thermal radiative properties in thermal emission devices. These advancements are essential for applications such as thermal imaging, night vision, and thermophotovoltaic systems. The study presents a simple, cost‐effective design of a polymer‐coated multilayer perfect absorber (MPA) metamaterial optimized for the SWIR spectral region. The proposed MPA structure is composed of four distinct layers: a top layer made of polymethyl methacrylate (PMMA) polymer, a second layer featuring arrays of circular titanium nitride (TiN) disks, a dielectric middle layer consisting of a pure zinc oxide (ZnO) film, and a bottom metallic layer formed by a thin film of TiN. The results demonstrate that the MPA achieves near‐perfect absorption, with a remarkable 99% efficiency centered at a wavelength of 1.3 µm. The absorption properties are further investigated with respect to various structural parameters to ensure better performance of the absorber. These absorbers hold great promise for applications in energy absorption, infrared sensing, thermal emission, and related fields.

X-ray polarisation signatures in bombarded magnetar atmospheres

Abstract Magnetars are neutron stars that host huge, complex magnetic fields which require supporting currents to flow along the closed field lines. This makes magnetar atmospheres different from those of passively cooling neutron stars because of the heat deposited by backflowing charges impinging on the star surface layers. This particle bombardment is expected to imprint the spectral and, even more, the polarisation properties of the emitted thermal radiation. We present solutions for the radiative transfer problem for bombarded plane-parallel atmospheres in the high magnetic field regime. The temperature profile is assumed a priori, and selected in such a way to reflect the varying rate of energy deposition in the slab (from the impinging currents and/or from the cooling crust). We find that thermal X–ray emission powered entirely by the energy released in the atmosphere by the magnetospheric back–bombardment is linearly polarised and X-mode dominated, but its polarisation degree is significantly reduced (down to 10%–50%) when compared with that expected from a standard atmosphere heated only from the cooling crust below. By increasing the fraction of heat flowing in from the crust the polarisation degree of the emergent radiation increases, first at higher energies (∼10 keV) and then in the entire soft X-ray band. We use our models inside a ray-tracing code to derive the expected emission properties as measured by a distant observer and compare our results with recent IXPE observations of magnetar sources.

Analysis of Brownian motion and thermophoresis effects with chemical reaction on Williamson nanofluid flow over permeable stretching sheet

This study warrants a broad analysis on the simultaneous effects of Brownian and thermophoresis on the chemically reacting Williamson nanofluid flow via a permeable expanding sheet. The analysis includes the properties of slip velocity and thermal radiation, providing a more representative picture of the physical phenomena. The differential equations governed by demonstrating the fluid flow phenomena are renewed to a set of nonlinear differential equations utilizing similarity rules. These transformed equations are subsequently handled numerically adopting the fourth-order Runge-Kutta method. The results reveal the significant control of Brownian motion together with thermophoresis and additionally, the inclusion of velocity slip and thermal radiation remarkably affect the velocity, temperature, and concentration distributions. Parametric studies show the validation of the present system to variations in the Williamson fluid parameter, slip parameter, radiative heat parameter, Brownian motion parameter, and thermophoresis parameter.

Thermal analysis of MHD unsteady Darcy‐Forchheimer thin film flow in a porous system

AbstractThis study has investigated a Darcy‐Forchheimer thin film flow over an extended horizontal surface with thermal radiation and chemical reaction effects. The governing time‐dependent equations have been non‐dimensionalized using similarity transformations and solved numerically using the fourth‐order Runge‐Kutta method and the shooting technique. The influence of magnetohydrodynamics, non‐uniform heat sourcing, viscous heat radiation, and chemical reactions on temperature, velocity, skin friction, Nusselt, and Sherwood numbers has been examined. Results have shown that porous media, magnetic field, and transient effects decrease the velocity profile, while thermal radiation and variable thermal properties enhance temperature distributions. Findings have indicated that the magnetic field and porosity enhance the skin friction coefficient whereas the heat transfer rate increases with Eckert number and Prandtl number. Rising the chemical reaction parameter from 0.2 to 0.5 rises the mass transfer rate by approximately 9.85%. The thermal analysis of MHD Darcy‐Forchheimer thin film flow in a porous system has been crucial for understanding heat transfer and fluid dynamics in complex environments. It helped in optimizing various engineering processes, such as cooling systems, filtration, and energy conversion, by providing insights into temperature distribution, convective heat transfer, and fluid behavior. This analysis has aided in designing efficient and reliable systems with improved performance and reduced energy consumption.

Thermal radiation characteristic parameters of biomass mixed feedstock for concentrating solar gasification reaction

Solar energy and biomass are both important renewable energy, and the studies on them contribute to current goal of global carbon neutral. The solar gasification process directly employs solar radiation to drive the conversion from biomass to syngas via endothermic gasification reactions. This process relies on the biomass feedstock absorbing incident solar irradiation to sustain these reactions. The thermal radiation characteristics of biomass materials, such as spectral emissivity and absorptivity, determine its capacity for solar energy absorption versus losses from self-emission. Thus, these parameters are critical inputs for accurate thermal-balance modeling of the solar reactor. In this study, the reflectance of 9 biomass samples were experimentally measured in the main solar spectrum range of 200–2500 nm. Based on measurement results, the refractive index (n) and extinction coefficient (k) of each biomass materials are obtained via Kramers-Kronig relations. Besides, the dielectric function of the 9 biomass samples are also modeled using a 5-th Lorentz oscillator model and the model parameters are determined. The results indicate that the 5-th Lorentz oscillator model adequately characterizes the thermal radiation properties of diverse biomass feedstocks over the measured spectrum. This work contributes important spectral property data to enable accurate modeling and optimization of solar thermochemical conversion based on biomass gasification processes.

Analysis of absorption and thermal radiation performance of solar absorbers based on TiN, Nb2O5 and graphene

This work proposes a multi-layer structured solar absorber based on TiN, metal oxide Nb2O5 and graphene. Simulations and calculations are based on finite-difference time-domain (FDTD) method. The average absorption efficiency of the structure is 94.41 % across the spectrum of 280–3000 nm, with absorption bandwidths of 2360 nm (for absorption efficiency exceeding 90 %) and 1819 nm (for absorption efficiency exceeding 95 %). Moreover, the weighted average absorption under AM 1.5 reaches 95.71 %, underscoring the exceptional absorption capabilities of the structure. This structure also has the property of polarization insensitivity. The absorption spectrum varies weakly with the polarization angle, and there is some deviation as the incident light increasing from 0 to 60°. However, the absorption efficiency at 60° is still 81.16 %. We further investigated the thermal radiation performance, discovering an efficiency exceeding 80 % within the range of 300–1400 K, and surpassing 90 % within 800–1400 K. These outstanding absorption and thermal radiation properties position the structure as highly versatile, with potential applications spanning solar energy harvesting and radiation-related fields.

0D/2D Co-Doping Network Enhancing Thermal Conductivity of Radiative Cooling Film for Electronic Device Thermal Management.

The radiative cooling has great potential for electronic device cooling without requiring any energy consumption. However, a low thermal conductivity of most radiative cooling materials limits their application. Herein, a multishape codoping strategy was proposed to achieve collaborative enhancement of thermal conductivity and radiative properties. The hBN-coated hollow SiO2 particles were prepared based on electrostatic self-assembly technology, which were then mixed with hBN platelets and doped into a poly(vinylidene fluoride-co-hexafluoropropylene) substrate. Discrete dipole approximation theory was employed to reveal the mechanism and optimize the particle size. The results showed that the multishape codoping method can significantly improve the radiative performance, with 94.9% reflectivity and 91.2% emissivity. In addition, this zero-dimensional and two-dimensional composite doping structure facilitated the formation of a thermal conduction network, which enhanced the thermal conductivity of the film up to 1.32 W m-1 K-1. The high thermal conductivity radiative cooling film can decrease the heater temperature from 58.8 to 31.3 °C, with a further reduction of temperature by 7.2 °C compared to the radiative cooling substrates with low thermal conductivity. The net cooling power of the film can reach 102.5 W m-2 under direct sunlight. This work provides a novel strategy for high-efficiency electronic device cooling.

Tunable broadband absorbers with ultra-high thermal emissivity for the mxene/ti-based metamaterial

Solar energy was widely used in lots of fields, such as the heat pump technology, seawater desalination, wastewater treatment and photoelectric detection, where efficient use of solar energy was always the goal pursued by mankind. In the work, we proposed a simple and efficient MXene/Ti-based metamaterial absorber and investigated the optical and thermal radiation properties by using the finite-difference time-domain (FDTD) method. The results showed that the average absorption of the MXene/Ti-based metamaterial absorber was higher than 97.6 % from 400 nm to 1600 nm, the maximum absorption reached 99.6 %, and the solar spectrum weighted absorption was close to 98.5 %, and the physical mechanism of the broadband absorption was also explored by theoretical analysis. Compared with the latest reported absorbers, the MXene/Ti-based metamaterial not only had the advantages of low energy loss, high efficiency, and good thermal stability, but also its broadband absorption showed excellent robustness to structural parameters. Moreover, a 75° wide-angle absorption was obtained for the MXene/Ti-based metamaterial, which was independent of polarization. Last but not least, the MXene/Ti-based metamaterial achieved an ultra-high thermal emissivity of 98.3 % at 1600 K, which matched the blackbody radiation curves at 1600 K. These studies had significant implications for catalysis, solar photovoltaics, photovoltaic conversion and other fields.

Influence of the Structure of 3D Woven Fabrics on Radiation Heat Resistance and Thermophysiology Properties

The goal of this study was to investigate the influence of structural and constructional parameters of 3D fabric on two of the most significant properties of fabrics for thermal protection—resistance to radiation heat and thermophysiological properties. Today’s textile materials provide high thermal protection, but they display poor thermophysiological properties in extreme conditions. Six samples of 3D fabrics were developed using a laboratory weaving machine. The examined samples were made of identical warp, with a total of three different weft densities, and were woven in two different weaves. The conditions of the weaving process and construction were the same. EN ISO 6942:2022 and EN ISO 11092:2014 methods were used to determine the resistance of the samples to thermal radiation and thermophysiological properties. The results showed that the samples that contained folds in their structure with a larger volume of “trapped” air had better thermophysiological properties and better resistance to thermal radiation. The volume of air contained in the 3D structure was used as a thermal insulator and it did not have a negative effect on the thermophysiological properties. The described structure enabled the 3D fabric to have an optimal ratio of thermal protection and comfort, which is of crucial importance for fabrics used to make thermal protective clothing.

Dynamically manipulating long-wave infrared polarized thermal radiation by a vanadium dioxide metasurface.

Dynamically manipulating the spectra and polarization properties of thermal radiation is the key to counter an infrared polarization imaging system (IPIS) under the different background environments. In this Letter, we propose a phase-change metasurface thermal emitter (PCMTE) composed of vanadium dioxide (VO2) dipole antenna arrays to dynamically manipulate polarized radiation spectra in the long-wave infrared (LWIR) region of 8-14 µm. During the thermally induced and reversible insulator-to-metal transition (IMT) in VO2, by simulating the LWIR images at different polarization angles for the PCMTE and background plates, the PCMTE can realize dynamically tunable LWIR camouflage; then, their degree of linear polarization (DoLP) can be calculated, which can demonstrate that the PCMTE can also achieve dynamically tunable LWIR polarization camouflage at the specific radiation angles and backgrounds. Our proposed PCMTE provides an effective scheme for adaptive IR polarization camouflage.

Urban heat island analysis based on high resolution measurement data: A case study in Beijing

Urban heat island (UHI) is a widely concerned urban climate which impacts billions of residents worldwide. Nevertheless, inadequate rigorous air temperature (Tair) measurement has become an obstacle to UHI research and mitigation, especially in megacities like Beijing. In this study, we applied a 1-km hourly Tair dataset interpolated from records of 521 stations in Beijing. The dataset enables us to analyze UHI patterns on a block scale and the impacts of landscapes combined with the local climate zones (LCZ) scheme. Our results indicate that: (1) Tair and its temporal variation in each LCZ vary significantly, which are highly relevant to their morphology and thermal-radiative properties. (2) LCZ 1 and LCZ 2 have the highest nocturnal UHI intensities (UHII). Discrepancies among LCZs also cause various temporal variations in their UHII. (3) The spatial pattern of LCZs affects regional temperature. Area ratio and aggregation extent of LCZ 1&2 show significant positive correlations with regional temperature, while LCZ A&D&G have the opposite regularity. (4) Distinct mitigation strategies are put forward for each subarea in Beijing with various endowments of population and the LCZ structure. The study provides insight into Beijing UHI and plausible mitigation advice in megacities like Beijing.

Nonreciprocal thermal emitter for transverse electric wave via attenuated total reflection

Nonreciprocal radiation is very important in essentially improving energy conversion. There have been many approaches to enhance the nonreciprocal thermal radiation properties for transverse magnetic (TM) wave incidence. However, the nonreciprocal thermal emitters for both polarization states are desired in practice, such as solar cells. In this paper, we design and demonstrate a nonreciprocal thermal emitter for transverse electric (TE) wave. By using attenuated total reflection, the nonreciprocal radiation for TE wave in Weyl semimetal film can be notably enhanced. It shows that the reciprocity between absorption and emission can be strongly broken with the difference of 0.93 at wavelength of 12 μm. Furthermore, the co-polarization and cross-polarization in the reflected wave are calculated to analyze the physical mechanism of strong nonreciprocal radiation. In addition, we discuss the influence of structural parameters, such as the thickness of the air gap, the thickness of Weyl semimetal film, the azimuthal angle and the incident angle, on the nonreciprocity. This work not only provides theoretical guidance for the design of nonreciprocal thermal emitters for TE wave, but also has promising applications in solar cells.

Catalytic effects on peristaltic flow of Jeffrey fluid through a flexible porous duct under oblique magnetic field: Application in biomimetic pumps for hazardous materials

Homogenous and heterogeneous reactions play an essential role in polymer production, combustion, ceramic production, catalysis, distillation, and biochemical procedures. As a result of this advancement, a mathematical model is developed to examine the role of catalytic chemical reaction effects on the magneto-hydrodynamic peristaltic transport in a flexible divergent duct containing a non-deformable porous medium as a model for complex hazardous waste bio-inspired pumping mechanisms. The Jeffrey model is utilized to simulate strong non-Newtonian characteristics. Additional multi-physical features included in the model are heat generation, thermal radiation, Hall current, and complaint wall properties along with an inclined (oblique) magnetic field. The long wavelength and low Reynolds number approximations are deployed to transform the primitive conservation equations from a moving boundary problem to a fixed frame. Appropriate transformations are then utilized to render the model dimensionless. The exact solutions are obtained for stream function and velocity. Further, the R-K-Fehlberg integration scheme is applied to solve the energy and concentration equations. Velocity, temperature, concentration, skin friction, and Nusselt number profiles are visualized graphically. Streamline patterns are also included to capture bolus dynamics. Validation with previous simpler studies has been included. A detailed appraisal of key control parameters on transport characteristics is conducted. It is found that velocity is suppressed with elevation in the damping force parameter while it is enhanced with an increment in regime permeability i. e. Darcy number. Both homogeneous and heterogeneous reactions are observed to exert a significant impact on the species concentration. The volume of the trapped fluid bolus size is shown to be an increasing function of the peristaltic wave amplitude ratio. The present work generalizes existing studies to consider catalytic effects on dissipative peristaltic pumping of the Jeffrey fluid with heat generation and radiative flux, aspects which have been neglected in a single model previously. The simulations are relevant to better characterize the complex transport phenomena in nuclear reactor waste transport via biologically inspired pumping designs.

UTLIZATION OF GENERALIZED HEAT FLUX MODEL ON THERMAL TRANSPORT OF POWELL-EYRING MODEL VIA OHAM WITH HEAT GENEARTION ASPECTS

The focus of this work is on the flow of a spinning Powell-Eyring nanofluid in the boundary layer in three dimensions using magnetohydrodynamics (MHD). The research simulates mass transfer processes and heat transfer processes using non-Fick's mass flux theory and non-Fourier heat flux theory, respectively. Heat transport phenomena are analyzed by the integration of non-linear heat generation/absorption and thermal radiation properties. The boundary layer method is employed to solve a system of nonlinear partial differential equations (PDE) in the mathematical formulation. These equations are converted into nonlinear ordinary differential equations (ODES), and then the optimal OHAM with convergence control parameters is used to solve them. The impact of various physical movement circumstances on concentration and temperature profiles is visually represented through the generation of diagrams. This study provides important new understandings for both applied and scholarly research on complex heat transfer and fluid dynamics mechanisms in the context of three-dimensional MHD boundary layer flows of rotating Powell-Eyring nanofluids.

Unprecedented Spatial Manipulation and Transformation of Dynamic Thermal Radiation Based on Vanadium Dioxide.

Reconfigurable infrared (IR) materials have widespread applications in thermal management and smart IR concealment. Although various reconfigurable IR materials can be customized by positive or negative differential VO2-based resonators, their insightful mechanism remains unknown. Here, we comprehensively investigate the fundamental design rule of reconfigurable thermal radiation between positive and negative differential thermal radiation properties for the first time. Importantly, the skin depth of VO2 film in the metal state is investigated to clarify the transformation from positive to negative differential thermal radiation properties, and the critical thickness is further derived, providing important guidance in designing the reconfigurable thermal radiation regulator. Furthermore, the reconfigurable multistate thermal images had been presented into one plate. The resulting emittance variation (△ε8-14μm) of the VO2-based resonator can change from 0.61 to -0.53, which consummates the ability for diverse demands such as infrared concealment, thermal illusion, and thermal management. This work constitutes a promising and universal route toward designing whole smart devices and may create new scientific and technological opportunities for platforms that can benefit from reconfigurable electromagnetic manipulation.