Theory Of Thermal Radiation Research Articles

Designers' guided site shading strategies: A simplified model for radiative cooling

In the context of rising urban temperatures, the efficacy of cooling strategies, particularly shading installations, has garnered significant attention. However, prevalent issues in thermal radiation literature and assessment tools include challenging usability, insufficient guidance for design, and a lack of scientific data support. This study addresses these challenges by simplifying thermal radiation theory and integrating diverse assessment tools. The outcome unveils a site shading radiation cooling model, a user-friendly, design-guided, and scientifically supported approach for designers evaluating site shading.The research methodology involves conducting initial measurements on summer afternoons using ISO and Rayman to validate ENVI-met simulation accuracy. This study simplifies thermal radiation theory, creating a predictive model structure based on short- and long-wave radiation reception modes and translating scientific parameters into actionable design factors. Model parameters are derived from ENVI-met simulated Tmrt cooling benefits, followed by computations on numerous cases to verify and assess model applicability.Findings indicate a good match between the measured and simulated Tmrt data during summer afternoons. A common 1:1 width-to-height ratio colonnade in Taiwan contributes a 22 °C cooling effect in extremely hot afternoons, with an additional decrease of 5–8 °C if facing west. Each 10 % increase in the roof transmittance resulted in an approximately 3 °C Tmrt reduction benefit, with wood providing the best cooling effect and metal the least. Based on the obtained cooling data, a Site Shading Benefit (SSB) model was developed by incorporating area parameters, allowing for a simple calculation to assess the overall radiative heat reception of outdoor spaces on a site.

Study on the Influence of Offshore Elevated Flare on the Layout of LNG Terminal

In order to save land, the elevated flare of the LNG terminal is usually considered to be arranged on the sea. The thermal radiation and leakage evaporation diffusion of elevated flare are the key issues to be considered in the plane layout of the wharf. In this paper, the physical process of the flare thermal radiation and the evaporation and diffusion of the terminal sump are analyzed by using engineering knowledge. Combined with the theory of thermal radiation and vapor diffusion and the actual project scenario, the corresponding mathematical model is given and applied to the engineering practice for a large number of calculations. The following conclusions are drawn: (1) The thermal radiation received by the LNG terminal is weakly related to the flare height, that is, the effect of increasing the flare height to control the thermal radiation at the header is not obvious; There is a linear positive correlation with the flare treatment capacity; It is strongly inversely proportional to the distance from the wharf to the flare. It is preferred to reduce the thermal radiation intensity at the wharf by adjusting the distance between the wharf and the flare. When the distance between the wharf and the flare is greater than 100m, the thermal radiation value of the wharf is always less than the specified limit. (2) Within the scope of conventional design, the safe distance between the wharf working platform and the flare is about 20∼90m; The optimal safe distance between the wharf fire control room, bridge approach pipe gallery and the flare should be greater than 61m and 41m respectively. (3) The combustible vapor concentration at the flare is linearly and positively correlated with the flare height, so the flare height should be reduced as much as possible during design. (4) The combustible vapor concentration at the flare is negatively correlated with the distance from the flare to the terminal sump. It is found that the distance should not be less than 180m through calculation. When the distance is more than 300m, the combustible vapor concentration at the flare has little relationship with the flare height and the ambient wind speed. When the distance is more than 340m, the combustible vapor concentration at the flare is always less than the specified limit.

Establishment and experimental verification of 3D model of electrothermal film heating room

Based on turbulence simulation and thermal radiation theory, the physical and mathematical model of electric heating film heating room is established, the appropriate grid form is selected to be meshed, reasonable boundary conditions are set, and the grid independence test is carried out and combing with the experimental test results, the correctness of the model is verified. The results show that the simulation results are consistent with the experimental results, and the maximum error is 13%, indicating that the simulation model is accurate enough. The simulation model provides ideas for related research in the field of electrothermal film heating.

The Modeling and Simplification of a Thermal Model of a Planar Transformer Based on Internal Power Loss

With the development of high-performance wide-band-gap devices and increasing converter frequency, planar transformers are widely used in high-frequency and high-power-density power conversions. Due to the skin effect and proximity effect, accurate thermal analysis and a simplified thermal model of planar transformers are needed for quick thermal verification as well as system design. This paper proposes two thermal simplification models based on the planar transformer’s thermal impedance network. The internal power loss and thermal coupling between each component are first analyzed. Then, based on thermal radiation theory, the simplified thermal model of the planar transformer is presented. It only requires the input of the total power loss of the planar transformer to calculate the temperature rise, and it does not need the power loss of each component. Finally, the simulation and experimental verification are carried out on a MHz prototype.

Online Monitoring of Torpedo Car Shells Based on Equal Angle Scanning

Infrared sensors are being applied more and more widely in industrial production applications. Based on the theory of thermal radiation, this paper discusses the system design principle, temperature calibration method, and thermal image analysis method in detail. The system passed the measurement unit certification, showing that the field of view is 180°, the number of scanning points is 2048, the linear velocity is 10–100 Hz, the spatial resolution is 2.5 mrad, and the precision is ±1 °C. An online monitoring test of torpedo car was carried out in the steelmaking plant of Bao Steel. The results show that the system has strong anti-interference ability, stability, and reliability, and meets the application requirements of online monitoring.

Monitoring molten pool temperature, grain size and molten pool plasma with integrated area of the spectrum during laser additive manufacturing

A new approach is presented in this paper to link the integrated area of the spectral curve with the molten pool temperature, the grain size and molten pool plasma during laser additive manufacturing. A fiber laser was used to deposit the CoCrMo powder on the Q235 steel substrate. The spectra generated during the additive manufacturing process were collected with an optical spectrometer attached to the laser head. According to the thermal radiation theory and the rapid solidification theory, spectral information was applied to calculate the molten pool temperature and the grain size. The relationship between the molten pool temperature and the integrated area of the spectral curve, as well as the relationship between the grain size and the integrated area of the spectral curve was established, respectively. Meanwhile, the electron temperature and electron density of the molten pool plasma were calculated from two different Cr I spectral lines at 403.292 and 434.429 nm wavelength. The results show that the molten pool temperature and the grain size are closely related to the integrated area of the spectral curve. Furthermore, the electron temperature and electron density also increase with the integrated area of the spectral curve.

Radiative heat transfer in nanophotonics: From thermal radiation enhancement theory to radiative cooling applications

Thermal radiation, as a ubiquitous physical phenomenon, plays an important role in various research fields of science and engineering. Traditional understanding of thermal radiation mainly relies on Planck’s law, which describes the energy exchanging efficiency of entire thermal radiation process. However, recent studies indicated that comparing with the macroscopic object obeying Planck’s law, the thermal radiation in nanophotonic structures is obviously abnormal. This is due to the fact that the nanostructures’ featured size or neighboring space are much smaller than the thermal wavelength. It is important to notice that by well designing the material, size, and structure pattern, the thermal radiation is tunable and controllable. Furthermore, the nanophotonic structures enabling the radiative cooling effects promise to possess the tremendous applications including energy, ecology, etc. In this review paper, firstly, we briefly describe the fundamental theory of thermal radiation, as well as the history and latest progress, such as, enhanced radiative heat transfer, the near-field radiation in two-dimensional materials, and the overall far-field enhancement. Secondly, we focus on the newly available daytime radiative cooling system, which is based on metamaterials or desired nanophotonic structures, pursuing the best cooling performances. Finally, we detail the checklists of remarkable applications, ranging from building cooling and dew collection to solar cell cooling. In addition, we also point out the broad future of radiation cooling technology of nanometer optical materials in promoting the management and transformation of desert ecological environment.

FUZZY MODELING OF FAILURE PROBABILITY OF APARATES FOR PROTECTION FROM OVERVOLTAGE

Purpose. The aim of the article is to develop a mathematical model for a comprehensive assessment of the probability of failure of an overvoltage protection device using a fuzzy set device, which is based on expert knowledge and diagnostic data obtained during the operational period. Methodology. The study was carried out using the expert survey method, weight coefficients method, Saati pair comparison matrix method, fuzzy logic methods, fuzzy sets theory, high voltage technology theory, thermal radiation theory. Findings. The authors developed a fuzzy model for determining the probability of failure of a gate arrester and a voltage limiter, taking into account the influence of a combination of such factors as the state of insulation, the state of current-carrying nonlinear elements, the temperature state of the object under study, and the number of operations of the apparatus. On the basis of the model, an automated software system was developed, using which the state of the voltage limiter type 3ER2 276-2PF32-1NA1 of the «SIEMENS» company was diagnosed. It is operated at Dneprovskaya HPP-1, 330 kV for cell ОПН AT-331, and arresters of type РВМК -750M for cell PB 750 2 AT. Originality . The theory of technical diagnostics of high voltage overvoltage protection devices without disconnecting devices from the network (online) on the basis of a fuzzy model for determining the probability of failure of the device has been further developed. The known model differs from the known ones in that it takes into account the state of insulation, the state of the conductive parts, the number of operations of the apparatus, the thermal state of the apparatus and the contact connections, and allows calculating the probability of failure of the apparatus during its operation. Practical value. The developed mathematical model can be used in automated software and hardware-software systems for: diagnosis, maintenance and repair planning, and distribution of financial assets of electric power enterprises. The results of diagnosing different protection apparatus confirmed the adequacy of the developed model. The developed model can be used for all types of protection devices for high voltage switchgears. The model makes it possible to comprehensively evaluate the technical state of the investigated object by integrating the input parameters (current, resistance, temperature, etc.) that are inherently different in nature and which affect the technical state and the probability of its failure. The constructed model allows the machine to be put out of repair after the current state of the object, and not according to the schedule of repairs, which will save the material and human resource, and taking into account the state course for estimating the equipment resource according to the actual state and creating switchgears without a permanent maintenance staff is very relevant.

Nanoscale Thermal Transfer – An Invitation to Fluctuation Electrodynamics

Abstract An electromagnetic theory of thermal radiation is outlined, based on the fluctuation electrodynamics of Rytov and co-workers. We discuss the basic concepts and the status of different approximations. The physical content is illustrated with a few examples on near-field heat transfer.

Ion beam figuring approach for thermally sensitive space optics.

During the ion beam figuring (IBF) of a space mirror, thermal radiation of the neutral filament and particle collisions will heat the mirror. The adhesive layer used to bond the metal parts and the mirror is very sensitive to temperature rise. When the temperature exceeds the designed value, the mirror surface shape will change markedly because of the thermal deformation and stress release of the adhesive layer, thereby reducing the IBF accuracy. To suppress the thermal effect, we analyzed the heat generation mechanism. By using thermal radiation theory, we established a thermal radiation model of the neutral filament. Additionally, we acquired a surface-type Gaussian heat source model of the ion beam sputtering based on the removal function and Faraday scan result. Using the finite-element-method software ABAQUS, we developed a method that can simulate the thermal effect of the IBF for the full path and all dwell times. Based on the thermal model, which was experimentally confirmed, we simulated the thermal effects for a 675 mm×374 mm rectangular SiC space mirror. By optimizing the dwell time distribution, the peak temperature value of the adhesive layer during the figuring process was reduced under the designed value. After one round of figuring, the RMS value of the surface error changed from 0.094 to 0.015λ (λ=632.8 nm), which proved the effectiveness of the thermal analysis and suppression method.

Classical theory of thermal radiation from a solid.

In this work, a solid at a finite temperature is modeled as an ensemble of identical atoms, each of which moves around a lattice site inside an isotropic harmonic potential. The motion of one such atom is studied first. It is found that the atom moves like a time-dependent current density and, thus, can emit electromagnetic radiation. Since all the atoms are identical, they can radiate, too. The resultant radiation from the atoms is the familiar thermal radiation from the solid. After its general expression is obtained, the intensity of the thermal radiation is discussed for its properties, and specifically calculated in the low-temperature limit. Both atomic motion and radiation are formulated in the classical domain.

Remote sensing of lightning by a ground-based microwave radiometer

Based on the theory of thermal radiation and its transfer in the atmosphere, the response of a ground-based microwave radiometer to a lightning-superheated cylinder in the atmosphere is studied and the theoretical expressions are given for the relationship between brightness temperatures and parameters such as distance, size, duration and temperature of the lightning-superheated cylinder. The results from simulated calculations show that it is quite possible for a lightning-superheated cylinder to be observed by a microwave radiometer working in the 50–60GHz band with a sensitivity of 0.3K, typically used for atmospheric temperature profiling. The brightness temperature observed with any one of the channels in the band increases as the distance between the lightning and the radiometer decreases. Lightning at a short distance would make the brightness temperature observed by the channels near to 60GHz increase more while distant lightning would make the brightness temperature observed by the channels near to 50GHz increase more. This feature could be used to retrieve lightning distance and features of the lightning-heated air cylinder from brightness temperature observations. One lightning observation by a ground-based radiometer, the challenge of such observations, and a theoretical analysis are presented. Additional observations are needed for more thorough exploration of this unique remote sensing capability.

FUNDAMENTALS AND APPLICATIONS OF NEAR-FIELD RADIATIVE ENERGY TRANSFER

This article reviews the recent advances in near-field radiative energy transfer, particularly in its fundamentals and applications. When the geometrical features of radiating objects or their separating distances fall into the sub-wavelength range, near-field phenomena such as photon tunneling and surface polaritons begin to play a key role in energy transfer. The resulting heat transfer rate can greatly exceed the blackbody radiation limit by several orders magnitude. This astonishing feature cannot be conveyed by the conventional theory of thermal radiation, generating strong demands in fundamental research that can address thermal radiation in the near field. Important breakthroughs of near-field thermal radiation are presented here, covering from the essential physics that will help better understand the basics of near-field thermal radiation to the most recent theoretical as well as experimental findings that will further promote the fundamental understanding. Applications of near-field thermal radiation in various fields are also discussed, including the radiative property manipulation, near-field thermophotovoltaics, nanoinstrumentation and nanomanufacturing, and thermal rectification.

Radiation spectra of surface

The paper contributes to the theory of thermal radiation. In addition to the common energy spectrum of radiating surfaces, the entropic and exergetic spectrum of the perfectly black or perfectly grey surfaces is proposed. Also, besides the traditional surface emissivity, called in the considerations the energetic emissivity, the entropic and exergetic emissivities are introduced. The theoretical considerations are developed for a better understanding and interpretation of the radiative ability of a surface in comparison to the nature of the emission product.

Interference of spherical wave of thermal radiation emitted by a film system

This paper deals with the interference of spherical waves of thermal radiation emitted by a surface film system which consists of a metal substrate and a semi-transparent film. A spectroscopic experiment is made to reconfirm the clear interference in emission spectra of the film system. We present a theoretical model in which an electromagnetic theory for a spherical wave is combined with Planck’s theory of thermal radiation. The mechanism of interference of spherical waves is discussed, and it is suggested that thermal radiation waves emitted by a number of dipoles of the metal might be coherent among each other.

Theory of light emission in sonoluminescence as thermal radiation

Based on the model proposed by Hilgenfeldt [Nature (London) 398, 401 (1999)], we present here a comprehensive theory of thermal radiation in single-bubble sonoluminescence (SBSL). We first invoke the generalized Kirchhoff's law to obtain the thermal emissivity from the absorption cross section of a multilayered sphere (MLS). A sonoluminescing bubble, whose internal structure is determined from hydrodynamic simulations, is then modeled as a MLS and in turn the thermal radiation is evaluated. Numerical results obtained from simulations for argon bubbles show that our theory successfully captures the major features observed in SBSL experiments.

Interference of Spherical Wave of Thermal Radiation Emitted by a Film System

We deal with the emission characteristics of thermal radiation by a surface film system which consists of a metal substrate and a semi-transparent film. First, a spectroscopic experiment is made on emitted thermal radiation of this film system. It is reconfirmed that thermal radiation emitted by this system shows clear interference phenomenon. This system is suggested to be prospective for a spectrally-functional surface which emits radiation in a spectral band region selectively. Next, in order to analyze the thermal radiation emission of the film system, we present a theoretical model of an electromagnetic theory for spherical wave, which is combined with the Planck theory of thermal radiation. Mechanism of interference of emitted thermal radiation wave is discussed on the basis of the model. It is suggested that thermal radiation waves emitted by plural number of dipoles of the metal substrate can be coherent to each other.

Narrow-Duct-Streaming Calculations Using Generalized Configuration Factors Within the Discrete Ordinates Method

In calculating neutral particle transport through elongated voids with the discrete ordinates method, the problem of ray effect may occur if standard angular quadrature sets are used. To mitigate this ray effect, the configuration-factor concept developed in the theory of thermal radiation for calculating the radiation exchange among surfaces is applied here. The common configuration-factor concept is extended in such a way that the angular dependence of the radiation emitted from the surfaces can be considered. The method is applied to regular and annular cylinders with r-z geometry and incorporated into a two-dimensional discrete ordinates transport code. Calculations on a narrow-duct-streaming problem show that the ray effect is strongly reduced by this method. The new method gives results equivalent to or even better than a standard discrete ordinates calculation using a biased angular quadrature set with 166 directions at computing times for one inner iteration that are about a factor of 2 less.

The use of generalized configuration factors for calculating the radiant interchange between nondiffuse surfaces

The configuration-factor concept developed in the theory of thermal radiation to analyze the radiant interchange between diffusely emitting surfaces is extended in such a way that the directional dependence of the radiation emitted by engineering surfaces can be considered. It is assumed that the emissivity of a surface may vary between the angle bins determined by the angular quadrature of the discrete ordinates method. This leads to generalized configuration factors for which, as in the case of the common configuration factors, reciprocity relations, a distributive rule and a sum rule for enclosures can be defined. The generalized configuration factors are calculated analytically for basic spatial transitions in regular and annular cylinders with r- z geometry. The analytical expressions are evaluated numerically and configuration-factor algebra is used to determine the configuration factors for all transitions between the surface elements of a cylindrical system. The generalized configuration factors are used to calculate the absorbed energy densities in the walls of a cylinder with nondiffuse gray surfaces. Different wall materials are considered, the calorific brightness of which is described by experimental directional emissivities. The resulting absorbed energy densities are compared with those obtained by using direction-independent emissivities.

Computer Aided Infrared Imagery for Fabric Surface Temperature Fields Under Simulated Cigarette Exposure

This paper, the first of two parts, describes a technique of measuring dynamic temperature fields on thin, porous textile materials when exposed to a low energy, localized heat source. A methodology is outlined for studying the smoldering process via measurement of surface temperature profiles using calibrated infrared (IR) thermography, a non-intrusive technique for the measurement and analysis of a material's surface temperature. This paper outlines the essential elements necessary for proper use of IR thermography and provides a summary of thermal radiation theory, combined with computer enhancement of the thermographs. An advanced thermal imaging system couples non-contact infrared thermography with personal computer-based image processing routines for the measurement of real-time temperature and heat flow patterns. The instrumental set-up descri bed here facilitates instantaneous scanning, detection, and depiction of temperature variations and isotherms. Such a system allows continuous, real-time or post-experiment processing and analysis of thermal images in color or gray scale, via digitization followed by image enhancement. A typical protocol of computational techniques and image analysis steps are described for obtaining thermographic data and to analyze growth of conditions leading to smolder initiation, typically in a cellulosic fabric. This methodology can be employed for dynamic measurement of temperature and heat flow though porous materials such as upholstery cover fabric, insulation material, protective clothing, etc. Language: en