Showing papers on "Thermal radiation published in 2003"

Surface modes for near field thermophotovoltaics

Abstract: Thermal radiative energy transfer between closely spaced surfaces has been analyzed in the past and shown not to obey the laws of classical radiation heat transfer owing to evanescent waves and, more recently, electromagnetic surface modes. We have analyzed the energy transfer between layered media, one of the layers being the thermal source, using a Green’s functions method and the fluctuation-dissipation theorem. Based on the analysis, we propose a structure that can utilize the surface modes to increase the power density and efficiency of low temperature thermophotovoltaic generators.

High-temperature resistive surface grating for spectral control of thermal radiation

Abstract: Spectral emittance and thermal stability of two-dimensional W gratings are investigated to obtain high-temperature resistive selective emitters. Numerical calculations based on rigorous coupled-wave analysis are performed to determine the structural profile of gratings with good spectral selectivity. According to the determined parameters, two-dimensional W gratings composed of rectangular microcavities with the period of 1.0 μm are fabricated on single crystalline and polycrystalline W substrates. The grating shows a strong emission peak which can be explained by the confined modes inside the cavities. The grating with 200 nm wall thickness made from a single crystalline W shows very high thermal stability over 1400 K, while the polycrystalline grating is deformed at a high temperature because of the grain growth.

Thermal radiation effects on MHD forced convection flow adjacent to a non-isothermal wedge in the presence of a heat source or sink

Abstract: This work is focused on the steady-state, hydromagnetic forced convective boundary-layer flow of an incompressible Newtonian, electrically-conducting and heat-generating/absorbing fluid over a non-isothermal wedge in the presence of thermal radiation effects. The wedge surface is assumed permeable so as to allow for possible wall suction or injection. Also included in the model are the effects of viscous dissipation, Joule heating and stress work. The governing partial differential equations for this investigation are derived and transformed using a non-similarity transformation. In deriving the governing equations, a temperature-dependent heat source or sink term is employed and the Rossland approximation for the thermal radiation term is assumed to be valid. The obtained non-similar equations are solved numerically by an implicit, iterative, tri-diagonal finite-difference method. Comparisons with previously published work on various special cases of the problem are performed and the results are found to be in excellent agreement. Numerical results for the velocity and temperature profiles for a prescribed magnetic parameter as well as the development of the local skin-friction coefficient and local Nusselt number with the magnetic parameter are presented graphically and discussed. This is done in order to elucidate the influence of the various parameters involved in the problem on the solution.

Radiation Heat Transfer: A Statistical Approach

Abstract: Preface. Acknowledgments. FUNDAMENTALS OF THERMAL RADIATION. Introduction to Thermal Radiation. Basic Concepts the Blackbody. Description of Real Surfaces Surface Properties. Radiation Behavior of Surfaces. Wave Phenomena in Thermal Radiation. Radiation in a Participating Medium. TRADITIONAL METHODS OF RADIATION HEAT TRANSFER ANALYSIS. Solution of the Equation of Radiative Transfer. The Net Exchange Formulation for Diffuse, Gray Enclosures. Evaluation of Configuration Factors. Radiative Analysis of Nondiffuse, Nongray Surfaces Using the Net Exchange Formulation. THE MONTE CARLO RAY-TRACE (MCRT) METHOD. Introduction to the Monte Carlo Ray-Trace (MCRT) Method. The MCRT Method for Diffuse-Specular, Gray Enclosures: An Extended Example. The Distribution Factor for Nondiffuse, Nongray, Surface-to-Surface Radiation. The MCRT Method Applied to Radiation in a Participating Medium. Statistical Estimation of Uncertainty in the MCRT Method. Appendix A: Radiation from an Atomic Dipole. Appendix B: Mie Scattering by Homogeneous Spherical Particles: Program UNO. Appendix C: A Functional Environment for Longwave Infrared Exchange (FELIX). Appendix D: Random Number Generators and Autoregression Analysis. Index.

Application of Steenbeck's minimum principle for three-dimensional modelling of DC arc plasma torches

Abstract: In this paper, physical/mathematical models for the three-dimensional, quasi-steady modelling of the plasma flow and heat transfer inside a non-transferred DC arc plasma torch are described in detail. The Steenbeck's minimum principle (Finkelnburg W and Maecker H 1956 Electric arcs and thermal plasmas Encyclopedia of Physics vol XXII (Berlin: Springer)) is employed to determine the axial position of the anode arc-root at the anode surface. This principle postulates a minimum arc voltage for a given arc current, working gas flow rate, and torch configuration. The modelling results show that the temperature and flow fields inside the DC non-transferred arc plasma torch show significant three-dimensional features. The predicted anode arc-root attachment position and the arc shape by employing Steenbeck's minimum principle are reasonably consistent with experimental observations. The thermal efficiency and the torch power distribution are also calculated in this paper. The results show that the thermal efficiency of the torch always ranges from 30% to 45%, i.e. more than half of the total power input is taken away by the cathode and anode cooling water. The special heat transfer mechanisms at the plasma–anode interface, such as electron condensation, electron enthalpy and radiative heat transfer from the bulk plasma to the anode inner surface, are taken into account in this paper. The calculated results show that besides convective heat transfer, the contributions of electron condensation, electron enthalpy and radiation to the anode heat transfer are also important (~30% for parameter range of interest in this paper). Additional effects, such as the non-local thermodynamic equilibrium plasma state near the electrodes, the transient phenomena, etc, need to be considered in future physical/mathematical models, including corresponding measurements.

Numerical Modeling Of Pool Fires Using Les And Finite Volume Method For Radiation

Abstract: The thermal environment in small and moderate-scale pool flames is studied by Large Eddy Simulation and the Finite Volume Method for radiative transport. The spectral dependence of the local absorption coefficient is represented using a simple wide band model. The predicted radiative heat fluxes from methane/natural gas flames as well as methanol pool burning rates and flame temperatures are compared with measurements. The model can qualitatively predict the pool size dependence of the burning rate, but the accuracy of the radiation predictions is strongly affected by even small errors in prediction of the gas phase temperature.

Morphological Instability of a Confined Polymer Film in a Thermal Gradient

Abstract: We report the experimental observation of a morphological instability of a confined polymer-air double layer sandwiched between two plates set to different temperatures. The homogeneous temperature gradient across the double layer causes the breakup of the polymer film into columns or stripes spanning the two plates. Experimentally, the characteristic wavelength of these patterns varies with the inverse of the initial heat flux through the bilayer. To gain insight into the nature of the instability, we have developed a phenomenological model that describes the heat flow in terms of diffusion through the bilayer. In an idealized microscopic model for the heat flow through the bilayer system, thermal modes in the polymer film with wavelengths ranging from the film thickness to the Debye limit contribute to the heat flux. The low end of this frequency spectrum causes a thermal radiation pressure at the polymer-air surface that destabilizes the film, while the high-frequency modes ascertain the heat conduction through the bilayer.

Semiconductor device and method for fabricating the same

Abstract: The semiconductor device comprises insulation films 30a-30f formed on a semiconductor substrate 10, and a thermal conductor 42 buried in the insulation films. The thermal conductor is formed on a tube structure of carbon atoms. The thermal conductor is formed on a tube structure of carbon atoms, which is a material of very high thermal conductivity, can effectively radiate heat of a very high generated in semiconductor elements, etc., such as transistors 24a, 24b, etc. Accordingly, the semiconductor device can have good heat radiation characteristics.

Thermal diffusivity of upper mantle rocks: Influence of temperature, pressure, and the deformation fabric

Abstract: [1] Thermal diffusivity measurements of seven naturally deformed upper mantle rocks were made as a function of pressure (up to 1 GPa), temperature (up to 1250 K), and the deformation fabric of the samples. For each sample the strain-induced crystal preferred orientations of olivine and pyroxenes were measured, and petrophysical models, based on the thermal diffusivity tensors of the olivine and enstatite crystals, were used to evaluate the three-dimensional distribution of the thermal diffusivity. Both model predictions and measurements show that the anisotropy of thermal diffusivity remains large at the rock scale: 15–28%, depending on the strength of the olivine crystallographic fabric. The direction of maximum thermal diffusivity is parallel to the lineation (flow direction), and the minimum of thermal diffusivity is normal to the foliation plane (flow plane). This anisotropy is preserved at high temperature and pressure. However, measured thermal diffusivities are 20–30% lower than model predictions. This discrepancy between measurements and model predictions cannot be explained by the presence of cracks in the samples because the closure of these void spaces, evaluated through the high-pressure experiments, is found to have a negligible effect on measured thermal diffusivities. Thermal diffusivity for all samples displays a weak linear dependence on pressure of ∼10% GPa−1. Thermal diffusivities observed in the high-temperature experiments (1000–1250 K) are compatible with a weak radiative contribution to the total heat diffusion.

On observing the compositional variability of the surface of Venus using nightside near‐infrared thermal radiation

Abstract: [1] There are several windows in the near-infrared wavelength range (∼1 μm), in which thermal radiation emitted from the planetary surface penetrates through the thick Venus atmosphere and clouds. In this study we develop an improved method to estimate the surface emissivity on the basis of near-infrared thermal emission from the nightside Venus, which is observed through these windows. A simple radiative transfer model demonstrates that multiple reflection of thermal radiation between the atmosphere (including clouds) and the solid surface has a significant influence on the observed radiance under the condition of Venus, where reflectivity of overlying atmosphere and clouds is high. Thus it is necessary to take the effect of the reflection by the planetary surface into account in order to estimate accurately the variation in the surface emissivity on the basis of near-infrared observation of Venus. The net effect of multiple reflection of surface thermal radiation between the atmosphere and the surface is to significantly reduce the spatial contrast in thermal radiation due to surface compositional variation. The model calculation demonstrates that despite this effect, detection of granitic rocks on the Venus surface using near-infrared windows is feasible. Since granitic and basaltic rocks have dramatically different 1 μm emissivities, granitic rocks are distinguishable from basaltic rocks by ground-based telescopic observation. A Venus orbiter that measures both the near-infrared thermal radiation and the surface altitude with great accuracy will provide us with a reliable surface emissivity map of Venus, which is a very valuable tool to detect granitic (i.e., Earth-like continental) rocks on Venus.

Effects of radiation in an optically thin gray gas flowing past a vertical infinite plate in the presence of a magnetic field

Abstract: This paper studies the two dimensional flow of an electrically conducting fluid which is an optically thin gray gas past a stationary vertical infinite plate in the presence of radiation. It is assumed that the temperature of the plate and the suction at the plate are constant. The presence of the induced magnetic field is also taken into account. Numerical solutions for the velocity and the induced magnetic field are derived and the effects of the radiation parameter are discussed.

Comprehensive heat exchange model for a semiconductor laser diode

Abstract: By measuring the total energy flow from an optical device, we can develop new design strategies for thermal stabilization. Here we present a comprehensive model for heat exchange between a semiconductor laser diode and its environment that includes the mechanisms of conduction, convection, and radiation. We perform quantitative measurements of these processes for several devices, deriving parameters such as a laser's heat transfer coefficient, and then demonstrate the feasibility of thermal probing for the nondestructive wafer-scale characterization of optical devices.

Nonequilibrium kinetics of a radiative CO flow behind a shock wave.

Abstract: An investigation is presented of a highly nonequilibrium CO flow with consistently coupled vibrational energy exchanges, chemical reactions, and radiation. A detailed state-to-state model taking into account vibration-vibration, vibration-translation, and vibration-electronic transitions, dissociation-recombination reactions, and radiative transitions between vibrational and electronic states is developed on the basis of kinetic theory methods. A closed set of master equations for vibration-electronic level populations, number densities of atomic species, radiation intensity, temperature, and velocity is derived, and a one-dimensional inviscid carbon monoxide flow behind a plane shock wave is studied numerically. Several models of vibrational transition and dissociation rates in high temperature carbon monoxide are tested, and a model satisfying both accuracy and feasibility requirements is recommended. The role of various energy transfers and chemical reactions in the formation of nonequilibrium vibrational distributions in a shock heated CO flow is studied, and the influence of state-to-state distributions on macroscopic flow parameters and radiation intensity is discussed.

Combined turbulent forced convection and thermal radiation in a curved pipe with uniform wall temperature

Abstract: The combined turbulent forced-convective and radiative heat transfer of a participating medium in the entrance region of a curved pipe is investigated numerically. The P-1 radiation model and the renormalization group (RNG) k- k model are applied to simulate the turbulent convective heat transfer with thermal radiation in the curved pipe at a constant wall temperature. A control-volume finite-element method (CVFEM) with second-order accuracy is used to solve the governing equations. This study explores the interaction phenomena between turbulent forced convection and thermal radiation in a participating medium inside a curved pipe at different temperature ratio, optical thickness, and wall emissivity.

An Estimate of the Temperature of Semitransparent Oxide Particles in Thermal Spraying

Abstract: A considerable temperature difference in semitransparent oxide particles due to intensive heating in plasma spraying makes it difficult to interpret the optical measurements of their temperature. The problem of determining the bulk temperature of such particles from the experimental data on the color temperature is analyzed by using a recently proposed approximate model for the radiation transfer inside a nonisothermal refracting spherical particle. The same approximation is also employed for developing an improved model of particle heating, taking into account the radiation-conduction interaction inside the particle. Calculations for Al 2 O 3 and ZrO 2 particles in a typical plasma jet show that the color temperature of oxide particles may be less than or greater than their bulk temperature, depending on the spectral absorption coefficient of particle substance. This temperature difference during the melting of particles may reach the value of 200-300 K. A procedure for in situ evaluation of the absorpti...

The Angular Behavior of Emitted Thermal Infrared Radiation (8–12 μm) at a Semiarid Site

Abstract: Radiometric measurements of the angular distribution of infrared (8–12 μm) radiation from a field site in a semiarid sandy soil location are reported. The aim of this study is to investigate the variation of emitted infrared radiation with zenith view angle. The motivation arises through the need to correct wide-field-of-view satellite measurements of land surface temperature for surface-induced zenith-angle effects. A new self-calibrating, scanning radiometer is used to acquire near-continuous measurements for zenith view angles up to 70°. The results suggest that, during the day, the measured brightness temperature is evidently affected by a relation between solar illumination and viewing angle through differential heating and shading. During the nighttime, a significant angular variation (up to 8%) in surface emissivity is discerned. The angular behavior of surface emission at night stemming from this variation is accurately modeled using the δ-Eddington approximation. Implications for satelli...