Showing papers on "Thermal radiation published in 1992"

Thermal Radiative Transfer and Properties

Abstract: The Nature of Thermal Radiation. Radiative Properties and Simple Transfer. Diffuse Surface Transfer. Electromagnetic Theory Results. Classical Dispersion Theory. Monte Carlo Surface Transfer. Radiative Transfer Equation. Thermal Radiation Properties of Gases. Radiative Properties of Particles. Radiative Transfer in Nonscattering, Homogeneous Media. Nonisothermal Transfer: Radiative Equilibrium and Diffusion with Isotropic Scattering. Radiative Transfer with Anisotropic, Multiple Scattering. Radiative Transfer Coupled with Conduction and Convection. Monte Carlo in Participating Media. Appendices. Index.

Prediction of radiative transfer in cylindrical enclosures with the finite volume method

Abstract: This article shows how the finite volume method can be implemented to solve three-dimensional radiation problems in cylindrical enclosures. The medium is considered to be gray, and absorption, emission, and either isotropic or nonisotropic scattering are included. For the special case of axisymmetric radiation, a mapping is described that yields a complete solution by solving the intensity in a single azimuthal direction. The method is shown to rapidly converge to the solution of the radiation transfer equation as the spatial and directional grid is refined. Results from the solution of axisymmetric bench mark problems show that the method is stable, accurate, and computationally efficient. 25 refs.

Thermal radiation heat transfer - Third edition

Abstract: The authors have revised this text to incorporate new general information, advances in analytical and computational techniques, and new reference material. Wide coverage focuses on thres subject areas: radiation from opaque surfaces, radiation interchange between various types of surfaces enclosing a vacuum or transparent medium, and radiation including the effects of partially transmitting media, such as combustion gases, soot, or windows.

Schrödinger-cat states at finite temperature : influence of a finite-temperature heat bath on quantum interferences

Abstract: Recently several methods have been proposed for generation of superposition (Schrodinger-cat) states in microwave cavities. At microwave frequencies, thermal photons can significantly affect statistical properties of superposition states. In the present paper we study the influence of a thermal heat bath on nonclassical properties of quantum superposition states

Computational fluid dynamics modeling of multicomponent thermal plasmas

Abstract: A comprehensive computational model has been developed Jbr flowing thermal plasmas in the absence of electromagnetic fields, with particular emphasis on plasma jets. The plasma is represented as a rnulticomponent chemicalh, reacting ideal gas with temperature-dependent thermodynamic and transport properties. The plasma flow is governed by the transient compressible Navier-Stokes equations in two or three space dimensions. Turbulence is represented by subgrid-scale and k-e models. Species diffusion is calculated by an effective binary diffusion approximation, generalized to allow /or ambipolar diffusion of charged species. Ionization, dissociation, recombination, and other chemical reactions are computed by general kinetic and equilibrium chemistry algorithms. Radiation heat loss is currently modeled as a temperature-dependent energy sink. Finite-difference approximations to the governing equations are solved on a rectangular spatial mesh using explicit temporal differencing. Computational inefficiency at low Mach number is avoided br reducing the effective sound speed. The overall computational model is embodied in a new computer code called LAVA. Computational results and comparisons with experimental data are presented Jbr LAVA simulations of a steady-stare axisymmetric argon plasma jet flowing into cold argon.

A multi-layer discrete-ordinate method for vector radiative transfer in a vertically-inhomogeneous, emitting and scattering atmosphere—II. Application

Abstract: A theory is developed for discretizing the vector integro-differential radiative transfer equation including both solar and thermal radiation. A complete solution and boundary equations are obtained using the discrete-ordinate method. An efficient numerical procedure is presented for calculating the phase matrix and achieving computational stability. With natural light used as a beam source, the Stokes parameters from the model proposed here are compared with the analytical solutions of Chandrasekhar (1960) for a Rayleigh scattering atmosphere. The model is then applied to microwave frequencies with a thermal source, and the brightness temperatures are compared with those from Stamnes'(1988) radiative transfer model.

Measurement of thermal diffusion in thin films using a modulated laser technique: Application to chemical‐vapor‐deposited diamond films

Abstract: A method to determine the thermal diffusivity in thin films, based on the measurement and analysis of thermal waves induced by a modulated infrared laser, is demonstrated. A nearly exact mathematical description, independent of the film geometry and including surface heat losses, is presented. It is shown that the in‐plane thermal diffusivity and the heat loss through the surface can be determined independently by analysis of both the phase and the amplitude of the thermal waves. The validity of the method has been verified using high‐purity copper sheets of varying thickness, for different modulation frequencies. Several polycrystalline, chemical‐vapor‐deposited (CVD) diamond films have been investigated. The measurements were performed both on free‐standing films and on two‐layer systems of CVD diamond and copper. Thermal diffusivities for polycrystalline diamond up to 6.2 cm2 s−1 were recorded.

Temperature uniformity in RTP furnaces

Abstract: The heat transfer to a wafer in a rapid thermal processing (RTP) furnace is simulated by an analytical/numerical model. The model includes radiation heat transfer to the wafer from the lamps, heat conduction within the wafer, and emission of radiation from the wafer. Geometric optics are used to predict the radiant heat flux distribution over the wafer. The predicted wafer surface temperature distribution is compared to measurements made in an RTP furnace for two different reflector geometries. Lamp configurations and the resulting irradiance required to produce a uniform wafer temperature are defined. >

Natural Convection With Radiation in a Cavity With Open Top End

Abstract: The heat transfer by natural convection and radiation in a two-dimensional cavity with one side heated, one side and bottom insulated, and the top open was investigated numerically The first part of the study focused on natural convection alone, and concluded with closed-form correlations for the heat transfer from each of the side walls It was found that the fluid rises along both side walls in the boundary layer regime In the second part of the study, the natural convection correlations were incorporated into a seven-equation model for combined convection and radiation The procedure needed for calculating the floating temperature of the insulated wall was illustrated numerically The individual effects of the dimensions of the cavity, the temperature of the heated wall, and the emissivities of the two side walls were also documented numerically

A Thermal/Nonthermal Model for Solar Microwave Bursts

Abstract: A theoretical framework is developed for modeling high-resolution spectra of microwave bursts from the Owens Valley Radio Observatory which can account for departures from expectations based on simple thermal or nonthermal models. Specifically, 80 percent of the events show more than one spectral peak; many bursts have a low-side spectral index steeper than the maximum expected slope; and the peak frequency stays relatively constant and changes intensity in concert with the secondary peaks throughout a given event's solution. It is shown that the observed spectral features can be explained through gyrosynchrotron radiation. The 'secondary' components seen on the LF side of many spectra are nonthermal enhancements superposed upon thermal radiation, occurring between the thermal harmonics. A steep optically thick slope is accounted for by the thermal absorption of nonthermal radiation. If the coexistence of thermal and nonthermal particles is interpreted in terms of electron heating and acceleration in current sheets, a changing electric field strength can account for the gross evolution of the microwave spectra.

Incorporation of a time-dependent thermodynamic model and a radiation propagation model into IR 3D synthetic image generation

Abstract: A model is presented for generation of synthetic images representing what an airborne or satellite thermal infrared imaging sensor would record. The scene and the atmosphere are modeled spectrally with final bandwidth determined by integration over the spectral bandwidth of the sensor (the model will function from 0.25 to 20 μm). The scene is created using a computer-aided-design package to create objects, assign attributes to facets, and assemble the scene. Object temperatures are computed using a thermodynamic model incorporating 24-h worth of meteorological history, as well as pixel specific solar load (i.e., self-shadowing is fully supported). The radiance reaching the sensor is computed using a ray tracer and atmospheric propagation models that vary with wavelength and slant range. Objects can be modeled as specular or diffuse with emissivities (reflectivities) dependent on look angle and wavelength. The resulting images mimic the phenomenology commonly observed by high-resolution thermal infrared sensors to a point where the model can be used as a research tool to evaluate the limitations in our understanding of the thermal infrared imaging process.

Refractive index effects on radiative behavior of a heated absorbing-emitting layer

Abstract: Temperature distributions and other heat transfer characteristics are analyzed for a heated plane layer of semitransparent material with refractive index >1. The analysis includes heat conduction, emission, and absorption within the layer. The layer has diffuse interfaces; examples are a frosted quartz window used to diffuse incident radiation in high temperature surroundings, or a ceramic layer with small scattering used in hightemperature applications. Each side of the layer is heated by radiation and convection, and interface reflections are included. When the index of refraction is larger than unity, there are total internal reflections of some of the energy within the layer. This has a substantial effect on distributing energy across the layer, and considerably alters the temperature distribution from when the refractive index is unity. Results are given for a gray layer and for a two-band spectral variation of the absorption coefficient. Radiant energy leaving the surface was examined to determine when it could be used to measure surface temperature accurately.

Coating transparent substrate by cathode sputtering - to produce disks of high transmission behaviour in the visible region and giving high reflection to heat radiation

Abstract: Prodn. of panes comprises coating transparent substrates (s) by cathode sputtering. The coating comprises a 1st ZnO layer (1) of thickness 400 A, a 2nd Ag layer (2) of thickness 90 A, a 3rd metallic or sub-oxidic (sub-stoichiometric) layer (3) of Ti or NiCr of thickness 15 A, a 4th ZnO layer (4) of thickness 320 A and a 5th TiO2 layer (5) of thickness 70 A. The transparent panes produced by theprocess are also claimed. ADVANTAGE - The panes have a high transmission behaviour in the visible region and a high reflection behaviour to heat radiation.

Energy redistribution in cavities by thermal radiation

Abstract: A method has been developed to calculate the spatial temperature distribution on the interior wall of an arbitrarily shaped cavity in which the wall elements exchange energy by means of thermal radiation. The method is based on the separation of the geometrical problem of the radiant energy exchange processes from the detailed physics of reemission from a wall element heated by thermal radiation. The reemissive properties of the interior wall are self‐consistently calculated using a self‐similar solution to the space‐ and time‐dependent planar hydrodynamics equations with radiative heat conduction. As an example, the application of the method to the case of the cylindrical cavity is presented. The relevance of the model to the inertial confinement approach to fusion and its usefulness as a cavity designing tool is discussed.

Radiative Heat Transfer in Two-Phase Media

Abstract: The state of the art of approximate and numerical methods of the theory of radiation heat transfer is analyzed. The principles for producing engineering methods of computing the radiation heat-transfer characteristics in power plants are examined.

Principles of the radiosity method versus radiative transfer for canopy reflectance modeling

Abstract: The radiosity method is introduced to plant canopy reflectance modeling. The authors review the physics principles of the radiosity method which originates in thermal radiative transfer analysis when hot and cold surfaces are considered within a given enclosure. The radiosity equation, which is an energy balance equation for discrete surfaces, is described and contrasted with the radiative transfer equation, which is a volumetric energy balance equation. Comparing the strengths and weaknesses of the radiosity formulation with those of the radiative transfer formulation for canopy reflectance modeling, it is concluded that both methods are complementary to each other. Results of a sample calculation are given for a simplified canopy model with 4000 leaves. >

Development of models for thermal infrared radiation above and within plant canopies

Abstract: Any significant angular dependence of the emitted longwave radiation could result in errors in remotely estimated energy budgets or evapotranspiration. Empirical data and thermal infrared radiation models are reviewed in reference to anisotropic emissions from the plant canopy. The biometeorological aspects of linking longwave models with plant canopy energy budgets and micrometeorology are discussed. A new soil plant atmosphere model applied to anisotropic longwave emissions from a canopy is presented. Time variation of thermal infrared emission measurements is discussed.

Thermal radiation heat transfer (3rd revised and enlarged edition)

Abstract: This book first reviews the overall aspects and background information related to thermal radiation heat transfer and incorporates new general information, advances in analytical and computational techniques, and new reference material. Coverage focuses on radiation from opaque surfaces, radiation interchange between various types of surfaces enclosing a vacuum or transparent medium, and radiation including the effects of partially transmitting media, such as combustion gases, soot, or windows. Boundary conditions and multiple layers are discussed with information on radiation in materials with nonunity refractive indices.

Stagnation point nonequilibrium radiative heating and the influence of energy exchange models

Abstract: A nonequilibrium radiative heating prediction method has been used to evaluate several energy exchange models used in nonequilibrium computational fluid dynamics methods. The radiative heating measurements from the FIRE II flight experiment supply an experimental benchmark against which different formulations for these exchange models can be judged. The models which predict the lowest radiative heating are found to give the best agreement with the flight data. Examination of the spectral distribution of radiation indicates that despite close agreement of the total radiation, many of the models examined predict excessive molecular radiation. It is suggested that a study of the nonequilibrium chemical kinetics may lead to a correction for this problem.

Experimental investigation of radiation heat waves driven by laser-induced Planck radiation

Abstract: The propagation of a radiation heat wave through a thin foil of solid gold was investigated experimentally. The wave is driven by the intense thermal radiation in 1--3-mm-diam gold cavities heated by an intense laser pulse (duration 0.8--0.9 ns, wavelength 0.35 \ensuremath{\mu}m) to temperatures ranging from 80 to 240 eV. Evidence of the propagating wave was obtained from the delayed onset of thermal emission from the outer side of the foil. A detailed comparison of the results with the self-similar solution for the ablative heat wave and with numerical simulations is presented.

Effect of Index of Refraction on Radiation Characteristics in a Heated Absorbing, Emitting, and Scattering Layer

Abstract: The index of refraction can considerably influence the temperature distribution and radiative heat flow in semitransparent materials such as some ceramics. For external radiant heating, the refractive index influences the amount of energy transmitted into the interior of the material. Emission within a material depends on the square of its refractive index, and hence this emission can be many times that for a biackbody radiating into a vacuum. Since radiation exiting through an interface into a vacuum cannot exceed that of a blackbody, there is extensive reflection at the internal surface of an interface, mostly by total internal reflection. This redistributes energy within the layer and tends to make its temperature distribution more uniform. The purpose of the present analysis is to show that, for radiative equilibrium in a gray layer with diffuse interfaces, the temperature distribution and radiative heat flux for any index of refraction can be obtained very simply from the results for an index of refraction of unity. For the situation studied here, the layer is subjected to external radiative heating incident on each of its surfaces. The material emits, absorbs, and isotropically scatters radiation. For simplicity the index of refraction is unity in the medium surrounding the layer. The surfaces of the layer are assumed diffuse. This is probably a reasonable approximation for a ceramic layer that has not been polished. When transmitted radiation or radiation emitted from the interior reaches the inner surface of an interface, the radiation is diffused and some of it thereby placed into angular directions for which there is total internal reflection. This provides a trapping effect for retaining energy within the layer and tends to equalize its temperature distribution. An analysis of temperature distributions in absorbing-emitting layers, including index of refraction effects, was developed by Gardon (1958) to predict cooling and heat treating of glass plates. The interfaces were optically smooth; the resulting specular reflections were computed from the Fresnel reflection laws. This provides a somewhat different behavior than for diffuse interfaces. A similar application was for heating that occurs in a window of a re-entry vehicle (Fowle et al., 1969). A number of recent papers (Rokhsaz and Dougherty, 1989; Ping and Lallemand, 1989; Crosbie and Shieh, 1990) further examined the effects of Fresnel boundary reflections and nonunity refractive index. Other examples of analyses of both steady and transient heat transfer to single or multiple plane layers (Amlin and Korpela, 1979; Tarshis et al., 1969) have used diffuse assumptions at the interfaces as in the present study

Apparatus for preionization of gas in a pulsed gas laser

Abstract: An apparatus for preionization of gas in a pulsed gas laser by means of soft X-ray radiation comprises an elongated cathode (26) which is heated by thermal radiation or electron bombardment and which is arranged parallel to a likewise elongated anode (18) in an evacuated housing.

Viscous shock layer analysis of the Martian aerothermal environment

Abstract: Surface heating and flow field results for the stagnation region of a planetary exploration vehicle entering the Martian atmosphere are presented Solutions for the high-energy viscous flow fields with complete radiative heating are derived from a viscous-shock-layer analysis for laminar flow under chemical equilibrium conditions Results are shown with and without coupled radiation ablation injection utilizing the recently developed curve fits for the transport and thermodynamic properties of Martian atmospheric and ablation species This analysis includes a strongly absorbing boundary layer and, therefore, gives much lower radiative heat transfer rates than those obtained from inviscid analyses

Thermophoresis of a Radiating Aerosol in Laminar Boundary-Layer Flow

Abstract: The interaction between radiation and thermophoresis in forced convection laminar boundary-layer flow over an impermeable flat plate is investigated. The fluid is a radiatively nonparticipating constant-property gas containing emitting, absorbing, and isotropically scattering gray aerosol particles. The radiative properties of the gas-aerosol mixture are considered to be proportional to the local concentration of the particles in the mixture. The surface of the plate, maintained isothermal at a temperature lower than the freestream temperature, is assumed to be opaque, gray, and diffusely emitting and diffusely reflecting. Formal relations developed to the radiation part of the problem based on the Galerkin method are used together with the discretized forms of the energy and particle conservation equations to solve the problem numerically through an iterative scheme. The results show that radiation increases both the temperature gradients in the vicinity of the surface and the total heat flux to the surface, but decreases both the concentration of particles at the surface and the particle flux to the surface. It is also shown that with strong radiation the thermal boundary-layer thickness can increase up to one order of magnitude larger than the velocity boundary-layer thickness with an insignificant increase in the concentration boundary-layer thickness. 23more » refs.« less

Reinvestigation of the thermodynamics of blackbody radiation via classical physics

Abstract: A key part of the early thermodynamic work on backbody radiation by Wien, Stefan, Boltzmann, Planck, and others involved the thermodynamic behavior of a movable piston sliding in a cylinder containing classical electromagnetic thermal radiation. This early work used only classical physics concepts. Here, this analysis is reinvestigated with the change that the implicit assumption is not made that the thermal radiation spectrum reduces to zero at the temperature T=O

Optical radiation treatment instrument

Abstract: An optical radiation treatment instrument, especially an optical radiation treatment instrument employing the heat effect generated by radiation on the surface or interior surface of cavities of human body having pathological changes, the characteristic of which lies in that the radiation source is a thermal radiation source capable of reaching at a temperature up to 1900-2100 K, and it has radiation guide having total reflection to the majority of radiation transmitted. This instrument is simple in structure, of high utilization of radiation energy, and of excellent effect in treating cervical erosion.