Showing papers on "Thermal radiation published in 1988"

Theory and practice of radiation thermometry

Abstract: Partial table of contents: FUNDAMENTALS OF RADIOMETRIC TEMPERATURE MEASUREMENT. Physics of Thermal Radiation (D. DeWitt & F. Incropera). Thermal Radiative Properties of Materials (D. DeWitt & J. Richmond). RADIATION THERMOMETERS AND MEASUREMENT METHODS. Wide--Band Radiation Thermometers (R. Leftwich). Fast Radiation Thermometry (A. Cezairliyan, et al.). METHODS FOR CALIBRATION OF RADIATION THERMOMETERS. Calculation of Effective Emissivities of Cavity Sources of Thermal Radiation (R. Bedford). Detector--Based Traceability of Temperature Standards (A. Ono, et al.). APPLICATIONS OF RADIATION THERMOMETRY. Radiation Thermometry in the Steel Industry (F. Milhalow). The Application of Thermography for Building and Industrial Energy Management (P. Mill & G. McIntosh). Index.

Thermal and stress analysis of semiconductor wafers in a rapid thermal processing oven

Abstract: Results are presented from studies of heat transfer in a rapid thermal processing (RTP)-type oven used for several semiconductor wafer processes. These processes include: (1) rapid thermal annealing; (2) thermal gradient zone melting; and (3) lateral epitaxial growth over oxide. The heat transfer studies include the measurement of convective heat transfer in a similar apparatus, and the development of a numerical model that incorporates radiative and convective heat transfer. Thermal stresses that are induced in silicon wafers are calculated and compared to the yield stress of silicon at the appropriate temperature and strain rate. Some methods for improving the temperature uniformity and reducing thermal stresses in the wafers are discussed. >

Thermal Radiation in Packed and Fluidized Beds

Abstract: Etude du transfert radiatif dans les lits fluidises ou a garnissage. Presentation des techniques experimentales existantes pour la determination des proprietes radiatives. Analyse de l'interaction du rayonnement avec d'autres modes de transfert de chaleur

Breaking of Window Glass Close to Fire

Abstract: A heat conduction equation with linerized radiation cooling boundary conditions is used to calculate the thermal field in a long-strip window pane heated by thermal radiation (fire), except on narrow strips along edges built into the frame. This temperature field is used to calculate a quasi-static thermal stress field in the pane in the first-order planar stress approximation. Derived analytic equations of stresses are presented graphically. Thermal stresses build up at the edges in a narrow strip of a few times the pane thickness. In cool spots of the order of 100 K lower than the average temperature, stress build-up can cause a microcrack to become a fast-propagating fracture.

Parallel Thermal Wave Imaging Using a Vector Lock-In Video Technique

Abstract: The appearance of the IR video camera has extended the wavelength range of the visible video camera to the thermal IR range (3–12 µm), thus providing a powerful tool to researchers in thermal wave imaging. However, imaging in the thermal IR range has its special handicaps, not shared by its visible counterpart. Most objects in conventional photography reflect rather than emit light of their own. As a result one often has the freedom to choose the intensity, direction and color of illumination to accentuate the aspects of the object to be photographed. In thermal IR imaging the situation is very different in that nearly all objects emit thermal radiation of their own, in addition to reflecting radiation of other objects. What is recorded in a thermograph is always a mixture of emitted and reflected radiation, some of which even comes from components of the camera itself, including lenses and their supporting structures. This problem is particularly severe in the 8–12 µm range, because it corresponds to the peak of blackbody radiation at room temperature. It is this same range of wavelength that is most relevent in non-destructive evaluation. In conventional scanned thermal wave imaging applications this problem is overcome by the use of a lock-in analyzer synchronized to the source of the thermal wave. Without the lock-in technique, the IR video camera is capable of observing only very slow thermal phenomena[1], despite the fact that the intrinsic band width of the camera is very broad. This limitation offsets the main advantage of the IR video camera, namely its high data-acquisition rate. In this paper we report on instrumentation development which combines the lock-in technique with the IR video camera. With this technique the information of each pixel of an image is handled in the manner of a lock-in analyzer, while the object is illuminated (i.e., heated) or stimulated (e.g., joule heating) with a signal which is synchronous with the reference signal of the lock-in detection. This way the unsynchronous background radiation is rejected and the signal-to-noise ratio is enhanced.

Circulating fluidized bed heat transfer

Abstract: Heat transfer to the walls of a circulating bed is due to conduction from clusters of particles falling along the walls, thermal radiation, and convection to uncovered surface areas. Important hydrodynamic factors are the fraction of the wall covered by particles and the average contact time of particles at the wall. Small active heat transfer probes will give an upper limit to the heat transfer in a circulating bed. Experimental results show lower heat transfer coefficients for larger walls; heat transfer is limited by the temperature change of particle clusters moving down the walls. The contact time for clusters is related to their average displacement before breakup. For displacements of 15 cm or less, the cluster displacement approximates constant gravitational acceleration. The most pressing needs for commercial bed designers are heat transfer and hydrodynamic results valid for large diameter beds.

X-ray generation in a cavity heated by 1.3- or 0.44-μm laser light. III. Comparison of the experimental results with theoretical predictions for x-ray confinement

Abstract: Radiation confinement in laser-heated gold cavities is analyzed on the basis of self-similar solutions of the hydrodynamic equations. The analysis is extended to include radiation losses through holes in the cavity. The possibility that a conversion layer on the inner wall of the cavity contributes to the measured radiation is also taken into account. The comparison with experiments performed at laser wavelengths of 0.44 and 1.3 /mu/m with the Asterix iodine laser shows reasonable agreement with the theoretical predictions. The major difficulty in the comparison is the lack of detailed information about the conversion of laser light into x rays, especially in the 1.3-/mu/m experiments.

Analysis of combined conductive-radiative heat transfer in a two-dimensional rectangular enclosure with a gray medium

Abstract: Combined conductive-radiative heat transfer in a two-dimensional enclosure is considered. The numerical procedure is based on a combination of two previous techniques that have been demonstrated to be successful for a two-dimensional pure radiation problem and a one-dimensional combined conductive-radiative heat transfer problem, respectively. Both temperature profile and heat transfer distributions are generated efficiently and accurately. Numerical data are presented to serve as benchmark solutions for two-dimensional combined conductive-radiative heat transfer. The accuracy of two commonly used approximation procedures for multidimensional combined conductive-radiative heat transfer is assessed. The additive solution, which is effective in generating approximation to one-dimensional combined conductive-radiative heat transfer, appears to be an acceptable empirical approach in estimating heat transfer in the present two-dimensional problem. The diffusion approximation, on the other hand, is shown to be generally inaccurate. For all optical thicknesses and conduction-radiation parameters considered (including the optically thick limit), the diffusion approximation is shown to yield significant errors in both the temperature and heat flux predictions.

Nonequilibrium thermal radiation for an aeroassist flight experiment vehicle

Abstract: The direct-simulation Monte Carlo method incorporating a dissociating and ionizing gas model for air with thermal radiation is used to characterize the hypersonic flow about an axisymmetric representation of an aeroassist flight experiment (AFE) vehicle, whose freestream conditions correspond to selected points along the entry, aerobraking, and exit phases of the trajectory. Calculations for two trajectory conditions indicate that the radiative heating of the AFE forebody is lower than the convective heating, but becomes significant as the maximum convective heating rate condition is approached.

Evaporative Cutting of a Semitransparent Body With a Moving CW Laser

Abstract: The formation of a groove by partial evaporation of a moving semi-infinite and semitransparent solid is considered. Evaporative removal of material is achieved by focusing a high-power, highly concentrated Gaussian laser beam of continuous wave (CW) onto the surface of the solid. Surface heat losses due to radiation and convection are assumed to be negligible, and conductive losses are treated in an approximate fashion using a simple integral method. The relevant nonlinear partial differential equations are solved numerically, and results for groove depth and shape are presented for a variety of laser and solid parameters.

The computation of radiation from nonequilibrium hypersonic flows

Abstract: The results of the solution of the equations that describe a hypersonic ionized flow about an elliptically blunted cone are presented. The flow conditions correspond to those of the proposed Aeroassist Flight Experiment (AFE) vehicle at altitudes between the perigee at 78 km and the approximate limit of the continuum regime at 90 km. For the free-stream velocities of interest, about 9 km/sec, the flowfield is out of thermo-chemical equilibrium, electronically excited, ionized and radiating. The gas consists of eight-chemical species including free electrons. The thermal state of the gas is modeled with a translational-rotational temperature, four vibrational temperatures for the diatomic species and an electron-electronic temperature. The electronic excitation of molecules is included. The nonequilibrium air radiation from each fluid element is computed and the radiative heat flux at the body surface is determined. The stagnation point radiative heating result agrees with previous calculations.

A finite element solution of radiative heat transfer in participating media utilizing the moment method

Abstract: A finite element solution of the radiative heat transfer in participating media is presented. The expensive direct numerical treatment of the integrodifferential equations of radiation is avoided by employing the moment method, which allows the derivation of an approximate local field equation for the radiation intensity. This makes the procedure convenient for use in combined-mode heat transfer problems, where the coupling of the radiation model with the iterative convective flow solution is required. The approach is assessed by investigating several numerical examples.

Thermal conduction at a contact interface measured by pulsed photothermal radiometry

Abstract: We have used pulsed photothermal radiometry to measure the thermal contact resistance at the interface of a smooth polymer film and a polished metal substrate. This method relies on the heating of the film surface by a short light pulse and detecting the subsequent infrared thermal radiation from the surface. An analytical solution to the heat diffusion equation shows that in a suitable delayed time interval, the infrared signal decays exponentially in time with a time constant related to the thermal contact resistance of the interface. By changing gases in the interface at constant pressures, we are able to separate the thermal conductance into two components: that due to solid contacts and that due to gas conduction. The thermal conductance due to gas conduction in the interface is proportional to the thermal conductivity of the gas found in continuum fluid theory, except for He which is more than 30% lower. We believe that the discrepancy in He is partly due to the fact that the mean free path of He ga...

Thermal radiation and laminar forced convection in a gas pipe flow

Abstract: The interaction of forced convection and thermal radiation in laminar pipe flow is numerically studied in this paper. An absorbing and emitting gas is considered for the analysis and treated to be a gray medium. The method of moments is used to describe approximately the radiative heat flux in the energy equation. The conservation equations that govern the problem are reduced to a coupled system consisting of a partial and an ordinary differential equations. The resulting system was reformulated into an initial value problem with the help of the method of lines in conjunction with the control volume approach. Temperature distributions in the thermal entrance region of the gas flow are computed by the Runge-Kutta integration scheme. Results for the mean bulk temperatures and total Nusselt numbers showed a good quantitative agreement with those utilizing an exact description for the radiative heat flux. Moreover, this simple methodology provided great savings in CPU time. Therefore, the use of the method of moments in internal gas flows with combined modes of heat transfer seems justifiable.

Combined conduction and radiation in a two-dimensional rectangular enclosure

Abstract: The steady-state combined conduction and radiation heat transfer for an absorbing, emitting, and isotropically scattering two-dimensional rectangular enclosure is investigated. The boundary surfaces art considered to be black and subjected to a constant temperature on one surface and to zero temperature on others. The Galerkin method is used to obtain an exact solution to the radiation part of the problem, and a finite-difference scheme is applied to solve the conduction part. The effects of the conduction-to-radiation parameter, the single scattering albedo, and the aspect ratio on the temperature distribution are examined.

The anomalous thermal radiation from metals produced by ultrashort laser pulses. I

Abstract: The spectral-time characteristics of the secondary radiation induced in silver and tungsten by picosecond laser pulses of varying duration and fluence have been studied theoretically and experimentally. It is established that the secondary radiation is due to heating, but in silver, nevertheless, it is not usual and does not correspond, for example, to grey-body radiation. This radiation—the anomalous thermal radiation proceeds by the following mechanism: When the electron and phonon subsystems in a metal are heated (including also the nonisothermal process), there appears a glow with a continuous spectral distribution and an intensity exceeding the radiation intensity of the grey body whose temperature is equal to the temperature of the ion or electron subsystem of a metal. This anomaly is either due to overheating of the electron subsystem with respect to the ion subsystem or due to recombination of electrons and thermions in a microlayer above the metal surface.

Direct simulation of AFE forebody and wake flow with thermal radiation

Abstract: Calculated results for the flowfield structure and surface quantities are presented for an axisymmetric representation of an aeroassist flight experiment vehicle. The direct simulation Monte Carlo (DSMC) method is used to perform the calculations, since the flow is highly nonequilibrium about the vehicle during both the compression and expansion phases. The body configuration is an elliptically blunt nose followed by a skirt with a circular radius and an afterbody. Freestream conditions correspond to a single point along the entry trajectory at an altitude of 90 km and a velocity of 9.9 km/s. The calculations account for nonequilibrium in the translational and internal modes, dissociation, ionization, and thermal radiation. The degree of dissociation is large, but the maximum ionization is only about 2 percent by mole fraction. The blunt forebody flow experiences a high degree of thermal nonequilibrium in which the translational temperature is generally greater than the internal temperature. However, as the flow expands about the aerobrake skirt and afterbody, the internal temperature is generally greater than the translational temperature.

A theoretical model for simultaneous convective and radiative heat transfer in circulating fluidized beds

Abstract: A model is proposed for simultaneous convection and radiation in high temperature circulating fluidized beds. Turbulent convection is combined with discrete radiative fluxes in three transport equations, including a term for volumetric heat generation. The system of equations is nonlinear and requires numerical solution for the general case. Sample results are given for typical CFBC conditions.

Radiative transfer in an inhomogeneous sphere

Abstract: We connect the problem of radiation transfer in a diffusely-reflecting sphere containing an energy source and source-free radiation transfer with isotropic boundary conditions. An equation for the radiation heat flux is obtained for a polynomial source. In the special case of a uniform source, the radiation heat flux and the angular flux are obtained in terms of the albedo of the second problem. Numerical results are presented for inhomogeneous and homogeneous spheres, and the results for the homogeneous sphere are compared with those of Mordant.

Transient behaviors in thermal radiation characteristics of heat-resisting metals and alloys in oxidation processes

Abstract: A high-speed spectrophotometer system is developed to study radiation characteristics of materials. The system allows measurements of the spectra at wavelengths of 0.35–10μm repeatedly with a period of less than 1 s. It is applied to the study of transient behaviors in reflection characteristics of heat-resisting alloys and the constituent transition metals in air-oxidation processes at high temperatures. An interference phenomenon due to the multiple reflection at the upper and lower boundaries of the oxide film is observed in the diffuse reflection spectra of oxidizing rough-finished surfaces as well as in the specular reflection spectra of oxidizing specular-finished surfaces. The phenomenon is found to be fairly reproducible and consistent over all the materials investigated. It is attributed to the interference and diffraction of radiation at three-dimensional nonparallel film elements of the polycrystalline oxide grains. A possibility is suggested for the theoretical modeling of radiation characteristics of real surfaces in the actual environments of industry.