Showing papers on "Thermal radiation published in 1983"

Radiative heat transfer in fibrous insulations—Part I: Analytical study

Abstract: The purpose of this work is to develop models for predicting the radiant heat flux in lightweight fibrous insulations (LWFI). The radiative transport process is modeled by the two-flux solution and the linear anisotropic scattering solution of the equation of transfer. The radiative properties of LWFI consistent with these solutions have been determined based on extinction of electromagnetic radiation by the fibers. Their dependence on the physical characteristics of fibrous insulations has been investigated. It has been found that the radiant heat flux can be minimized by making the mean radius of the fibers close to that which yields the maximum extinction coefficient. The results obtained in this study are useful to those concerned with the design and application of LWFI.

Heterogeneous shock-induced thermal radiation in minerals

Abstract: A 500 channel optical imaging intensifying and spectral digital recording system is used to record the shock-induced radiation emitted from 406 to 821 nm from transparent minerals during the time interval that a shock wave propagates through the sample. Initial results obtained for single crystals of gypsum, calcite and halite in the 30 to 40 GPa (300 to 400 kbar) pressure range demonstrate greybody emission spectra corresponding to temperatures in the 3,000 to 4,000 K range and emissivities ranging from 0.003 to 0.02. In the case of gypsum and calcite, distinctive line spectra, are superimposed on the thermal radiation. The observed color temperatures are a factor of 2 to 10 greater than the Hugoniot temperature, calculable on the basis of continuum thermodynamics and equation of state models for the shock states achieved in the three minerals. These observed high temperatures are believed to be real. We conclude that we are detecting a large number of closed spaced high temperature shear-band regions immediately behind the shock front. A shear instability model, such as proposed independently by Grady (1977, 1980), Ananin et al. (1974), and Horie (1980), in which small zones of highly deforming and melted material are produced which are the source of the detected thermal radiation and have a fractional effective area approximately numerically equal to the measured emissivity, can be used to predict an effective emissivity of 0.0065 directly behind the shock front. If shear band instability arises from viscous flow processes, Grady's model and mineral thermal properties yield for the shocked mineral viscosities values in the range of 10^9 to 10^(15) P immediately behind the shock front.

Thermal conductivity of plastic foams

Abstract: A simple equation enabling the prediction of the thermal conductivity of plastic foams, without the aid of adjustable parameters, is proposed. The equation is based on a recurrent method, previously developed, that showed reasonable agreement with experimental results. Ways of decreasing the thermal radiation contribution are shown. In particular, the influence of cell size, radiation transmission through solid membranes, and low-emissivity boundary surfaces are analyzed. Errors involved in steady techniques of measuring the thermal conductivity associated with radiation are discussed.

Radiative heat transfer through opacified fibers and powders

Abstract: Radiative heat transfer through opacified (metallic or metallized) cylindrical fibers and spherical powders is investigated theoretically. The radiative properties of these packed particles are evaluated by using the solutions of electromagnetic theory. The large optical constants and large particle size parameters require an improved numerical scheme for evaluation of these properties. The results show that fine metal fibers provide excellent thermal radiation resistance. For the packed spheres, the high solid volume fraction restricts the present model to the geometric scattering regime. The results in this regime indicate better radiation resistance for smaller spheres. It is also interesting to note that, relative to unopacified spheres, the opacified spheres have higher thermal radiation resistance only at high temperatures.

Thermal diffusivity in thin films measured by noncontact single-ended pulsed-laser-induced thermal radiometry. Technical report

Abstract: A pulsed nitrogen laser is used to induce a sharp thermal gradient in a thin film, and the thermal radiation (infrared) transient from the irradiated region is monitored from the same side as the excitation beam (ie.e, single-ended detection). We show that this pulsed photothermal radiometry lineshape can be analyzed to provide the thermal diffusivity or thickness of the sample, as well as information on subsurface modifications or the degree of thermal contact with a substrate. We present data for several important classes of films, including metal, polymer and paper (e.g., in currency) and show the important features of the present technique for thin-film characterization, namely nondestructive, fast and remote sensing.

H2O heating in molecular clouds - Line transfer and thermal balance in a warm dusty medium

Abstract: An investigation is undertaken into the possibility of the heating of molecular gas through collisions with radiatively pumped H2O, in the context of the overall thermal balance of optically thick molecular clouds with embedded sources. In order to solve the line transfer equation, which includes warm dust grains, an extended method of escape probability approximation is developed in which the equilibrium gas temperature arises from the balance of heating by cosmic ray ionization of H2, and by collisions with warm dust grains and radiatively pumped H2O molecules against cooling by collisions with CO and C I. The equilibrium gas temperature for a given dust temperature strongly depends on the efficiency of the cooling species, and is therefore most sensitive to the cloud optical depth. It is less dependent, in decreasing order, on H2O abundance, gas density, and velocity dispersion.

Emission, absorption and polarization of gyrosynchrotron radiation of mildly relativistic particles

Abstract: In this paper are presented approximate analytic expressions for the emissivity and absorption coefficient of synchrotron radiation of mildly relativistic particles with an arbitrary energy spectrum and pitch angle distribution. From these, an expression for the degree of polarization is derived. The analytic results are compared with numerical results for both thermal and nonthermal (power law) distributions of particles.

Computation of radiation heat transfer in diesel combustion

Abstract: A theoretical model of radiation heat transfer has been developed. A computation of radiation heat flux at a particular location in the combustion chamber by using the present model requires in-cylinder time- and space-resolved species data and cylinder pressure. From the species data, the burned fuel/air ratio distribution is inferred to compute space-resolved adiabatic flame temperature. For the computation of the spectral emissivity of an isothermal volume of adiabatic temperature containing soot, the Rayleigh-limit expression is used. The refraction indices in the expression are obtained by using the dispersion equations based on the electronic theory encompassing both free and bound electrons. For the spectral emissivity from the gaseous component in the volume, the semi-empirical band model is used. A parametric analysis of radiation heat transfer in diesel combustion is made by using the present model; a prediction by the model qualitatively compares with some of the reported experimental data.

Infrared to visible up‐conversion using GaP light‐emitting diodes

Abstract: Electroluminescence excited by infrared radiation has been observed in GaP light‐emitting diodes (LED’s) at low temperatures providing a new efficient method to convert infrared radiation within a broad spectral range into visible light. Using 10.6‐μm radiation of a CO2 laser an up‐conversion quantum efficiency of 3.4×10−6 was found. If a low dark current photomultiplier is employed to detect the LED emission the dominant noise source is due to conversion of thermal background radiation yielding a noise equivalent power of NEP=1.6×10−9 W/Hz1/2.

Stationary Thermal Ignition of Particle Suspensions

Abstract: A calculational method is presented for the stationary thermal ignition of pulverized coal suspensions, based on radiative energy transport in a heat generating medium. A diffusion-limited, Arrhenius model for heat generation is used in the description of the heterogeneous ignition and combustion of particles with the gases in which they are dispersed. The discrete ordinates method, which is used to solve numerically the radiative transfer equation, is combined with an iterative procedure to obtain both the temperature and radiation intensity distributions throughout the reacting system. Numerical examples are presented to show the variation in the critical behavior of a system in plane geometry with wall temperature and reflectivity, optical thickness of the system, particle size, optical parameters, anisotropy of the scattering, and the parameters of the heat generation model.

Window glass shielding electromagnetic radiation

Abstract: PURPOSE: To provide a window glass shielding electromagnetic radiation and remarkably suppressing the transmission of infrared radiation, by laminating a transparent conductive thin film for the shielding of electromagnetic radiation and a heat radiation reflection film to a glass substrate. CONSTITUTION: A window glass shielding electromagnetic radiation, remarkably suppressing the transmission of infrared radiation and useful as a window glass of vehicles, aircrafts, buildings, etc. is manufactured by laminating a glass substrate with a transparent conductive thin film for the shielding of electromagnetic radiation and a heat radiation reflection film. For example, an automobile window glass is manufactured by applying a transparent conductive thin film 2 for the shielding of electromagnetic radiation and composed of a solid solution of In 2 O 3 and SnO 2 and having a thickness of 100ÅWseveral μm by vacuum metallizing, and laminating a heat radiation reflection film 3 composed of a plurality of alternately laminated TiO 2 layers 3a having high refractive index and SiO 2 layers 3b having low refractive index each having a thickness of λ/4 (λ is wavelength of the infrared radiation to be reflected) and topped with an SiO 2 layer having a thickness of λ/8. COPYRIGHT: (C)1985,JPO&Japio

Apparatus for accurately measuring high temperatures

Abstract: The present invention is a thermometer used for measuring furnace temperaes in the range of about 1800° to 2700° C. The thermometer comprises a broadband multicolor thermal radiation sensor positioned to be in optical alignment with the end of a blackbody sight tube extending into the furnace. A valve-shutter arrangement is positioned between the radiation sensor and the sight tube and a chamber for containing a charge of high pressure gas is positioned between the valve-shutter arrangement and the radiation sensor. A momentary opening of the valve shutter arrangement allows a pulse of the high gas to purge the sight tube of air-borne thermal radiation contaminants which permits the radiation sensor to accurately measure the thermal radiation emanating from the end of the sight tube.

On calculating thermal radiation from cloudless skies

Abstract: Several recent empirical findings and theoretical developments related to the estimation of clear-sky atmospheric thermal radiation are discussed. It is demonstrated that the radiative behavior of water vapor at air temperatures above freezing has been parameterized as well as can or need be done, but that there may be room for some improvement at air temperatures below freezing. It is additionally shown that any procedure designed to accurately calculate atmospheric thermal radiation must be able to handle effects of airborne dust variability of both a temporal and spatial nature.

Experimental determination of vapor species from laser-ablated carbon phenolic composites

Abstract: The thermal loadings approximating those to be encountered by heat-shield materials at peak heating during vehicle entry into the atmospheres of the outer planets have been simulated with laser irradiation. The relative concentrations of the resulting vapors as they emanate from the ablating material have been measured, and the technique for vaporizing the surface of bulk samples by laser irradiation while measuring in situ the vapor species by mass spectrometry is described. Results from carbon phenolic show that vapor composition varies with irradiance level and with depth of heating (or extent of pyrolysis). Attempts are made to compare these experimental results with the theoretical predictions from computer codes. N view of the paucity of measurement data identifying the chemical species generated by vaporization of heat-shield materials, the objective in this work has been to determine experimentally the composition of blow-off gasses produced by carbon phenolic composites when subjected to the level of incident thermal energy encountered during entry into planetary atmospheres. This information is important as a basis for predicting the blockage factors for incident thermal radiation, and as a means of verifying the computer codes that predict chemical mole fractions on the basis of ther- modynamic and chemical equilibrium. The approach in this work has been to measure the vapors in situ as they emerge from the surface of the heated material prior to striking container walls or condensing on any surfaces, thus making possible a more complete determination of the chemical composition of the gaseous components including the free radicals and condensables as well as the more stable molecules. Although carbon/phenolic heat shield materials are not new, heretofore the amount of experimental work that has been done to define the vaporization products of the com- posite material has been limited both in extent and in in- strumentation employed. In most cases, the heating has been accomplished by placing the sample on a resistively heated surface or by putting it in a furnace, and the gas analysis carried out subsequently by gas chromatography or mass spectrometry. This inherently limits analysis to the stable vapor species. The major contribution of the work reported here lies both in the results and in the technique used to heat ablation materials by incident thermal radiation in an attempt to simulate the thermal levels encountered under vehicle flight conditions, while simultaneously sampling the gaseous products by instrumentati on that can best determine the initial pyrolysis species, including the transient intermediates. Experimental As in earlier work,1 the technique used for studying the materials of interest has been to vaporize an area of the sample surface by laser irradiation while measuring the vapor products using a mass spectrometer as the in situ diagnostic tool; the sample and spectrometer are within the same high- vacuum chamber and are positioned so that the ion source of the mass spectrometer is in a line-of-sight, collision-free path from the heated surface. The instrumentation used in this work is shown in Fig. 1; it has been described previously along with the associated data acquisition system.2 A time-of-flight (TOP) mass spec- trometer was selected because of its unique ability to present up to 50 complete mass spectra per millisecond plus its capability of measuring quantitatively several vapor species simultaneously, thereby permitting an in situ analysis during each laser-induced vaporization process. When the pulsed laser was employed, mass spectra were recorded only as the initial vapor cloud passed through the ion source; this insured equal measurement of the condensables and short-lived species along with the fixed gases. Although absolute calibration of the instrument has not been achieved at this time, sensitivity factors for the various gases were derived from the literature and from experimentation so that relative concentrations could be determined. Two types of laser heating have been employed: 1) a pulsed Ndrglass laser in the normal (or burst) mode, and 2) a con- tinuous wave (cw) carbon dioxide laser operating at a wavelength of 10.6 pm. Although pulsed lasers operating in the burst mode characteristically produce a highly irregular time-intensity distribution of output energy, their lower power densities and longer radiating periods better simulate the heating encountered by planetary probes than would those operating in the Q-switched mode. Furthermore, it is necessary to minimize any laser beam-vapor interactions that produce plasma, etc.—typically a result of the very high power intensities associated with Q-switched lasers. The pulsed laser heating conditions used here are shown in Table 1. Earlier work3 has shown that under the given conditions a laser beam having a uniform cross section and focused onto a planar surface—thereby vaporizing material in a circular spot within a reduced ambient pressure (or vacuum)—produces a gas-dynamic phenomenon which is a quasisteady, supersonic, free-jet expansion of the vapor products. Thus, the spot acts as a sonic orifice for the vapors and produces isentropic flow with streamlines appearing to radiate from a point source.

Finite element analysis of radiative transport in fibrous insulation

Abstract: The finite element method is used to solve the radiative transport equation for the problem of an absorbing, emitting, and scattering fibrous insulating medium. This finite element solution is compared to the Chandrasekhar discrete ordinate solution. Heat-transfer results are presented as a function of substrate reflectance, optical thickness, scattering albedo, and temperature gradient as parameters. The top boundary is considered as a transparent interface with a diffusely incident flux and the substrate is considered to be opaque. The radiation heat transfer is shown to be significant when compared to the conductive heat transfer; the radiation heat transfer can be greater or less than the conduction heat transfer depending upon the substrate reflectance.

Radiative transfer in spectrally dissimilar absorbing-emitting-scattering adjacent mediums

Abstract: Structure of radiation field in a cylindrical medium having two regions of different, but uniform absorption and scattering coefficients is analyzed. Fundamental aspects of the problem are elucidated by considering the case of a gray medium. It is shown for example that for unequal absorption coefficients in the two regions, both emission and absorption rates are discontinuous at the interface of the two regions, but the heat flux and incident radiation are continuous. As an application of the analysis, the influence on heat transfer of spatial distribution of particles in a coal-burning swirl combustor is investigated. In the example application, spectral calculations are performed spanning over the broad frequency range of the thermal radiation spectrum.

Method for continuously measuring surface temperature of heated steel strip

Abstract: A method for continuously measuring the surface temperature of a heated steel strip, includes providing a flat reflecting plate so as to face a heated steel strip at an angle of inclination (α) with the steel strip. A radiation thermometer measures the amount of heat radiation energy which is emitted from an arbitrary point on the surface of the steel strip and comes directly into the radiation thermometer; and the thermometer also measures the total sum of heat radiation energy which (a) is emitted from a different point on the surface of the steel strip and comes into the radiation thermometer after having been reflected at least twice between the steel strip and the reflecting plate and, (b) is emitted from a final reflecting point, on the steel strip, of the heat radiation from said different point. The emissivity of the steel strip is computed on the basis of said total sum of the energies of the heat radiations and the amount of energy of the heat radiation from the arbitrary point; and the surface temperature of the steel strip is measured on the basis of the computed emissivity and the amount of energy of a reference heat radiation. The final angle of reflection (θ) from the steel strip of the heat radiation from said different point, and the angle of inclination (α) of the reflecting plate, are set at values which satisfy specific limits.

Horizontal semiconductor vapor growth apparatus lising indirect heating

Abstract: PURPOSE:To improve the working ratio by radiating with a plurality of bar- shaped heating lamps arranged in proximity to and in parallel with a reaction tube a semicondutor retaining apparatus having a holder made from materials with good light absorption properties and large thermal conductivity. CONSTITUTION:A plurality of tubular lamps 11 are arranged at a constant interval in parallel with and in proximity to a reaction tube 1. A reflector 12 is used to increase the amount of heat radiation into the reaction tube. A suceptor 13, which a semiconductor substrate is to be placed upon, is heated by the radiation of the tubular lamps 11, and is made from a material having good heat absorption properties and large thermal conductivity, such as a SiC-coated graphite. A holder-retaing board 14 is made from a material through which radiation light can be transmitted, such as quartz.

Dichroic radiation thermometer

Abstract: PURPOSE:To improve accuracy and to enable continuous measurement, by a method wherein the ratio of spectral emissivity is obtained based upon the correlation between head rediation energy and an object to be measured at two different wave bands, and the ratio of the heat radiation energy is compensated. CONSTITUTION:An output detector 2 is provided to detect heat radiation energy from the object to be measured at two different wave bands lambda1 and lambda2, and to apply detected values to an operation circuit 3. The operation circuit 3 operates the temperature as a black body, and then operates the value of exponential ratio epsilon 1/epsilon 2 of each spectral emissivity epsilon1 and epsilon2 at lambda1 and lambda2 according to the temperature operated. Then, the value of epsilon 1/epsilon /2 is applied to a converter 4 which stores correlation curves of epsilon 1/epsilon 2 and the ratio epsilon1/epsilon2. The converter 4 converts the value of epsilon 1/epsilon 2 to the value of epsilon1/epsilon2. After that, heat radiation energy at lambda1 and lambda2 detected by the detector 2 is applied to an operation circuit 5, which operates the applied values as the temperature outputs. Finally, an output compensator 6 compensates the output of the circuit 5 utilizing the value of epsilon1/epsilon2.