Showing papers on "Thermal radiation published in 1991"
TL;DR: In this article, a plane-parallel polarized radiative transfer model was used to compute the radiance exiting a vertically inhomogeneous atmosphere containing randomly-oriented particles, where both solar and thermal sources of radiation were considered.
Abstract: A plane-parallel polarized radiative transfer model is described. The model is used to compute the radiance exiting a vertically inhomogeneous atmosphere containing randomly-oriented particles. Both solar and thermal sources of radiation are considered. A direct method of incorporating the polarized scattering information is combined with the doubling and adding method to produce a relatively simple formulation. Several numerical results are presented for verification and comparison.
360 citations
TL;DR: In this article, the melting of chondrule-sized grains is most directly associated with those dust-rich and optically thick zones in which thermal radiation from neighboring grains balances grain radiative cooling.
129 citations
TL;DR: In this paper, the rotational and vibrational temperatures were determined in both the equilibrium and nonequilibrium regions, contradicting the two-temperature assumption of Park (1988), but the measured vibrational temperature agrees with Park's model.
Abstract: The intensities of the radiation emitted behind a normal shock wave in N were measured in an electric-arc driven shock tube at a shock velocity of 6.2 km/sec. Both a time-resolved broad-band radiation intensity measurement and a time-frozen spectral measurement were conducted. The rotational and vibrational temperatures are determined in both the equilibrium and the nonequilibrium regions. The results are compared with the similar data obtained by Allen et al. (1961). The measured rotational temperature seems to be in nonequilibrium, contradicting the two-temperature assumption of Park (1988), but the measured vibrational temperature agrees with Park's model.
102 citations
TL;DR: New data for the thermal conductivity of liquid toluene near the saturation line, between 298 and 550 K, are presented and can be used to illustrate the importance of radiative heat transfer in transient hot-wire measurements.
Abstract: A new apparatus for measuring both the thermal conductivity and thermal diffusivity of fluids at temperatures from 220 to 775 K at pressures to 70 MPa is described. The instrument is based on the step-power-forced transient hot-wire technique. Two hot wires are arranged in different arms of a Wheatstone bridge such that the response of the shorter compensating wire is subtracted from the response of the primary wire. Both hot wires are 12.7 µm diameter platinum wire and are simultaneously used as electrical heat sources and as resistance thermometers. A microcomputer controls bridge nulling, applies the power pulse, monitors the bridge response, and stores the results. Performance of the instrument was verified with measurements on liquid toluene as well as argon and nitrogen gas. In particular, new data for the thermal conductivity of liquid toluene near the saturation line, between 298 and 550 K, are presented. These new data can be used to illustrate the importance of radiative heat transfer in transient hot-wire measurements. Thermal conductivity data for liquid toluene, which are corrected for radiation, are reported. The precision of the thermal conductivity data is ± 0.3% and the accuracy is about ±1%. The accuracy of the thermal diffusivity data is about ± 5%. From the measured thermal conductivity and thermal diffusivity, we can calculate the specific heat, Cp , of the fluid, provided that the density is measured, or available through an equation of state.
87 citations
TL;DR: In this article, a laser heating system is described for use with diamond anvil high pressure cells that directly senses and stabilizes visible thermal radiation emitted by hot samples, which stabilizes sample temperatures better than other methods and allows superior temperature control.
Abstract: A laser heating system is described for use with diamond anvil high pressure cells that directly senses and stabilizes visible thermal radiation emitted by hot samples. This technique stabilizes sample temperatures better than other methods and allows superior temperature control. Calibration of the system was checked by measuring the melting temperatures of five metals at ambient pressure. Assuming literature values for spectral emissivity, the calibration was found to be accurate to 3.3% (based upon one standard deviation of the percentage error from published melting temperatures). Performance of the laser heating system was verified by heating iron foil at 13 GPa. With the sample intensity unstabilized, mean temperature was 3003 K with a standard deviation of 144 K, while with it stabilized, mean temperature was 3051 K with a standard deviation of 8 K. For a given wavelength‐dependent emissivity, the difference between the actual temperature and the greybody temperature increases as the temperature in...
70 citations
TL;DR: In this article, a numerical analysis based on the finite difference scheme and Hottel's zonal method generalized by the ray tracing method is carried out to treat the one-dimensional transient and steady-state combined radiative-conductive heat transfer in non-gray Semi-Transparent Materials (STM), especially glasses, subjected to an external pulse or a step of irradiation.
Abstract: A numerical analysis based on the finite difference scheme and Hottel’s zonal method generalized by the ray tracing method is carried out to treat the one-dimensional transient and steady-state combined radiative-conductive heat transfer in non-gray Semi-Transparent Materials (STM), especially glasses, subjected to an external pulse or a step of irradiation. Coupling problems are studied for two optical boundary conditions: opaque and vitreous interfaces with specular reflections. The influence of slab thickness, spectral properties of the STM, wavelength of the incident radiation, and diffusivity coefficient are examined. It is pointed out that the application of the laser flash method in thermal metrology may give irrelevant results if the basic heat transfer model is not able to take into account radiative-conductive coupling phenomena. The effect of semi-transparency on the steady-state temperature distribution is also examined for materials ranging from fully opaque to fully transparent.
50 citations
TL;DR: A finite element quasi-steady state modeling of heat transfer during the growth of a silicon single crystal by the Czochralski (CZ) method is presented in this paper.
49 citations
TL;DR: In this article, a theoretical model is developed of flame spread over a thin solid fuel into an opposing flow of oxidizer, the opposing flow being present in the quiescent environment in flame-fixed coordinates, including the effects of radiative heat transfer from the fuel surface.
49 citations
TL;DR: In this paper, the authors considered the problem of a combustible gas in a vertical cylinder, in the presence of radiative heat transfer, affords the closest model to a biomass moving bed gasifier operating at temperatures between 750 and 1500 K.
Abstract: The flow of a combustible gas in a vertical cylinder, in the presence of radiative heat transfer, affords the closest model to biomass moving bed gasifier operating at temperatures between 750 and 1500 K. This problem forms the subject matter of the paper under the simplistic assumption of a binary reaction A B. Under the general differential approximation for radiation, the temperature is perturbed about the wall temperature, and the nonlinear differential equations are subsequently integrated in a closed form. Consequences of the effect of the Arrhenius activation energy are discussed quantitatively.
46 citations
Patent•
19 Apr 1991
TL;DR: In this article, a thermal radiation sensor is joined with a shutter that is adapted for reversible interruption of radiation from an object to the sensor, and the shutter includes an integral electrically operated heater for maintaining a portion of the shutter at a predetermined temperature as a thermal reference for the sensor.
Abstract: A thermal radiation sensor is joined with a shutter that is adapted for reversible interruption of radiation from an object to the sensor. The shutter includes an integral electrically operated heater for maintaining a portion of the shutter at a predetermined temperature as a thermal reference for the sensor. The sensor is alternatively exposed to radiation from the object and the thermal reference portion of the shutter, and provides a first signal representative of the radiation that it receives from the object and a second signal representative of the radiation that it receives from the reference portion. An electronic circuit is connected to the sensor for receiving the first and second signals, for calculating the temperature of the object, and for providing a signal representative of the calculated temperature.
44 citations
TL;DR: A transient analysis of a solar still integrated with a panel of collectors through a heat exchanger has been developed by incorporating the effect of all possible system parameters as mentioned in this paper, which has also been validated by experimental results through an experiment carried out at CES, IIT Delhi.
01 Nov 1991
TL;DR: In this article, an analysis was executed to reveal the flame stabilization mechanism in the surface combustion burners (porous radiant burners) which can emit a high intensity of thermal radiation depending on the flow velocity as well as the equivalence ratio of combustible mixture.
Abstract: An analysis was executed to reveal the flame stabilization mechanism in the surface combustion burners (porous radiant burners) which can emit a high intensity of thermal radiation depending on the flow velocity as well as the equivalence ratio of combustible mixture. Numerical calculations have shown some detailed behaviors of flame with respect to time for understanding the stabilization mechanism and have also illustrated the criteria of the three critical limits of blowoff, flashback and extinction correlated to the flow velocity, flame structure and thermal radiation propagation. These results have all been successful more or less for predicting the empirical behaviors of flames stabilized around the porous surface for a wide range of working parameters.
TL;DR: In this article, a volumetric solar receiver for central receiver systems is presented, which consists of a ceramic foil receiver, which is covered by a matrix of square channels of quartz glass.
TL;DR: In this article, the authors present algorithms for efficiently computing the radiative heat exchange between four wall surfaces, several fires and two interior gases in a two-wall and a ten-wall radiation model.
Abstract: Radiation, convection and conduction are the three mechanisms which a zone fire model must consider when calculating the heat transfer between fires, wall surfaces and room gases. Radiation dominates the other two modes of heat transfer in rooms where there are fires or hot smoke layers. The computational requirements of a radiation model can also easily dominate the work required to calculate other physical sub-models in a zone fire model.This paper presents algorithms for efficiently computing the radiative heat exchange between four wall surfaces, several fires and two interior gases. A two-wall and a ten-wall radiation model are also discussed. The structure of this radiation model is exploited to show that only a few configuration factors need to be calculated directly (two rather than 16 for the four-wall model and eight rather than 100 for the ten-wall model) and matrices needed to solve for the net radiative flux striking each surface are shown, after the appropriate transformation is taken, to be diagonally dominant. Iterative methods may then be used to solve the linear equations more efficiently than direct methods such as Gaussian elimination.
TL;DR: In this paper, the authors present the analysis and a methodology for estimating the error in the measurement of mixed convective-radiative heat flux, which is the difference between the true surface-sensed heat flux and the flux determined from the gage output using a calibration based on purely radiative heat heat flux.
Abstract: Principles of heat flux measurement by circular foil heat flux sensors, also known as Gardon gages, are analyzed when the gages are subjected to a mixed convective/radiative heat flux. The specific objective of this work is to present the analysis and a methodology for estimating the error in the measurement of mixed convective-radiative heat flux, which is the difference between the true surface-sensed heat flux and the flux determined from the gage output using a calibration based on purely radiative heat flux.
TL;DR: In this article, the influence of radiation on thermal turbulence spectra is studied theoretically in the case of homogeneous and isotropic turbulence in high-temperature radiating gases, and it is found that radiation acts as a dissipative process with a coefficient N(k) smaller than the conductive one ak for small eddies and greater than ak for large eddies.
Abstract: The influence of radiation on thermal turbulence spectra is studied theoretically in the case of homogeneous and isotropic turbulence in high-temperature radiating gases. A statistical narrow-band model is used to compute radiative properties of real gases such as CO2 and H2O, and an Onsager-type model is used as closure for the temperature variance spectrum equation. It is found that radiation acts as a dissipative process with a coefficient N(k) smaller than the conductive one ak for small eddies and greater than ak for large eddies. The critical wave number, for which conductive and radiative processes are of the same order of magnitude, is found to be close to k = 100 m" for pure H2O or pure CO2 in the temperature range [400 K, 2000 K]. At high temperature and small values of the viscous dissipation rate of turbulent kinetic energy, e, radiation significantly modifies the temperature variance spectrum in the region typically between 10 ~ kd and kd, where kd is the Kolmogorov wave number. The effects of radiation increase with temperature but decrease with e.
TL;DR: In this article, the thermal conductivity of liquid toluene between 300 and 550 K has been used to study the importance of radiative heat transfer when using the transient hot-wire technique.
Abstract: New measurements of the thermal conductivity of liquid toluene between 300 and 550 K have been used to study the importance of radiative heat transfer when using the transient hot-wire technique. The experimental data were used to obtain the radiation correction to the hot-wire temperature rises. Radiationcorrected values of thermal conductivity are reported. This study shows that the transient hot-wire method is much less affected by radiation than steady-state techniques.
TL;DR: In this article, a series of thermophysical computer models for solid-surfaced planetary bodies whose surface roughness is modeled as paraboloidal craters of specified depth/diameter ratio attempts to characterize the nongrey-body brightness temperature spectra of the moon and of the Galilean satellites.
Patent•
24 Oct 1991
TL;DR: In this paper, a convection baffle which transmits light and thermal radiation is used to improve the thermal resistance and/or reduce the cost of low emissivity layers, and an improved partition means separating the space between the layers into compartments.
Abstract: A light admitting thermal insulating structure (10) having controllable transmissivity to visible radiation (11) comprises a first layer (15) generally transparent to light, a second layer (17) generally transparent or absorptive to light and spaced from the first layer; an improved partition means separates the space between the layers into compartments; a thermal radiation suppression device (16) for suppressing thermal radiation transmission; and a variable transparency device (18) for controlling transmission of light. A suitable partition includes a novel convection baffle which transmits light and thermal radiation which improves the thermal resistance and/or reduces the cost of low emissivity layers (16).
TL;DR: In this article, Monte-Carlo simulations show that the major problems with a multi-lamp arrangement with surrounding reflector are due to nonuniform irradiation by the lamps, non-uniform energy loss of the wafer, and additional energy loss at the edge, respectively.
Abstract: The temperature within a rapid thermal processing system is characterized by the intensity distributions of the lamp light and of the reabsorbed heat radiation of the wafer. The intensity to the front and back side of the wafer and to the wafer edge have to be considered for pattern induced effects and additional energy loss at the edge, respectively. Monte-Carlo simulations show that the major problems with a multi lamp arrangement with surrounding reflector are due to nonuniform irradiation by the lamps, nonuniform energy loss of the wafer, and additional energy loss at the wafer edge. The temperature influencing quantities cannot be optimized at the same time without modifications of the reflector geometry or without a subsidiary light flux which is controllable independently of the lamp light.
TL;DR: In this paper, a new approach for deriving the temperature distribution in biological tissues of microwave radiometry is proposed, which consists in the measurement of the thermal radiation of the body, at a given frequency, as a function of the observation angle, for two mutually orthogonal polarizations.
Abstract: A new approach for deriving the temperature distribution in biological tissues of microwave radiometry is proposed. It consists in the measurement of the thermal radiation of the body, at a given frequency, as a function of the observation angle, for two mutually orthogonal polarizations. Theoretically, this method yields results comparable to those obtained with the multispectral method. In order to derive the relations between the body temperature and the emitted thermal signal, the biological body is modeled by a set of parallel planar layers, each characterized by constant permittivity and temperature. It is demonstrated that for all practical purposes the radiation pattern of the antenna may be approximated by that of an unbounded plane wave. >
TL;DR: In this paper, a three-dimensional numerical study was performed on interactions of natural convection and radiation in a cubical enclosure filled with carbon dioxide gas, where the enclosure was heated differentially by two opposing vertical walls, and the mean heat transfer correlation was proposed as Nu = 0·323 Ra0·342 in the surface/gas radiation mode, where Nu is the time and spatially averaged Nusselt number at the isothermal walls.
Abstract: A three-dimensional numerical study was performed on interactions of natural convection and radiation in a cubical enclosure filled with carbon dioxide gas. The enclosure was heated differentially by two opposing vertical walls. Gas radiation was analyzed by the P1 differential approximation method and the weighted sum of gray gas model. Computations were carried out over a range of the Rayleigh number, Ra, between 105 and 109. The Prandtl number and the overheat ratio were held fixed at 0·68 and 1·0, respectively. Unsteady transitional flows were computed by a direct simulation method, without using any explicit turbulence models. From the predictions, a mean heat transfer correlation has been proposed as Nu = 0·323 Ra0·342 in the surface/gas radiation mode, where Nu is the time and spatially averaged Nusselt number at the isothermal walls.
TL;DR: In this article, the long-term averages of the atmospheric, net thermal and net total radiation fluxes, as well as their day-today and year-to-year variabilities, were studied and are predicted with data from Lisbon.
TL;DR: In this paper, the authors focused on the factors influencing the constant drying rate of a granular bed irradiated by infrared radiation, and calculated the calculated results were quantitatively compared with the experimental results, and agreed consistently with the latter by taking account of the spectral distribution of absorption of irradiation power by the granular beds.
Abstract: The present study aims at gaining a good understanding of the mechanism of infrared radiation drying of a wet granular bed in the constant-rate period. Our attention was focussed on the factors influencing the constant drying rate of a granular bed irradiated by infrared radiation. As the variables, the conditions of the granular bed (emissivity of the powder materials and the particle size of the powders) and the radiative heat source (the spectral distribution of irradiation power) were examined. Infrared radiation drying of the granular bed was performed and the heat transfer model in the constant-rate period was studied. The constant drying rate was calculated by using the model. The calculated results were quantitatively compared with the experimental results, and agreed consistently with the latter by taking account of the spectral distribution of absorption of irradiation power by the granular bed.
TL;DR: In this paper, it was shown that the flux density of latent heat gained at the coat surface on the back of an animal such as a sheep could exceed 30 W m −2, such that the coat accumulates up to 0.1 kg of water during the night.
TL;DR: In this paper, the influence of thermal radiation on natural convection in a participating fluid contained in a square cavity is studied numerically, and the radiative transfer process is solved from the PI approximation.
Abstract: The influence of thermal radiation on natural convection in a participating fluid contained in a square cavity is studied numerically. The radiative transfer process is solved from the PI approximation. The Navier-Stokes equations are solved by a finite difference scheme integrated over control volumes. A numerical study of the so-called window problem (thermally driven cavity) shows the influence of thermal radiation on this reference problem for Rayleigh numbers in the range of 103-107 and Planck numbers varying from 1 to 0.05. The isotherms, streamlines, and heat lines show an increase of the dynamical effects in the central part of the cavity and a significant modification of the boundary layers. Results obtained from the simulation of an isotropically scattering medium are given.
TL;DR: In this article, the heat transfer rate of a thin solid combustible from an attached diffusion flame, spreading across the surface of the combustible in a quiescent, microgravity environment, was determined from measurements made in the drop tower facility at NASA-Lewis Research Center.
Abstract: The heat transfer rate to a thin solid combustible from an attached diffusion flame, spreading across the surface of the combustible in a quiescent, microgravity environment, was determined from measurements made in the drop tower facility at NASA-Lewis Research Center. With first-order Arrhenius pyrolysis kinetics, the solid-phase mass and energy equations along with the measured spread rate and surface temperature profiles were used to calculate the net heat flux to the surface. Results of the measurements are compared to the numerical solution of the complete set of coupled differential equations that describes the temperature, species, and velocity fields in the gas and solid phases. The theory and experiment agree on the major qualitative features of the heat transfer. Some fundamental differences are attributed to the neglect of radiation in the theoretical model.
01 Jan 1991
TL;DR: In this paper, the authors considered quasi-one-dimensional nonequilibrium nozzle flows with coupled radiative transfer and presented a fully implicit numerical method using the full matrix inversion or block iteration methods to solve these equations.
Abstract: Quasi-one-dimensional nonequilibrium nozzle flows with coupled radiative transfer are considered. The strongly coupled formulation of radiation and flowfield leads to a governing set of integro-differential equations. A fully implicit numerical method using the full matrix inversion or block iteration methods is presented to solve these equations. The nonequilibrium gas model consists of two chemical species, molecular and atomic nitrogen. The thermodynamic state of the gas is described by two temperatures, translational-rotational and vibrational, and the thermal radiation is assumed to be governed by the vibrational temperature. In radiative transfer, gases are assumed to be absorbing and emitting, and a detailed spectral dependency of the absorption coefficient is prescribed for a non-gray gas. The numerical solutions of strongly radiating nonequilibrium flows are presented for both gray and non-gray gases.
TL;DR: In this paper, the effects of the Peclet number and its interaction with the conduction-radiation parameter and optical thickness on heat transfer behavior in the thermal entrance region are investigated.