Showing papers on "Thermal radiation published in 1999"

Temporal artery temperature detector

Abstract: Body temperature measurements are obtained by scanning a thermal radiation sensor across the side of the forehead over the temporal artery. A peak temperature measurement is processed to compute an internal temperature of the body as a function of ambient temperature and the sensed surface temperature. The function includes a weighted difference of surface temperature and ambient temperature, the weighting being varied with target temperature through a minimum in the range of 96° F. and 100° F. The radiation sensor views the target surface through an emissivity compensating cup which is spaced from the skin by a circular lip of low thermal conductivity.

A spectroscopic method to measure the spectral emissivity of semi-transparent materials up to high temperature

Abstract: A spectroscopic method to measure directional spectral emissivity for homogeneous and heterogeneous semi-transparent materials, giving access to a large spectral 10–12 000 cm−1 range and to temperatures lying between 600 and 3000 K is reported Sample heating is supplied by a carbon dioxide laser and the blackbody flux reference is obtained with a lanthanum chromite furnace Experimental results obtained with this setup on several dielectric oxides such as silica, alumina, and magnesia are in good agreement with the results obtained by an indirect method based on the Kirchhoff’s laws A brief overview of the setup abilities and a detailed discussion of the emissivity spectra are also proposed

Thermal model of pulsed laser ablation under the conditions of formation and heating of a radiation-absorbing plasma

Abstract: A model is proposed for the description of the dynamics of the absorption of radiation by a plasma formed on evaporation of a solid material by nanosecond laser pulses of moderate intensity when a thermal ablation regime is established The model takes into account the nonisothermal nature of the plasma heated during a pulse as a consequence of the absorption of radiation and makes it possible to calculate the laser energy balance Measurements were made of the vapourised mass and of the attenuation of radiation during laser ablation of graphite and a satisfactory agreement with the results of calculations was obtained

Fatigue characteristics of a glass‐fiber‐reinforced polyamide

Abstract: This paper deals with prediction of the temperature rise in the stress-controlled fatigue process of a glass-fiber-reinforced polyamide and the application of a temperature and frequency superposition procedure to the S-N curve An experimental equation was derived to predict the temperature rise from calculations based on the fatigue test conditions and viscoelastic properties of the material The temperature rise (ΔT) can be expressed as a product of a coefficient term Φ(L, κ) concerning heat radiation and the test-specimen shape and a function term Pfat concerning the viscoelastic properties and fatigue test conditions Φ(L, κ) was found experimentally to derive the equation for predicting the temperature rise blow or above the glass transition temperature (Tg) of the material The equation σR = −STfA log NfR + STfB was obtained as a procedure for applying temperature and frequency superposition to S-N curves in consideration of ΔT This procedure was obtained by combining both temperature- and frequency-superposition techniques Here, σR and log NfR represents the stress and the fatigue lifetime calculated at a given temperature and frequency, A and B denote the slope and intercept of any arbitrarily chosen S-N curve, and STf is a shift factor for temperature and frequency superposition © 1999 John Wiley & Sons, Inc J Appl Polym Sci 72: 1783–1793, 1999

Thermal radiation effect on thermal explosion in gas containing fuel droplets

Abstract: The effect of thermal radiation on the dynamics of a thermal explosion of a flammable gas mixture with the addition of volatile fuel droplets is studied. This is based on an original physical model of self-ignition. The thermal radiation energy exchange between the evaporating surface of the fuel droplets and burning gas is described using the P-1 model with Marshak boundary conditions. The original system of equations describing the effects of heating, evaporation and the combustion of fuel droplets is simplified to enable their analysis using asymptotic methods. The mathematical formulation is eventually reduced to a singularly perturbed system of ordinary differential equations. This allows us to apply the advanced geometric asymptotic technique (integral manifold method) for the qualitative analysis of the behaviour of the solution. Possible types of dynamic behaviour of the system are classified and parametric regions of their existence are determined analytically. The main attention is concentrated ...

Mechanism of single-bubble sonoluminescence.

Abstract: The mechanism of the light emission of single-bubble sonoluminescence (SBSL) is studied theoretically based on the quasiadiabatic compression model. It is concluded that SBSL is not the blackbody radiation but the thermal radiation. It is clarified that the shape of the spectrum is determined by the temperature inside the bubble and the intensity is determined by the rates of the microscopic processes of the light emission. For a noble-gas bubble, radiative recombination of electrons and ions and electron-atom bremsstrahlung are the dominant microscopic processes of the light emission, and the intensity is mainly determined by the degree of ionization of the gas inside the bubble. It is also clarified that for a noble-gas bubble the pulse width of the light is nearly independent of wavelength.

Theoretical radiative transport results for a free-burning arc using a line-by-line technique

Abstract: Many thermal radiation results for a two-dimensional, axisymmetric, atmospheric, free-burning arc for several different wavelength intervals, as well as the entire thermal spectrum, are presented. Quantities such as the emission, average intensity, radiative source term and radial flux are calculated from a theoretically rigorous technique for handling radiative transport in a medium such as a plasma in which the absorption coefficient is a strong function of the wavelength. An S-N discrete ordinates method is used on a line-by-line basis to perform this task. Most of the results presented are for a pure-argon arc; however, results indicating the effect of copper contamination on the radiative quantities are also given. Comparisons between the pure-argon and copper-contaminated arcs show that a small amount of copper greatly affects the radiative characteristics of the plasma.

Thermal profiles and thermal runaway in microwave heated slabs

Abstract: The microwave heating of slabs of water bound with a gel is modeled and analyzed without any restriction to the Biot number regime. Despite the fact that the temperature distribution over the slab is not uniform at all, the phenomenon of thermal runaway is basically caused by resonance of the electromagnetic waves within the object, combined with heat loss. A plot of the steady-state temperature at any position within the slab, versus the microwave power, is an S-shaped or a multi S-shaped curve. With respect to thermal runaway there is a strong similarity between isothermal and nonisothermal slabs. Using the average temperature of the nonisothermal slab, regardless of its Biot number, yields a reasonable approximation to describe the runaway. This is caused by the specific characteristic of the dielectric loss factor of water, which decreases with increasing temperature. This results in an almost constant absorption of energy over the whole slab without disturbing the wave character of the absorption. It turned out that this smoothing of the absorbed power plays a dominant role in the calculations of the temperature profiles. Any calculation where the temperature dependence of the permittivity is omitted, will not only pass the phenomenon of thermal runaway, but its temperature profiles will differ substantially from the ones where the temperature dependence has been taken into account.

Determination of the true temperature of emitted radiation bodies from generalized Wien's displacement law

Abstract: The temperature dependence of the 'generalized' Wien displacement law for tantalum and luminous-flames has been investigated. It is shown that the emitted thermal radiation of tantalum belongs to the same universality class as that of tungsten and zirconium and titanium carbides. The emitted thermal radiation of luminous flames belongs to the universality class as that of a black body. The true temperatures of investigated matter are defined.

Turbulence radiation interaction modeling in hydrocarbon pool fire simulations

Abstract: The importance of turbulent fluctuations in temperature and species concentration in thermal radiation transport modeling for combustion applications is well accepted by the radiation transport and combustion communities. A number of experimental and theoretical studies over the last twenty years have shown that fluctuations in the temperature and species concentrations may increase the effective emittance of a turbulent flame by as much as 50% to 300% over the value that would be expected from the mean temperatures and concentrations. With the possibility of such a large effect on the principal mode of heat transfer from a fire, it is extremely important for fire modeling efforts that turbulence radiation interaction be well characterized and possible modeling approaches understood. Toward this end, this report seeks to accomplish three goals. First, the principal turbulence radiation interaction closure terms are defined. Second, an order of magnitude analysis is performed to understand the relative importance of the various closure terms. Finally, the state of the art in turbulence radiation interaction closure modeling is reviewed. Hydrocarbon pool fire applications are of particular interest in this report and this is the perspective from which this review proceeds. Experimental and theoretical analysis suggests that, for this type of heavily sooting flame, the turbulent radiation interaction effect is dominated by the nonlinear dependence of the Planck function on the temperature. Additional effects due to the correlation between turbulent fluctuations in the absorptivity and temperature may be small relative to the Planck function effect for heavily sooting flames. This observation is drawn from a number of experimental and theoretical discussions. Nevertheless, additional analysis and data is needed to validate this observation for heavily sooting buoyancy dominated plumes.

Natural Convection Phenomena Affected by Radiation in Concentric and Eccentric Horizontal Cylindrical Annuli

Abstract: A numerical investigation has been performed to study the radiation-affected steady-laminar natural convection induced by a hot inner cylinder under a large temperature difference in the cylindrical annuli filled with a gray gas. To examine the effects of thermal radiation on thermofluid dynamics behavior in the eccentric geometry, the generalized body-fitted coordinate system is introduced while the finite volume method is used for solving the radiative transport equation. After validating numerical results for the case without radiation, the detailed radiation effect is discussed. Based on the results of this study, when there exists a large temperature difference between two cylinders, the existence of a radiatively participating medium is found to incur a distinct difference in fluid dynamics as well as thermal behavior.

A thermal study of optical fibres transmitting concentrated solar energy

Abstract: In this paper we develop a theoretical thermal study of optical fibres transmitting concentrated solar energy. An energy equation for simultaneous conduction and radiation of heat through optical fibres is obtained. To transmit concentrated solar energy an optical fibre tip is placed in the focus of a small paraboloidal mirror. The role of aluminium and silver as the reflective surface on the mirror that allows one to concentrate the solar energy is studied. The power supply is estimated to be 26 W at the end of a 10 m long fibre with 88% transmission efficiency. The thermal study considers a wavelength-dependent absorption coefficient of the optical fibre core in order to obtain the radiative heat flux in the fibre. The time evolution of the temperature distribution is obtained by a finite-difference method. With this result we predict that the fibre can be used 6 h.

Optimization of thin-film thermoelectric radiation sensor with comb thermoelectric transducer

Abstract: An analytical optimization of the structure of the thin-film thermoelectric radiation sensor with the comb thermoelectric transducer is presented. Expressions for the specific total volt–watt sensitivity and the thermal time constant of the thin-film thermoelectric radiation sensor have been obtained. A problem of the optimization of this sensor is solved by the method of Lagrange multipliers. The specific total volt–watt sensitivity has been chosen as a goal function and expression of the thermal time constant has been used as a constraint. The length of the absorbing layer of the radiation sensor and the distance between the boundary of this layer and the line of the disposition of cold thermojunctions of the thermoelectric transducer have been chosen as independent variables. The obtained system of equations for components of the gradient of Lagrange function in extremum point is solved by numerical method. Dependencies of optimum values of the specific total volt–watt sensitivity and corresponding values of independent variables on the thermal time constant, the thickness of the substrate layer, the thermal conductivity of the material of the substrate layer and the convection coefficient of the structure have been determined. The present analytical model of the optimization of the thermoelectric radiation sensor can be used in order to obtain the maximum value of the specific total volt–watt sensitivity under the given value of the thermal time constant.

Investigation of Droplet Combustion with Nongray Gas Radiation Effects

Abstract: Single droplet combustion processes including heating, evaporation, burning, soot formation and flame radiation were theoretically investigated by adopting nongray gas radiation model for the radiative transfer equation (RTE). n-Heptane was chosen as a fuel in the numerical calculation and the results were compared with the experimental data available in the literature. The discrete ordinate method (DOM) was employed to solve the radiative transfer equation and the weighted sum of gray gases model (WSGGM) was applied to account for nongray gas radiation effect by CO2 and H2O while soot was assumed gray. Therefore, very detailed effects by nongray gases could be figured out in the results. The results have shown that the total burning time increases due to a decrease in total heat flux with the nongrey gas model. It is also found that for the nongray case the radiative loss to external environment is higher, thereby reducing the maximum gas temperature and the flame thickness. Consequently, a better agreem...

Performance Computation of a Low-Power Hydrogen Arcjet

Abstract: A numerical analysis of a low-power hydrogen arcjet has been conducted by taking account of the chemical and thermal nonequilibria by separating the electron temperature from the heavy species temperature. A sheath model is introduced to the electrode boundaries to evaluate the electrode potential drops in a coupled manner with the flow calculation. Comparison of calculated performance for the IRS ARTUS-4 thruster with experimental results shows good agreement regarding the discharge voltage and specific impulses, although the heat loss is somewhat underestimated. To account for these discrepancies, the radiative loss is computed in detail, taking account of the bound-bound, free-bound, and free-free electronic transitions in the hydrogen plasma. The estimated radiation is found to become significant as the electron temperature exceeds approximately 12,000 K. Contribution of the radiative heat transfer to the total heat loss is discussed briefly. The results suggest that the radiation analysis may be necessary for further accurate prediction of thruster performance, even under low-power operation.

Transient Thermal Analysis of Parallel Translucent Layers by Using Green's Functions

Abstract: An analysis is developed for computing transient thermal behavior in a composite of two parallel translucent layers with a space between them. The radiative two-flux equation is coupled with the transient energy equation, and both equations are solved by using Green's functions. Illustrative results are provided for transient heating of two parallel translucent layers that exchange radiation. The external boundaries of the two-layer combination are each exposed to a radiative environment, and all boundaries can be convectively heated or cooled. The layer refractive indices are larger than one, and internal reflections are included with boundaries assumed diffuse. The analysis includes internal emission, absorption, isotropic scattering, and heat conduction. Transient results from the present method are verified for a single gray layer by comparison with a finite difference solution that incorporates a numerical solution of the exact radiative transfer equations for the radiative heat source. Illustrative transient temperature distributions show the effects of an insulating gap between layers, when one side of the twolayer composite is subjected to heating by radiation and convection, while the other side is being cooled.

Ftir transmission–emission spectroscopy of gases at high temperatures: experimental set-up and analytical procedures

Abstract: An experimental laboratory set-up for high-temperature gas analysis is presented. The set-up, which comprises an FTIR instrument with an internal detector, an external blackbody source and a heated gas cell, can be used to measure the transmissive and emissive properties of gases at elevated temperatures. The stainless-steel cell designed for this work was heated to temperatures ranging from 294 to 1273 K. Measurements of the spectral transmittance and radiance (4 cm-1) of heated carbon dioxide (CO2) in various concentrations (0.5, 10, 100 vol%) were performed to test the experimental set-up. A solution to the problem is given of how to express analytically both the transmitted and especially the emitted radiation of a heated gas sample enclosed in a gas cell. In order to measure the gas radiation, it is necessary to measure the wave-number-dependent thermal radiation from the heated sapphire gas cell windows. It is shown that the gas temperature can be determined at low temperatures (473 K), if the measured thermal radiation of the gas is corrected for the thermal radiation emitted by the FTIR instrument.

Non-thermal Radiation of Cosmological gamma-ray Bursters

Abstract: We use 1+1/2 dimensional particle-in-cell plasma simulations to study the interaction of a relativistic, strongly magnetized wind with an ambient medium. Such an interaction is a plausible mechanism which leads to generation of cosmological gamma-ray bursts. We confirm the idea of Meszaros and Rees (1992) that an essential part (about 20%) of the energy that is lost by the wind in the process of its deceleration may be transferred to high-energy electrons and then to high-frequency (X-ray and gamma-ray) emission. We show that in the wind frame the spectrum of electrons which are accelerated at the wind front and move ahead of the front is nearly a two-dimensional relativistic Maxwellian with a relativistic temperature $T=6*10^9\Gamma_T$ K, where $\Gamma_T=200\Gamma_0$ with the accuracy of ~20%, and $\Gamma_0$ is the Lorentz factor of the wind, $\Gamma_0>100$ for winds outflowing from cosmological gamma-ray bursters. Our simulations point to an existence of a high-energy tail of accelerated electrons with a Lorentz factor of more than $700\Gamma_0$. Large-amplitude electromagnetic waves are generated by the oscillating currents at the wind front. The mean field of these waves ahead of the wind front is an order of magnitude less than the magnetic field of the wind. High-energy electrons which are accelerated at the wind front and injected into the region ahead of the front generate synchro-Compton radiation in the fields of large-amplitude electromagnetic waves. This radiation closely resembles synchrotron radiation and can reproduce the non-thermal radiation of gamma-ray bursts observed in the Ginga and BATSE ranges (from a few keV to a few MeV).

A complete conjugate conduction convection and radiation problem for a heated block in a vertical differentially heated square enclosure

Abstract: The complete conjugate heat conduction, convection and radiation problem for a heated block in a differentially heated square enclosure is solved by an operator-splitting pseudo-time-stepping finite element method. The main feature of the solution procedure is that the multi-phases are treated as a single computational domain with unknown interfacial boundary conditions. The temperature distribution in the heated block and in the enclosure fluid, together with the convective flow pattern are obtained simultaneously by the solution technique. The heated block has a resistant effect to the heat transfer between the differentially heated walls. When more heat is generated in the block, its emissivity has significant influence on the global flow. With increasing emissivity, the global convective flow decreases and the fraction of thermal radiation can be more than 30% of the total heat transfer.

Radiative Heat Transfer in Arbitrary Configurations With Nongray Absorbing, Emitting, and Anisotropic Scattering Media

Abstract: Radiative heat transfer in absorbing, emitting, and scattering media is a problem of practical significance, e.g., in the design of industrial furnaces and many combustion devices, and in the prediction of the effect of ducts, CO{sub 2} and other participating gases on the global environment. Recently, much attention has been given to solve the problem using numerical approaches such as the Monte Carlo method by Farmer and Howell (1994), the discrete ordinate method by Fiveland and Jessee (1995), and the YIX method by Hsu et al. (1992). A solution method that is reasonably accurate, efficient in both computing time and storage, flexible with arbitrary three-dimensional geometry, and can be applied to real gas and particles is needed for the prediction of the radiation transport. The radiation element method by the ray emission model, REM (Maruyama and Aihara 1997), is an extension of the zone method and is a generalized numerical method for analyzing radiation transfer in participating media and specular and/or diffuse surfaces, with which arbitrary configurations can be coped with easily using finite element grids. In this paper, the REM is developed to incorporate the spectral dependence of radiation properties using the narrow band model and assuming anisotropic scattering.more » The zeroth-order delta function approximation is used to scale the anisotropic scattering. The radiative heat transfer within a complex three-dimensional boiler furnace is analyzed as an example of application of engineering interest. Both the Elsasser narrow band model and the exponential wide-band model are adopted to consider the spectral characteristics of CO{sub 2} and H{sub 2}O gases. The results of heat flux on the walls and heat flux divergence in the boiler are compared between the analyses of the narrow-band model and the wide-band model. The effects of the anisotropic scattering and particle density are also discussed.« less

Substrate for heat radiation, and its manufacture

Abstract: PROBLEM TO BE SOLVED: To provide a substrate for heat radiation which is high in coefficient of heat conduction, low in coefficient of thermal expansion and small in thermal strain. SOLUTION: A porous material formed of a thermal expansion suppression material such as SiC powder is arranged in a casting cavity, a molten base material of =400 deg.C and below or equal to the solidification temperature. The thermal stress in an internal layer and a surface layer different in coefficient of thermal expansion from each other, is sufficiently removed, and the alloy composition to be added to improve the fluidity is sufficiently precipitated.

Photon Statistics of a Random Laser

Abstract: A general relationship is presented between the statistics of thermal radiation from a random medium and its scattering matrix S. Familiar results for black-body radiation are recovered in the limit S → 0. The mean photocount n is proportional to the trace of 1—S · S †, in accordance with Kirchhoff’s law relating emissivity and absorptivity. Higher moments of the photocount distribution are related to traces of powers of 1-S · S †, a generalization of Kirchhoff’s law. The theory can be applied to a random amplifying medium (or “random laser”) below the laser threshold, by evaluating the Bose-Einstein function at a negative temperature. Anomalously large fluctuations are predicted in the photocount upon approaching the laser threshold, as a consequence of overlapping cavity modes with a broad distribution of spectral widths.

Thermally developing poiseuille flow affected by radiation

Abstract: A combined convective and radiative heat transfer problem in thermally developing Poiseuille flow in a cylindrical tube is analyzed. A complex form of the nonlinear integrodifferential radiative transfer equation is solved by the discrete ordinates method in an axisymmetric geometry. To check its accuracy, the solution obtained by the discrete ordinates method is compared with that solved by the integral method. A parametric study is also performed for the conduction-to-radiation parameter, optical thickness, wall emissivity, scattering albedo, and linear anisotropic scattering coefficient. The results show a significant effect of the radiation on the thermal characteristics.