Showing papers on "Thermal radiation published in 2000"

The Role of the Plumage in Heat Transfer Processes of Birds1

Abstract: The plumage of birds provides a critical thermal buffer between the animal and its environment. Rates of energy expenditure are strongly influenced by the thermal properties of the environment or the microclimates the animal occupies. Current data suggest that the addition of solar radiation is equivalent to three to four-fold changes in wind speed and that solar heat gain can be extremely sensitive to changes in wind speed. Dry heat transfer through the plumage occurs by three avenues 1) conduction and free convection through air 2) conduction along the solid elements of the plumage and 3) radiation. Overall, about 95% of the total heat flow is evenly divided between the first two avenues. Radiative heat transfer accounts for only about 5% of total heat flow. Plumage color, as well as the microstructure and micro-optical properties of plumage elements, when combined with environmental properties (e.g., wind speed), determine the radiative heat loads that birds acquire from solar radiation. Altho...

Prediction of the radiation term in the thermal conductivity of crosslinked closed cell polyolefin foams

Abstract: The thermal conductivity and the cellular structure as well as the matrix polymer morphology of a collection of chemically crosslinked low-density closed cell polyolefin foams, manufactured by a high-pressure nitrogen gas solution process, have been studied. With the aid of a useful theoretical model, the relative contribution of each heat-transfer mechanism (conduction through the gas and solid phases and thermal radiation) has been evaluated. The thermal radiation can be calculated by using a theoretical model, which takes into account the dependence of this heat-transfer mechanism with cell size, foam thickness, chemical composition, and matrix polymer morphology. A simple equation, which can be used to predict the thermal conductivity of a given material, is presented.

Reference Data for the Thermal Conductivity of Saturated Liquid Toluene Over a Wide Range of Temperatures

Abstract: Efficient design of industrial processes and equipment requires accurate thermal conductivity data for a variety of fluids, such as alternative refrigerants, fuels, petrochemicals, aqueous systems, molten salts, and molten metals. The accuracy of experimental thermal conductivity data is a function of the operating conditions of the instrument. Reference data are required over a wide range of conditions to verify the claimed uncertainties of absolute instruments and to calibrate relative instruments, since either type may be used to measure the thermal conductivity of fluids. Recently, accurate experimental data for the thermal conductivity of liquid toluene near the saturation line have been obtained, which allow the upper temperature limit of the previous reference-data correlation to be extended from 360 to 553 K. The thermal conductivity was measured using two transient hot-wire instruments from 300 to 550 K, the first with a bare 12.7 μm platinum wire and the second using an anodized 25 μm tantalum wire. Uncertainties due to the contribution of thermal radiation and the purity of the samples are discussed. The proposed value of the thermal conductivity of liquid toluene at 298.15 K and 0.1 MPa is 0.13 088±0.000 85. The quality of the data is such that new improved recommendations and recommended values can be proposed with uncertainties at 95% confidence of 1% for 189

The effects of radiation on natural convection in a rectangular enclosure divided by two partitions

Abstract: The phenomena of radiation-affected steady-laminar natural convection in a rectangular enclosure with two incomplete partitions are numerically examined under a large temperature difference. Pure convection, convection with surface radiation, and convection with surface rgas radiation are considered and compared. To examine the effects of two incomplete partitions on thermofluid dynamics behavior, they are assumed to be very thin ( ) and adiabatic. The finite-volume method FVM is used for solving the radiative transport equation, assuming that partitions are radiatively opaque. After validating the numerical procedures, the detailed radiation effects were sought. Based on the results of this study, it was found that the radiation played a significant role in developing the fluid dynamic and thermal distributions compared with cases without radiation. Once radiation was involved, the surface radiation was dominant over the gas radiation. The baffle configuration was also found to affect the results of radiation.

A fast monte carlo scheme for thermal radiation in semiconductor processing applications

Abstract: Thermal radiation is the most effective way for rapid thermal processing (RTP) and rapid thermal chemical vapor deposition (RTCVD) of wafers. It is well known in the semiconductor equipment design community that the Monte Carlo method for radiation is the only method that can accurately model radiative transport in RTP and RTCVD reactors. However, it has often been argued that it is expensive and difficult to use as a commercial design tool. In this article, a fast Monte Carlo scheme is presented. The basic algorithm is the classical surface-to-surface ray-tracing algorithm. In addition, a modified form of the binary spatial partitioning (BSP) algorithm is implemented to speed up ray tracing by at least a factor of 3. The results demonstrate a high level of accuracy with fairly low computational cost.

Classical dielectric models of fullerenes and estimation of heat radiation

Abstract: With the aim of describing the cooling of highly excited fullerene molecules by heat radiation, we consider simple classical, dielectric models for calculation of the electromagnetic response and show that the overall distribution of oscillator strength for electronic transitions can be represented fairly well by such a model. The connection to a layer model for graphite is discussed. For thermal emission of radiation from fullerenes, which depends on the oscillator strength at low frequencies only, the classical dielectric model leads to a prediction which should be applicable at high temperatures where the fine structure of the oscillator strength distribution is smeared out. We also estimate the emission from infrared-active vibrations, which dominate at low temperatures but play a minor role at the high temperatures where formation and decay of fullerene molecules take place.

Radiation-heated fluidized-bed reactor

Abstract: A radiation-heated fluidized-bed reactor and a process for producing high-purity polycrystalline silicon by using this reactor are provided. In this reactor, a heater device ( 14 ) is a radiation source for thermal radiation which is arranged outside the inner reactor tube and as a cylinder around the heater zone, without being in direct contact with the inner reactor tube. The inner reactor tube is designed in such a manner that it uses thermal radiation to heat the silicon particles in the heating zone to a temperature which is such that the reaction temperature is established in the reaction zone.

Apparatus and method for producing a chip-substrate connection

Abstract: An apparatus for producing a chip-substrate connection, in particular by soldering a semiconductor chip on a substrate The apparatus has a support, on which the substrate is temporarily supported, and a heating device which is provided for forming the chip-substrate connection The heating device has a radiation source in the form of a laser in the infrared wavelength range The support is formed by a heat body, which is assigned to the chip-substrate connection and is heated with thermal radiation by the radiation source A surface of the heat body is coated with a material, in particular a material containing chromium, exhibiting high absorption with respect to the light radiation emitted by the radiation source

Thermal radiation properties of turbulent lean premixed methane air flames

Abstract: Thermal radiation properties of turbulent premixed flames have received little attention in the past perhaps because of the lower radiative heat loss compared with that for non-premixed flames. However, the high-temperature sensitivity of NO kinetics and the importance of radiation in near-limit laminar premixed flames provide fundamental reasons for studies of radiation properties of turbulent premixed flames. Reduced cooling airflows in lean premixed combustors, miniaturization of combustors, and the possible use of radiation sensors in combustion control schemes are some of the practical reasons for studying radiation heat transfer in these flames. Motivated by this, we report the first (to our knowledge) study of spectral radiation properties of turbulent premixed flames. Measurements of mean, root mean square (rms) and probability density functions (PDFs) of spectral radiation intensities leaving diametric paths at five heights in two turbulent lean premixed methane/air jet flames stabilized using small H2/air pilot flames in a coflow of air were completed. Measurements of spectral radiation intensities leaving three laminar flames were also completed. These data were used to evaluate narrowband radiation calculations independent of the treatment of turbulent fluctuations. Stochastic spatial series analysis was used to estimate instantaneous distributions of temperature. The analysis requires the specification of mean and rms temperature distributions, integral length scale distributions, and an assumption of exponential spatial correlation function. We specified the mean and rms temperature distributions measured by calibrated narrowband thin filament pyrometry. A simple flame and mixing model was used to relate the concentrations of CO2 and H2O to the temperature. We used scalar spatial series in conjunction with a radiation model to calculate the mean, rms, and PDFs of spectral radiation intensities. Overall, the model predictions are in reasonable agreement with the data. The only improvement needed is in the area of capturing correlated occurrences of high temperatures along the radiation path.

Thermal effusivity profile characterization from pulse photothermal data

Abstract: An inversion method is proposed for depth profiling of the thermal effusivity from the surface temperature evolution after an excitation. Focus is on pulse heating. The effusivity profile is obtained through a Laplace inversion. The Stehfest method is implemented and we propose to use the number of elements in the Stehfest series N as a regularizing parameter. The optimum N value is defined by plotting a characteristic C curve with the norm of the solution derivative and the norm of the residues of the so-called apparent effusivity function. Examples of inversion results are given for linear and Gaussian effusivity profiles. For this purpose, we extended the formalism of thermal quadrupoles to the case of linearly varying effusivity. A statistical analysis is performed to assess the influence of noise on the inversion results. Recommendations on the thermogram minimum duration are derived therefrom. Experimental results obtained with a case-hardened steel sample show the potential of the present nondestructive approach.

Radiative transport in a two-dimensional axisymmetric thermal plasma using the S–N discrete ordinates method on a line-by-line basis

Abstract: A theoretically rigorous method for handling the transport of radiant energy in a two-dimensional, axisymmetric, thermal plasma is presented. A S–N discrete ordinates method is used to solve the radiative equation of transfer on a line-by-line basis. A line-by-line solution of the radiative equation of transfer is an exact method of handling the spectral characteristics of thermal radiation. Plasmas are highly non-gray emitters and absorbers of radiant energy, making proper handling of the spectral characteristics extremely important. To demonstrate this method a few results are presented for a 200 A, free-burning, argon arc.

A theoretical investigation of the influence of optical constants and particle size on the radiative properties and heat transfer involving ash clouds and deposits

Abstract: This paper presents an analysis of the influence of optical constants and particle size on the radiative properties and heat transfer involving ash clouds and deposits. Previous reported studies are mostly based on grey values of complex refractive index, which fails to reflect the true nature of the ash cloud and ash deposits. The analysis indicates that for radiative heat transfer calculations, information on size distribution of the ash cloud and wall emittance are more important than the radiative properties of ash cloud. For prediction of emittance of an opaque particulate ash deposit, careful estimation of absorption index is more important than the real index, which may be taken to be constant at 1.5, unless the deposit material is weakly absorbing and composed of fine particles. In such cases knowledge of spectral values of both real and absorption index appears to be necessary.

Variable emissivity through MEMS technology

Abstract: This paper discusses a new technology for variable emissivity (vari-e) radiator surfaces, which has significant advantages over traditional radiators and promises an alternative design technique for future spacecraft thermal control systems. All spacecraft rely on radiative surfaces to dissipate waste heat. These radiators have special coatings, typically with a low solar absorptivity and a high infrared-red emissivity, that are intended to optimize performance under the expected heat load and thermal sink environment. The dynamics of the heat loads and thermal environment make it a challenge to properly size the radiator and often require some means of regulating the heat rejection rate of the radiators in order to achieve proper thermal balance. Specialized thermal control coatings, which can passively or actively adjust their emissivity offer an attractive solution to these design challenges. Such systems would allow intelligent control of the rate of heat loss from a radiator in response to heat load and thermal environmental variations. Intelligent thermal control through variable emissivity systems is well suited for nano and pico spacecraft applications where large thermal fluctuations are expected due to the small thermal mass and limited electric resources. Presently there are three different types of vari-e technologies under development: Micro Electro-Mechanical Systems (MEMS) louvers, Electrochromic devices, and Electrophoretic devices. This paper will describe several prototypes of micromachined (MEMS) louvers and experimental results for the emissivity variations measured on theses prototypes. It will further discuss possible actuation mechanisms and space reliability aspects for different designs. Finally, for comparison, parametric evaluations of the thermal performance of the new vari-e technology and standard thermal control systems are also presented in this paper.

Heat transfer sheet, heating structure, heat radiation structure, electric examination method and apparatus using the same

Abstract: PROBLEM TO BE SOLVED: To obtain a heat transfer sheet having excellent nonadhesion suitable for constructing a heating structure and a heat radiation structure, capable of preventing a body from making an adhesion state between the heat transfer sheet and the body even in the case of contact of the body pressing against the surface of the heat transfer sheet under a high-temperature condition and slightly contaminating the connection surface of the body and to provide the heating structure, the heat radiation structure, an electric examination method and an apparatus using the same. SOLUTION: This heat transfer sheet is characterized by comprising a polymer part and a heat transfer member and having the surface subjected to nonadhesion treatment. This heating structure this heat radiation structure, this electric examination method and this apparatus are obtained by using the heat transfer sheet.

A finite-volume scheme for radiative heat transfer in semitransparent media

Abstract: Radiation in semi-transparent media occurs in a variety of industrial applications. In the HVAC area, the selective transmission of thermal radiation through windows governs the heat load of rooms. In fiber drawing applications, the rate of quenching of the semi-transparent glass fiber is critically dependent on the radiant exchange with the hot furnace. In ceramics processing, the high index of refraction leads to strong internal reflection effects, and greatly influences the thermal field. It would be useful to develop numerical methods for computing this type of radiation heat transfer in the complex geometries encountered in most industrial applications. Here, a procedure for computing radiation in semi-transparent media is presented. A conservative cell-based finite volume method is developed for unstructured meshes composed of arbitrary polyhedra. The angular domain is discretized into a finite number of control angles over which radiant energy is conserved. At Fresnel interfaces, numerical procedures are developed to conservatively transfer radiant energy from one angular direction to another as a result of reflection and refraction, while accounting for control angle overhang. Similar procedures are also employed at specular surfaces and symmetry boundaries. The method is tested against analytical solutions and shown to perform satisfactorily.

Ultra sensitive silicon sensor

Abstract: Electro-thermal feedback is utilized for removing thermal conductance between a bolometer's absorber element of a pixel in a thermal radiation sensor assembly and the environments through its mechanical support structure and electrical interconnects, thereby limiting the thermal conductance primarily through photon radiation. Zeroing the thermal conductance associated with the mechanical support structure and electrical interconnects is achieved by electro-thermal feedback that adjust the temperature of an intermediate stage of the mechanical support structure and electrical interconnects to equal the bolometer's absorber element temperature.