Showing papers on "Thermal radiation published in 1977"

Significance of Vegetation in Interpreting Thermal Radiation from a Terrestrial Surface

Abstract: The regions between crop rows are modeled as infinitely long diffuse cavities. Geometrical view factors are calculated, accounting for reflected radiation emanating internal to the cavity and from the background sky. A 'cavity' emissivity dependent on local geometry is defined to allow for correcting apparent temperatures to true temperatures. The total emissivity appropriate for correcting aircraft thermal data is then calculated by averaging all emissivity components to account for soil, crop, and background. It is shown that even for the lowest crop and vegetation emissivities, if the crop height-to-spacing ratio is greater than unity, the composite emissivity is greatly increased, giving rise to a decreased error in remotely sensed temperature data.

The Use of the Milne-Eddington Absorption Coefficient for Radiative Heat Transfer in Combustion Systems

Abstract: The applicability of the Milne-Eddington absorption coefficient approximation is discussed in relation to the calculation of radiative transport involving the two distinct types of species produced in combustion systems: gases and soot particles. The approximation is found to apply well to hydrocarbon soot particles and as a result analytical closed-form solutions are derived for the radiative heat transfer inside one-dimensional slab shaped soot clouds. (The applicability of the gray approximation to soot is also discussed.) For the calculation of total band radiation from gases, however, the Milne-Eddington approximation is found to be questionable. The meaning of its assumption is discussed in light of an established Curtis-Godson wide band scaling approximation. Its usefulness for real gases is then assessed through the calculation and comparison of slab radiation by both techniques.

Downward Flame Spread Under the Influence of Externally Applied Thermal Radiation

Abstract: Downward flame spread velocity over vertical sheets of polymethylmethacrylate (PMMA) and Filter Paper were measured under the influence of externally applied radiant fluxes ranging from 0 to 2.0 W/cm2. The flame spread rate was found to be dependent primarily on the surface temperature of the fuel prior to flame arrival. A power law correlation exists between the flame spread velocity and the difference between the vaporization temperature of the fuel and its surface temperature in the region not affected by the heat transferred from the flame. Present theoretical models for downward flame spread were extended to account for the additional effect of external radiation. It is shown that the predictions of the theoretical models agree qualitatively with the experimental observations.

Upward Laminar Flame Spread Under the Influence of Externally Applied Thermal Radiation

Abstract: Rates of flame spread for the upward laminar propagation of flames over thick vertical sheets of Polymethylmethacrylate (PMMA) were measured under the influence of externally applied thermal radiant fluxes ranging from 0 to 2 W/cms. A previously developed theoretical model for the upward laminar spread of flames over vertical fuel surfaces was extended to account for the additional effect of the external radiation. It is shown that the theoretical predictions agree qualitatively with the experimental measurements and that the temperature of the fuel prior to flame tip arrival plays a critical role in the magnitude of the spread rate. It is found experimentally and predicted theoretically that a correlation in the form of a power law exists between the flame spread rate and the difference between the vaporization temperature of the fuel and its surface temperature prior to flame tip arrival.

The formation of solar prominences by thermal instability in a current sheet

Abstract: The energy balance equation for the upper chromosphere or lower corona contains a radiative loss term which is destabilizing, because a slight decrease in temperature from the equilibrium value causes more radiation and hence a cooling of the plasma; also a slight increase in temperature has the effect of heating the plasma. In spite of this tendency towards thermal instability, most of the solar atmosphere is remarkably stable, since thermal conduction is very efficient at equalizing any temperature irregularity which may arise. However, the effectiveness of thermal conduction in transporting heat is decreased considerably in a current sheet or a magnetic flux tube, since heat can be conducted quickly only along the magnetic field lines. This paper presents a simple model for the thermal equilibrium and stability of a current sheet. It is found that, when its length exceeds a certain maximum value, no equilibrium is possible and the plasma in the sheet cools. The results may be relevant for the formation of a quiescent prominence.

A Theoretical and Experimental Study of Radiation–Convection Interaction in a Diffusion Flame

Abstract: An experimental and theoretical investigation of the interaction of gaseous thermal radiation with natural convection was made for a laminar methane-air diffusion flame in the lower stagnation region of a horizontal porous cylinder. The exponential wide-band gas radiation model was employed in this nonhomogeneous (nonuniform in temperature and composition) problem through the use of scaling techniques. Using a numerical scheme, the compressible energy, flow, and species-diffusion equations were solved simultaneously with and without the radiative component. In the experiment, methane was blown uniformly from the surface of the porous cylinder, setting up (upon ignition) a diffusion flame within the free-convection boundary layer. Using a Mach-Zehnder interferometer and a gas chromatograph, temperature and composition measurements were obtained along the stangation line. Excellent agreement was found between the results based the the nongray wide-band model and the experimental data. Furthermore, it was found that the wide-band model yielded results that were superior to those results that excluded radiation-interaction effects. Thus, this study demonstrates that the exponential wide-band model can be accurately applied to nonhomogeneous combustion situations in order to account for the radiation-convection interactions. 10 figures, 4 tables, 31 references.

Fur-like photothermal converter surface

Abstract: In order to reduce energy losses by convection and/or thermal radiation from the radiation-absorbing surface of a photothermal energy converter for the utilization of solar energy, the said surface is provided with a multiplicity of projecting fibres sufficiently close to one another to suppress convection, each fibre consisting of a material which is permeable to the incident luminous radiation to be absorbed and at least partly opaque to infrared thermal radiation which may be reemitted from the said surface whereby energy losses by radiation are reduced. The fibres can be, for example, glass or plastic fibres and can be integral with or implanted in the said surface. Preferably, the fibres have diameters in the range 25 to 500 micrometers, a height of the order of 5 cm, and an average distance between fibres in the range 100 to 5000 micrometers.

Thermal radiation model for solid rocket booster plumes

Abstract: The Monte Carlo method is used to model the thermal radiation field of the plumes for the dual solid rocket boosters astride the Space Shuttle launch configuration. The model accounts for axial and radial variations in radiative properties of the plumes. The plumes are considered to be composed of a dispersion of aluminum oxide (Al2O3) particles immersed in the gaseous products of combustion. The principal emitting gases are taken to be CO, CO2, H2O, and HCl. The thermal model is based on local thermodynamic equilibrium. Scattering of radiant energy by Al2O3 particles may be treated as isotropic or anisotropic. Sample radiant heating rates to the base region of the Space Shuttle are shown. Space Shuttle geometries are simulated as combinations of quadric surfaces.

The thermally saturated SUPARAMP

Abstract: The superconducting unbiased parametric amplifier can be saturated by low levels of broadband thermal radiation. Saturation increases the fluctuation noise temperature and complicates the determination of the operating parameters of this device. In this paper the theory of the thermally saturated SUPARAMP is presented. It is found that a particular amplifier can be described by a characteristic temperature, its maximum possible output brightness temperature. The implications of this theory for the interpretation of past experiments and for the design of future experiments are discussed.

The thermal balance of the atmosphere of Venus

Abstract: Current knowledge of the temperature structure of the atmosphere of Venus is briefly summarized. The principal features to be explained are the high surface temperature, the small horizontal temperature contrasts near the cloud tops in the presence of strong apparent motions, and the low value of the exospheric temperature. In order to understand the role of radiative and dynamical processes in maintaining the thermal balance of the atmosphere, a great deal of additional data on the global temperature structure, solar and thermal radiation fields, structure and optical properties of the clouds, and circulation of the atmosphere are needed. The ability of the Pioneer Venus Orbiter and Multiprobe Missions to provide these data is indicated.

Thermal microwave emission from a random inhomogeneous layer over a homogeneous medium using the method of invariant imbedding

Abstract: The paper studies thermal microwave emission from an inhomogeneous slab of a random medium, with possible nonuniform absorption, scattering, and temperature profiles, bounded by different dielectrics on both sides. The invariant imbedding method is used to cast the boundary value problem of the radiative transfer equations into an initial value problem at zero slab thickness. As a numerical example, the angular and polarization variations of brightness temperatures for ice over water are considered.

Techniques for reducing thermal conduction and natural convection heat losses in annular receiver geometries

Abstract: An effective device for the collection of solar energy which has received widespread attention is the so called parabolic-cylindrical solar collector. In this design a circular receiver tube, with a suitable selective coating, is enclosed by a concentric glass envelope and situated along the focal line of a parabolic trough reflector. The heat transfer processes which occur in the annular space between the receiver tube and the glass envelope are important in determining the overall heat loss from the receiver tube. In typical high temperature receiver tube designs the rate of energy loss by combined thermal conduction and natural convection is of the same order of magnitude as that due to thermal radiation, and can amount to approximately 6 percent of the total rate at which energy is absorbed by the solar collector. The elimination of conduction and natural convection losses can significantly improve the performance of a large collector field. Several techniques useful for the reduction of energy loss by thermal conduction and natural convection are considered. The receiver configuration chosen for study is typical of those used in the Solar Total Energy System at Sandia Laboratories. The receiver tube has a ''black chrome'' selective coating and is 2.54 more » cm in outside diameter. The inside diameter of the glass envelope is approximately 4.4 cm. Typical operating temperatures of the receiver tube and glass envelope are approximately 300/sup 0/C and 100/sup 0/C, respectively. « less

Ground truth measurements for thermal infrared remote sensing

Abstract: Since 1971, field measurements have been made in order to establish interpretation keys for remotely sensed thermal infrared radiation in the 9.5 to 11.5 micrometer spectral range. The infrared radiation emitted by different land surfaces has been measured with a Barnes PRT5 radiometer and compared with different environmental parameters (solar radiation, net radiation, air and soil temperature at various depths, air and soil moisture, etc.). The parameters that give the closest correlation with the remotely sensed thermal radiation vary with the type of vegetable cover and with the seasons. The best correlations are obtained with soil surface temperature over bare soil and with air temperature at half the canopy height over vegetated areas. Seasonal variations of regression coefficients between soil surface temperatures and remotely sensed thermal radiation are higher on vegetated areas than on bare soil. /Author/

Solar heating system

Abstract: A heating system is provided to convert radiant solar energy into heat for use in buildings. The apparatus includes a solar energy collection and heat radiation means, a heat storage means utilizing a heat retention medium, ducting means for providing pneumatic communication within the system, and fluid communication means for providing liquid communication within the system. A method of heating buildings is also disclosed.

Thermodynamic processes induced by coherent radiation

Abstract: It is shown by quantum statistics that under certain stated conditions the entropy of coherent radiation is zero and it is still negligible for multimode laser operation. This makes possible gas kinetic processes which, to a small extent, have already been observed or even utilized, but which can be greatly enhanced by an optimized choice of molecular structures and radiation conditions. Radiative cooling of gases is discussed in detail. The conditions for maximum heat withdrawal are derived, and it is proposed that the processes of cooling and relaxation heating can be sufficiently separated in time to achieve certain effects and thermodynamic cycles. One of these is the complete conversion, possible in principle, of coherent radiation into work. This concept is based on a heat pump process followed by heat‐to‐work conversion, the heat rejected being just equal to that withdrawn by radiation. The conditions for complete conversion turn out to be the same as for maximum heat withdrawal. The feasibility of these processes depends on the degree to which practical conditions can be met, and on the validity of certain assumptions which have to await experimental verification.

Solar energy collector and method

Abstract: A solar energy collector and method including an insulated, box-like enclosure having a transparent wall on one side thereof for the transmittance of solar energy into the enclosure. An energy absorption plate is placed in spaced relationship in the enclosure where it will be exposed to incident solar radiation passing through the transparent wall. An insulated divider behind the solar energy absorption plate separates the remainder of the enclosure into a heat chamber adjacent the solar energy absorption plate and a return air chamber. Air duct means and a plurality of water conduits are mounted in heat exchange relationship on the solar energy absorption plate to provide means for collecting the absorbed heat. The surfaces of the ducts, conduits, and solar energy absorption plate are selectively coated with a heat-absorbing black for improved solar energy absorption and conversion to heat. The appropriate surfaces of the transparent wall are coated with an infrared reflective surface to reduce radiation heat losses from the solar energy collector.

Heat insulating closed system with sunlight transmitting walls - with gas-filled chamber with gas impermeable partitions

Abstract: The gas-impermeable partitions transmit solar radiation and >=1 of them transmits heat radiation. >=1 walls has a coating which transmits light but reflects heat radiation. Pref. the partitions are made of plastic e.g. polyethylene or polypropylene with a thickness of is not 100 mum. >=1 additional partitions may be impermeable to heat radiation, pref. consisting of glass with a thickness of >1.5 mm. The system prevents heat loss effectively, and has a relatively low heat transition coefft.

Solar collector with circuit contg. heat exchanger - using dark fluid with high absorption capacity for heat of given wavelength

Abstract: Method for collecting solar energy is carried out with a chamber with a solar radiation-permeable transparent cover facing towards the sun, contg. a heat transfer medium which is connected to a circulating system with a heat exchanger. The heat transfer medium is a dark fluid with a high absorption capacity of heat radiation in the wavelength range 0.8 . 10-3 to 400 . 10-3mm, pref. with a surface having an emission coefft. of 0.8-1.0. It may consist of dark -coloured water, or an oil-water emulsion contg. oil of which the surface has a low reflection capacity. The solar radiation is absorbed according to the intensity of colour of the fluid, only a small fraction of it being lost at the chamber surface together with radiation which is reflected directly by the chamber surface.

Radiative acceleration of gas above a luminous disk

Abstract: Radiative acceleration as a mechanism for ejection of matter from quasistellar objects is considered, and calculations are presented showing that a strongly beamed outflow will result if the source of the driving radiation is a disk. The net forces exerted by an infinitesimally thin, optically thick disk emitting thermal radiation with given intensity on clouds or particles is calculated, and conditions for beaming are obtained. Apparently it is possible to establish strong beaming within a distance of the order of the disk radius.

Thermal-radiation excited vibrational-exchange pumped laser generator

Abstract: Thermal radiation, or any incoherent radiation at the desired wavelenths, is converted into laser energy by using radiant absorption from a radiation source by a cold gas. The cold gas absorbs vibrational energy while remaining otherwise cold, and exchange of vibrational energy between molecules at this low temperature causes population inversions.

A method of computing the emergent radiation by the atmosphere in the region ranging from ultraviolet to infrared

Abstract: A method of computing the diffuse reflection and transmission radiation by an inhomogeneous, plane-parallel planetary atmosphere with internal emission source is discussed by use of the adding method. If the atmosphere is simulated by a number of homogeneous sub-layers, the radiation diffusely reflected or transmitted by the atmosphere can be expressed in terms of the reflection and transmission matrices of the radiation of sub-layers. The diffusely transmitted radiation due to the internal emission source can be also easily computed in the same manner. These equations for the emergent radiation are in a quite general form and are applicable to radiative transfer in the atmosphere in the region from ultraviolet to infrared radiation. With this method, the tiresome treatment due to the polarity effect of radiation is overcome.