Visible Radiation Transfer in a Black Ink Suspension

1980 ◽  
Vol 102 (4) ◽  
pp. 709-714 ◽  
Author(s):  
T. R. Wagner ◽  
F. P. Incropera ◽  
W. G. Houf
Keyword(s):  
Radiation Intensity ◽  
Forward Direction ◽  
Radiative Properties ◽  
Discrete Ordinate ◽  
Visible Radiation ◽  
Intensity Measurements ◽  
Radiation Fluxes ◽  
India Ink ◽  
Half Angle ◽  
Good Agreement

Measurements of the directional and spatial distribution of the radiation intensity have been made for an irradiated India ink suspension, and the results have been used to determine radiation fluxes associated with the forward and backward directions. The inherent radiative properties of the ink have also been measured and used with appropriate theories (the discrete ordinate and three-flux methods) to predict the radiation field within the suspension. For the prescribed laboratory conditions, the radiation is concentrated within a cone of half angle θ ≈ 0.85 rad throughout the suspension, and for this region good agreement is obtained between the intensity measurements and predictions based on the discrete ordinate method. Good agreement is also obtained between radiation fluxes measured for the forward direction and predictions based on both the discrete ordinate and three-flux methods. Agreement between the predicted and measured intensities for θ ≳ 0.85 rad, as well as agreement between predicted and measured radiation fluxes for the backward direction, is less satisfactory. Differences are attributed to uncertainties in the radiation intensity and phase function measurements.

Characterizing the convective heat exchange with plastic shading nets under natural arid conditions

2019 ◽  
pp. 11-20
Author(s):  
Ahmed M Abdel-Ghanya ◽  
Ibrahim M Al-Helal
Keyword(s):  
Wind Speed ◽  
Thermal Radiation ◽  
Convective Heat ◽  
Convective Heat Transfer Coefficient ◽  
Convective Heat Exchange ◽  
Radiative Properties ◽  
Wooden Frame ◽  
Arid Conditions ◽  
Air Temperatures ◽  
Radiation Fluxes

Plastic nets are extensively used for shading purposes in arid regions such as in the Arabian Peninsula. Quantifying the convection exchange with shading net and understanding the mechanisms (free, mixed and forced) of convection are essential for analyzing energy exchange with shading nets. Unlike solar and thermal radiation, the convective energy, convective heat transfer coefficient and the nature of convection have never been theoretically estimated or experimentally measured for plastic nets under arid conditions. In this study, the convected heat exchanges with different plastic nets were quantified based on an energy balance applied to the nets under outdoor natural conditions. Therefore, each net was tacked onto a wooden frame, fixed horizontally at 1.5-m height over the floor. The downward and upward solar and thermal radiation fluxes were measured below and above each net on sunny days; also the wind speed over the net, and the net and air temperatures were measured, simultaneously. Nets with different porosities, colors and texture structures were used for the study. The short and long wave’s radiative properties of the nets were pre-determined in previous studies to be used. Re and Gr numbers were determined and used to characterize the convection mechanism over each net. The results showed that forced and mixed convection are the dominant modes existing over the nets during most of the day and night times. The nature of convection over nets depends mainly on the wind speed, net-air temperature difference and texture shape of the net rather than its color and its porosity.

scholarly journals Modelling and Simulation of the Radiant Field in an Annular Heterogeneous Photoreactor Using a Four-Flux Model

2018 ◽  
Vol 2018 ◽  
pp. 1-16 ◽  
Author(s):  
O. Alvarado-Rolon ◽  
R. Natividad ◽  
R. Romero ◽  
L. Hurtado ◽  
A. Ramírez-Serrano
Keyword(s):  
Photocatalytic Oxidation ◽  
Reaction Rate ◽  
Comsol Multiphysics ◽  
Discrete Ordinate Method ◽  
Discrete Ordinate ◽  
Cylindrical Coordinates ◽  
Volumetric Rate ◽  
Flux Model ◽  
Reaction Rate Equation ◽  
Good Agreement

This work focuses on modeling and simulating the absorption and scattering of radiation in a photocatalytic annular reactor. To achieve so, a model based on four fluxes (FFM) of radiation in cylindrical coordinates to describe the radiant field is assessed. This model allows calculating the local volumetric rate energy absorption (LVREA) profiles when the reaction space of the reactors is not a thin film. The obtained results were compared to radiation experimental data from other authors and with the results obtained by discrete ordinate method (DOM) carried out with the Heat Transfer Module of Comsol Multiphysics® 4.4. The FFM showed a good agreement with the results of Monte Carlo method (MC) and the six-flux model (SFM). Through this model, the LVREA is obtained, which is an important parameter to establish the reaction rate equation. In this study, the photocatalytic oxidation of benzyl alcohol to benzaldehyde was carried out, and the kinetic equation for this process was obtained. To perform the simulation, the commercial software COMSOL Multiphysics v. 4.4 was employed.

PWA OF πN SCATTERING WITH FIXED-t DISPERSION RELATIONS

2005 ◽  
Vol 20 (08n09) ◽  
pp. 1810-1813
Author(s):  
PEKKO PIIROLA ◽  
M. E. SAINIO
Keyword(s):  
Data Base ◽  
Forward Direction ◽  
Dispersion Relations ◽  
Data Sets ◽  
Coupling Constant ◽  
Partial Waves ◽  
Scattering Measurements ◽  
Pion Nucleon ◽  
Good Agreement

The πN scattering measurements from last couple of decades are not in very good agreement with each other. In fact, using the different data sets one finds different values for the pion-nucleon coupling constant. An analysis with theoretical constraints is the only way to produce accurate partial waves. In this analysis, the fixed-t dispersion relations are used to ensure analyticity in the invariant amplitudes and to decrease the effects of inaccuracies in the data base. Pietarinen's expansion is the method used to enforce the dispersion constraints. The strength of the analyticity constraints is illustrated with C± amplitudes in the forward direction.

Competitive reactions in the irradiation of anthracene + cyclohexane solutions

1959 ◽  
Vol 249 (1256) ◽  
pp. 51-64 ◽  
Keyword(s):  
Radiation Intensity ◽  
Quantitative Agreement ◽  
Radical Scavenger ◽  
Organic Systems ◽  
Low Concentrations ◽  
Radiation Induced ◽  
Experimental Values ◽  
Very High ◽  
Intensity Radiation ◽  
Good Agreement

Anthracene acts as a radical scavenger when present at low concentrations in irradiated hydrocarbons. A study has been made of the effect of radiation intensity and anthracene concentration on G( — A) , the number of anthracene molecules lost per 100 eV of energy absorbed. A theoretical calculation is made of the dependence of G( — A) on radiation intensity 1 and anthracene concentration ( A ), assuming that radiation-induced radicals (R.) are formed at random, and can either disappear by direct combination with one another, or with the anthracene to give RAR or RAAR bridges, or possibly some form of stabilized RA molecules. This theory is in good agreement with the experimental values of G( — A) measured at various low radiation intensities and anthracene concentrations. From the comparison estimates of the reactivity constants are derived. With very high intensity radiation quantitative agreement is less satisfactory, due to the non-steady conditions prevailing in a pulsed beam. The results obtained are compared with previous work on anthracene + hexane and iodine + cyclo hexane mixtures, in which the effect of radiation intensity was not investigated. The results reported here are of interest to the study of reaction kinetics in irradiated organic systems.

scholarly journals Effects of Drifting Snow on Surface Radiation Budget in the Katabatic Wind Zone, Antarctica

1985 ◽  
Vol 6 ◽  
pp. 238-241 ◽  
Author(s):  
Takashi Yamanouchi ◽  
Sadao Kawaguchi
Keyword(s):  
Wind Speed ◽  
Longwave Radiation ◽  
Surface Radiation ◽  
Radiative Properties ◽  
Radiation Budget ◽  
Katabatic Wind ◽  
Drifting Snow ◽  
Radiation Fluxes ◽  
Snow Drift ◽  
The Difference

Effects of drifting snow are examined from measurements of radiation fluxes at Mizuho Station in the katabatic wind zone, Antarctica. A good correlation is found between the difference of downward longwave fluxes measured at two heights and wind speed used as an index of drifting snow. The wind increases the downward flux at a rate of 2 W m-2/m s-2 when wind speed is higher than 13 m/s. Drifting snow suppresses the net longwave cooling at the surface. Direct solar radiation is depleted greatly by the drifting snow; however, the global flux decreases only slightly, compensated by the large increase of the diffuse flux, at a rate of about 1% for each 1 m/s increase in wind speed. At Mizuho Station, the effect on longwave radiation prevails throughout the year. The relation between snow drift content and wind speed is obtained from shortwave optical depth measurements as a function of wind speed. A simple parameterization of radiative properties is given.

Quartz-Fiber Thermal Insulation: Infrared Radiative Properties and Calculation of Radiative-Conductive Heat Transfer

1996 ◽  
Vol 118 (2) ◽  
pp. 408-414 ◽  
Author(s):  
L. A. Dombrovsky
Keyword(s):  
Heat Transfer ◽  
Disperse Material ◽  
Conductive Heat Transfer ◽  
Radiative Properties ◽  
Conductive Heat ◽  
Radiation Diffusion ◽  
Fiber Thermal Insulation ◽  
Good Agreement ◽  
Scattering And Radiation

Calculations of absorption, transport scattering, and radiation diffusion coefficients for a highly porous material of quartz fibers are performed by use of rigorous scattering theory for arbitrarily oriented cylinders. New results concerning resonance absorption in the semitransparency region and intensive “scattering by absorption” at refractive index n ≈ 1 in the opacity region are obtained. Numerical results for the radiation diffusion coefficient from a theoretical model without taking into account both dependent scattering and interference effects are in a good agreement with the experimental data for isotropic fibrous material of density 144 kg/m3. Calculations allow us to give practical proposals to simplify the determination of optical properties of poly disperse material with randomly oriented fibers. Some results on the radiative–conductive heat transfer in the material considered are presented. The radiation transfer is described in the P1 approximation. A two-band spectral model with bands corresponding to semitransparency and opacity regions is proposed. Applicability of a modified radiative conduction approximation both to transient and to steady-state calculations is discussed.

ELECTRONIC AND MAGNETIC STUCTURE OF HEXAGONAL FeGe

1993 ◽  
Vol 07 (01n03) ◽  
pp. 1023-1026 ◽  
Author(s):  
ANDERS HJELM
Keyword(s):  
Spin Structure ◽  
Band Structure Calculations ◽  
Easy Direction ◽  
Spin Polarized ◽  
Unit Cells ◽  
Half Angle ◽  
Experimental Values ◽  
Antiferromagnetic Spin ◽  
Structure Calculations ◽  
Good Agreement

Al low temperatures hexagonal FeGe (B 35) exhibits a double—cone antiferromagnetic spin structure. In the present work spin polarized, self consistent band structure calculations are presented for one (ferromagnetic) and two (antiferromagnetic) unit cells. The calculated sublattice magnetization along the c axis, 1.47 μB/Fe atom, is smaller than the experimental values, 1.53–1.78 μB/Fe atom. It is also shown that the easy direction deviates from the c axis, and the cone half angle is estimated to be 12°, in good agreement with the experimental value of 14°.

Viscous flow over a cone at moderate incidence. Part 2. Supersonic boundary layer

1973 ◽  
Vol 59 (3) ◽  
pp. 593-620 ◽  
Author(s):  
T. C. Lin ◽  
S. G. Rubin
Keyword(s):  
Boundary Layer ◽  
Viscous Flow ◽  
Three Dimensional ◽  
Cross Flow ◽  
Lateral Diffusion ◽  
Supersonic Boundary Layer ◽  
Half Angle ◽  
Local Shear ◽  
Sharp Cone ◽  
Good Agreement

A finite-difference method recently developed to study three-dimensional viscous flow is applied here to the supersonic boundary layer on a sharp cone at moderate angles of incidence (α/θ [les ] 2, angle of attack α, cone half-angle θ). The present analysis differs from previous investigations of this region in that (i) boundary-layer similarity is not assumed, (ii) the system of governing equations incorporates lateral diffusion and centrifugal force effects, and (iii) an improved numerical scheme for three-dimensional viscous flows of the type considered here is used. Solutions are shown to be non-similar at the separation streamline with local shear-layer formation. Detailed flow structure, including surface heat transfer, boundary-layer profiles and thickness, and the formation of swirling pairwise symmetric vortices, associated with cross-flow separation, are obtained. Good agreement is obtained between the present theoretical results and the existing experimental data.

scholarly journals Design aspects of Bi2Sr2CaCu2O8+δ THz sources: optimization of thermal and radiative properties

2021 ◽  
Vol 12 ◽  
pp. 1392-1403
Author(s):  
Mikhail M Krasnov ◽  
Natalia D Novikova ◽  
Roger Cattaneo ◽  
Alexey A Kalenyuk ◽  
Vladimir M Krasnov
Keyword(s):  
Experimental Data ◽  
Power Efficiency ◽  
Open Space ◽  
Radiation Power ◽  
Impedance Matching ◽  
Dipole Antenna ◽  
Radiative Properties ◽  
Heat Management ◽  
Order Of Magnitude ◽  
Good Agreement

Impedance matching and heat management are important factors influencing the performance of terahertz sources. In this work we analyze thermal and radiative properties of such devices based on mesa structures of a layered high-temperature superconductor Bi2Sr2CaCu2O8+δ. Two types of devices are considered containing either a conventional large single crystal or a whisker. We perform numerical simulations for various geometrical configurations and parameters and make a comparison with experimental data for the two types of devices. It is demonstrated that the structure and the geometry of both the superconductor and the electrodes play important roles. In crystal-based devices an overlap between the crystal and the electrode leads to appearance of a large parasitic capacitance, which shunts terahertz emission and prevents impedance matching with open space. The overlap is avoided in whisker-based devices. Furthermore, the whisker and the electrodes form a turnstile (crossed-dipole) antenna facilitating good impedance matching. This leads to more than an order of magnitude enhancement of the radiation power efficiency in whisker-based, compared to crystal-based, devices. These results are in good agreement with presented experimental data.

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