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01641 Raman spectra of stoichiometric and hyperstoichiometric uranium dioxide
16 Fuel science and technology (fundamental science, analysis, instrumentation)
Francioso, O. et al. Bioresource Technology, 2003, 8, (3), 189-195. Humic acids extracted from peats (P), brown coals (BC) and lignites (L), were characterized using different (chemical, 1H-nuclear magnetic resonance spectroscopy and differential thermal analysis) techniques. Fourteen variables were obtained from these analyses and only five were selected because uncorrelated in multiple partial correlation. The chosen variables were C concentration, aliphatic and aromatic components and the heat of reaction of the second exothermic peak. The multivariate discriminant analysis was performed on these variables and a discriminant function was obtained which was able to efficiently separate the P, BC and L. This function enables simple predictions on samples of unknown origin. The straightforward method proposed and the results obtained are discussed. 1H-NMR
A numerical simulation has been performed of the disturbed flow through and over a two-dimensional array of rectangular buildings immersed in a neutrally stratified deep rough-walled turbulent boundary-layer flow. The model used for the simulation was the steady-state Reynolds-averaged Navier-Stokes equations with linear and non-linear eddy viscosity formulations for the Reynolds stresses. The eddy viscosity was determined using a high-Reynolds number form of the k e turbulence-closure model with the boundary conditions at the wall obtained with a standard wall-function approach. The resulting system of partial differential equations was solved using the SIMPLE algorithm in conjunction with a non-orthogonal, colocated, cell-centred, finite volume procedure. The predictive capabilities of the high-resolution computational fluid dynamics (CFD) simulations of urban flow are validated against a very detailed and comprehensive wind tunnel data set. Vertical profiles of the mean streamwise velocity and the turbulence kinetic energy are presented and compared to those measured in the wind tunnel simulation. It is found that the performance of all the turbulence models investigated is generally good most of the qualitative features in the disturbed turbulent flow field through and over the building array are correctly reproduced. The quantitative agreement is also fairly good (especially for the mean velocity field). Overall, the non-linear k-e model gave the best performance among four different turbulence closure models examined. The turbulence energy levels within the street canyons and in the exit region downstream of the last building were underestimated by all four turbulence closure models. This appears to contradict the 'stagnation point anomaly' associated with the standard k-e model which is a result of the excessive turbulence energy production due to normal straining. A possible explanation for this is the inability of the present models to account properly for the effects of secondary strains on the turbulence and/or for the effects of large-scale flapping of the strong shear layer at the canopy top. The results of the high-resolution CFD simulations have been used to diagnose values of the drag coefficient to be used in a distributed drag force representation of the obstacles in the array. Comparisons of the measured spatially-averaged time-mean mean velocity and turbulence kinetic energy in the array with predictions of the disturbed flow using the distributed drag force approach have been made.
04/01641 Raman spectra of stoichiometric and hyperstoichiometric uranium dioxide
04/01644 Simulation of process for electrical energy production based on molten carbonate fuel cells
An efficient depression of coal sulphides in the flotation process means a healthier environment and may be essential for the sustainability of a coal operation. Nitric and ferric oxidative pre-treatment of coal pyrite have been tested to improve pyrite depression, and the results are compared with those from the process of raw, not pre-treated coal. The removal indexes point to nitric pre-treatment as the best, but depression is still low. The microscopic study of feed and products, coupled to Digital Image Analysis (DIA) in all the cases, provide important clues to understand the behaviour of pyrite, which can be related to quantitative parameters, such as the exposition ratio (ER), and to qualified interpretation of the textures. Pyrite shows in the first float an unexpected hydrophobic behaviour, which is due to its occurrence as framboids, or porous particles which may be intergrown with organic matter and behave as coal. In general, the flotation results can be predicted from the DIA-data, e.g. depression of liberated pyrite into the tailings, increased by oxidative pre-treatments by 300% (ferric) or by > 400% (nitric); or concentration of middlings with lower pyrite ER in the floats. DIA is an efficient tool to obtain some important quantitative information, which otherwise would be inaccessible (e.g. the morphological data on > 1 000 000 pyrite particles for this study), and its use should be enhanced to check ore processing.
04101640 Quantitative estimation of peat, brown coal and lignite humic acids using chemical parameters, 1H-NMR and DTA analyses
Manara, D. and Renker, B. Journal of Nuclear Materials, 2003, 321, (23), 233-237. Raman spectra of stoichiometric and hyperstoichiometric uranium dioxide are presented, as measured on nuclear-grade UO2 pellets treated under oxidizing conditions to obtain different levels of hyperstoichiometry. The precipitation of higher oxides on the sample surface in contact with air, depending on the oxidation of the specimen, is observed. Modes revealing the formation on the surface of the compound U208, such as the line at 750 cm -1, are detected in specimens with bulk O/U > 2.09. Particular attention is given to the behaviour of the line observed for stoichiometric UO2 at 1151 cm -1, attributed to the crystal electric field Ps--+ F~ transition. According to the presented measurements, such line can be regarded as a fingerprint of the quasi-perfect fluorite structure. Results are discussed and compared with those of some previous publications results on the same subject.
04•01642 Raman spectroscopy of HiPCO single-walled carbon nanotubes at 300 and 5 K Karachevtsev, V. A. et al. Carbon, 2003, 41, (8), 1567-1574. Single-walled carbon nanotubes (SWNTs) produced by the high pressure CO disproportionation (HiPCO method) and purified by controlled thermal oxidation in air have been studied by Raman spectroscopy at 300 and 5 K. Raman spectra have been observed at Aexo=632.8 and 441.6 nm laser excitation in the range of 160-1800 cm -1. In the low-frequency part of the spectra (the radial breathing mode range) eleven narrow lines can be detected at low temperatures, enabling an estimation of nanotube diameters (0.8-1.3 nm) and chirality. The width at half-maximum intensity of these spectral lines is about 3-4 cm -1 at 5 K. The Stokes and anti-Stokes spectra are measured at ),~c=632.8 nm at room temperature. The most intense lines in these spectra are caused with the resonant Raman-scattering process. With increasing temperature from 5 to 300 K the shift (3-4 cm -~) of the most intense high-frequency component of the tangential mode (G mode) to lower frequency is observed. Based on the analysis of the Stokes/anti-Stokes spectra and the G band shape, the corresponding lines were identified with metallic or semiconducting type of nanotubes.
04/01643 Simulation of mean flow and turbulence over a 2D building array using high-resolution CFD and a distributed drag force approach Lien, F. S. et al. Journal of Wind Engineering and Industrial Aerodynamics, 2004, 92, (2), 117-158.
222
Fuel and Energy Abstracts
May 2004
De Simon, G. et al. Journal of Power Sources, 2003, 115, (2), 210 218. A global molten carbonate fuel cells (MCFC) power plant steady-state simulation is presented. A performance fuel cell numerical model is developed and integrated as a custom block in Aspen plus T M for the whole process simulation. The burner/reformer compact unit is built assembling existing Aspen plus T M internal blocks. A simulation is obtained with the preliminary input specification to get to the base case and a sensitivity analysis is conducted, in order to find the process parameters whose change improves the global efficiency.
04101645 Soot size distributions in rich premixed ethylene flames Maricq, M. M. et al. Combustion and Flame, 2003, 132, (3), 328-342. Electrical mobility measurements of the soot particles generated in rich premixed ethylene/air flat flames reveal a characteristic lognormal size distribution that is distinct from the self preserving distribution expected from coagulation dominated aerosol dynamics. The distribution changes to a bimodal form as the equivalence ratio and the height above the burner increase. The soot particles are sampled using a three-stage ejector pump, with an overall dilution of the soot mole fraction by 3000 that quenches the flame chemistry and dilutes the sample for analysis by a nano-differential mobility analyser. The measured soot volume fraction is in good agreement with optical extinction data, quantitatively reproducing the increases previously noted with respect to increasing equivalence ratio and height above the burner. The trends for mean particle diameter are also reproduced, but the mobility diameters are roughly threefold smaller than their light scattering counterparts. Particle number density is found to increase with height, whereas the optical data exhibit the opposite trend. Residence chamber experiments show that with sufficient time the quenched soot sample evolves from the lognormal shape found in the flame to the expected self preserving distribution.
04•01646 Source apportionment of polychlorinated biphenyls using compound specific isotope analysis Yanik, P. J. et al. Organic Geochemistry, 2003, 34, (2), 239-251. Reported here are results of the compound specific carbon isotopic analysis (CSIA) of individual PCB congeners. This investigation was designed to determine the suitability of CSIA on this class of compounds in natural materials. Samples of duck tissue, duck liver, duck egg and grass carp were collected from the Housatonic River, Massachusetts, and compared with samples of fresh Aroclor ~' 1242, 1254, 1260, and 1262. Twenty congeners were selected for isotopic analysis based on their ability to be separated chromatographically and
Francioso, O. et al. Bioresource Technology, 2003, 8, (3), 189-195. Humic acids extracted from peats (P), brown coals (BC) and lignites (L), were characterized using different (chemical, 1H-nuclear magnetic resonance spectroscopy and differential thermal analysis) techniques. Fourteen variables were obtained from these analyses and only five were selected because uncorrelated in multiple partial correlation. The chosen variables were C concentration, aliphatic and aromatic components and the heat of reaction of the second exothermic peak. The multivariate discriminant analysis was performed on these variables and a discriminant function was obtained which was able to efficiently separate the P, BC and L. This function enables simple predictions on samples of unknown origin. The straightforward method proposed and the results obtained are discussed. 1H-NMR
A numerical simulation has been performed of the disturbed flow through and over a two-dimensional array of rectangular buildings immersed in a neutrally stratified deep rough-walled turbulent boundary-layer flow. The model used for the simulation was the steady-state Reynolds-averaged Navier-Stokes equations with linear and non-linear eddy viscosity formulations for the Reynolds stresses. The eddy viscosity was determined using a high-Reynolds number form of the k e turbulence-closure model with the boundary conditions at the wall obtained with a standard wall-function approach. The resulting system of partial differential equations was solved using the SIMPLE algorithm in conjunction with a non-orthogonal, colocated, cell-centred, finite volume procedure. The predictive capabilities of the high-resolution computational fluid dynamics (CFD) simulations of urban flow are validated against a very detailed and comprehensive wind tunnel data set. Vertical profiles of the mean streamwise velocity and the turbulence kinetic energy are presented and compared to those measured in the wind tunnel simulation. It is found that the performance of all the turbulence models investigated is generally good most of the qualitative features in the disturbed turbulent flow field through and over the building array are correctly reproduced. The quantitative agreement is also fairly good (especially for the mean velocity field). Overall, the non-linear k-e model gave the best performance among four different turbulence closure models examined. The turbulence energy levels within the street canyons and in the exit region downstream of the last building were underestimated by all four turbulence closure models. This appears to contradict the 'stagnation point anomaly' associated with the standard k-e model which is a result of the excessive turbulence energy production due to normal straining. A possible explanation for this is the inability of the present models to account properly for the effects of secondary strains on the turbulence and/or for the effects of large-scale flapping of the strong shear layer at the canopy top. The results of the high-resolution CFD simulations have been used to diagnose values of the drag coefficient to be used in a distributed drag force representation of the obstacles in the array. Comparisons of the measured spatially-averaged time-mean mean velocity and turbulence kinetic energy in the array with predictions of the disturbed flow using the distributed drag force approach have been made.
04/01641 Raman spectra of stoichiometric and hyperstoichiometric uranium dioxide
04/01644 Simulation of process for electrical energy production based on molten carbonate fuel cells
An efficient depression of coal sulphides in the flotation process means a healthier environment and may be essential for the sustainability of a coal operation. Nitric and ferric oxidative pre-treatment of coal pyrite have been tested to improve pyrite depression, and the results are compared with those from the process of raw, not pre-treated coal. The removal indexes point to nitric pre-treatment as the best, but depression is still low. The microscopic study of feed and products, coupled to Digital Image Analysis (DIA) in all the cases, provide important clues to understand the behaviour of pyrite, which can be related to quantitative parameters, such as the exposition ratio (ER), and to qualified interpretation of the textures. Pyrite shows in the first float an unexpected hydrophobic behaviour, which is due to its occurrence as framboids, or porous particles which may be intergrown with organic matter and behave as coal. In general, the flotation results can be predicted from the DIA-data, e.g. depression of liberated pyrite into the tailings, increased by oxidative pre-treatments by 300% (ferric) or by > 400% (nitric); or concentration of middlings with lower pyrite ER in the floats. DIA is an efficient tool to obtain some important quantitative information, which otherwise would be inaccessible (e.g. the morphological data on > 1 000 000 pyrite particles for this study), and its use should be enhanced to check ore processing.
04101640 Quantitative estimation of peat, brown coal and lignite humic acids using chemical parameters, 1H-NMR and DTA analyses
Manara, D. and Renker, B. Journal of Nuclear Materials, 2003, 321, (23), 233-237. Raman spectra of stoichiometric and hyperstoichiometric uranium dioxide are presented, as measured on nuclear-grade UO2 pellets treated under oxidizing conditions to obtain different levels of hyperstoichiometry. The precipitation of higher oxides on the sample surface in contact with air, depending on the oxidation of the specimen, is observed. Modes revealing the formation on the surface of the compound U208, such as the line at 750 cm -1, are detected in specimens with bulk O/U > 2.09. Particular attention is given to the behaviour of the line observed for stoichiometric UO2 at 1151 cm -1, attributed to the crystal electric field Ps--+ F~ transition. According to the presented measurements, such line can be regarded as a fingerprint of the quasi-perfect fluorite structure. Results are discussed and compared with those of some previous publications results on the same subject.
04•01642 Raman spectroscopy of HiPCO single-walled carbon nanotubes at 300 and 5 K Karachevtsev, V. A. et al. Carbon, 2003, 41, (8), 1567-1574. Single-walled carbon nanotubes (SWNTs) produced by the high pressure CO disproportionation (HiPCO method) and purified by controlled thermal oxidation in air have been studied by Raman spectroscopy at 300 and 5 K. Raman spectra have been observed at Aexo=632.8 and 441.6 nm laser excitation in the range of 160-1800 cm -1. In the low-frequency part of the spectra (the radial breathing mode range) eleven narrow lines can be detected at low temperatures, enabling an estimation of nanotube diameters (0.8-1.3 nm) and chirality. The width at half-maximum intensity of these spectral lines is about 3-4 cm -1 at 5 K. The Stokes and anti-Stokes spectra are measured at ),~c=632.8 nm at room temperature. The most intense lines in these spectra are caused with the resonant Raman-scattering process. With increasing temperature from 5 to 300 K the shift (3-4 cm -~) of the most intense high-frequency component of the tangential mode (G mode) to lower frequency is observed. Based on the analysis of the Stokes/anti-Stokes spectra and the G band shape, the corresponding lines were identified with metallic or semiconducting type of nanotubes.
04/01643 Simulation of mean flow and turbulence over a 2D building array using high-resolution CFD and a distributed drag force approach Lien, F. S. et al. Journal of Wind Engineering and Industrial Aerodynamics, 2004, 92, (2), 117-158.
222
Fuel and Energy Abstracts
May 2004
De Simon, G. et al. Journal of Power Sources, 2003, 115, (2), 210 218. A global molten carbonate fuel cells (MCFC) power plant steady-state simulation is presented. A performance fuel cell numerical model is developed and integrated as a custom block in Aspen plus T M for the whole process simulation. The burner/reformer compact unit is built assembling existing Aspen plus T M internal blocks. A simulation is obtained with the preliminary input specification to get to the base case and a sensitivity analysis is conducted, in order to find the process parameters whose change improves the global efficiency.
04101645 Soot size distributions in rich premixed ethylene flames Maricq, M. M. et al. Combustion and Flame, 2003, 132, (3), 328-342. Electrical mobility measurements of the soot particles generated in rich premixed ethylene/air flat flames reveal a characteristic lognormal size distribution that is distinct from the self preserving distribution expected from coagulation dominated aerosol dynamics. The distribution changes to a bimodal form as the equivalence ratio and the height above the burner increase. The soot particles are sampled using a three-stage ejector pump, with an overall dilution of the soot mole fraction by 3000 that quenches the flame chemistry and dilutes the sample for analysis by a nano-differential mobility analyser. The measured soot volume fraction is in good agreement with optical extinction data, quantitatively reproducing the increases previously noted with respect to increasing equivalence ratio and height above the burner. The trends for mean particle diameter are also reproduced, but the mobility diameters are roughly threefold smaller than their light scattering counterparts. Particle number density is found to increase with height, whereas the optical data exhibit the opposite trend. Residence chamber experiments show that with sufficient time the quenched soot sample evolves from the lognormal shape found in the flame to the expected self preserving distribution.
04•01646 Source apportionment of polychlorinated biphenyls using compound specific isotope analysis Yanik, P. J. et al. Organic Geochemistry, 2003, 34, (2), 239-251. Reported here are results of the compound specific carbon isotopic analysis (CSIA) of individual PCB congeners. This investigation was designed to determine the suitability of CSIA on this class of compounds in natural materials. Samples of duck tissue, duck liver, duck egg and grass carp were collected from the Housatonic River, Massachusetts, and compared with samples of fresh Aroclor ~' 1242, 1254, 1260, and 1262. Twenty congeners were selected for isotopic analysis based on their ability to be separated chromatographically and