| 1. |
- Al-Adili, Ali, et al.
(författare)
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Ion counting efficiencies at the IGISOL facility
- 2014
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- At the IGISOL-JYFLTRAP facility, fission mass yields can be studied at high precision. Fission fragments from a U target are passing through a Ni foil and entering a gas filled chamber. The collected fragments are guided through a mass separator to a Penning trap where their masses are identified. This simulation work focuses on how different fission fragment properties (mass, charge and energy) affect the stopping efficiency in the gas cell. In addition, different experimental parameters are varied (e. g. U and Ni thickness and He gas pressure) to study their impact on the stopping efficiency. The simulations were performed using the Geant4 package and the SRIM code. The main results suggest a small variation in the stopping efficiency as a function of mass, charge and kinetic energy. It is predicted that heavy fragments are stopped about 9% less efficiently than the light fragments. However it was found that the properties of the U, Ni and the He gas influences this behavior. Hence it could be possible to optimize the efficiency.
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| 2. |
- Baudoin, Eric, et al.
(författare)
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Effect of partial premixing on stabilization and local extinction of turbulent methane/air flames
- 2013
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Ingår i: Flow, Turbulence and Combustion. - : Springer Science and Business Media LLC. - 1573-1987 .- 1386-6184. ; 90:2, s. 269-284
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Tidskriftsartikel (refereegranskat)abstract
- Abstract in UndeterminedThe stabilization characteristics and local extinction structures of partially premixed methane/air flames were studied using simultaneous OH-PLIF/PIV techniques, and large eddy simulations employing a two-scalar flamelet model. Partial premixing was made in a mixing chamber comprised of two concentric tubes, where the degree of partial premixing of fuel and air was controlled by varying the mixing length of the chamber. At the exit of the mixing chamber a cone was mounted to stabilize the flames at high turbulence intensities. The stability regime of flames was determined for different degree of partial premixing and Reynolds numbers. It was found that in general partially premixed flames at low Reynolds numbers become more stable when the level of partial premixing of air to the fuel stream decreases. At high Reynolds numbers, for the presently studied burner configuration there is an optimal partial premixing level of air to the fuel stream at which the flame is most stable. OH-PLIF images revealed that for the stable flames not very close to the blowout regime, significant local extinction holes appear already. By increasing premixing air to fuel stream successively, local extinction holes grow in size leading to eventual flame blowout. Local flame extinction was found to frequently attain to locations where locally high velocity flows impinging to the flame. The local flame extinction poses a future challenge for model simulations and the present flames provide a possible test case for such study.
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| 3. |
- Baudoin, Eric, et al.
(författare)
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Effect of partial premixing on stabilization and local extinction of turbulent methane/air flames
- 2011
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Ingår i: Proceedings of the 17th Mediterranean Combustion symposium, MCS 7. - 9788888104126
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Konferensbidrag (refereegranskat)abstract
- The stabilization characteristics and local extinction structures of partially premixed methane/air flames were studied using simultaneous OH-PLIF/PIV techniques, and large eddy simulations employing a two-scalar flamelet model. Partial premixing was made in a mixing chamber comprised of two concentric tubes, where the degree of partial premixing of fuel and air was controlled by varying the mixing length of the chamber. At the exit of the mixing chamber a cone was mounted to stabilize the flames at high turbulence intensities. The stability regime of flames was determined for different degree of partial premixing and Reynolds numbers. It was found that in general partially premixed flames at low Reynolds numbers become more stable when the level of partial premixing of air to the fuel stream decreases. At high Reynolds numbers, for the presently studied burner configuration there is an optimal partial premixing level of air to the fuel stream at which the flame is most stable. OH-PLIF images revealed that for the stable flames not very close to the blowout regime,significant local extinction holes appear already. By increasing premixing air to fuel stream successively, local extinction holes grow in size leading to eventual flame blowout. Local flame extinction was found to frequently attain to locations where locally high velocity flows impinging to the flame. The local flame extinction poses a future challenge for model simulations and the present flames provide a possible test case for such study.
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| 4. |
- Blunden, Jessica, et al.
(författare)
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State of the climate in 2013
- 2014
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Ingår i: Bulletin of the American Meteorological Society. - 0003-0007. ; 95
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Tidskriftsartikel (refereegranskat)abstract
- © 2014, American Meteorological Society. All rights reserved. In 2013, the vast majority of the monitored climate variables reported here maintained trends established in recent decades. ENSO was in a neutral state during the entire year, remaining mostly on the cool side of neutral with modest impacts on regional weather patterns around the world. This follows several years dominated by the effects of either La Niña or El Niño events. According to several independent analyses, 2013 was again among the 10 warmest years on record at the global scale, both at the Earth’s surface and through the troposphere. Some regions in the Southern Hemisphere had record or near-record high temperatures for the year. Australia observed its hottest year on record, while Argentina and New Zealand reported their second and third hottest years, respectively. In Antarctica, Amundsen-Scott South Pole Station reported its highest annual temperature since records began in 1957. At the opposite pole, the Arctic observed its seventh warmest year since records began in the early 20th century. At 20-m depth, record high temperatures were measured at some permafrost stations on the North Slope of Alaska and in the Brooks Range. In the Northern Hemisphere extratropics, anomalous meridional atmospheric circulation occurred throughout much of the year, leading to marked regional extremes of both temperature and precipitation. Cold temperature anomalies during winter across Eurasia were followed by warm spring temperature anomalies, which were linked to a new record low Eurasian snow cover extent in May. Minimum sea ice extent in the Arctic was the sixth lowest since satellite observations began in 1979. Including 2013, all seven lowest extents on record have occurred in the past seven years. Antarctica, on the other hand, had above-average sea ice extent throughout 2013, with 116 days of new daily high extent records, including a new daily maximum sea ice area of 19.57 million km2 reached on 1 October. ENSO-neutral conditions in the eastern central Pacific Ocean and a negative Pacific decadal oscillation pattern in the North Pacific had the largest impacts on the global sea surface temperature in 2013. The North Pacific reached a historic high temperature in 2013 and on balance the globally-averaged sea surface temperature was among the 10 highest on record. Overall, the salt content in nearsurface ocean waters increased while in intermediate waters it decreased. Global mean sea level continued to rise during 2013, on pace with a trend of 3.2 mm yr-1 over the past two decades. A portion of this trend (0.5 mm yr-1) has been attributed to natural variability associated with the Pacific decadal oscillation as well as to ongoing contributions from the melting of glaciers and ice sheets and ocean warming. Global tropical cyclone frequency during 2013 was slightly above average with a total of 94 storms, although the North Atlantic Basin had its quietest hurricane season since 1994. In the Western North Pacific Basin, Super Typhoon Haiyan, the deadliest tropical cyclone of 2013, had 1-minute sustained winds estimated to be 170 kt (87.5 m s-1) on 7 November, the highest wind speed ever assigned to a tropical cyclone. High storm surge was also associated with Haiyan as it made landfall over the central Philippines, an area where sea level is currently at historic highs, increasing by 200 mm since 1970. In the atmosphere, carbon dioxide, methane, and nitrous oxide all continued to increase in 2013. As in previous years, each of these major greenhouse gases once again reached historic high concentrations. In the Arctic, carbon dioxide and methane increased at the same rate as the global increase. These increases are likely due to export from lower latitudes rather than a consequence of increases in Arctic sources, such as thawing permafrost. At Mauna Loa, Hawaii, for the first time since measurements began in 1958, the daily average mixing ratio of carbon dioxide exceeded 400 ppm on 9 May. The state of these variables, along with dozens of others, and the 2013 climate conditions of regions around the world are discussed in further detail in this 24th edition of the State of the Climate series.
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| 5. |
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| 6. |
- Gorelov, D., et al.
(författare)
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Isomeric Yield Ratios of Fission Products Measured with the Jyfltrap
- 2014
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Ingår i: Acta Physica Polonica B. - 0587-4254 .- 1509-5770. ; 45:2, s. 211-216
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Tidskriftsartikel (refereegranskat)abstract
- Experimental methods to determine isomeric yield ratios usually apply gamma-spectroscopic techniques. In such methods, ground and isomeric states are distinguished by their decays. In the present work, several isomeric yield ratios of fission products have been measured by utilizing capabilities of the double Penning-trap mass spectrometer JYFLTRAP, where isomeric and ground state were separated by their masses. To verify the new experimental technique, the results were compared to those from gamma-spectroscopy measurements.
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| 7. |
- Hosseini, Seyed Mohammad, et al.
(författare)
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Study of Flame Dynamics and Flashback Mechanism in a Gas Turbine Combustor Using Simultaneous OH-PLIF and PIV
- 2010
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Ingår i: AIAA 2010-6668. - Reston, Virigina : American Institute of Aeronautics and Astronautics.
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Konferensbidrag (refereegranskat)abstract
- The present study aims to investigate the effects of burner geometry on flame characteristics, stabilization, and the occurrence of flashback using the Triple Annular Research Swirler (TARS). A premixing tube is placed at the exit of the burner. Simultaneous Planar Laser Induced Fluorescence (PLIF) of OH radicals indicating the reacting zone and Particle Image Velocimetry (PIV) for flow field mapping, were applied to study the flow- and flame-dynamics during transition from flame stabilized in the combustion chamber to flame flashback in the mixing tube. Particular attention was placed on the flame behavior/dynamics near the lean blow out (LBO). The flow field featured a central recirculation zone (CRZ), and an annular swirling jet with internal and external shears layers. The movement of the flame front relative to the upstream stagnation point of the vortex breakdown at different conditions was studied. Simultaneous planar measurements using laser diagnostics, namely, Planar Laser Induced Fluorescence (PLIF) of OH radicals and Particle Image Velocimetry (PIV), have been carried out. With mixing tube and at lean cases, vortex breakdown and the flame holding occurred close to the tube exit. As the equivalence ratio was increased, the flame entered intermittently into the premixing tube. Increasing further the equivalence ratio, the flame was stabilized inside the premixing tube. Different statistical evaluations were performed on the data to obtain better understanding of the flame stabilization mechanism. They included PDF of the axial velocity, mean velocity field and mean intensity of the OH radical, two-dimensional correlation between PIV and LIF data, POD analysis of the velocity vectors, distribution of OH radical intensity and binary images of density distribution of the seeding particles.
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| 8. |
- Iudiciani, Piero, et al.
(författare)
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Proper Orthogonal Decomposition for experimental investigation of swirling flame instabilities
- 2010
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Ingår i: Paper AIAA 2010-584. - Reston, Virigina : American Institute of Aeronautics and Astronautics.
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Konferensbidrag (refereegranskat)abstract
- An experimental investigation of both confined and unconfined flames on a Triple Annular Research Swirler (TARS) is presented. The paper focuses on post-processing techniques aiming at extracting information on the dynamics that are lost through classical statistics approach. POD together with a derived a-posteriori phase averaging procedure successfully reconstructed the dynamics of flames under thermo-acoustic instabilities in the confined case. For unconfined flames, an analysis of the azimuthal modes is performed.
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| 9. |
- Lantz, Andreas
(författare)
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Application of Laser Techniques in Combustion Environments of Relevance for Gas Turbine Studies
- 2012
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In the work presented in this thesis, different laser-based techniques were employed for measurements in different combustion devices. Laser-based techniques enable non-intrusive and in-situ measurements to be carried out, in which high spatial and temporal resolution can be obtained. Different parameters related to combustion research can be visualized, such as species concentrations, temperature, velocities and particle sizes. The combustion devices investigated can be related in one way or another to gas turbine combustion, the measurements being performed in devices ranging from laboratory-scale burners to industrial gas turbine burners. The Triple Annular Research Swirler (TARS) is a laboratory burner that simulates the character of a gas turbine, in terms of both fuel injection and flame stabilization. Studies using planar laser-induced fluorescence (PLIF) were carried out here to demonstrate how different swirler configurations affect flame and flow dynamics and how flashback depends on different operating conditions. Simultaneous measurements of OH PLIF and of acetone PLIF were employed to visualize flame position and fuel distribution, respectively, the measurements being carried out simultaneously with velocity measurements involving particle image velocimetry (PIV). Visualization of flame position and of fuel distribution through use of OH PLIF and acetone PLIF was applied to several industrial gas turbine burners to investigate their combustion characteristics. The measurements were performed on-site at Siemens in Finsp\r{a}ng, in burners fueled with natural gas or with a mixture of natural gas and hydrogen. The aim of the experimental investigations was to obtain a better understanding both of the mixing of air and fuel and of the flame dynamics, knowledge of which can hopefully be used to further reduce the emission levels from gas turbines. Part of the experimental results was used for the validation of computational fluid dynamics (CFD) models, used to simulate the flow and the turbulent combustion inside the combustion chamber. A Multi-YAG laser system which can generate a rapid burst of laser pulses, and a high-speed framing camera capable of recording sequences of up to eight images, were used to study fuel vaporization, and its consequent mixing with air, in a Jet A or biojet fueled gas turbine pilot burner under elevated pressure conditions. Fuel PLIF was used to visualize both the liquid and the gas phase of the fuel, Mie scattering being used to visualize only the liquid phase of the fuel. The liquid phase of the fuel was found, as expected, to be close to the burner nozzle and the evaporated fuel to be found a distance downstream from the burner nozzle. High-speed OH PLIF was also employed for visualizing the flame position. Additional work carried out included characterization of partially premixed and diffusion flames in a high-pressure vessel and burner (HPVB) using OH PLIF and PAH PLIF for the visualization of flame position and of polyaromatic hydrocarbon distribution, respectively. Flames using liquid fuels (n-heptane, n-decane and ethanol) as well as gaseous (methane) fuels were studied. The results are intended to be used as data base for kinetic mechanisms and as validation data for CFD models.
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| 10. |
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