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- Martens, C.S., et al.
(författare)
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Radon fluxes in tropical forest ecosystems of Brazilian Amazonia: night-time CO2 net ecosystem exchange derived from radon and eddy covariance methods.
- 2004
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Ingår i: Global Change Biology. - : Wiley. - 1354-1013 .- 1365-2486. ; 10:5, s. 618-629
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Tidskriftsartikel (refereegranskat)abstract
- Radon-222 (Rn-222) is used as a transport tracer of forest canopy–atmosphere CO2 exchange in an old-growth, tropical rain forest site near km 67 of the Tapajós National Forest, Pará, Brazil. Initial results, from month-long periods at the end of the wet season (June–July) and the end of the dry season (November–December) in 2001, demonstrate the potential of new Rn measurement instruments and methods to quantify mass transport processes between forest canopies and the atmosphere. Gas exchange rates yield mean canopy air residence times ranging from minutes during turbulent daytime hours to greater than 12 h during calm nights. Rn is an effective tracer for net ecosystem exchange of CO2 (CO2 NEE) during calm, night-time hours when eddy covariance-based NEE measurements are less certain because of low atmospheric turbulence. Rn-derived night-time CO2 NEE (9.00±0.99 μmol m−2 s−1 in the wet season, 6.39±0.59 in the dry season) was significantly higher than raw uncorrected, eddy covariance-derived CO2 NEE (5.96±0.51 wet season, 5.57±0.53 dry season), but agrees with corrected eddy covariance results (8.65±1.07 wet season, 6.56±0.73 dry season) derived by filtering out lower NEE values obtained during calm periods using independent meteorological criteria. The Rn CO2 results suggest that uncorrected eddy covariance values underestimate night-time CO2 loss at this site. If generalizable to other sites, these observations indicate that previous reports of strong net CO2 uptake in Amazonian terra firme forest may be overestimated.
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| 2. |
- Oliveira de Souza, Luis C. Eduardo, et al.
(författare)
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Assessment of turbulence modelling for CFD simulations into hydroturbines: spiral casings
- 2003
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Ingår i: 17th International Mechanical Engineering Congress (COBEM 2003) at São Paulo (Brazil).
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Konferensbidrag (refereegranskat)abstract
- Spiral casings are applied to distribute the water, as evenly as possible, to the stay vanes and wicket gates and then to the turbine runner. In a well-designed spiral casing, the pressure head of the fluid should be made available to the runner with minimum loss, hence the analysis of the flow through a spiral casing is important for the design of efficient hydraulic turbines. The goal of this work is based on turbo machines spiral casings three-dimensional flow modeling, simulation and characterization. Governing equations related to their study are used in the mathematical modeling part. Therefore, several turbulence models available will be tested with a finite volume method based commercial software CFX 5.5.1 which generates default tetrahedral meshing. Qualitative and quantitative results validation are proved by workshop benchmark experiments already done, in order these results can obtain a turbulence model that represents better the flow complexity inside spiral casings.
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