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Cyclones
Kinds of Cyclones Terms modified by Cyclones Selected AbstractsTHE STORM OF NOVEMBER 1826 IN THE CANARY ISLANDS: POSSIBLY A TROPICAL CYCLONE?GEOGRAFISKA ANNALER SERIES A: PHYSICAL GEOGRAPHY, Issue 3 2010JOSÉ BETHENCOURT-GONZÁLEZ ABSTRACT. This work analyses a storm that occurred in the Canary Islands early in November 1826. Through a study based on historical climate data, some of the adverse effects of the storm are described and some of the possible causes are discussed. The main goal of this work is to establish an approximate reconstruction of this historical event which will allow us to compare it to a recent meteorological event that had a great impact on the archipelago: "Tropical Storm Delta", in November 2005. Studying and reviewing the origin of the 1826 storm verifies the hypothesis that extremely violent perturbations have not only occurred in the Canaries on other occasions, but that these past events were also more intense and had more serious consequences than Delta. Therefore, the idea that other tropical perturbations have occurred in the region of the Canary Islands before Delta is presented. [source] ,We All Knew that a Cyclone Was Coming': Disaster Preparedness and the Cyclone of 1999 in Orissa, IndiaDISASTERS, Issue 4 2004Frank Thomalla Imagine that a cyclone is coming, but that those living in the affected areas do nothing or too little to protect themselves. This is precisely what happened in the coastal state of Orissa, India. Individuals and communities living in regions where natural hazards are a part of daily life develop strategies to cope with and adapt to the impacts of extreme events. In October 1999, a cyclone killed 10,000 people according to government statistics, however, the unofficial death toll is much higher. This article examines why such a large loss of life occurred and looks at measures taken since then to initiate comprehensive disaster-preparedness programmes and to construct more cyclone shelters. The role of both governmental organisations and NGOs in this is critically analysed. The good news is that, based on an assessment of disaster preparedness during a small cyclone in November 2002, it can be seen that at community-level awareness was high and that many of the lessons learnt in 1999 were put into practice. Less positive, however, is the finding that at the state level collaboration continues to be problematic. [source] Applications of the Liquid Cyclone in Biological SeparationsENGINEERING IN LIFE SCIENCES (ELECTRONIC), Issue 2 2004E. Ortega-Rivas Abstract Hydrocyclone technology has been suggested as a practical alternative in solid/liquid separations involving biological materials. This paper reviews applications of hydrocyclones in food processing, considering the non-Newtonian nature of most suspensions treated in the food industry. The hydrocyclone is easy to install and operate, and requires very limited space. It represents an unsophisticated piece of equipment, which runs in a continuous manner and it can be operated at lower costs than most solid/liquid separation techniques. Hydrocyclones have been used in the food industry for the refining of starch, to separate gossypol from cottonseed protein in cottonseed oil processing, and for some other applications, such as multi-stage mixer/separator extraction systems for soluble coffee. More recently, some other applications in biological systems, which will be discussed in this article, have also been tested. [source] Australian tropical forest canopy crane: New tools for new frontiersAUSTRAL ECOLOGY, Issue 1 2007NIGEL E. STORK Abstract An industrial crane was installed in the Daintree lowland rainforest in 1998 to provide a new means of accessing the canopy. Approximately 0.95 ha of forest, including 680 trees of 82 species with a diameter at breast height of greater than 10 cm, are accessible using the crane. The site was hit by a Category 3 Cyclone in 1999 and has shown a remarkable rate of recovery. The crane has been used for a very wide range of research including tree physiology and ecology, interactions with vertebrate and invertebrate biodiversity and studies of carbon and water fluxes. Results from studies on this crane and 11 other cranes around the world are changing views of the importance of the rainforest canopy. [source] Spreadsheet for cyclone and hydrocyclone design considering nonspherical particle geometryCOMPUTER APPLICATIONS IN ENGINEERING EDUCATION, Issue 2 2007Marcelo K. Lenzi Abstract Cyclones and hydrocyclones are widely used for gas,solid and liquid,solid particle separations, respectively. The key feature is the presence of a centrifugal field. Equilibrium zone concept is one of the most used approaches for equipment design. This work revisits the design equations for nonspherical particles and compares design results considering nonspherical geometry to results considering spherical geometry and correcting the values to the non-spherical particle geometry. A didactic spreadsheet was prepared for analysis and instruction, and depending on the particle shape and on the particle orientation, errors up to 38% may be obtained in the cut diameter and 10% in the global collection efficiency. © 2007 Wiley Periodicals, Inc. Comput Appl Eng Educ. 15: 134,142, 2007; Published online in Wiley InterScience (www.interscience.wiley.com); DOI 10.1002/cae.20102 [source] Recruitment dynamics of invasive species in rainforest habitats following Cyclone LarryAUSTRAL ECOLOGY, Issue 4 2008H. T. MURPHY Abstract In tropical forests, natural disturbance creates opportunities for species to claim previously utilized space and resources and is considered an important mechanism in the maintenance of species diversity. However, ecologists have long recognized that disturbance also promotes exotic plant invasions. Cyclones cause extensive defoliation, loss of major branches and multiple tree falls, resulting in a significantly more open canopy and increased light and heat levels in the understorey. The widespread and massive disturbance caused by cyclones provides ideal conditions for rapid recruitment and spread of invasive species. The ecological roles of invasive species in rainforest habitats following such a severe disturbance are poorly understood. Severe category 4 Cyclone Larry crossed the North Queensland coast in March 2006 causing massive disturbance to rainforest habitats from Tully to Cairns and west to the Atherton Tablelands. We established 10 plots in an area extensively damaged by this cyclone near El Arish in North Queensland. On each plot nine 2 × 2 m quadrats were established with three quadrats per plot in each of the following treatments: (i) complete debris removal down to the soil layer, (ii) removal of coarse woody debris only, and (iii) uncleared. We monitored recruitment, growth and mortality of all native and invasive species in the 90 quadrats every 3 months since the cyclone. Here we present the recruitment dynamics of invasive species across the study area in relation to the level of disturbance, the type of quadrat treatment, and the diversity and abundance of the native recruiting flora over the first 12 months post-cyclone. Our results suggest that invasive species will mostly comprise a transient component of the flora in the early stages of the successional response. However, some species may have longer-term effects on the successional trajectory of the rainforest and future forest composition and structure. [source] Spreadsheet for cyclone and hydrocyclone design considering nonspherical particle geometryCOMPUTER APPLICATIONS IN ENGINEERING EDUCATION, Issue 2 2007Marcelo K. Lenzi Abstract Cyclones and hydrocyclones are widely used for gas,solid and liquid,solid particle separations, respectively. The key feature is the presence of a centrifugal field. Equilibrium zone concept is one of the most used approaches for equipment design. This work revisits the design equations for nonspherical particles and compares design results considering nonspherical geometry to results considering spherical geometry and correcting the values to the non-spherical particle geometry. A didactic spreadsheet was prepared for analysis and instruction, and depending on the particle shape and on the particle orientation, errors up to 38% may be obtained in the cut diameter and 10% in the global collection efficiency. © 2007 Wiley Periodicals, Inc. Comput Appl Eng Educ. 15: 134,142, 2007; Published online in Wiley InterScience (www.interscience.wiley.com); DOI 10.1002/cae.20102 [source] Cyclone disaster vulnerability and response experiences in coastal BangladeshDISASTERS, Issue 4 2010Edris Alam For generations, cyclones and tidal surges have frequently devastated lives and property in coastal and island Bangladesh. This study explores vulnerability to cyclone hazards using first-hand coping recollections from prior to, during and after these events. Qualitative field data suggest that, beyond extreme cyclone forces, localised vulnerability is defined in terms of response processes, infrastructure, socially uneven exposure, settlement development patterns, and livelihoods. Prior to cyclones, religious activities increase and people try to save food and valuable possessions. Those in dispersed settlements who fail to reach cyclone shelters take refuge in thatched-roof houses and big-branch trees. However, women and children are affected more despite the modification of traditional hierarchies during cyclone periods. Instinctive survival strategies and intra-community cooperation improve coping post cyclone. This study recommends that disaster reduction programmes encourage cyclone mitigation while being aware of localised realities, endogenous risk analyses, and coping and adaptation of affected communities (as active survivors rather than helpless victims). [source] ,We All Knew that a Cyclone Was Coming': Disaster Preparedness and the Cyclone of 1999 in Orissa, IndiaDISASTERS, Issue 4 2004Frank Thomalla Imagine that a cyclone is coming, but that those living in the affected areas do nothing or too little to protect themselves. This is precisely what happened in the coastal state of Orissa, India. Individuals and communities living in regions where natural hazards are a part of daily life develop strategies to cope with and adapt to the impacts of extreme events. In October 1999, a cyclone killed 10,000 people according to government statistics, however, the unofficial death toll is much higher. This article examines why such a large loss of life occurred and looks at measures taken since then to initiate comprehensive disaster-preparedness programmes and to construct more cyclone shelters. The role of both governmental organisations and NGOs in this is critically analysed. The good news is that, based on an assessment of disaster preparedness during a small cyclone in November 2002, it can be seen that at community-level awareness was high and that many of the lessons learnt in 1999 were put into practice. Less positive, however, is the finding that at the state level collaboration continues to be problematic. [source] Effects of earthquake and cyclone sequencing on landsliding and fluvial sediment transfer in a mountain catchmentEARTH SURFACE PROCESSES AND LANDFORMS, Issue 9 2008Guan-Wei Lin Abstract Patterns and rates of landsliding and fluvial sediment transfer in mountain catchments are determined by the strength and location of rain storms and earthquakes, and by the sequence in which they occur. To explore this notion, landslides caused by three tropical cyclones and a very large earthquake have been mapped in the Chenyoulan catchment in the Taiwan Central Range, where water and sediment discharges and rock strengths are well known. Prior to the MW 7·6 Chi-Chi earthquake in 1999, storm-driven landslide rates were modest. Landslides occurred primarily low within the landscape in shallow slopes, reworking older colluvial material. The Chi-Chi earthquake caused wide-spread landsliding in the steepest bedrock slopes high within the catchment due to topographic focusing of incoming seismic waves. After the earthquake landslide rates remained elevated, landslide patterns closely tracking the distribution of coseismic landslides. These patterns have not been strongly affected by rock strength. Sediment loads of the Chenyoulan River have been limited by supply from hillslopes. Prior to the Chi-Chi earthquake, the erosion budget was dominated by one exceptionally large flood, with anomalously high sediment concentrations, caused by typhoon Herb in 1996. Sediment concentrations were much higher than normal in intermediate size floods during the first 5 years after the earthquake, giving high sediment yields. In 2005, sediment concentrations had decreased to values prevalent before 1999. The hillslope response to the Chi-Chi earthquake has been much stronger than the five-fold increase of fluvial sediment loads and concentrations, but since the earthquake, hillslope sediment sources have become increasingly disconnected from the channel system, with 90 per cent of landslides not reaching into channels. Downslope advection of landslide debris associated with the Chi-Chi earthquake is driven by the impact of tropical cyclones, but occurs on a time-scale longer than this study. Copyright © 2008 John Wiley & Sons, Ltd. [source] Comparative study of the continuous phase flow in a cyclone separator using different turbulence models,INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 11 2005H. Shalaby Abstract Numerical calculations were carried out at the apex cone and various axial positions of a gas cyclone separator for industrial applications. Two different NS-solvers (a commercial one (CFX 4.4 ANSYS GmbH, Munich, Germany, CFX Solver Documentation, 1998), and a research code (Post-doctoral Thesis, Technical University of Chemnitz, Germany, September, 2002)) based on a pressure correction algorithm of the SIMPLE method have been applied to predict the flow behaviour. The flow was assumed as unsteady, incompressible and isothermal. A k,, turbulence model has been applied first using the commercial code to investigate the gas flow. Due to the nature of cyclone flows, which exhibit highly curved streamlines and anisotropic turbulence, advanced turbulence models such as Reynolds stress model (RSM) and large eddy simulation (LES) have been used as well. The RSM simulation was performed using the commercial package activating the Launder et al.'s (J. Fluid. Mech. 1975; 68(3):537,566) approach, while for the LES calculations the research code has been applied utilizing the Smagorinsky model. It was found that the k,, model cannot predict flow phenomena inside the cyclone properly due to the strong curvature of the streamlines. The RSM results are comparable with LES results in the area of the apex cone plane. However, the application of the LES reveals qualitative agreement with the experimental data, but requires higher computer capacity and longer running times than RSM. This paper is organized into five sections. The first section consists of an introduction and a summary of previous work. Section 2 deals with turbulence modelling including the governing equations and the three turbulence models used. In Section 3, computational parameters are discussed such as computational grids, boundary conditions and the solution algorithm with respect to the use of MISTRAL/PartFlow-3D. In Section 4, prediction profiles of the gas flow at axial and apex cone positions are presented and discussed. Section 5 summarizes and concludes the paper. Copyright © 2005 John Wiley & Sons, Ltd. [source] Interannual and interdecadal variations of tropical cyclone activity in the South China SeaINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 6 2010Andy Zung-Ching Goh Abstract This study attempts to identify the factors affecting annual tropical cyclone (TC) activity in the South China Sea (SCS) using data during the period 1965,2005. The results indicate that the total number of TCs and number of TCs entering the SCS from the Western North Pacific are below normal in El Niño events but above normal during La Niña events. However, for TCs formed inside the SCS, the difference in numbers between the two phases of the El Niño-Southern Oscillation (ENSO) is not as obvious. In addition, the positive phase of the Pacific Decadal Oscillation (PDO) generally favours less TCs in all categories, while the negative PDO phase favours more. These results may be explained by the fact that the ENSO and the PDO affect TC behaviour through altering the conditions in the WNP to be favourable or unfavourable for TC genesis and movement into the SCS. Copyright © 2009 Royal Meteorological Society [source] Southern hemisphere cyclones and anticyclones: recent trends and links with decadal variability in the Pacific OceanINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 11 2007Dr Alexandre Bernardes Pezza Abstract The aim of this paper is to study the association between the extratropical Southern Hemisphere and the decadal variability in the Pacific Ocean (PO). We discuss a pattern of coherent large-scale anomalies and trends in cyclone and anticyclone behaviour in light of the climate variability in the PO over the ERA40 reanalysis period (1957,2002). The two representative PO indices are the Pacific Decadal and Interdecadal Oscillations (PDO and IPO), and here the PDO is chosen owing to it being less associated with the southern oscillation index (SOI). Composites of the indicators of the density and intensity of cyclones/anticyclones given by an automatic tracking scheme were calculated for the years when the PDOI was more than one standard deviation above or below its mean. Although the ERA40 is not free from noise and assimilation changes, the results show a large-scale feature, which seems to be robust and agrees with earlier studies using different data sets. The sea-level pressure shows a strong annular structure related to the PDO, which is not seen for the SOI, with lower pressure around Antarctica during the positive phase and vice versa. More intense (and fewer) cyclones and anticyclones were observed during the positive PDO. This is less consistent for the SOI, particularly during the summer when a different PDO/SOI pattern arises at high latitudes. The trends project a pattern coincident with the positive PDO phase and seem to be linked with the main climate shift in the late seventies. Trends observed over the Tasman Sea are consistent with declining winter rainfall over southeastern Australia. Most patterns are statistically significant and seem robust, but random changes in ENSO may play a part, to a certain degree, in modulating the results, and a physical mechanism of causality has not been demonstrated. Although global warming and related changes in the Southern Annular Mode (SAM) may also help explain the observed behaviour, the large-scale response presented here provides a new insight and would be of considerable interest for further modelling studies. Copyright © 2007 Royal Meteorological Society [source] Preliminary climatology and improved modelling of south Indian Ocean and Southern Ocean mid-latitude cyclonesINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 10 2004Bruce W. Buckley Abstract The intense mid-latitude cyclones that traverse the southern waters of the Indian Ocean, between South Africa and southwestern Western Australia, are among the strongest depressions found anywhere in the world, outside tropical waters. Near-surface winds that exceed storm force (i.e. 24 m/s or 48 knots), and central pressures of 960 hPa and lower, are relatively common for these systems. They pose a constant threat to both open ocean and coastal shipping, and regularly generate severe weather over the populated southwestern corner of Australia. Large ocean waves and swell produce extensive coastal inundation and erosion. There were two main aims in this study. The first aim was to develop a preliminary climatology of these intense mid-latitude cyclones, for the region 20,60 °S, 30,130 °E. The climatology, which is the first that we are aware of for this notoriously data-sparse region, is based largely upon satellite observations, particularly scatterometer data, and is supplemented by ship, buoy and all available land observations. The climatology revealed that, historically, the frequency and intensity of the mid-latitude cyclones in this domain have been significantly underestimated. This underestimation has resulted in analyses that have serious flaws, and the resultant operational forecasts provided to the duty forecasters in the regional forecast centre located in Perth, Western Australia, are of highly variable quality. A number of other climatological features of these storms are discussed in this article. The second aim was to identify the factors that can contribute to a significant improvement in model forecasts of these storms. So far, there have been very few studies of explosively developing cyclones over this part of the world. Results are presented here from a series of high-resolution numerical simulations of an intense cool season Southern Ocean cyclone that developed in 2003, using the HIRES numerical weather prediction model developed by L.M. Leslie. Here, we examine the sensitivity of the cyclone predictions to both model resolution and the initial analyses. The predicted variables of most interest are the central pressure, maximum sustained near-surface wind speeds, extent of storm-force winds, and the horizontal and vertical structure of the storm. Increased detail in the initial state is provided mainly by the assimilation into the archived global operational analyses of high-resolution satellite-derived data, including QuikSCAT scatterometer winds and sea-surface temperatures. The combination of increased horizontal and vertical model resolution, and improved initial model states, was found to produce numerical forecasts with significantly more accurate wind speeds than those obtained from the coarser resolution operational models, which also did not have the benefits of all the additional data. Finally, areas of future research are outlined, including coupling the HIRES atmospheric model with ocean and wave models, to improve forecasts of the sea state, including wind wave heights, swell and storm surges. Copyright © 2004 Royal Meteorological Society [source] Effects of a tropical cyclone on the distribution of hatchery-reared black-spot tuskfish Choerodon schoenleinii determined by acoustic telemetryJOURNAL OF FISH BIOLOGY, Issue 3 2010Y. Kawabata The effects of a tropical cyclone on the distribution of hatchery-reared black-spot tuskfish Choerodon schoenleinii were examined using acoustic telemetry. Nine fish were released in Urasoko Bay, Ishigaki Island, Japan, in September 2006, and another nine were released in June to July 2007, before a cyclone's passing through the area in September 2007. Data for the fish released in 2006 were used as the cyclone-inexperienced group to compare their distribution pattern to that of the 2007 cyclone-experienced group. Both groups of fish were monitored for up to 150 days. Of the nine fish in each group, four (44%) and two (22%) were monitored for over 150 days in the cyclone-inexperienced and the cyclone-experienced groups, respectively. Three of the five fish that had settled in the monitoring area left the area within a few days of the cyclone event. To estimate the time of disappearance of the fish, maximum wind speed during a period of 7 days (indicating the occurrence and intensity of the tropical cyclone), fish size and release year were evaluated as explanatory variables using a Cox proportional hazards model with Akaike's information criterion. The best predictive model included the effect of maximum wind speed. One fish that left the monitoring area displayed movement patterns related to strong winds, suggesting that wind-associated strong currents swept the fish away. No relationships were found between the movement patterns of the other two fish and any physical environmental data. The daily detection periods of one of the two fish gradually decreased after the cyclone hit, and this fish eventually left the monitoring area within 3 days, suggesting that it shifted to a habitat outside the monitoring area. These results indicate that tropical cyclones have both direct and indirect effects on the distribution of hatchery-reared C. schoenleinii. [source] Computational investigation of the mechanisms of particle separation and "fish-hook" phenomenon in hydrocyclonesAICHE JOURNAL, Issue 7 2010B. Wang Abstract The motion of solid particles and the "fish-hook" phenomenon in an industrial classifying hydrocyclone of body diameter 355 mm is studied by a computational fluid dynamics model. In the model, the turbulent flow of gas and liquid is modeled using the Reynolds Stress Model, and the interface between the liquid and air core is modeled using the volume of fluid multiphase model. The outcomes are then applied in the simulation of particle flow described by the stochastic Lagrangian model. The results are analyzed in terms of velocity and force field in the cyclone. It is shown that the pressure gradient force plays an important role in particle separation, and it balances the centrifugal force on particles in the radial direction in hydrocyclones. As particle size decreases, the effect of drag force whose direction varies increases sharply. As a result, particles have an apparent fluctuating velocity. Some particles pass the locus of zero vertical velocity (LZVV) and join the upward flow and have a certain moving orbit. The moving orbit of particles in the upward flow becomes wider as their size decreases. When the size is below a critical value, the moving orbit is even beyond the LZVV. Some fine particles would recircuit between the downward and upward flows, resulting in a relatively high separation efficiency and the "fish-hook" effect. Numerical experiments were also extended to study the effects of cyclone size and liquid viscosity. The results suggest that the mechanisms identified are valid, although they are quantitatively different. © 2009 American Institute of Chemical Engineers AIChE J, 2010 [source] Integration of methanation into the hydrogenation process of benzoic acidAICHE JOURNAL, Issue 1 2009Baoning Zong Abstract The traditional industrial process for hydrogenation of benzoic acid to cyclohexanecarboxylic acid (CCA) has drawbacks of low-activity and fast deactivation of the Pd/C catalyst due to the poisoning of CO arising from the decarboxylation of CCA. A novel rapidly quenched skeletal NiCrFe promoter (RQ NiCrFe) is developed for the methanation of CO to harmless CH4. Evaluations in bench-scale autoclave and in traditional industrial equipment verified that RQ NiCrFe was very effective in promoting the activity of the Pd/C catalyst in the hydrogenation of benzoic acid. In order to solve the catalyst recycle and separation problem introduced by RQ NiCrFe, the industrial process was modified by incorporating a hydraulic cyclone and a magnetic separator to the separation unit. The modified process showed merits of lower costs of catalyst and operation, higher productivity, and better product purity than the traditional process. © 2008 American Institute of Chemical Engineers AIChE J, 2009 [source] Erosion-corrosion of laser and thermally deposited coatings exposed in fluidised bed combustion plantsMATERIALS AND CORROSION/WERKSTOFFE UND KORROSION, Issue 4 2006A. Hjörnhede Abstract Coated low alloyed steel tubes were exposed in two combustion power plants of the type Circulating Fluidised Bed (CFB) and Pressurised Fluidised Bed Combustion (PFBC). The power plants were fired with wood chips and coal with a small addition of olive seeds, respectively. In addition to laser coating two thermal spray techniques were used; arc-spray (air as carrier gas) and High Velocity Oxy Fuel (HVOF). The sample locations in the PFBC plant were at the highest and lowest loops of a platen immersed in the fluidising bed. The material temperatures in each loop were 450 °C and 400 °C, respectively. The exposure lasted over two firing seasons for a total time of 8089 h. In the CFB plant a probe was located at the cyclone entrance where the material temperature was 630 °C for an exposure time of about 2100 h before being reduced to 480 °C for a further 920 h. The material wastage was determined from metallographic studies on cross-sections of rings cut from the exposed tubes. The nature and chemical composition of the corrosion products and deposits formed were determined by SEM/EDX, Auger spectroscopy, XPS and XRD. Cobalt based coatings show the best performance in both the PFBC plant and the CFB plant, while nickel based coatings are resistant to a corrosive atmosphere but very sensitive to erosion. The degree of corrosion is much larger in the CFB plant as is clearly seen from the chromium carbide containing coating, which totally degraded in this environment. Contrary the performance of the same coating was excellent in the fluidised bed due to its high erosion resistance. The material wastage of a coating with a specific composition is independent of the deposition method. No significant differences in spallation behaviour occurred among coatings deposited with the different techniques. [source] Development of a new high-efficiency simple structure cycloneTHE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 3 2009Z. Tan Abstract A novel uniflow cyclone design was evaluated using three prototype cyclones. For the first two, the efficiency and Euler number were determined using airborne solid particles with a number mean diameter of 12.5 µm. Then a larger scale prototype based on the optimized geometry was compared with an existing conventional high efficiency cyclone and a vane-induced uniflow cyclone, using mineral oil droplets with a number mean diameter of 8.9 µm. Both sets of experiments showed that the newly designed cyclone had a higher efficiency at a higher pressure requirement, in addition to the feature of a small footprint. Un nouveau modèle de cyclone uniflow a été évalué à l'aide de trois cyclones prototypes. Pour les deux premiers cyclones, l'efficacité et la perte de charge ont été déterminées avec des particules solides transportées par le gaz de diamètre moyen en nombre de 12,5 micromètres. Puis un prototype à plus grande échelle basé sur la géométrie optimisée a été comparé à un cyclone conventionnel existant à haute efficacité et à un cyclone uniflow à ailettes, en utilisant des gouttelettes d'huile minérale d'un diamètre moyen en nombre de 8,9 micromètres. Les deux séries d'expériences montrent que le nouveau modèle de cyclone a une plus grande efficacité ou une demande de pression moins grande, en plus d'être plus compact. [source] Modélisation de l'efficacité de filtration d'un échangeur cycloneTHE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 2 2003Richard Caetano Abstract This work is a modelling of the Aireco® filtration system. This heat exchanger, with particle catching capabilities, is made of a cyclonic body which contains refrigerated coils. The water vapour contained in the gas to be treated condensed on the coils surface. Our modelling considers two main capture surfaces: the entry zone in which particles are collected by inertial impaction and the cyclonic body in which particles diffused by centrifugal force is the main phenomena. We found that these considerations explain our experimental results with an accuracy more than 90%, when the Aireco® is on a normal point of working. Ce travail consiste à modéliser l'efficacité de filtration du système d'épuration Aireco®. Cet échangeur épurateur se compose d'un corps cyclonique et de nappes de serpentins réfrigérés provoquant la condensation de la vapeur d'eau contenue dans le gaz pollué traité. Dans ce modèle nous modélisons l'échangeur en considérant les zones de piégeage prépondérantes que sont l'entrée et le corps cyclonique. Notre modèle prend en compte les effets d'impaction inertielle en entrée et la centrifugation dans le corps du système. Cette démarche théorique corrobore à plus de 95 % les valeurs obtenues expérimentalement lorsque l'Aireco® fonctionne dans ses conditions nominales. [source] Collection efficiencies of various designs of post-cycloneTHE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 5 2001Wennan Zhao Abstract Post-cyclone (PoC) is a novel secondary dust separator, which collects a certain fraction of the particles escaping through the vortex finder of a reverse flow cyclone. Due to the residual swirl in the vortex finder, the particles in the effluent air are concentrated at the wall of the vortex finder in an outer annulus. The particles in the outer annulus are split from the main stream and collected in a bleed flow. This paper presents the experimentally determined collection efficiencies of various designs of PoC. Depending on the design, operating conditions and the size and density of the particles, PoC can reduce the emission of the parent cyclones by 5% to 50%. In some experiments, the bleed flow from PoC is recycled back to the inlet of the cyclone. Significant improvement in the removal of fines occurs when the bleed flow is recycled to the inlet. Le post-cyclone (PoC) est un nouveau séparateur de poussières secondaire, qui récupère une partie des particules s'échappant du dispositif de capture du vortex d'un cyclone à écoulement inverse. À cause du tourbillon résiduel présent dans ce dispositif, les particules dans l'air de l'effluent sont concentrees à la paroi du dispositif dans un espace annulaire extérieur. Les particules dans l'espace annulaire extérieur sont séparées du courant principal et récupérées dans un écoulement de purge. On présente dans cet article les rendements de récupération déterminées expérimentalement pour diverses conceptions de PoC. Selon la conception, les conditions opératoires ainsi que la taille et la rnasse volumique des particules, le PoC peut réduire l'émission des cyclones parents de 5% à 50%. Dans certaines expériences, l'écoulement de purge venant d'un PoC est recyclé de nouveau vers l'entrée du cyclone. Une amélioration significative est obtenue dans le retrait des fines lorsque l'écoulernent de purge est recyclé vers l'entrée. [source] Barotropic instability in the tropical cyclone outer regionTHE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 641 2009Jiayi Peng Abstract The growth of asymmetric perturbations and their interactions with the symmetric flow are investigated for wind profiles in a tropical cyclone with instability in its outer region. Three tangential wind profiles are examined: TC1, a strong barotropic instability profile in the outer region; TC2, a stable wind profile; and TC3, a weaker instability profile comparing to TC1 with a larger distance between the inner negative and the outer positive vorticity gradient centres. An eigenvalue analysis indicates that azimuthal wave-number two is the most unstable mode in both TC1 and TC3, with an e-folding time-scale of about 1 and 9 days, respectively. Numerical simulations using a linear barotropic model, with an initial asymmetry specified in the outer region, confirm the eigenvalue analysis. A mechanism is provided to explain the difference between simulations in TC1 and TC2. In both the stable and unstable case, an inner asymmetry is induced by the initial outer asymmetry acting on the symmetric vorticity gradient. Subsequently, the newly generated inner asymmetry feeds back positively to the outer asymmetry with the unstable profile. Because of this positive feedback, the inner and the outer asymmetries maintain an up-shear phase tilting, leading to a continuous energy transfer from the symmetric flow to the asymmetric perturbation. In the stable TC2, the inner asymmetry could not amplify the outer initial asymmetry as there is no basic-state radial vorticity gradient there. Also due to this feedback process, disturbances grow faster where the (absolute) basic-state vorticity gradients are large. Therefore, the position of an initial disturbance plays a minor role in determining the outcome of the system. Simulations with a nonlinear barotropic model and a primitive equation model further confirm the significant weakening of the maximum tangential wind due to the positive feedback process in TC1. Simulations for TC3 show a smaller change of the symmetric tangential wind, as expected. Copyright © 2009 Royal Meteorological Society [source] Sources of water vapour contributing to the Elbe flood in August 2002,A tagging study in a mesoscale modelTHE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 638 2009H. Sodemann Abstract In this study we investigate the contribution of various moisture sources to the Elbe flood that occurred in Central Europe during August 2002. An 8-day simulation with the mesoscale numerical weather prediction model CHRM, including newly implemented water vapour tracers, has been performed. According to the simulation, rather than drawing moisture from one single dominant source region, water vapour from widely separated moisture sources contributed to the extreme precipitation in the most affected area, notably at distinct, subsequent periods of time, and each in significant amounts. These moisture sources include the Atlantic and Mediterranean ocean areas inside the model domain, evapotranspiration from land areas, and long-range advection from subtropical areas outside the model domain. The results highlight the importance of the concurrent upper-level circulation and the mesoscale flow structures associated with the cyclone for producing extreme precipitation in parts of Germany, Austria, and the Czech Republic during that period. Furthermore, the numerical and technical problems of implementing water vapour tracers into a limited-area model are discussed, including conservative tracer advection, initialization, boundary treatment, and the handling of precipitation parametrizations. An evaluation of the consistency of the method in terms of water vapour, cloud water, and precipitation is provided, with generally satisfying results. The model with its detailed water vapour tracer implementation can now be used for further case-studies and climatological simulations, and serve as a reference for evaluating the performance of other moisture tracking methods, such as those based on backward trajectories. Copyright © 2009 Royal Meteorological Society [source] A note on boundary-layer friction in baroclinic cyclonesTHE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 629 2007I. A. Boutle Abstract The interaction between extratropical cyclones and the underlying boundary layer has been a topic of recent discussion in papers by Adamson et al. (2006) and Beare (2007). Their results emphasize different mechanisms through which the boundary-layer dynamics may modify the growth of a baroclinic cyclone. By using different sea-surface temperature distributions and comparing the low-level winds, the differences are exposed and both of the proposed mechanisms appear to be acting within a single simulation. Copyright © 2007 Royal Meteorological Society [source] Baroclinic development within zonally-varying flowsTHE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 626 2007David M. Schultz Abstract Previous idealized-modelling studies have shown the importance of across-jet barotropic shear to the resulting evolution of cyclones, anticyclones, surface-based fronts, and upper-level fronts. Meanwhile, many observational studies of cyclones have shown the importance of along-jet variations in the horizontal wind speed (i.e. confluence and diffluence). This study investigates the importance of these along-jet (zonal, for zonally-oriented jets) variations in the horizontal wind speed to the resulting structures and evolutions of baroclinic waves, using idealized models of growing baroclinic waves. An idealized primitive-equation channel model is configured with growing baroclinic perturbations embedded within confluent and diffluent background flows. When the baroclinic perturbations are placed in background confluence, the lower-tropospheric frontal structure and evolution initially resemble the Shapiro,Keyser cyclone model, with a zonally-oriented cyclone, strong warm front, and bent-back warm front. Later, as the baroclinic wave is amplified in the stronger downstream baroclinicity, the warm sector of the cyclone narrows, becoming more reminiscent of the Norwegian cyclone model. The upper-level frontal structure develops with a southwest,northeast orientation, and becomes strongest at the base of the trough, where geostrophic cold advection is occurring. In contrast, when the baroclinic perturbations are placed in background diffluence, the lower-tropospheric frontal structure and evolution resemble the Norwegian cyclone model, with a meridionally-oriented cyclone, strong cold front, and occluded front. The upper-level frontal structure is initially oriented northwest,southeast on the western side of the trough, before becoming zonally oriented. Weak geostrophic temperature advection occurs along its length. These results are compared to those from previous observational and idealized-modelling studies. Copyright © 2007 Royal Meteorological Society [source] Boundary layer mechanisms in extratropical cyclonesTHE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 623 2007Robert J. Beare Abstract This paper revisits the mechanism for the interaction of the boundary layer with extratropical cyclones. Two diagnostic approaches are compared: Ekman pumping and potential vorticity. Ekman pumping derives from the boundary layer stress which induces convergence and ascent. boundary layer potential vorticity contains in a single quantity both the vorticity and stratification. These quantities are compared for an idealized extratropical cyclone life cycle simulated with the Met Office Unified Model. A significant component of the boundary layer stress and thus Ekman pumping at occlusion is forced by the cold conveyor-belt jet in the unstable boundary layer. In contrast, much of the boundary layer depth-averaged potential vorticity is contained within the stable warm-sector region. Inversion of the warm-sector PV indicates a small local deepening of about 2.5 hPa. Moreover, switching off the boundary layer mixing in the unstable cold sector has much more impact than in the stable warm sector. The sensitivity of the cyclone and its boundary layer to basic-state jet strength is then investigated. The maximum friction velocity scales closely with the initial maximum jet strength. This demonstrates the important role of the large-scale flow in organizing the boundary layer structure. Changes in the minimum pressure produced by altering the boundary layer parametrization correspond closely to changes in the surface stress averaged over the cyclone. Different operational changes to the boundary layer scheme produce small and compensating changes to the cyclone minimum pressure over three days. © Crown Copyright 2007. Reproduced with the permission of the Controller of HMSO. Published by John Wiley & Sons, Ltd [source] The extratropical transition of hurricane Irene (1999): A potential-vorticity perspectiveTHE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 598 2004A. Agusti-panareda Abstract Extratropical transition (ET) of tropical cyclones is common in all ocean basins where tropical cyclones recurve polewards. After the tropical cyclone experiences ET, a rapid deepening can take place resulting in the development of a very large and deep extratropical cyclone. The ET of hurricane Irene (1999) was an example of such an ,explosive' ET. Irene formed in the Caribbean and experienced ET as it moved poleward, resulting in a low-pressure system which deepened 39 hPa in 24 hours (according to the Met Office analyses). The extent to which the hurricane was responsible for the explosive extratropical development has been determined by performing Met Office Unified Model forecasts from initial states with and without the hurricane. The circulation and temperature anomalies associated with the hurricane were removed from the initial state using potential-vorticity inversion. The moisture anomaly co-located with the hurricane core was also removed. The results show that an extratropical cyclogenesis event takes place regardless of the presence of the hurricane in the initial conditions. However, the hurricane makes a significant difference to the track and central mean-sea-level pressure evolution of the resulting extratropical cyclone. When Irene was present the track of the extratropical cyclone was more zonal and the cyclone deepening rate was twice as fast as when Irene was not present. These effects appear to be particularly associated with a negative potential-vorticity anomaly and enhanced divergent flow in the region of the upper-level outflow of the transforming hurricane rather than with the hurricane vortex. Results also show that the presence of the hurricane resulted in a significant downstream surface-low development in the eastern Atlantic. Copyright © 2004 Royal Meteorological Society. [source] The sting at the end of the tail: Damaging winds associated with extratropical cyclonesTHE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 597 2004K. A. Browning Abstract Strong surface winds often accompany the low-level jets that occur along the cold fronts of extratropical cyclones, but there is evidence that the strongest surface winds occur in a distinctly different part of a certain class of cyclone. The most damaging extratropical cyclones go through an evolution that involves the formation of a bent-back front and cloud head separated from the main polar-front cloud band by a dry slot. When the cyclone attains its minimum central pressure, the trailing tip of the cloud head bounding the bent-back front forms a hook which goes on to encircle a seclusion of warm air. The most damaging winds occur near the tip of this hook,the sting at the end of the tail. Observations of the Great Storm of October 1987 in south-east England are re-examined in some detail to study this phenomenon. The cloud head is shown to have a banded structure consistent with the existence of multiple mesoscale slantwise circulations. Air within these circulations leaves the hooked tip of the cloud head (and enters the dry slot) much faster than the rate of travel of the cloud-head tip, implying rapid evaporation and diabatic cooling immediately upwind of the area of damaging surface winds. The circumstantial evidence from the observational study leads one to hypothesize that the mesoscale circulations and the associated evaporative heat sinks may play an active role in strengthening the damaging winds. Regardless of how important this role may be, the evolution of the cloud pattern seen in satellite imagery is a useful tool for nowcasting the occurrence and location of the worst winds. Copyright © 2004 Royal Meteorological Society [source] Three-dimensional simulation of the ASTEX Lagrangian 1 field experiment with a regional numerical weather prediction modelTHE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 597 2004Robert Sigg Abstract The Atlantic Stratocumulus Transition Experiment (ASTEX) first Lagrangian experiment (Lagrangian 1) is here simulated with a modified version of the regional forecast model HIRLAM (High Resolution Limited Area Model). The main modification is that moist turbulent fluxes are accounted for in the model. Trajectory calculations show good agreement with earlier estimations. The initially rather shallow stratocumulus topped marine boundary layer is deepening along the trajectory, and in the end cumulus clouds are formed that penetrate the boundary-layer top. The model predicts this change in cloudiness, but the boundary layer is too shallow in the model. A simulation with modified initial conditions shows improved results, but is still too slow in increasing the boundary-layer depth. Additional factors that influence the boundary-layer growth are: the increase in sea surface temperatures, lower modelled wind speeds, low entrainment rates due to coarse vertical resolution, and synoptic-scale subsidence. An anticyclone at the surface moved slightly northward during the simulation. The anticyclone was accompanied at 500 hPa by a deepening cyclone and, therefore, one would expect synoptic subsidence in the area of the Lagrangian 1. The modelled negative vertical wind component at the boundary-layer top oscillates, and this is examined using spectral analysis. The results show that the vertical velocity is influenced by cumulus clouds on time-scales up to 15 h with a peak at 9 h. The horizontal and vertical wavelengths of the vertical velocity disturbances are estimated from model output to be 400,500 km and 6,10 km, respectively. Using the estimated vertical wavelength and linear theory for hydrostatic inertia,gravity waves, a horizontal wavelength of 350,550 km was calculated for a frequency of 9 h. The model results thus indicate that these types of waves are responsible for the undulating vertical velocity. Finally, an estimation of the synoptic-scale vertical velocity is calculated by filtering out all scales smaller than 15 h from the vertical velocity signal. This results in subsidence both at the beginning and the end of the Lagrangian with vertical velocities between ,0.1 and ,0.4 cm s,1. Copyright © 2004 Royal Meteorological Society [source] Experimental study on gasification characteristics and slagging behavior of Chinese typical high ash fusion temperature coal in lab scale downflow gasifierASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 3 2010Xiaojiang Wu Abstract In order to extend the applicability of entrained flow gasification technology by using Chinese high ash fusion temperature (AFT) coal with dry ash extraction, gasification characteristics and slagging behavior of Chinese high AFT coal were studied in a lab scale downflow gasifier. The results showed that under this experimental condition, the optimum temperature window which is suitable for dry ash extraction with high AFT coal ranges from 1573 to 1623 K, as well as the corresponding optimum O2/coal mass ratio ranges from 0.93 to 1.13. The cold gas efficiency and carbon conversion are around 42 and 90%, respectively in this experiment. The slag on the bottom of the gasifier and in the cyclone existed, on the whole, as solid except that some small parts were melted with several micrometers in diameter, while the slag in the bag filter had remained unmelted when continue operating at an optimum condition for 1.5 h. Due to the small percentage of melted parts in the slag, the tendency of plugging is small and the problems of plugging can be avoided at the exit of gasifier by gasifying Chinese high AFT coal at around 1623 K. Copyright © 2009 Curtin University of Technology and John Wiley & Sons, Ltd. [source] | |||||||||||||||||||||||||