Cyclone Type Research Articles

CFD-DEM simulation and optimization of gas-cyclone performance with realistic macroscopic particulate matter

Most of research concerns have been focused on developing new methods and parameters to make the cyclone separator performance better. In this work, the inverse-flow cyclone type geometry was performed and optimized through the modulation of changing the position and dimensions of the involute inlet portion and cyclone barrel section length at a fixed inlet air velocity of 30 ms−1. Cyclones of different inlet sizes and portions were computationally modeled which named as cyclones I, II, III, IV, and V. The study was successfully accomplished for two heterogeneous groups of particulate matter mixed with air flow for applications pertinent to agricultural engineering. To capture the phenomena of constitutive air-granular materials behavior in the optimized separator, numerical simulations were generated using one-way coupling of commercial ANSYS-Fluent® 18.0 (CFD) and Rocky® 4.13 (DEM) software, which is considered as the first head start research approach in the cyclonic separation and purification field. Discrete Element Method (DEM) which was represented by Rocky® package simulates the movement of each particle individually, taking into consideration the interaction and collision of the particles. Whereas, the highly curved streamlines and the chaotic turbulence of the continuum air flow in the cyclone separator were modeled through the Computational Fluid Dynamics (CFD-Fluent®) technique using advanced turbulence model RNG k-ε. The numerical results successfully captured the effects of new geometrical modifications done on the original cyclone separator. Numerically, the cyclone inlet height significantly improved the cyclone performance by increasing the separation efficiency, cleaning efficiency, and cyclone effectiveness, while other parameters had a negative effect. These data were useful for considering cyclone (III) as the most suitable modification and optimization design geometry for harvesting jojoba seeds with the lowest operation cost and highest performance.

Improvement of the calculation method of cyclone dust collectors

The object of research is a method for calculating the efficiency of cyclones using the magnitude of the velocity of transverse pulsations of a turbulent gas flow in the inlet of the cyclone. One of the most problematic issues when creating a new cyclonic technique for gas dust cleaning is the need to carry out a fairly large amount of work – modeling cyclones in laboratory conditions on model cyclones, taking into account the large-scale transition, etc. Therefore, the development of the most accurate analytical method for calculating the efficiency of cyclones is an important problem since it makes it possible to quickly and accurately determine all the necessary cyclone parameters for specific production conditions.During the study, patterns of dust particle deposition in the approximation of the «diffusion boundary layer» were used, which made it possible to calculate with high accuracy the efficiency of cleaning industrial dust in cyclones of various designs. At the same time, the time and the amount of experimental work are also significantly reduced in the development of new types of cyclones or in their modernization or selection.The most accurate dependencies are obtained for evaluating the most important parameters of dust cleaning efficiency in various cyclones. This is due to the fact that the method for calculating cyclones proposed in the work has a number of features, in particular, the development of new dependences for calculating the cut-off diameter «dh=50», the inertial capture coefficient of dust particles «E», and others. It is also proposed to use the average cross section the inlet pipe of the cyclone of the velocity of transverse pulsations of the turbulent gas flow and the new interpolation dependence of the coefficient of inertial capture of dust particles «E» at the potential flow regime in the inlet pipe of the cyclone x machines. Thanks to this, it is possible to obtain accurate values of the indicators of cleaning efficiency in cyclones of various design parameters. Compared with similar well-known calculation methods, this provides such advantages as accuracy of calculations, speed of execution and reliability of the results.

Climatology and change of extreme precipitation events in Taiwan based on weather types

AbstractTaiwan's most significant natural hazards are caused by hydrological extremes resulting from excessive precipitation. The threat of extreme precipitation is posed by several different types of weather patterns that affect Taiwan. This study examined the bi‐decadal changes in rainfall by defining an extreme precipitation occurrence (EPO) for a range of event durations from 1 to 24 hr. Three major weather types affecting EPO in Taiwan were identified from 1993 to 2015: the front type consisting of either a frontal zone or convective systems developing with an apparent Meiyu cloudband, diurnal rainfall events when no apparent synoptic features are present, and a tropical cyclone (TC) type according to the maximum sustained wind radius of a TC. Results show that TC‐type events have the greatest overall contribution to EPO at longer (>6 hr) durations. Diurnal/afternoon convection events contribute most to the shorter (<3 hr) duration EPO, while frontal/Meiyu systems prevail in the medium (3–6 hr) duration. EPO of almost all durations have experienced an increase, with the 3‐ and 12‐hr EPO having increased by 4.6 days each over the 23 years. However, apparent decadal‐scale variability exists in these EPO associated with the decreasing tendency of EPO after the mid‐2000s, particularly the longer duration (>6 hr) EPO associated with the TC‐type events in summer. The distinction between EPO trends for the entire island of Taiwan and for the Taipei metropolitan area alone (northern Taiwan, population of 7 million) were compared, and an intriguing interannual variation is reported in the TC‐type EPO associated with the TC season 1 year to a year and half just before an El Niño–Southern Oscillation event. The analysis here provides refined statistical distributions of extreme rainfall, and these can contribute to the revision of governmental definitions for weather disasters that are used in mitigation and response strategies.

Separation performance of new type of multi-stage axial cyclone used as demister in power plant emission system

This paper presents an investigation of the performance of a multi-stage axial flow cyclone used as a demister in power plants to reduce pollution emissions. Four axial cyclones with different structural parameters were studied by numerical simulation and verification experiments. A numerical model of a two-phase flow in the cyclone separator was established and the separation efficiency and pressure loss of cyclone separators were simulated by employing the Reynolds stress model (RSM) for turbulence modeling. A test rig was constructed and the diameter distributions of droplets at the inlet and outlet of the separator were measured by a Malvern laser particle size analyzer to verify the simulation model. The results indicated that a multi-stage swirler can improve the tangential velocity to strengthen the gas swirling in the cyclone body effectively, thereby improving the separation efficiency of the cyclone. The effects of the multi-stage swirler on the flow field were analyzed, for a better understanding of the mechanisms of the flow field in the separation region for improved performance. The tangential velocities of cyclones Sep-C and Sep-B were found to be 1.5 to 2 times higher than that of the single-stage cyclone Sep-O, although the separation efficiency of Sep-C was reduced significantly when the velocity was greater than 7.9 m/s. Based on the results of this study, cyclone Sep-B was considered to be the best performing axial-flow cyclone within the acceptable pressure drop range and was proposed as a demister in power plant.

Parameter Sweep Experiments on a Spectrum of Cyclones with Diabatic and Baroclinic Processes

Abstract A wide range of environments that prevail over the globe generate various types of cyclones such as tropical, extratropical, and hybrid cyclones. In this paper, idealized numerical experiments are used to explore a spectrum of cyclones ranging from the diabatic type to the baroclinic type in a parameter space consisting of three environmental factors: temperature, vertical shear, and planetary vorticity. The experiments reproduce not only typical dynamics of tropical and extratropical cyclones but also their modified dynamics, which are consistent with theoretical studies; tropical cyclones are suppressed by vertical shear, while extratropical cyclones are intensified by condensational heating. The experiments also reproduce hybrid cyclones in environments with high temperature and large baroclinicity. The hybrid cyclones show multiscale dynamics in which synoptic-scale baroclinic systems spawn smaller-scale tropical cyclone–like convective cores. The spectrum of cyclones is found to be nonmonotonic in the parameter space because of a two-sided effect of the vertical shear: moderate shear weakens a tropical cyclone by tilting the small-scale vortex to the downshear, while strong shear develops a large-scale vortex of an extratropical cyclone or a hybrid cyclone through warm-air advection from the south. The indices based on the energetics and the symmetric and asymmetric structures overview the different types of cyclones in the parameter space. These parameter sweep experiments provide useful information on what environment is favorable for cyclones, particularly for intermediate environments where cyclone mechanisms are yet to be fully defined.

A Comparative Study on the Effect of Upstream Trough on Intensity Changes of Two Types of Tropical Cyclones during Extratropical Transition

Based on the China Meteorological Administration (CMA) tropical cyclone (TC) database and the reanalysis data from the European Centre for Medium-Range Weather Forecasts (ECMWF), the post-transition intensifying tropical cyclones (ITC) and weakening tropical cyclones (WTC) which landed in China and underwent extratropical transition (ET) are discussed in this paper. The TCs with upper-level trough are selected in order to identify different effects of the trough on the ITC and the WTC. The dynamic composite analysis is applied to explore their structure characteristics, environment fields and dynamic diagnosis. Results show that affected by the South Asia high and the subtropical high, the trough of ITC (WTC) extends from northwest to southeast (northeast to southwest) in the ET process. Thus, the zonal wind shear of ITC drops off after ET due to the approach of trough and its northwest-southeast direction, while the zonal and total wind shears of WTC continue to increase because of the steering westerly flow at the upper level. In terms of the ITC, the cold air carried by the upper-level trough intrudes into TC inner area and mostly encircles the TC center, making the ITC characterized by a warm seclusion. While for the WTC, the cold air only wanders on the northwest side of TC without further intrusion. The upper-level divergence is also in favor of the ITC by the pumping influence. According to the diagnostic analysis of moist potential vorticity, the moist baroclinity can lead to changes in vertical vorticity to some extent. The vertical vorticity budget analysis further indicates that there is stronger and wider positive vorticity advection in the upper troposphere near the TC center for ITC. The contribution of the baroclinic term to the growth of vertical vorticity is more significant in ITC than WTC but it is also deeply influenced by the strength of upper-level trough.

Egy automata és egy empirikus légcirkulációs osztályozási rendszer összehasonlító elemzése a kárpát-medencére

The aim of the study is to compare the performance of the two classification methods, based on the atmospheric circulation types over the Pannonian basin in Central Europe. Moreover, relationships including seasonal occurrences and correlation coefficients, as well as comparative diagrams of the seasonal occurrences of the circulation types of the two classification systems are presented. When comparing of the automated (objective) and empirical (subjective) classification methods, it was found that the frequency of the empirical anticyclonic (cyclonic) types is much higher (lower) than that of the automated anticyclonic (cyclonic) types both on an annual and seasonal basis. The highest and statistically significant correlations between the circulation types of the two classification systems, as well as those between the cumulated seasonal anticyclonic and cyclonic types occur in winter for both classifications, since the weather-influencing effect of the atmospheric circulation in this season is the most prevalent. Precipitation amounts in Budapest display a decreasing trend in accordance with the decrease in the occurrence of the automated cyclonic types. In contrast, the occurrence of the empirical cyclonic types displays an increasing trend. There occur types in a given classification that are usually accompanied by high ratios of certain types in the other classification.

Charging effect on separation performance of outer vortex type cyclone for submicron particles at different operating parameters

Eliminating fine particles from flue gas is of vital importance to improve air quality, so an outer vortex type electrocyclone (EC) designed with corona wires was built and used to trap submicron particles. Besides, a mathematical model under multi-field coupling effect was established and the charging effect rule on collection efficiency of submicron particles was revealed by comparing the performance of electrocyclone with cyclone and changing operating conditions. The results indicate that the application of charging effect greatly reduces the escape of submicron particles, making that the collection efficiency in EC is far higher than the one in cyclone. Compared to the cyclone, the ability of charging effect to promote the separation performance of EC increases with the increasing working voltage and the decreasing flue gas velocity and temperature and the trapping performance is better at a higher working voltage, lower flue gas velocity, and lower temperature. Furthermore, for outer vortex type EC, the charging effect is more prominent with the decrease of working voltage, flue gas velocity and temperature. The obtained results were evaluated to provide a reliable guide for designing an outer vortex type EC, thus greatly decreasing the number of tests and effectively reducing the research cost.HighlightsA physical model of outer vortex type cyclone with corona wires was built.A theoretical model with four-field coupling interaction is established.The charging effect on collection efficiency of submicron particles is explored.Charging effect can availably improve the separation performance of cyclone.Charging effect is more prominent at lower voltage, flue velocity, and temperature.

Economic Efficiency of Energy-Saving Devices in Cyclones

The methodology and results of a calculation of economic and energy-saving effects in cyclones through the use of vane-type whirling devices are presented. Data on the reduction in hydraulic resistance and energy consumption achieved with gas cleaning by means of such devices in СN-11 and СN-15 cyclones, the types of cyclones that are the most common, are given. It is shown that the use of energysaving devices is economically profitable, with a recoupment period of less than a year on average.

3D-Simulation of Cyclone Separator

3-D CFD simulation of cyclone separator has been carried out in this section. Fluid flow and particle dynamics are studied to determine the performance of the three cyclone types in ANSYS Fluent 14.5. The three cyclone separators studied here are 1D3D, 2D2D and 1D2D. In 1D3D, !D represents the length of the cylindrical part of the body is 1 times the diameter of the body, and 3D represents the length of the conical part is three times the diameter of the body.

MATHEMATICAL MODELS TO DETERMINE OF THIN LAYER DRYING KINETIC OF GINGER SLICES

In the present work, the effects of some parametric values on the thin layer drying process of ginger slices were investigated. Drying was done in the laboratory by using cyclone type convective dryer. The drying air temperature was varied as 40, 50, 60 and 70 ˚C and the air velocity is 0.8, 1.5 and 3 m/s. All drying experiments had only falling rate period. The drying data were fitted to the twelve mathematical models and performance of these models was investigated by comparing the determination of coefficient (R2), reduced chi-square (χ2) and root mean square error (RMSE) between the observed and predicted moisture ratios. Among these models, drying model developed by Midilli and Kucuk model showed good agreement with the data obtained from the experiments.

Spatio‐temporal variations of cloud fraction based on circulation types in the Iberian Peninsula

This paper presents the first systematic study of the relationships between atmospheric circulation types (CT) and cloud fraction (CF) over the whole Iberian Peninsula, using satellite data from the MODIS (MOD09GA and MYD09GA) cloud mask for the period 2001–2017. The high level of detail, in combination with a classification for circulation patterns, provides us with relevant information about the spatio‐temporal variability of cloudiness and the main mechanisms affecting the genesis of clouds. The results show that westerly CTs are the most influential, followed by cyclonic types, in cloudiness in the west of the Iberian Peninsula. Westerly flows, however, do not affect the Mediterranean coastline, which is dominated by easterly CTs, suggesting that local factors such as convective processes, orography and proximity to a body of warm water could play a major role in cloudiness processes. The Cantabrian Coast also has a particularly characteristic cloudiness dominated by northerly CTs. In general, the results found in this study are in line with the few studies that exist on cloudiness in the Iberian Peninsula. Furthermore, the results are geographically consistent, showing links to synoptic forcing in terms of atmospheric circulation patterns and the impact of the Iberian Peninsula's complex orography upon this element of the climate system.

Subcritical transition to turbulence in accretion disc boundary layer

Context. Enhanced angular momentum transfer through the boundary layer near the surface of weakly magnetised accreting star is required in order to explain the observed accretion timescales in low-mass X-ray binaries, cataclysmic variables, or young stars with massive protoplanetary discs. The accretion disc boundary layer is locally represented by incompressible homogeneous and boundless flow of the cyclonic type, which is linearly stable. Its non-linear instability at the shear rates of the order of the rotational frequency remains an issue. Aims. We put forward a conjecture that hydrodynamical subcritical turbulence in such a flow is sustained by the non-linear feedback from essentially three-dimensional vortices, which are generated by quasi-two-dimensional trailing shearing spirals grown to high amplitude via the swing amplification. We refer to those three-dimensional vortices as cross-rolls, since they are aligned in the shearwise direction in contrast to streamwise rolls generated by the anti-lift-up mechanism in rotating shear flow on the Rayleigh line. Methods. Transient growth of cross-rolls is studied analytically and further confronted with direct numerical simulations (DNS) of the dynamics of non-linear perturbations in the shearing box approximation. Results. A substantial decrease of transition Reynolds number RT is revealed as one changes a cubic box to a tall box. DNS performed in a tall box show that RT as a function of shear rate accords with the line of constant maximum transient growth of cross-rolls. The transition in the tall box has been observed until the shear rate is three times higher than the rotational frequency, when RT ∼ 50 000. Conclusions. Assuming that the cross-rolls are also responsible for turbulence in the Keplerian flow, we estimate R T ≲ 108 in this case. Our results imply that non-linear stability of Keplerian flow should be verified by extending turbulent solutions found in the cyclonic regime across the solid-body line rather than entering a quasi-Keplerian regime from the side of the Rayleigh line. The most favourable shear rate to test the existence of turbulence in the quasi-Keplerian regime may be sub-Keplerian and equal approximately to 1/2.

Spatio-temporal changes in energetic characteristics of eddy atmospheric circulation in the troposphere of West Siberia in the end of XX – the beginning of XXI centuries

In the framework of the study based on ERA-Interim reanalysis dataset the analysis of average values of available potential energy, kinetic energy, their eddy components and parameter of relative vorticity, characterizing cyclonic and anticyclonic types of circulation, was carried out over the period of 1979-2015 for the territory of West Siberia. Also coefficients of their linear trends were calculated. It was revealed that the distribution in positive and negative tendencies of energetic characteristics was significantly changed upon transition from the period of 1979-1998 to the period of 1999-2015 along with considerable increase in their trend values. Their trend areas with negative values were located close to each other and were slightly covered in zone 60°-64°N. The greatest dissipation intensity was observed in the middle troposphere. At the earth’s surface eddy circulation generation along the Arctic coast was shifted to East Siberia. The beginning of XXI century was characterized by the significant decrease in eddy circulation activity over West Siberia that was especially pronounced in winter. Furthermore, eddy circulation (cyclonic type) increased just in the certain zones - in the interfluve area of the Ob and the Irtysh rivers. This indicates the possibility of anomalies in meteorological parameters formation there.

Analysis of rainfall time structures on a scale of hours

The paper is motivated by the enormous variability of short-term rainfall time structures which need to be discretized into several typical variants and explained from the viewpoint of rainfall types producing them. We present six variants of the time structure of 6-h rainfalls in Czechia, distinguished by a novel methodology for designing synthetic hyetographs. Reference 6-h rainfall episodes were extracted from radar-derived precipitation time series with a time resolution of 10 min, adjusted by daily data from rain gauges. The variants were distinguished by three indexes that quantify the precipitation concentration within time steps from one to six hours. The episodes with steady precipitation intensity during the entire episode are mainly stratiform or possibly mixed and frequently take much longer than six hours because of circulation patterns producing them; central and northeastern cyclonic types are most represented. All other variants of episodes frequently occur when a trough is situated above Central Europe. Episodes with steady intensity lasting about three hours are still mainly stratiform or mixed while two variants represented by “two-humped” hyetographs are usually mixed or convective. Two variants of most concentrated episodes are mainly convective or possibly mixed; they are characterized by enhanced frequency of southwestern and eastern cyclonic types. Future research on cluster frequencies among maximum precipitation episodes in various regions will enable the improvement of design hydrographs of small streams where runoff is basically influenced by the rainfall time structure.

Gasification of Furniture Waste Sawdust in a Cyclone Gasifier

Sawdust is one of the major biomass that was produced over 1 million ton per year in Thailand. A large amount of sawdust can be used as renewable energy. Gasification is one of the high-efficiency processes to convert biomass to the gaseous product. Sawdust is suitable to be converted to the gaseous product due to its high proportion of volatile (73%). In this work, sawdust thermal conversion was investigated by using a stairmand type cyclone gasifier with 100 mm diameter. The operation of the cyclone with short residence time and high efficiency of particulate separation from the gaseous product is suitable for a small particle like sawdust. The influences of equivalence ratio (0.15-0.60) and reactor temperature (700°C, 800°C and 900°C) on the waste conversion performance were determined. The gas composition (CO, CO2, CH4, H2, and CnHm), carbon and hydrogen conversions, lower heating value and cold gasification efficiency were reported. The data analysis indicated the optimum equivalence ratio is 0.45. Excessively lower or higher equivalence ratio negatively affected the gas composition and heating value of gaseous product. The optimum of reactor temperature is 900°C. The lower temperature also adversely affected the gaseous product, conversion of carbon and hydrogen. The lower heating value of product gas is range from 0.95-3.45 MJ/m3 and the cold gasification efficiency is range from 28-68%. The optimal condition of sawdust gasification in cyclone gasifier is equivalence ratio of 0.45 and temperature of 900°C at which total carbon and hydrogen conversionsare 90% and 60%, respectively.

Evaluation of the turbulence models for gas flow and particle transport in URANS and LES of a cyclone separator

Gas-solid separators have played an important role for process or emission control of many facilities including fluidized bed reactors. The flow field and collection efficiency were investigated for a Stairmand- type cyclone separator by Reynolds stress transport model (RSTM) and large eddy simulation (LES) in this work. RSTM and LES both showed good agreement with measured mean tangential velocity, whereas LES reproduced unsteady flow in the core with better agreement of the mean axial velocity profile. The particle dispersion model is required to obtain an accurate overall collection efficiency in both RSTM and LES. Anisotropy in velocity fluctuation should be taken into account, whereas its effect is more significant in RSTM than in LES. The continuous random walk (CRW) model gave more accurate results than the discrete random walk (DRW) model in RSTM, whereas there was no significant difference in LES resolving most large scale eddies. LES made better prediction of the overall particle collection efficiency than RSTM, although further investigation may be required for deviation in the maximum inlet flow case of the cyclone separator.

Meteorological Driving Mechanisms and Human Impacts of the February 1979 Extreme Hydro-Geomorphological Event in Western Iberia

The large number of floods and landslides that occurred on 5–16 February 1979 in Portugal was a major hydro-geomorphologic extreme event according to the DISASTER database in terms of number of displaced people. The February 1979 event is the top ranked episode in terms of the total number of evacuated people (4244), displaced people (14,322) and also on the number of days of event duration (12 days) for the period 1865–2015. In this event, 62 damaging floods and five damaging landslides causing eight fatalities were recorded in Portugal. This event was driven by an unusually intense atmospheric forcing mechanism acting at different time scales. Despite the intense magnitude and the widespread impact on the population, this event has not been studied in detail. In this study, we show that the precipitation period of February 1979 had produced several multi-day accumulated precipitation events over the Portuguese continental territory, ranking among the top 10 events observed between 1950–2008. Additionally, most of the precipitation from this event occured in days in which atmospheric circulation was dominated by “wet” circulation weather types (CWTs), namely, cyclonic (C), west (W) or southwest (SW) types.

Comparison of an automated classification system with an empirical classification of circulation patterns over the Pannonian basin, Central Europe

The aim of the study is to compare the performance of the two classification methods, based on the atmospheric circulation types over the Pannonian basin in Central Europe. Moreover, relationships including seasonal occurrences and correlation coefficients, as well as comparative diagrams of the seasonal occurrences of the circulation types of the two classification systems are presented. When comparing of the automated (objective) and empirical (subjective) classification methods, it was found that the frequency of the empirical anticyclonic (cyclonic) types is much higher (lower) than that of the automated anticyclonic (cyclonic) types both on an annual and seasonal basis. The highest and statistically significant correlations between the circulation types of the two classification systems, as well as those between the cumulated seasonal anticyclonic and cyclonic types occur in winter for both classifications, since the weather-influencing effect of the atmospheric circulation in this season is the most prevalent. Precipitation amounts in Budapest display a decreasing trend in accordance with the decrease in the occurrence of the automated cyclonic types. In contrast, the occurrence of the empirical cyclonic types displays an increasing trend. There occur types in a given classification that are usually accompanied by high ratios of certain types in the other classification.

Research on the effects of operating conditions and inlet channel configuration on exergy loss, heat transfer and irreversibility of the fluid flow in single and double inlet cyclones

Entropy generation method is employed to scrutinize the exergy loss and entropy generation of the air flow during the cleaning process inside three conventional types of industrial cyclones, i.e. single inlet, conventional double inlet and spiral double inlet. Different mechanisms of the entropy generation including; direct, turbulent and thermal dissipations are studied. Results show that the presence of the second inlet decreases irreversibility. Spiral double inlet cyclone saves up to 12.33% of the flow exergy in comparison with the single inlet one, while for the simple double inlet cyclone this value is about 7.63%. The highest value of irreversibility is observed at the entrance region of the vortex finder. While, this value is lower in double inlet cyclones in comparison with single inlet one. Moreover, the interesting relation between the convection coefficient and irreversibility indicates that 75% increase in convection coefficient leads to a 5% reduction in averaged turbulent entropy generation.