Cyclonic Chamber Research Articles

Carry-over of particles in a cyclone chamber

The carry-over of clay and crushed-rice particles in a cyclone chamber of diameter 0.393 m was experimentally investigated for different heights of introduction of a polyfractional disperse material. The maximum diameter of the carried particles was calculated in relation to the velocity of air at the output of the nozzles and the diameter of the outlet (exhaust port) of the chamber. The influence of the bottom flow on the carryover of particles in the indicated chamber was determined.

Analytical evaluation of nebulizers for the introduction of acetic acid extracts aiming at the determination of trace elements by inductively coupled plasma mass spectrometry

Most of the official procedures aiming at classification of solid waste toxicity take into account metal solubility and bioavailability by means of extraction experiments using acetic acid solutions. Hence, the aim of this work was to investigate and optimize conditions to suppress the effect of acetic acid on the determination of trace elements using inductively coupled plasma mass spectrometry. The performance of four nebulizers (cross-flow (CFN), ultrasonic (USN), Meinhard (MN) and MicroMist (MMN)) were compared as to their efficiency in minimizing spectral and non-spectral effects on the determination of Ag, As, Ba, Cd, Cr, Hg, Pb and Se, with the ultimate goal to analyze acetic acid extracts obtained from solid waste residues. Operating conditions (desolvation temperatures for USN, RF power and nebulizer gas flow rates) were optimized individually for each nebulizer and for all analytes maintained in 0.14molL−1 HNO3 solutions and in solutions prepared with acetic acid and acetic acid+NaOH, adjusted to pH 2.88 and 4.93, respectively. Pronounced non-spectral interferences for 75As and 82Se were observed in the presence of acetic acid for CF and MN, although to a less extent also for MMN and USN. Signal increase for blank solutions measured at m/z 208 (208Pb) for CFN and MN, 107 (107Ag) for USN and MN coupled to a cyclonic chamber and, m/z 82 (82Se) for USN was observed, indicating an increased risk of spectral interference upon an increase in the concentration of acetic acid. Signal increase at specific m/z ratios, however, was not significant when the MMN was used, with the exception of m/z 52 (52Cr) in acetic acid solutions, arising from the formation of 40Ar12C+. This same effect was noticed for all nebulizers, although at noticeably different intensities. A signal stability study was performed, demonstrating that variations in the analytical signal were within a 20% range for all analytes, with the exception of Hg, after continuous aspiration for 70min. The nebulization efficiency ranged from 4.6% to 64% for CF and MM nebulizers, respectively. Leaching solution from a solid waste residue was analyzed using all the studied systems in three different calibration media. In general, the results indicate that calibration solutions should be prepared in the same medium as the leachate, although for USN and MMN a reasonable agreement among the results was obtained regardless of the calibration solution used. Detection limits ranging from 0.01μgL−1 to 2μgL−1 were obtained, with little discrepancy among the different nebulizers used.

Investigation of the structure of swirling flows in a cyclone chamber under various conditions of gas inlet and outlet

The features of swirling flows in a cyclone chamber of diameter 0.4 m have been investigated experimen- tally for various configurations of inlet nozzles and sizes of the outlet hole. The existence of general laws of swirling flows independent of the inlet and outlet geometry of the chamber, as well as of the air blow velocity has been established. Equations for calculating the main characteristics of the swirling flow in the above chamber have been obtained and their comparison with the dependences established for chambers with other geometric parameters has been made. As analysis of the literature has shown, it is still not clearly understood how the conditions of gas injection into the cyclone chamber and the diameter of its outlet hole influence the character of swirling flows determining such important indices as the separating power of the chamber, its aerodynamic drag, and the inlet blast air distribution over the chamber height. This information is especially topical in creating cyclone-spreader furnaces using the tangential character of air inlet. In this paper, we present the results of the experimental investigation of flows in the cyclone furnace model and their generalization at various configurations, positions, and cross-sectional areas of inlet nozzles in the charac- teristic range of change in the relative diameter of the inlet hole (0.2-0.7). Experimental Setup. In the vertical isothermal cyclone chamber of the experimental setup (10) having an inner diameter D = 0.393 m and a height H = 0.408 m, the top cover with the outlet hole was replaceable. The rela- tive diameter of the outlet hole (d out ⁄ D) was 0.2, 0.3, 0.5, and 0.7. The outlet nozzles with a section of width b n = 15.2 mm had the following configurations and location: 1) the height of the air inlet channel was equal to the cham- ber height: H n = 0.4 m; 2) H n = 0.124 m, the air inlet channel was located in the upper part of the chamber; 3) H n = 0.124 m, the inlet channel was located in the lower part of the chamber; 4) five inlet channels with a total height H n = 0.0248 × 5 = 0.124 m were uniformly distributed over the height of the chamber (Fig. 1). The inlet air velocity was 4.2-13.6 m ⁄ s. The measurement procedure is described in (10). Analysis of the Measurement Data. Flow structure in the cyclone chamber at a height of the air inlet chan- nel H n = 0.4 m. Measurements have shown that the velocity and pressure in the chamber strongly depend on the rela- tive diameter of its outlet hole (Figs. 2-5). However, the profiles of the measured characteristics throughout the range of change in this diameter have qualitatively equal features. They point to the presence of zones of quasi-uniform and

Development of a Two–Stage Biomass Combustion System for Reducing The Emission Pollutant

One of the most popular technological processes of converting biomass to a more useful energy is through direct combustion of biomass or gasification in a two stage combustion system. This combustion system configuration comprises of gasifier, gas ejector, cyclonic chamber and swirl burner, which are enclosed by the circular chamber. A series of tests were carried out to investigate the effect of each device in contributing to the reduction of gas emission. The results show that the staged combustion method, including the installation of gas ejector, cyclone chamber and swirl burner in the current gasifier system has shown as significant device to reduce the CO concentration as well as NOx reduction.

Universal calibration for metal determination in fuels and biofuels by inductively coupled plasma atomic emission spectrometry based on segmented flow injection and a 350 °C heated chamber

The benefits of using a 350 °C heated single pass spray chamber following a segmented flow injection methodology were demonstrated for the analysis of petroleum products through inductively coupled plasma atomic emission spectrometry (ICP-OES). The present work shows that a small sample volume (i.e., 5 μl or less) can be precisely injected into the system following a manual procedure. Two different sample introduction systems were employed: a Cyclonic spray chamber and a single pass spray chamber (a modified version of the Torch Integrated Sample Introduction System, TISIS) equipped with a heating brass hollow cylinder. First the effect of temperature on the peak shape and sensitivity has been studied for a set of nineteen different organic products (gasoline, superethanol, diesel and biodiesel diluted in xylene). The results have proved that the higher the chamber walls temperature, the higher the sensitivity. As a result limits of detection decreased below 7 μg l−1 for elements such as manganese, vanadium and silicon. Furthermore, memory effects were less severe as the temperature raised. Another benefit of increasing the TISIS chamber walls temperature is that matrix effects became less pronounced as compared to a Cyclonic chamber. Thus, at 350 °C non-spectral interferences are eliminated likely because the analyte transport efficiency to the plasma is close to 100% irrespective of the sample analyzed. This has two important consequences: (i) it is possible to obtain a calibration line by merely modifying the injected solution volume and (ii) a single xylene based solution can be used as a universal standard. The developed procedure was applied to the analysis of nineteen spiked petroleum derivatives with recoveries for manganese, silicon, vanadium and copper in the range 95–106%.

Modified high performance concentric nebulizer for inductively coupled plasma optical emission spectrometry

The high performance triple-tube concentric nebulizer (HPCN) was modified and evaluated for sample introduction into inductively coupled plasma optical emission spectrometry (ICP-OES) at liquid flow rates of 0.25 to 0.8 mL min−1. The acceptable liquid flow rate for the use of HPCN was extended by replacing the tapered center capillary tube of the nebulizer (i.d./o.d.: 50 μm/150 μm) with a large bore tube (i.d./o.d.: 110 μm/170 μm). The nebulization efficiency was much improved by reducing the inner diameter of the nebulizer nozzle from 250 μm to 200 μm. At a liquid flow rate of 0.8 mL min−1 and a nebulizer gas flow rate of 1 L min−1, the Sauter mean diameter (D3,2) of the primary aerosol generated by the modified HPCN was 3.4 μm, and over 90% (v/v) of the aerosol droplets were below 10 μm in diameter. The D3,2 value was smaller than those generated by conventional nebulizers, Meinhard nebulizer type C (8.2 μm), Glass Expansion Conikal nebulizer (15.8 μm), SeaSpray (14.8 μm), and MiraMist (5.6 μm). The amount of the tertiary aerosol of the modified HPCN generated through a non-baffled cyclone chamber was approximately 1.8 to 3.1 times higher than those of the other nebulizers, with similar size distributions. The sensitivity in ICP-OES with the modified HPCN was 1.5- to 3.2-fold higher than those with the other nebulizers when the liquid flow rates were the same. The plasma robustness estimated from the commonly used ratio Mg(II)/Mg(I) was the same or slightly better than that of the conventional nebulizers. The HPCN also showed a good tolerance to high total dissolved solids (TDS) using 20% NaCl solution. Validation of the modified HPCN was performed by a recovery test of spiked seawater and analyzing the NMIJ CRM 7502-a white rice flour. The observed values for the ten elements Na, Mg, P, K, Ca, Mn, Fe, Cu, Zn and Cd were in good agreement with their certified values. We concluded the modified HPCN is a very useful nebulizer for ICP-OES with good performance at a large range of sample flow rates.

Multielement analysis of micro-volume biological samples by ICP-MS with highly efficient sample introduction system

A method for multielement analysis of micro-volume biological sample by inductively coupled plasma mass spectrometry (ICP-MS) with a highly efficient sample introduction system was presented. The sample introduction system was the combination of (1) an inert loop injection unit and (2) a high performance concentric nebulizer (HPCN) coupled with a temperature controllable cyclone chamber. The loop injection unit could introduce 20μL samples into the carrier liquid flow of 10μLmin−1 producing a stable signal for 100s without any dilution. The injection loop is continuously washed with 0.1M HNO3 carrier solution during the measurement, thereby much improving sample throughput. The HPCN is a triple tube concentric nebulizer, which can generate fine aerosols and provide a stable and highly measurement sensitivity in ICP-MS at a liquid flow rate less than 10μLmin−1. With the combination of the chamber heating at 60°C, the sensitivity obtained with the proposed sample introduction system at the liquid flow rate of 10μLmin−1 was almost the same as that with a common concentric nebulizer and cyclone chamber system at the liquid flow rate of 1mLmin−1, though the sample consumption rate of the HPCN was two orders of the magnitude lower than that of the common nebulizer. The validation of the proposed system was performed by analyzing the NIST SRM 1577b Bovine Liver. The observed values for 12 elements such as Na, P, S, K, Ca, Mn, Fe, Co, Cu, Zn, Mo, Cd were in good agreement with their certified values and information value. Satisfactory analytical results for 14 elements such as Na, Mg, P, S, K, Ca, Cr, Mn, Fe, Ni, Cu, Zn, Y, Ba in Escherichia coli sample were also obtained. The proposed sample introduction system was quite effective in the cases when only micro-volume of biological sample is available.

Axial view inductively coupled plasma optical emission spectrometry for monitoring tin concentration in canned tomato sauce samples

In this study it was evaluated the variation of tin concentration in function of storage time in canned food samples by using an axial view inductively coupled plasma optical emission spectrometry (AX ICP OES). The effect of various parameters of the ICP OES, such as analytical lines, sample introduction systems and interferences were investigated. Eight emission lines for tin were tested, but only 283.998nm line was found to be robust enough with respect to interferences and sensitivity, presenting a limit of quantification of 0.094mgkg−1. A concentric nebuliser combined with a cyclonic chamber has shown better sensitivity than a V-groove nebuliser. Tin was determined in canned tomato sauce stored at room temperature (20.0±1.8°C) for 0, 30, 60, 90, 120 and 150days. After 150days, tin contents increased in the 43–91% range. Despite an increase of almost 100% for one sample, tin contents are well below the maximum level allowed by Agência Nacional de Vigilância Sanitária (ANVISA) regulation of 250mgkg−1.

Study of flows in a cyclone chamber

Parameters of the vortex air flow in an isothermal model of the cyclone chamber are studied. The effect of the air velocity in nozzles on the values and character of the distribution of pressure and tangential and longitudinal velocities of air in the chamber is determined. Numerical modeling of the flow is performed, and it is shown that numerical calculation by the k-w turbulence model is in agreement with experimental data.

Biomass downdraft gasifier with internal cyclonic combustion chamber: Design, construction, and experimental results

An exploratory downdraft gasifier design with unique biomass pyrolysis and tar cracking mechanism is evolved at Oklahoma State University. This design has an internal separate combustion section where turbulent, swirling high-temperature combustion flows are generated. A series of research trials were conducted using wood shavings as the gasifier feedstock. Maximum tar cracking temperatures were above 1100 °C. Average volumetric concentration levels of major combustible components in the product gas were 22% CO and 11% H 2. Hot and cold gas efficiencies were 72% and 66%, respectively.

On steady rotational cyclonic flows: The viscous bidirectional vortex

This study is focused on the tangential boundary layers of a bidirectional vortex, specifically those forming at the core and the sidewall of a swirl-driven cyclonic chamber. Our analysis is based on the regularized, tangential momentum equation which is rescaled in a manner to capture the forced vortex near the chamber axis and the no slip requirement at the sidewall. After identifying the coordinate transformations needed to resolve the rapid changes in the regions of nonuniformity, two inner expansions are constructed. These expansions are then matched with the outer, free vortex solution that is sandwiched between the core and the hard wall. By combining inner and outer expansions, uniformly valid approximations are subsequently obtained for the swirl velocity, vorticity, and pressure. These are shown to be strongly influenced by a dimensionless grouping that we refer to as the vortex Reynolds number, V. This keystone parameter appears as a ratio of the mean flow Reynolds number and the product of the swirl number and the chamber aspect ratio. Based on V, several fundamental features of the bidirectional vortex are quantified. Among them are the thicknesses of the viscous core and sidewall boundary layers; these decrease with V1/2 and V, respectively. The converse may be said of the peak velocity which increases with V1/2. In the same vein, the angular speed of the rigid-body rotation of the forced vortex is found to be linearly proportional to V. Our laminar swirl velocity is reminiscent of Sullivan’s two-cell vortex except for its additional dependence on the aspect ratio of the chamber. For the purpose of verification, theoretical predictions are compared to particle image velocimetry measurements and Navier–Stokes simulations at high vortex Reynolds numbers. By properly accounting for the turbulent eddy viscosity in the analytical model, local agreement is obtained with both laboratory measurements and computer simulations.

Performance of a Dual Sample Introduction System with Conventional Concentric Nebulizers for Simultaneous Determination of Hydride and Non-Hydride Forming Elements by ICP-OES

A dual sample introduction system that combines the benefits of nebulization and vapour generation in a single device is described. It consists of two commercial conventional concentric nebulizers coupled to a modified cyclonic chamber. The effect(s) of the solvent load produced by the amount of liquid carried for the system by the two nebulizer assemblies is investigated. Better sensitivities, similar precision and DL's (with the exception of hydride forming elements) were obtained compared with those obtained with the system working in single mode. Long term stability was less than 7% with the dual mode, being 2% and 6% for the non-hydride and hydride forming elements, respectively, in the single mode operation. DL's obtained are of the same order of magnitude as those reported by several authors, with the exception of Se whose conditions were in compromise with the optimal reached for the rest of the elements. Accuracy of the dual system was proved by analyzing NIST 1648, urban particulate matter, with satisfactory results.

Evaluation of different nebulizers and spray chambers for the on-line coupling of ion chromatography with ICP-OES

The aim of this study was to evaluate nebulization devices and spray chambers used to couple ion chromatography with ICP-OES. In this prospect, the chromatographic performances for the separation of Cr(III), Cd(II), Ga(III) and Fe(III) were compared for all the nebulizers and chambers tested. In fact, the choice of a suitable interfacing device is mainly dictated by its sensitivity. However, this study shows that chromatographic efficiency could also be important. The results indicate that the difference in volume between the conventional and miniaturized cyclonic chambers is not critical with respect to extra-column band broadening for the case of classical columns. So, the conventional chamber, which presented the highest sensitivities and limits of detection, was selected. However, the study of five nebulizers, a conventional pneumatic concentric nebulizer and four micronebulizers, showed that they influenced the number of theoretical plates more. The Aspire micronebulizer presented the highest sensitivities, detection limits and chromatographic efficiencies and was recommended for microchromatography. However, the pneumatic concentric nebulizer exhibited better performances at 1 mL min−1.

Simple Model for Turbulent Tip Vortices

V ORTICES are interwoven into the fabric of fluid mechanics transporting mass momentum and energy in the majority of natural and industrial flows. In technology these are either produced deliberately to accomplish the task, improve the function of devices, or emerge as a parasitic by-product of fluid motion. Aeronautical applications are very susceptible to these flow manifestations. Consequences of lift, tip vortices cause considerable drag, noise, and/or hazard in fixedand/or rotating-wing aircraft. Although complicated in nature simple mathematical models are routinely used to elaborate on some of their fundamental properties [1,2]. It is a well-known fact that, irrespective of the host flowfield, intense vortices are analogous. Theoretically, intense (or strong) vortices are those where the tangential velocity component is orders of magnitude larger than the radial and axial. In practice, however, the property is also maintained by vortices where the swirl velocity component is dominant, but not necessarily of a magnitude enormously greater than the other two. Under these conditions the vortex appears to develop in amanner that the swirling action ignores the secondarylike flow in the azimuthal plane. Consequently, simple Rankine-like formulations have been used widely to model a variety of geophysical, wingtip, cyclone chamber, ship propeller, intake, and other types of vortices. The physics of laminar vortices is relatively well known. Simple exact solutions of the Navier–Stokes equations are due to Rankine [3], Oseen [4], Lamb [5], Burgers [6], and others. Every one of them represents a possible solution, applicable to low vortex Reynolds numbers (Re ) defined as the total circulation divided by the kinematic viscosity. In antithesis, our grasp reduces exponentially for turbulent vortices. Certainly this is not accidental. Turbulent flows are considerably more complex both analytically and experimentally. Even today the turbulent vortex is among the not very well-explored territories in aerodynamics. Not long ago, Ramasamy and Leishman [7] examined turbulent helicopter tip vortices using state of the art instruments and experimental techniques. Their high-resolution visualizations revealed that these types of whirls display the already familiar path to turbulence (probably slow, through spectral development). Inside the core, they have confirmed that helicopter tip vortices do enjoy laminarlike conditions. Approaching the core from the origin, past the laminar core and when a critical local Reynolds number is reached, the flow enters a transition region. This condition persists until a second critical Reynolds number where the flowfield changes into the “turbulent state” at larger radii. Most important of all, the accompanied high-fidelity velocity data (at Re 48; 000) exposed the following particular behavior for the azimuthal velocity component. In the region where the vortex is turbulent, the velocity decreases at a rate noticeably smaller than that of a laminar vortex. As a consequence of the new experimental evidence it became amply evident that high Re helicopter tip vortices cannot be modeled by the laminar formulations of the past. Instead one has to seek analytical representations of the phenomenon where at least the most fundamental effects of turbulence are included. Previous, theoretically more involved developments on the subject are those of Newman [8], Inversen [9], Tang [10], and Ramasamy and Leishman [7]. Here we present a new simple mathematically convenient formulation that accounts for the flattening effect in the tangential velocity profile.

UV/spray chamber for generation of volatile photo-induced products having enhanced sample introduction efficiency

A combined spray chamber/UV photolysis unit is described which is shown to substantially enhance sample introduction efficiency for several elements in the presence of 1–5% concentrations of formic, acetic and propionic acids. Enhancement factors of 2–40-fold were achieved for Ag, As, Se, Sb, Hg, I, Bi, Pb and Sn when the aerosol field within the cyclonic chamber produced during conventional concentric nebulizer sample introduction was illuminated by an axially placed 6 W mercury pen lamp. UV photolysis of the organic acids likely initiates radical reactions, generating volatile analyte species.

Detection of a Chemical Warfare Agent Simulant in Various Aerosol Matrixes by Ion Mobility Time-of-Flight Mass Spectrometry

For the first time, a traditional radioactive nickel (63Ni) beta emission ionization source for ion mobility spectrometry was employed with an atmospheric pressure ion mobility orthogonal reflector time-of-flight mass spectrometer (IM(tof)MS) to detect a chemical warfare agent (CWA) simulant from aerosol samples. Aerosol-phase sampling employed a quartz cyclonic chamber for sample introduction. The simulant reference material, which closely mimicked the characteristic chemical structure of CWAs as defined and described by Schedule 1, 2, or 3 of the Chemical Warfare Convention treaty verification, was used in this study. An overall elevation in arbitrary signal intensity of approximately 1.0 orders of magnitude was obtained by the progressive increase of the thermal AP-IMS temperature from 75 to 275 degrees C. A mixture of one G-type nerve simulant (dimethyl methylphosphonate (DMMP)) in four (water, kerosene, gasoline, diesel) matrixes was found in each case (AP-IMS temperature 75-275 degrees C) to be clearly resolved in less than 2.20 x 10(4) micros using the IM(tof)MS instrument. Corresponding ions, masses, drift times, K(o) values, and arbitrary signal intensities for each of the sample matrixes are reported for the CWA simulant DMMP.

Effect of nebulizer/spray chamber interfaces on simultaneous, axial view inductively coupled plasma optical emission spectrometry for the direct determination of As and Se species separated by ion exchange high-performance liquid chromatography

Different nebulizer/expansion chamber combinations were evaluated to assess their performance for sample introduction in the direct coupling with an axial view inductively coupled plasma multielement spectrometer for on-line determination of As and Se species previously separated by ion exchange–high performance liquid chromatography. The column effluents were injected into the plasma without prior derivatization. The instrument operation software was adapted for data acquisition and processing to allow multi-wavelength recording of the transient chromatographic peaks. After optimization of the chromatographic operating conditions, separation of mixtures of inorganic As and Se species, and of inorganic and two organic As species (monomethylarsonic and dimethylarsinic acids), was achieved with excellent resolution. Species discrimination from mixtures of As and Se oxyanions was further improved by the simultaneous element detection at specific analytical wavelengths. Three nebulizers and three spray chambers, employed in seven combinations, were tested as interfaces. Concentric nebulizers associated to a glass cyclonic chamber appear most suitable regarding sensitivity and signal to noise ratio. Measured element detection limits (3 σ) were around 10 ng ml − 1 for all the species considered, making the method a viable alternative to similar procedures that employ volatile hydride generation previous to sample injection into the plasma. Analytical recoveries both for inorganic and organic species ranged between 92 and 107%. The method was demonstrated to be apt for the analysis of surface waters potentially subjected to natural contamination with arsenic.

Development of gas–solid direct contact heat exchanger by use of axial flow cyclone

A heat exchanger between particulate or granular materials and gas is developed. It makes use of a swirling gas flow similar to the usual cyclone separators but the difference from them is that the swirl making gas is issued into the cyclone chamber with downward axial velocity component. After it turns the flow direction near the bottom of the chamber, the low temperature gas receives heat from high temperature particles supplied from above at the chamber's center. Through this configuration, a direct contact and quasi counter-flow heat exchange pattern is realized so that the effective recovery of heat carried by particles is achieved. A model heat exchanger was manufactured via several numerical experiments and its performances of heat exchange as well as particle recovery were examined. Attaching a small particle diffuser below the particle-feeding nozzle brought about a drastic improvement of the heat exchange performance without deteriorating the particle recovery efficiency. The outlet gas temperature much higher than the particle outlet temperature was finally obtained, which is never realized in the parallel flow heat exchanger.

Static electrification of powders during spray drying

In the field of pharmaceutics, spray drying is often used for producing particles with predetermined qualities. Produced particles are usually insulating in nature, and this property combined with small particle size, might lead to electrostatic problems. These problems involve, for example, dust explosions, fires, reduced process efficiency and particle accumulation on the walls. In the spray drying process, the static charge might be generated in different ways: double layer charging in the feed pipe, double layer or induction charging at the spray nozzle, and contact and frictional charging at the walls of the spray cylinder and the cyclone chamber. In this paper, these charging processes are assessed using electric field measurements and Faraday pail.

Investigation of the flow pattern in different dust outlet geometries of a gas cyclone by laser Doppler anemometry

The separation process in a gas cyclone can be divided in three determining steps: (1) the movement of the particles in the cyclone chamber towards the cyclone wall due to centrifugal force, (2) agglomeration of particles at the wall and in the dust bin and (3) separation of the particles and/or agglomerates in the bin. For many years the dust outlet has been considered to be very important for the separation process. However, the actual geometry of the dust outlet was rarely investigated. Tests performed by the authors prove that different dust outlet geometries have significantly different separation efficiencies.Laser Doppler anemometry measurements in a cyclone equipped with three different dust outlet geometries show that both the gas flow in the dust outlet and the gas flow within the lower part of the cyclone change. By examining the different flows within the different dust outlet geometries the influence of the geometry on the separation efficiency can be explained. The best dust outlet of a cyclone is a downcomer tube, due to the “additional” separation process which takes place within it.