Small Cyclone Research Articles

27.P.05 Particle collection by small cyclones as a function of flow rate, geometric dimensions and particle size

27.P.05 Particle collection by small cyclones as a function of flow rate, geometric dimensions and particle size

Dry Submicron Classification by a Small Blow Down Cyclone [Translated]<sup>†</sup>

Dry Submicron Classification by a Small Blow Down Cyclone [Translated]<sup>†</sup>

39 P 10 A numerical calculation of the penetration efficiency of a small cyclone

39 P 10 A numerical calculation of the penetration efficiency of a small cyclone

An assessment of the application of computational fluid dynamics (CFD) to model the performance of a range of small sampling cyclones

An investigation was carried out to examine the effectiveness of two Computational Fluid Dynamics (CFD) packages to model the collection performance of a range of small sampling cyclones which can be used to collect airborne particles, especially microorganisms. A comparison was made between the results obtained from (1) CFD, (2) experiment, and (3) 3 theoretical/semi-empirical sources, using the 50% cut-off size as the parameter for comparison. For cyclones, where experimental data are available, there was very good agreement between experimental and CFD modelled results. Only a fair agreement was found in the case of the theoretical/semi-empirical approaches. The computer models (CFD) have been shown to be useful in assessing the performance of such cyclones with a geometry described in this report. It has been shown that the effects on cyclone performance of any small change in geometry and/or sampling rate can be monitored by the CFD model. This type of approach reduces the need of having to carry out expensive and time consuming experimental work. However, the CFD packages require reference to experimental results, obtained with the generic cyclone, ie. they require a calibration, before being used to monitor the changes described above.

DESIGN GUIDELINES FOR CYCLONE IMPROVEMENT

ABSTRACT There is a potential for improving cyclone separators by design and operating conditions. Secondary flow detrimental to dust separation can be avoided by proper gas inlets, dimensioning of body and swirl, or by use of a flow guide in the area of separation. Cyclone and bin are to be treated as one unit. Scavenging of the bin is most effective for high effiency. Cut sizes smaller than 1 μm can be realized with a cyclone separator unit consisting of a preseparator, a battery of small cyclones, and a scavenging cyclone with gas recirculation. Such arrangements are capable to cope with dust streaks and to make positive use of dust agglomeration. These principles are applicable also for big cyclone batteries as used behind rotary dryers for wood chips, etc.

Design of Stairmand-Type Sampling Cyclones

An empirical, nondimensional correlation of cut-point Stokes number (Stk0.5) and flow Reynolds number (Re) has been established for small Stairmand-type sampling cyclones. Four cyclones with body diameters of 38, 57, 89, and 140 mm were constructed and tested with monodisperse aerosols over a range of flow rates. The flow rates were chosen to provide preselected increments of particle Froude numbers. These flow rates for the four cyclones spanned the range of 9.4 to 1080 L/min and provided Froude numbers of 1.5, 2.0, 2.5, and 6.0. The resulting Reynolds numbers (based upon cyclone body diameter and inlet flow rate) covered the range of 2.1 x 10(3) to 6.4 x 10(4). Sizes of monodisperse aerosols used in this study were from 3.0- to 17.4-microns aerodynamic diameter. The graphical correlation between cut-point Stokes number and Reynolds number showed there to be no effect of Froude number (for the range of Froude numbers tested). The data have been fit by a least squares procedure to a quadratic logarithmic function. In addition to development of the empirical correlation, the results of this study also provide data pertinent to the regional deposition of liquid particles within the cyclone and to the transmission of solid particles through the cyclone. The carryover of solid, 19-microns diameter particles is only 0.5% greater than that of liquid particles of the same size.

Design of Stairmand-Type Sampling Cyclones

An empirical, nondimensional correlation of cut-point Stokes number (Stk0.5) and flow Reynolds number (Re) has been established for small Stairmand-type sampling cyclones. Four cyclones with body diameters of 38,57,89, and 140 mm were constructed and tested with monodisperse aerosols over a range of flow rates. The flow rates were chosen to provide preselected increments of particle Froude numbers. These flow rates for the four cyclones spanned the range of 9.4 to 1080 L/min and provided Froude numbers of 1.5, 2.0, 2.5, and 6.0. The resulting Reynolds numbers (based upon cyclone body diameter and inlet flow rate) covered the range of 2.1×103 to 6.4×104. Sizes of monodisperse aerosols used in this study were from 3.0- to 17.4-µm aerodynamic diameter. The graphical correlation between cut-point Stokes number and Reynolds number showed there to be no effect of Froude number (for the range of Froude numbers tested). The data have been fit by a least squares procedure to a quadratic logarithmic function. In addition to development of the empirical correlation, the results of this study also provide data pertinent to the regional deposition of liquid particles within the cyclone and to the transmission of solid particles through the cyclone. The carryover of solid, 19-µm diameter particles is only 0.5% greater than that of liquid particles of the same size.

A Model for the Prediction of the Collection Efficiency Characteristics of a Small, Cylindrical Aerosol Sampling Cyclone

Velocity data from a previous study were nondimensionalized and used in conjunction with a computer program which solves the equations for particle trajectory to predict the collection efficiency for the cyclone. Results for the prediction of cutpoint at the same Reynolds number as that for which the velocities were measured, both for a large cyclone of 88.9 mm diameter and another geometrically similar at one half the scale, are excellent. The model predicts cutpoints of 10 μm and 5.1 μm for the large and small cyclone, respectively, while the actual cutpoints determined from aerosol tests were 9.9 μm and 5.2 μ m. The efficiency curve generated by the model was steeper (geometric standard deviation of 1.1) than the efficiency curve determined through the aerosol testing (geometric standard deviation of 1.4). A simplification of the Dirgo and Leith equation fitting Barth's design curve is suggested which provides a significantly better fit of the aerosol data (geometric standard deviation of 1.3). At 1.5N...

Experimental Study of Particle Collection by Small Cyclones

A new set of experimental data on the particle collection characteristics of small cyclones is reported. The collection efficiency for particles ranging from 2 to 10 μm in diameter was measured systematically for nine cyclones at flow rates ranging from 8.8 to 18.4 L/min. Special emphasis was given to the effects of the exit tube size and of the cyclone body size on the particle collection efficiency. The size ratio of the exit tube to the cyclone body was varied from 0.24 to 0.80. The experimental results show that the stiffness of the particle collection cutoff with size does not change noticeably with a change in the cyclone body size while operation of a cyclone at a low flow rate can cause the particle collection characteristics to become less stiff. It was also found that the exit tube diameter influences the particle collection efficiency substantially, with results showing that as the exit tube size is decreased, the collection efficiency increases. A large cyclone body size increases the efficien...

Particle collection in small laboratory cyclones as a basis for the design of large‐scale cyclones

AbstractGrade efficiencies must be measured in order to characterize particle collection in cyclones. For real, irregularly shaped partcles, the grade efficiencies depend on the shape and orientation of the particles and the flow around them. Therefore, the collection characteristics of cyclones should be defined in relation to spherical particles. Deviations occurring on the use of real, irregularly shaped dusts can then be attributed to a material influence. A fast and accurate measuring technique to determine the collection characteristic for spherical particles is described, followed by the presentation of results of extensive investigations on small model cyclones. A similarity relationship is presented. The validity of this relationship was confirmed by investigations with similar, larger cyclones.

Aerial observations of stratospheric descent in a Gulf of Genoa cyclone

The structure of a cyclone in the Gulf of Genoa on April 24, 25, 1982 is examined using an enhanced rawinsonde network, data from four ALPEX research flights, and satellite ozone and water vapor observations. This particular cyclone had, as a precursor, a mesoscale upper level vortex which approached the Alps from the north at a rate of about 400 km/6 hours. This small cyclone had a roughly axisymmetric tropopause fold. Cold air below the cyclone prevented it from having a surface pressure signature. Upon encountering the Alps, the cold air appeared to be deflected, allowing the cyclone reaching the Gulf of Genoa to extend to the surface. Aircraft data at thep≈447 mb level reveal a small volume of stratospheric air slightly ahead of the vortex center. This air is marked by high ozone concentration, low water vapor mixing ratio, and high relative vorticity. The boundaries of this region are very well defined with a horizontal scale of about 20 km, but with some evidence of advection and mixing processes. Satellite derived maps of vertically integrated ozone (TOMS) agree with the aircraft data regarding the position of the ozone maximum. Satellite images in the water vapor band /6.7 μm) also agree with the aircraft data, and provide some information on the time evolution of the stratospheric intrusion.

Evaluation of Recycling Cyclone Spray Chambers for ICP-AES

Two cyclone spray chambers of different sizes are evaluated for inductively coupled plasma/atomic emission spectrometry. On the basis of a simplified mathematical model, the cut-off diameters of the aerosol droplets are estimated to be 2.2 to 4.3 and 1.8 to 3.5 μm for the large and the small cyclones, respectively. The sample consumption rate can be reduced to about 50 μL/min when the cyclone chamber is used in a recycling mode. In general, the signal-to-background ratios, detection limits, and precisions of the analyte signal intensities obtained with the small cyclone chamber are slightly superior to those achieved with a Scott spray chamber and a recycling gravitational sedimentation chamber. The performance of the recycling cyclone chamber is also evaluated for the determination of copper in the NBS freeze-dried urine.

A Further Study of Comma Cloud Development in the Eastern Pacific

In a companion paper the authors presented a case study of the development of a comma-shaped cloud pattern and associated small cyclone that formed in a cold air mass over the eastern Pacific. This paper confirms the reproducibility of the previous analysis by documenting a second, similar case. A schematic model of comma cloud development appearing in the companion paper is based in part on this second example. An added feature of the present paper is a detailed examination of the physical processes responsible for the enhanced convective activity that occurred during the intensifying stage of the disturbance. It is found that the lifted index decreased markedly in the vicinity of the developing comma and that the decrease was associated with warming and moistening of the surface air and cooling of the air at 500 mb. Sensible and latent heat fluxes from the surface of approximately 100 and 300 W m−2, respectively were essential to the low-level warming and moistening. Amplification of an upper-level long-wave trough contributed to the cooling aloft. As the system came ashore in southern California, convective activity was much more severe in this case than in the previous one. A likely important factor in this difference was the greater warmth of the coastal waters in this (November) case than in the earlier (March) case.

Investigation on particle collection in small cyclones

Investigation on particle collection in small cyclones

Small‐scale cyclones on the periphery of a Gulf Stream warm‐core ring

Small‐scale cyclones found around Gulf Stream warm‐core ring 82B are investigated by using infrared satellite images and current information obtained with an acoustic‐Doppler velocimeter. Currents in these cyclones reveal speeds ranging from 20 to 80 cm/s. One small cyclone or “ringlet” found in June 1982 was studied extensively by removing the basic rotational velocities of 82B. The azimuthal velocity field for this ringlet was used with the gradient current equation to calculate the absolute dynamic topography at 100 dbar. It was found that the ringlet was 13 dyn‐cm lower than its surroundings. In addition, neglect of the centrifugal term would have changed the dynamic topography of the ringlet by 30%. From a comparison with CTD data the absolute reference level was determined, and a vertical profile of horizontal currents was calculated for the ringlet. Other cyclones were found throughout the slope water region around warm‐core ring 82B with observable lifetimes of 1 to 2 weeks. The northeast quadrant of 82B was a favored generation site for ringlets. Two cyclones were observed to form in this region and were advected anticyclonically around 82B. Typically, at any one time, six cyclones with diameters of approximately 40 to 50 km can be detected north of the Gulf Stream by using satellite images.

Generalized Performance Characteristics of Miniature Cyclones for Atmospheric Particulate Sampling

Small cyclones are advantageous for size selective sampling of atmospheric particulate matter because they are capable of collecting large samples and are less subject than impactors to particle bounceoff and reentrainment. However, there has been a lack of an accurate generalized quantitative description of their performance, which has necessitated extensive calibrations of each design. Collection efficiency data for 30 cyclones have been accurately fitted by two simple equations using outlet Reynolds number as a variable rather than flow rates. They also fitted the limited available data for the effects of temperatures ranging from 25 to 204 °C. Normalized particle sizes plotted on log probability paper vs collection efficiency as a single straight line for all experimental flow rates. Three constants fully described the performance of each cyclone, and these constants could be estimated since they varied over a small range for most of the cyclones. The new generalized empirical equations should facilit...

A Comparison of Large and Small Tropical Cyclones

In this paper the climatology and structure of, and possible reasons for, tropical cyclones of different sizes are examined. The climatology of tropical cyclone sizes confirms that tropical cyclones of the western North Pacific are characteristically twice as large as their Atlantic counterparts, and also reveals that the typical size of tropical cyclones varies seasonally and regionally and is only weakly correlated with cyclone intensity (maximum surface wind or minimum surface pressure). Rawinsonde composities of large and small tropical cyclones show that large cyclones have much more relative angular momentum (RAM) than small cyclones, while the differences in RAM between intense and weaker cyclones of equivalent size are less. Some of the implications of this observance are discussed, and a hypothesis that cyclones grow as a result of an increased convergence of angular momentum forced by their environment is presented.

Rotary Filters: Proposals for Efficient Industrial Dust Collection Systems

Modifications of methods currently used in the textile industry for dust collection are proposed for use in other industries to effect savings in capital costs and energy for air pollution control equipment. A rotary filter, with large air permeability and continuous cleaning, extracts all of the dust from the carrier air and condenses the dust into 17.5% of the initial air. If secondary processing is needed, another rotary filter can be used to condense all of the dust into 3% of the original carrier air. Final collection of the dust is made in a small baghouse. If the initial dust concentration is large, small tube cyclones may be used after the rotary filter to reduce the load of dust to the baghouse.

A separator for obtaining samples of cloud water in aircraft

In order to study the effect of SO 2 emissions from power stations on the formation of acid rain, cloud water sampled in the presence of the effluent gases is required for analysis. A small axial flow cyclone is described for separating the liquid water from cloud sampled by aircraft to provide these samples. The description covers structural aspects, the installation in the aircraft and a theoretical prediction of its service performance. It is shown that the separator will remove all droplets of greater than 5-μm diameter under the action only of the ram pressure generated by the forward speed of the aircraft. The optimisation of the design in a simple ground based cloud tunnel is then described and test results are given which indicate that adequate cloud water samples for chemical analyses should be obtained when the liquid water content of the sampled cloud exceeds 0.35 g m −3. This is supported by the results of early flight tests and it is concluded that the separator will provide useful cloud water samples in most homogeneous cloud conditions.

Performance of small cyclones for aerosol sampling

Performance of small cyclones for aerosol sampling