Horizontal Elutriator Research Articles

Numerical investigation of powder aerosolization in a mining rock dust dispersion chamber

We have conducted numerical simulations of dust dispersion within the NIOSH Rock Dust Dispersion Chamber. The apparatus consists of a low-speed background ventilation flow down a long box in which is placed a tray containing a rock dust powder. A nozzle upstream of the tray introduces a short pulse of a turbulent horizontal jet flow just above the powder surface. We have utilized an incompressible Reynolds-Averaged Navier-Stokes k-ω model for the turbulent flow; particles are incorporated within a one-way Euler-Lagrangian formalism. The Rock Dust Dispersion Chamber ventilation flow exhibits a recirculation zone just above the powder-containing tray. Aerosolization proceeds via the interplay of the jet pulse flow with the background recirculation flow. The air flow is not well-mixed. The aerosolized dust is convected as a concentration cloud downstream towards the detection zone. For larger particles, gravitational settling depletes the convected cloud, so the instrument behaves as a horizontal elutriator. The instrument is robust with respect to misalignment of the jet nozzle. However, reduced streamwise drift velocity allows mixing to disperse the optically detected dust cloud concentration pulse. Our large particle simulation results compare favorably with published experimental results for large, polydisperse calcium carbonate rock dust.

Redesign of a Static Horizontal Elutriator to Perform According to the ISO 7708 Respirable Convention

A static horizontal elutriator (multi-channel elutriator C-30, Sibata Scientific Instruments Ltd, Tokyo) has been widely used as a dust size classifier for a low-volume air sampler in Japan. The sampler uses the historical criterion defined by the British Medical Research Council (BMRC). However, a new sampling convention based on the ISO 7708 respirable dust convention was recently introduced into the Japanese standard for work environment measurement. It is necessary to modify the multi-channel static horizontal elutriator to satisfy the ISO 7708 respirable convention. We propose a modification of the horizontal elutriator, involving the shortening of 11 of the 36 plates to meet the ISO 7708 respirable convention. The relationship between aerosol particle size and penetration for the elutriator was measured in calm air. The measured penetrations were compared with the calculated performance of the sampler and with the sampling convention for the ISO respirable dust. The calculated bias of sampled masses with respect to the ISO respirable mass was almost zero for the workplace aerosols.

A Simple Theoretical Model for the Air Flow and Particle Penetration in a Modified Horizontal Elutriator with Plates of Unequal Lengths

A simple theoretical model is presented for the distribution of air speeds in a modified horizontal elutriator consisting of groups of plates with different lengths. Equations are presented for calculating the particle penetration both in channels of shortended plate lengths, as downstream the end of a shortended plate.

作業環境測定基準に基づく吸入性粉じんとロウボリウムサンプラ用多段分粒装置の性能評価

The relationship between dust size and penetration for a static horizontal elutriator (Sibata C-30) was measured in calm air. The elutriator as a low-volume air sampler is widely used as a dust size classifier in work environment measurements. The actual penetrations were compared with the theoretical models of the sampler and with sampling convention for respirable dust in work environment measurement. The sampling convention was recently introduced into the Japanese standard for work environment measurement and is based on the ISO 7708 respirable dust convention. The bias of sampled masses from the respirable dust was calculated for two flow rates of the sampler, i.e., 50% cut sizes of 4 microm and 5 microm, from measured penetration curves. The bias of the sampler was overestimated in the 5 microm, 50% cut condition and underestimated in the 4 microm, 50% cut condition for most workplace sampling situations.

Determination of large aerosol particle size by elutriation.

Inhalable dust fraction determination requires aerodynamic size information for large aerosol particles. Operation of cascade impactors at flows that collect these particles leads to jet Reynolds numbers outside the range of established impactor performance. Horizontal elutriators, designed to match earlier respirable dust curves at a single flow rate, may be used to provide aerodynamic size information for particles larger than 50 microm. Operation of these elutriators at higher than design flow rates and angles other than horizontal provides for particle penetration over the size range of the inhalable dust curve. Equations are provided that relate penetration, flow rate, and angle to aerodynamic diameter to allow for bracketing the desired size and distribution. The use of impactor data reduction methods to determine size distributions with the MRE horizontal elutriator is examined with a spreadsheet model. Comparison of elutriator size determination with an impactor in the 10 to 15 microm range, where both methods could be used, resulted in reasonable agreement. This method provides for determination of aerodynamic characteristics of large aerosols in field sampling conditions.

Evaluation of instruments for dust monitoring in United Kingdom coal mines

The United Kingdom Respirable Dust Regulations for underground coal mines are currently under review; new regulations that are under development will introduce new dust measurement methods and monitoring strategies.Research was undertaken to evaluate instruments for the monitoring of dust and quartz in United Kingdom coal mines and to determine current levels of personal dust exposure in the industry. The aim of the research was to identify instruments capable of being deployed more flexibly in a range of mine workings. The CIP10 respirable dust sampler, developed by CHERCHAR, was identified as a suitable instrument for both personal and fixed-point measurements of respirable dust and quartz. In fixed-point measurements the CIP10 results were highly correlated with colocated results obtained with the MRE 113a horizontal elutriator—the instrument stipulated in the current United Kingdom regulations. As the CIP10 is small, light and has a long battery life, it can be used for full-shift personal dust monitoring in both large and small mines.Personal respirable dust exposures measured during an underground survey that formed part of the research were lognormally distributed with a median value of 1.8 mg/m3 and a geometric standard deviation of approximately two. There was limited evidence of higher mean exposures for certain mine-workers. In general, personal exposure measurements did not differ greatly from fixed-point measurements. The introduction of personal monitoring in United Kingdom coal mines will, however, enable the most highly exposed individual mine-workers to be identified and dust control measures to be directed in a cost-effective manner. Personal monitoring was found to be particularly useful in the assessment of localized dust concentrations in smaller mines and in the development areas of larger mines, where representative fixed-point sampling can be problematic.

Development and Evaluation of an Inhalable Bioaerosol Manifold Sampler

This paper describes the development and evaluation of an inhalable bioaerosol manifold sampler for the collection of replicate samples over sequential sampling periods. Wind tunnel experiments at wind velocities ≤0.6 m/sec (≤~120 ft/min) and at a sampling velocity of 0.6 m/sec yielded sampling efficiencies within 10% of the American Conference of Governmental Industrial Hygienists' inhalable curve up to particle diameters of about 18 urn and efficiencies within 18% for diameters up to 26 urn. At wind velocities ≥0.6 m/sec, a sampling velocity of 0.8 m/sec yielded efficiencies that were within 15% of the inhalable curve up to diameters of about 22 μm and within 20% for diameters up to 25 μm. Microscopic counts of 15.6-μm and 25.6-μm monodisperse polystyrene beads aerosolized in the wind tunnel and collected with the manifold sampler yielded precise concentrations (pooled CV=9.0 and 5.3%, respectively) averaging 115% and 92%, respectively, of measurements with the APS Model 3310 aerodynamic particle sizer. Field tests in a cotton dust environment demonstrated the ability to generate a time/concentration profile of fungal spores similar to that indicated for cotton dust levels determined with horizontal elutriators. Cotton dust was sampled efficiently while cotton fibers were excluded. Field tests on a dairy farm indicated no statistically significant bias (p=0.72) between spore concentrations determined with the manifold sampler and concentrations determined through a central test port.

Development and evaluation of an inhalable bioaerosol manifold sampler.

This paper describes the development and evaluation of an inhalable bioaerosol manifold sampler for the collection of replicate samples over sequential sampling periods. Wind tunnel experiments at wind velocities < or = 0.6 m/sec (< or = approximately 120 ft/min) and at a sampling velocity of 0.6 m/sec yielded sampling efficiencies within 10% of the American Conference of Governmental Industrial Hygienists' inhalable curve up to particle diameters of about 18 microns and efficiencies within 18% for diameters up to 26 microns. At wind velocities > or = 0.6 m/sec, a sampling velocity of 0.8 m/sec yielded efficiencies that were within 15% of the inhalable curve up to diameters of about 22 microns and within 20% for diameters up to 25 microns. Microscopic counts of 15.6-micron and 25.6-micron monodisperse polystyrene beads aerosolized in the wind tunnel and collected with the manifold sampler yielded precise concentrations (pooled CV = 9.0 and 5.3%, respectively) averaging 115% and 92%, respectively, of measurements with the APS Model 3310 aerodynamic particle sizer. Field tests in a cotton dust environment demonstrated the ability to generate a time/concentration profile of fungal spores similar to that indicated for cotton dust levels determined with horizontal elutriators. Cotton dust was sampled efficiently while cotton fibers were excluded. Field tests on a dairy farm indicated no statistically significant bias (p = 0.72) between spore concentrations determined with the manifold sampler and concentrations determined through a central test port.

Sampling errors associated with sampling plate-like particles using the Higgins- and Dewell-type personal respirable cyclone

An investigation has been carried out into possible differences in personal Higgins- and Dewell-type cyclone performance when sampling plate-like particles such as talc or metallic flakes, in contrast to spherical particles. Theoretical calculations indicate that particle shape effects will be dominated by particles assuming a preferred orientation that is different in the respiratory system and the cyclone. Experimental comparisons with MRE 113A horizontal elutriators indicated talc particles to align randomly in the cyclone. If a maximum drag orientation is assumed in the respiratory system, this will lead to the respirable fraction of an aerosol of plate-like particles being underestimated by approximately 15% on average. However, more information is needed on how non-spherical particles behave in the respiratory tract before the degree of undersampling can be further quantified.

Optimization of the Performance of Existing Respirable Dust Samplers

Abstract This article describes the evaluation of optimal operating modes for three existing respirable dust samplers by computer modeling of their experimentally determined sampling characteristics. The motivation behind this study is the agreement, in principle, to replace the diverse United States, European, and International conventions for respirable dust sampling with a single new convention. In assessing the sampler performance with respect to the new convention, some questions of general importance in the development of performance specifications for dust sampling instruments are discussed. The three instruments considered in this study were the U.K. SIMPEDS cyclone, the U.S. 10-mm nylon cyclone, and the MRE 113A horizontal elutriator. Although there is a considerable body of experimental data on these instruments, in no case is the complete picture available. The experimental data were used to computer model the mass that the instruments would sample from a range of ideal lognormally distributed ...

Comparison of the 10-mm Nylon Cyclone, Horizontal Elutriator, and Aluminum Cyclone for Silica and Wood Dust Measurements

Abstract The relative performance of the 10-mm nylon cyclone, the horizontal elutriator, and the aluminum cyclone were compared for silica and for wood dust by determining respirable dust concentrations simultaneously using the three devices in an environmentally controlled chamber at various humidity levels. The aluminum cyclone consistently reported significantly higher levels than the elutriator (22 percent higher for silica and 25 percent higher for wood dust), which in turn reported significantly higher levels than the nylon cyclone (21 percent for silica and 41 percent for wood dust). Humidity was found to significantly affect the ratio of nylon cyclone/ elutriator concentration and the ratio of nylon cyclone/aluminum cyclone concentration for respirable silica, with the ratio decreasing as humidity decreased. The type of dust was found to significantly alter the relationships between the various size-selective devices. The nylon cyclone appeared to collect proportionately less wood dust than silica...

COMPARISON OF MEASURED RESPIRABLE DUST SAMPLER PENETRATION CURVES WITH SAMPLING CONVENTIONS

Measured sampler penetration curves are presented for British personal cyclone samplers and the MRE 113A static horizontal elutriator in calm air. These curves are compared with previous results for these instruments, and with theoretical models of sampler behaviour. The sampling efficiency of the elutriator when facing a moderate wind is discussed. The penetration curves are assessed by comparison with standard sampling conventions for respirable dust.

Size selection of fibres by cyclone and horizontal elutriator

The size selection characteristics of a horizontal elutriator and a cyclone when sampling a fibrous aerosol have been investigated using an Aerodynamic Particle Sizer (APS). An aerosol of spherical particles was also used to validate the experiment. Methods of data treatment were assessed by comparing experimental error with that predicted by the Poisson distribution. The measurement of fibres by the APS and the size selection of fibres by the lung are discussed. It is suggested that selection by the lung would be best characterized by the aerodynamic diameter of fibres in random orientation. Using this parameter the results indicate that relative to the BMRC respirability curve; (1) the horizontal elutriator collects a slightly larger fraction when sampling straight symmetrical fibres; and (2) the cyclone selection curve approximates to the BMRC curve, but is somewhat steeper.

Sedimentation Method in Calibrating Optical Particle Counters

The use of a horizontal elutriator in calibrating optical particle counters according to aerodynamic particle size has been studied. As elutriator a ceramic component with 4800 parallel square channels with dimensions of 0.1 × 0.1 × 15.2 cm has been used. The advantage of the present method is that the particle penetration characteristic of the elutriator can be easily changed simply by varying the flow rate. The elutriator has been used in studying the properties of an optical particle size analyzer (PMS Las-X). The relationship between the equivalent aerodynamic particle size and the corresponding particle size indicated by the analyzer has been determined by using Arizona road dust particles and dioctylphthalate particles. The practical size range of the method is Dp ≥ 0.3 μm.

COMPARATIVE LABORATORY TRIALS OF TWO PORTABLE DIRECT-READING DUST MONITORS

Two commercially available portable direct-reading respirable-dust monitors have been tested in a laboratory calm air chamber against a range of airborne dusts. Relative to concentrations measured with the MRE 113A horizontal elutriator the instruments showed a variable degree of agreement, and could be influenced both by particle size distribution and by particle composition. For a given composition and particle size distribution however it should be possible to calibrate the instruments to give consistent agreement with the horizontal elutriator. Continuous recording of data from the instruments was successfully achieved using a data logger. This proved extremely useful in the calculation of time-weighted dust concentrations, and in revealing dust concentration histories for each monitor.

A Reference Size-Selective Sampler for Respirable Dust

Theoretically calculated stepped horizontal elutriator samplers are proposed as reference size-selective dust samplers for use in calibration of practical respirable dust samplers. The practical calibration could be carried out in polydisperse or monodisperse dust clouds by direct comparison. It is shown that a good match to the proposed American Conference of Governmental Industrial Hygienists (ACGIH) respirable dust specification can be obtained when using multiple horizontal elutriator channels with the same width and airflow but with differing lengths.

A Reference Size-Selective Sampler for Respirable Dust

Theoretically calculated stepped horizontal elutriator samplers are proposed as reference size-selective dust samplers for use in calibration of practical respirable dust samplers. The practical calibration could be carried out in polydisperse or monodisperse dust clouds by direct comparison. It is shown that a good match to the proposed American Conference of Governmental Industrial Hygienists (ACGIH) respirable dust specification can be obtained when using multiple horizontal elutriator channels with the same width and airflow but with differing lengths.

Comparison of Respirable Dust Samplers for Use in Hard Rock Mines

Five respirable dust size selectors and eleven filter holders were compared, some at two flow rates. These included horizontal elutriators, impactors, metal cyclones and nylon cyclones. The comparisons were carried out both in the laboratory and in mines. The respirable dust on the filters was assessed by weighing, and where relevant, by X-ray diffraction for quartz with the use of a direct-on-filter method. The results obtained showed that the relation between most pairs of samplers could be represented by a straight line through the origin and that the personal samplers collecting more dust—the CAMPEDS impactor and the B.C.I.R.A. cyclone—gave higher reproducibility in the low dust concentrations found in many hard rock mines. The samplers based on the nylon cyclone were less suitable for hard rock mines containing a substantial proportion of quartz, though satisfactory in coal mines with their higher dust control standards.

Horizontal Elutriator Preliminary Test Results under Nonstill Air Conditions

Recently, a high-volume horizontal elutriator with a flared inlet was developed to monitor inhalable particulates in the ambient air. Preliminary results of a study to evaluate the performance of the horizontal elutriator under nonstill air conditions are presented. Collection efficiency data were obtained for monodisperse aerosols with particle sizes of 4.0, 9.25, 20.0, and 30.7 um aerodynamic diam. Experimental results indicate that the device does not meet the established performance criteria. The main cause of nonperformance is prrobably a combination of exterior turbulent propagation into the initial part of the elutriator, nonisokinetic sampling conditions and particle diffusion.

Growth and Deposition of Saline Droplets Covered with a Monolayer of Surfactant

Experiments and theoretical calculations were carried out to investigate the effects of a surfactant monolayer on the growth and deposition of saline droplets in a horizontal elutriator. Cetyl alcohol was used as the surfactant in the study. In the calculations, the condensation coefficient of water vapor on the surface of a droplet covered with a surfactant monolayer was determined from the specific evaporation resistance data. It was found, in the presence of a surfactant monolayer, the growth of saline droplets is retarded and the deposition efficiency in the elutriator is reduced. The deposition pattern in the elutriator is mainly determined by two time scales: the growth retardation time and the time for gravitational settling. When these two time scales are comparable, the distribution of particle deposits in the elutriator is markedly nonuniform.