David Leith

Cyclone Collection Efficiency: Comparison of Experimental Results with Theoretical Predictions

This paper describes the results of tests conducted on a Stairmand high-efficiency cyclone. The cyclone was pilot-plant scale with a design air flow of 0.139 m3/s (300 cfm). Collection efficiency and pressure drop were measured over a range of air flows at ambient temperature and pressure. An oil mist was used as a test aerosol because it consisted of spherical drops of uniform density unlikely to bounce or reentrain after striking the cyclone wall. At each air flow, a fractional efficiency curve (collection efficiency versus particle diameter) was determined. Experimental curves were compared with fractional efficiency curves generated by several cyclone efficiency theories. Over the range of particle sizes measured (1 to 7 μm), the predictions of a modified version of Barths theory and the Leith-Licht theory were closest to experimental results.

A study of characterize indoor particles in three non-smoking homes

Aerosol concentrations and particle size distributions in three middle income homes were characterized over a three day period. Occupants of the homes were non-smokers. A single central sampling location between the kitchen and dining room areas was used in each of the homes. Thirty-seven and 47 mm prototype personal sampling inlets were collocated with two fixed PM10 dichotomous ambient samplers to determine the average concentration of particulate mass during daytime and evening-early morning sampling periods. Particulate concentrations in the three homes ranged from 14 to 42 μg m−3. On average, 37% of the particle mass was collected in a fine (2.5 μm aerodynamic diameter or below) fraction, 26% was observed in a coarse fraction between 2.5 and 10 μm, and 37% was found in a fraction greater than 10 μm. Particle concentrations obtained with prototype personal samplers compared reasonably well to those obtained with 10 μm ambient air dichotomous samplers. Aerosol size information obtained from automated aerosol instruments suggests that the most significant event for generating small particles in all of the households was cooking. Household vacuum sweeping was the most significant large particle generating event. Electron photomicrographs indicated that particles below 1 μm dominate the particle size-number distribution. Biological and mineral based particles predominantly make up the 2.5–10 μm size range.

Concentration measurement and counting efficiency of the aerodynamic particle sizer 3321

The aerodynamic particle sizer (APS) model 3321 (TSI, Inc., St. Paul, MN) aims to resolve issues identi3ed with an earlier APS, model 3320. These issues include discrepancies between concentrations measured in summing and in correlated modes, and the creation of “anomalous”, large particles caused by recirculation within the detection region. In the present work, the number concentration of a laboratory aerosol was measured with the APS 3321 to be statistically the same in summing mode and in correlated mode for all particles except those in bin 1, i 0:523 � m. Further, anomalous large particles were not measured with the APS 3321. The counting e ciency of the APS 3321 was lower than that for the APS 3320 and ranged from 40% to 60% for particles from 0.8 to 4 � m, respectively. Thus, concentrations reported by the APS 3321 were lower than those measured by the impactor. However, because counting e ciencies were roughly constant with particle size and anomalous particles were absent, the shape of the size distribution was similar to that obtained using the impactor. ? 2003 Elsevier Science Ltd. All rights reserved.

Concentration measurement and counting efficiency for the aerodynamic particle sizer 3320

Abstract The aerodynamic particle sizer (APS, Model 3320, TSI Inc., St. Paul, MN) is an instrument that counts and sizes particles by time-of-flight, an aerodynamic property, and/or by light-scattering intensity, an optical property. If the counting efficiency of the APS 3320, defined as the number of particles counted divided by the number sampled is not 1.0 for particles of all sizes, then the reported size distributions and particle concentrations will be biased. A laboratory aerosol was sampled with two APS 3320s alternating between collecting only time-of-flight data in summing mode and collecting simultaneous time-of-flight and light-scattering intensity data in correlated mode. Collecting data in correlated mode resulted in errors in the reported aerodynamic size distributions and concentrations. The magnitude of the concentration error was an inverse function of concentration, ranging from approximately 10% at 500 particles / cm 3 to 45% at 50 particles / cm 3 . Experiments were also conducted to determine the counting efficiency of the APS 3320 in summing mode by comparing size distributions obtained with the analyzer to those obtained with a cascade impactor. Counting efficiency increased from 30% for 0.5 μm particles to 100% for 0.9 μm particles, then decreased to 60% for 5 μm particles. For particles larger than about 5 μm , the size distribution reported by the APS 3320 was distorted by artificial particle counts. To determine accurate particle size distributions and concentrations, the values reported by this instrument must be adjusted for counting efficiency.

The Logistic Function and Cyclone Fractional Efficiency

The relationship between fractional efficiency and particle size for a cyclone can be described using a logistic equation: efficiency = 1/(1 + (d 50/d)β. To use this equation, cyclone cut diameter, d 50, and the logistic slope parameter, β, must be known. Although cyclone cut diameter can be predicted from equations previously published, no method has been available to predict β. Collection efficiency was measured for particles between 1.4 and 7.4 μm in diameter using pilot-scale apparatus to determine the dependence of d 50 and β on cyclone dimensions and operating conditions. An equation for β was developed from a statistical analysis of these data. Although important questions remain concerning the extent to which the p equation can be generalized beyond the experimental conditions for which it was developed, predictions from this equation seem to allow better prediction of fractional efficiency for data presented here and taken from similar experiments in the literature than is found using the efficie...

Drag on Nonspherical Objects

Stokess law describes drag force on a sphere in creeping flow. This law can be extended to a nonspherical object by allocating the interaction of the fluid with the object into its interaction with two analogous spheres, one with the same projected area and one with the same surface area as the object. This approach was used to characterize dynamic shape factor for objects whose shape factors are reported in the literature. Agreement between data and the equation for shape factor based on this approach was excellent for prisms: R 2 = 0.998. This equation and empirical equations from the literature were used to predict shape factor for a sphere, cylinders, prisms, spheroids, and double conicals whose shape factors have been reported. The equation based on the Stokess law extension predicted shape factors better than the empirical equations, as judged by a least-squares index of performance.

Effect of Cyclone Dimensions on Gas Flow Pattern and Collection Efficiency

According to the static-particle theory for particle collection in a cyclone, a partical of critical size remains suspended at the edge of an “inner core,” where tangential velocity is at a maximum, and inertial and drag forces on the particle balance. This article reports an investigation of the tangential velocity profile of the gas within a pilot-scale cyclone with adjustable inlet, outlet, length, and airflow. Equations to predict the maximum tangential velocity and the length of the inner core from cyclone dimensions can be used with the static-particle theory to predict cyclone collection efficiency. This approach has a better least-squares performance index than the theories of Lapple (1950), Barth (1956), Leith-Licht (1972), and Dietz (1981) for cyclone efficiency data taken from the literature.

Passive aerosol sampler. Part I: Principle of operation

A method has been developed to estimate average concentrations and size distributions with a miniature passive aerosol sampler. To use the passive sampler, one exposes it to an environment for a period of hours to weeks. The passive sampler is intended to monitor ambient, indoor, or occupational aerosols and has potential utility as a personal sampler. The sampler is inexpensive and easy to operate and is capable of taking long-term samples to investigate chronic exposures. After sampling, the passive sampler is covered and brought to the lab. Scanning electron microscopy (SEM) and automated image analysis are used to count and size collected particles with dp

Cyclone performance and design

Abstract Cyclones are probably the most widely used industrial dust collecting devices. Although many procedures for calculating cyclone pressure drop and collection efficiency have been developed, current design practice emphasizes past experience rather than an analytical design procedure. In this paper, five pressure drop theories and four efficiency theories are evaluated against experimental data taken from the literature. One pressure drop and one efficiency theory are judged “best” and used with an optimization procedure to develop a cyclone design method. This design method gives a means of calculating the dimensions of a theoretically optimum cyclone for any set of design criteria. A cyclone designed by this procedure is compared with a standard high efficiency cyclone, and is found theoretically to have better efficiency under identical operating conditions.

Indoor air pollutants and health in the United Arab Emirates

Background: Comprehensive global data on the health effects of indoor air pollutants are lacking. There are few large population-based multi–air pollutant health assessments. Further, little is known about indoor air health risks in the Middle East, especially in countries undergoing rapid economic development. Objectives: To provide multifactorial indoor air exposure and health data, we conducted a population-based study of indoor air pollution and health in the United Arab Emirates (UAE). Methods: We conducted a cross-sectional study in a population-based sample of 628 households in the UAE. Indoor air pollutants [sulfur dioxide (SO2), nitrogen dioxide (NO2), hydrogen sulfide (H2S), formaldehyde (HCHO), carbon monoxide (CO), and particulate matter] were measured using passive samplers over a 7-day period. Health information was collected from 1,590 household members via in-person interviews. Results: Participants in households with quantified SO2, NO2, and H2S (i.e., with measured concentrations above the limit of quantification) were twice as likely to report doctor-diagnosed asthma. Participants in homes with quantified SO2 were more likely to report wheezing symptoms {ever wheezing, prevalence odds ratio [POR] 1.79 [95% confidence interval (CI) 1.05, 3.05]; speech-limiting wheeze, POR 3.53 (95% CI: 1.06, 11.74)}. NO2 and H2S were similarly associated with wheezing symptoms. Quantified HCHO was associated with neurologic symptoms (difficulty concentrating POR 1.47; 95% CI: 1.02, 2.13). Burning incense daily was associated with increased headaches (POR 1.87; 95% CI: 1.09, 3.21), difficulty concentrating (POR 3.08; 95% CI: 1.70, 5.58), and forgetfulness (POR 2.68: 95% CI: 1.47, 4.89). Conclusions: This study provides new information regarding potential health risks from pollutants commonly found in indoor environments in the UAE and other countries. Multipollutant exposure and health assessments in cohort studies are needed to better characterize health effects of indoor air pollutants.