Residual Particle Size Distribution Research Articles

Effects of residual effective stress and particle size distribution on reconsolidation characteristics of granular materials after undrained cyclic shear: a 3D DEM study

Effects of residual effective stress and particle size distribution on reconsolidation characteristics of granular materials after undrained cyclic shear: a 3D DEM study

Performance Analysis of Electrodynamic Screens Based on Residual Particle Size Distribution

Dust accumulation on the optical surfaces of solar collectors causes significant losses in their energy yield. Fine dust particles, compared with coarse ones, contribute significantly more in the performance loss, assuming identical surface mass concentration. This study examines the performance of different electrodynamic screen (EDS) prototypes, operated under different conditions, in removing fine dust particles in the laboratory environment. After going through several cycles of dust deposition and cleaning using EDS, the dust residue left on each EDS prototype is collected and analyzed using a Horiba particle size distribution (PSD) analyzer. The PSD analyses determine which EDS design has performed superior in removing a given size range and in which operational condition. The results are advantageous in the optimization procedure of EDS to attain maximum dust removal efficiency and minimum optical interference.

Modeling and Understanding Combination pMDI Formulations with Both Dissolved and Suspended Drugs.

A simulation model has been established to predict the residual aerodynamic particle size distribution (APSD) of dual-component pressurized metered dose inhalers (pMDIs). More specifically, this model estimates the APSD of pMDI formulations containing dissolved and suspended compounds for various formulations, and has been verified experimentally. Simulated and experimental data illustrate that APSDs of the dissolved and suspended components of the pMDI are influenced by concentrations of the dissolved and micronized suspended drugs, along with suspended drug size. Atomized droplets from such combination formulations may contain varying number of suspended drug particles and a representative concentration of dissolved drug. These sub-populations of atomized droplets may explain the residual APSDs. The suspended drug follows a monomodal, lognormal distribution and is more greatly impacted by the size and concentration of the suspended drug in comparison to the concentration of dissolved drug. On the other hand, dissolved drug illustrates a bimodal, lognormal residual particle size distribution both theoretically and experimentally. The smaller mode consists of residual particles made of dissolved drug only, while the larger mode consists of residual particles that contain both dissolved and suspended drugs. The model effectively predicted the size distributions of both the dissolved and suspended components of combination formulations (r(2) value of 0.914 for the comparison of simulated versus experimental MMAD values for the formulations examined). The results demonstrate that this model is a useful tool that may be able to expedite the development of combination pMDI formulation.

Optimization of a Crystallization Process for Orantinib Active Pharmaceutical Ingredient by Design of Experiment To Control Residual Solvent Amount and Particle Size Distribution

Orantinib is obtained as a final active pharmaceutical ingredient (API) through crystallization by neutralizing the potassium salt of orantinib in a mixed solvent of isopropyl alcohol (IPA) and H2O. However, the amount of residual IPA in the orantinib API varies, and the neutralizing crystallization makes control of the particle size distribution of the orantinib API difficult. We performed 36 experiments using the design of experiment approach to screen and optimize the process parameters for an orantinib API crystallization process. The screening clarified the strength and trends in the effects of various parameters on the amount of residual IPA and the particle size, and the temperature and solvent ratio were critical process parameters. Next, we constructed a design space for the temperature and solvent ratio by optimizing the process parameters, prepared a response surface model, and calculated the optimal conditions under which both the amount of residual IPA and the particle size distribution could...

Assessment of sediment exclusion efficiency for several modified labyrinth weirs

A trapezoidal labyrinth weir is a general transverse hydro-structure typically placed across rivers that causes longitudinal sediment discontinuity and affects riparian ecological system. A sediment exclusion labyrinth (SEL) weir is a modification designed to increase sediment exclusion from upstream to downstream over or through it. Hydraulic model experiments were carried out in straight rectangular cross-sectional open channel (15 m in length and 0.82 m in width). Four different shapes of weirs were examined. type 1 was a general labyrinth weir, whereas types 2–4 were SEL weirs with an inclined bottom slope (type 2), open slots (type 3), and reversed-wedge type holes (type 4). Standard sand (Jumunjin, Korea, d50 = 0.56 mm, σg = 1.48, SG = 2.65) was uniformly supplied upstream using an in-house grooved drum, and sediment exclusion efficiency was calculated from the ratio of sediment amount to excluded sediment yield for each type of weir. Higher efficiencies were founded in all SEL weirs compared with the sediment exclusion efficiency of the type 1 weir. In particular, type 2 and type 4 weirs were easy to construct and their flow patterns and hydraulic performance were similar to those of type 1. Finally, their sediment exclusion efficiencies were higher under a normal water level (Fr ≤ 0.2), whereas the type 3 weir was the pattern favorable for a high water level (Fr > 0.2) because its discharge capacity was significantly higher. Sediment exclusion characteristics were analyzed in terms of flow rate based on the decomposition analysis of residual sediment particle size distribution. It is expected that the results from this study will be used to design SEL weirs as basic materials if more hydrodynamic parameters are studied and combined with field monitoring.

The influence of initial atomized droplet size on residual particle size from pressurized metered dose inhalers

Pressurized metered dose inhalers (pMDIs) are widely used for the treatment of diseases of the lung, including asthma and chronic obstructive pulmonary disease. The mass median aerodynamic diameter of the residual particles (MMADR) delivered from a pMDI plays a key role in determining the amount and location of drug deposition in the lung and thereby the efficacy of the inhaler. The mass median diameter of the initial droplets (MMDI), upon atomization of a formulation, is a significant factor influencing the final particle size. The purpose of this study was to evaluate the extent that MMDI and initial droplet geometric standard deviation (GSD) influence the residual aerodynamic particle size distribution (APSDR) of solution and suspension formulations. From 48 solution pMDI configurations with varying ethanol concentrations, valve sizes and actuator orifice diameters, it was experimentally found that the effective MMDI ranged from 7.8 to 13.3 μm. Subsequently, computational methods were utilized to determine the influence of MMDI on MMADR, by modulating the MMDI for solution and suspension pMDIs. For solution HFA-134a formulations of 0.5% drug in 10% ethanol, varying the MMDI from 7.5 to 13.5 μm increased the MMADR from 1.4 to 2.5 μm. For a suspension formulation with a representative particle size distribution of micronized drug (MMAD=2.5 μm, GSD=1.8), the same increase in MMDI resulted in an increase in the MMADR from 2.7 to only 3.3 μm. Hence, the same increase in MMDI resulted in a 79% increase in MMADR for the solution formulation compared to only a 22% increase for the suspension formulation. Similar trends were obtained for a range of drug concentrations and input micronized drug sizes. Thus, APSDR is more sensitive to changes in MMDI for solution formulations than suspension formulations; however, there are situations in which hypothetically small micronized drug in suspension (e.g. 500 nm MMAD) could resemble trends observed for solution formulations. Furthermore, the relationship between APSDR and drug concentration and MMDI is predictable for solution pMDIs, but this is not as straightforward for suspension formulations. In addition, the MMADR was relatively insensitive to changes in initial droplet GSD (from 1.6 to 2.0) and the solution and suspension pMDI residual particle GSDs were essentially identical to the initial droplet GSDs.

Continuous stand-alone controllable aerosol/cloud droplet dryer for atmospheric sampling

Abstract. We describe a general-purpose dryer designed for continuous sampling of atmospheric aerosol, where a specified relative humidity (RH) of the sample flow (lower than the atmospheric humidity) is required. It is often prescribed to measure the properties of dried aerosol, for instance for monitoring networks. The specific purpose of our dryer is to dry cloud droplets (maximum diameter approximately 25 μm, highly charged, up to 5 × 102 charges). One criterion is to minimise losses from the droplet size distribution entering the dryer as well as on the residual dry particle size distribution exiting the dryer. This is achieved by using a straight vertical downwards path from the aerosol inlet mounted above the dryer, and removing humidity to a dry, closed loop airflow on the other side of a semi-permeable GORE-TEX membrane (total area 0.134 m2). The water vapour transfer coefficient, k, was measured to be 4.6 × 10-7 kg m−2 s−1% RH−1 in the laboratory (temperature 294 K) and is used for design purposes. A net water vapour transfer rate of up to 1.2 × 10-6 kg s−1 was achieved in the field. This corresponds to drying a 5.7 L min−1 (0.35 m3 h−1) aerosol sample flow from 100% RH to 27% RH at 293 K (with a drying air total flow of 8.7 L min−1). The system was used outdoors from 9 May until 20 October 2010, on the mountain Brocken (51.80° N, 10.67° E, 1142 m a.s.l.) in the Harz region in central Germany. Sample air relative humidity of less than 30% was obtained 72% of the time period. The total availability of the measurement system was >94% during these five months.

Effect of Focused Ultrasound on Residual Particle Size Distribution in Water

The residual particle distribution in pure water could be a problem in the nanoscience fields because nanoparticles are usually suspended in pure water such as deionized or distilled water. The effect of ultrasound on the residual particle distribution in pure water should be analyzed because the nano particles used in nanoscience are usually dispersed using ultrasound power. In this study, using a cylindrical piezoelectric vibrator, a noncontact-type focusing ultrasound system was fabricated to keep the purity of the water. The residual particle distribution in pure water was investigated. The number of residual particles increased as the ultrasound exposure time increased.

Effect of Focused Ultrasound on Residual Particle Size Distribution in Water

Effect of Focused Ultrasound on Residual Particle Size Distribution in Water

A model for predicting size distributions delivered from pMDIs with suspended drug

A new model has been developed for predicting size distributions delivered from pressurized metered dose inhalers (pMDIs) that contain suspended drug particles. This model enables the residual particle size distribution to be predicted for a broad range of formulations. It expands on previous models by allowing for polydisperse micronized input drug, multiple suspended drugs, dissolved drug, and dissolved or suspended excipient to be included in the formulation. The model indicates that for most pMDI configurations, the majority of droplets contain no drug or a single drug particle and the residual particle size distribution delivered from the pMDI is essentially equivalent to the size distribution of the micronized drug used in the formulation. However, for pMDIs with a high drug concentration or that use small micronized drug particles, there can be a substantial fraction of the droplets that contain multiple drug particles. The residual particle size distribution obtained from these pMDIs can be substantially larger than the size distribution of the micronized drug. Excellent agreement was observed between size distributions predicted using this model and those obtained from experimental cascade impactor measurements ( r 2 = 0.97), thus demonstrating the ability of the model to accurately predict the size distributions obtained from suspension pMDIs.

Measurements of the relation between aerosol properties and microphysics and chemistry of low level liquid water clouds in Northern Finland

Abstract. Physical and chemical properties of boundary layer clouds, together with relevant aerosol properties, were investigated during the first Pallas Cloud Experiment (First Pace) conducted in northern Finland between 20 October and 9 November 2004. Two stations located 6 km apart from each other at different altitudes were employed in measurements. The low-altitude station was always below the cloud layer, whereas the high-altitude station was inside clouds about 75% of the time during the campaign. Direct measurements of cloud droplet populations showed that our earlier approach of determining cloud droplet residual particle size distributions and corresponding activated fractions using continuous aerosol number size distribution measurements at the two stations is valid, as long as the cloud events are carefully screened to exclude precipitating clouds and to make sure the same air mass has been measured at both stations. We observed that a non-negligible fraction of cloud droplets originated from Aitken mode particles even at moderately-polluted air masses. We found clear evidence on first indirect aerosol effect on clouds but demonstrated also that no simple relation between the cloud droplet number concentration and aerosol particle number concentration exists for this type of clouds. The chemical composition of aerosol particles was dominated by particulate organic matter (POM) and sulphate in continental air masses and POM, sodium and chlorine in marine air masses. The inorganic composition of cloud water behaved similarly to that of the aerosol phase and was not influenced by inorganic trace gases.

Monitoring the channel process of a stream restoration project in an urbanizing watershed: a case study of Kelley Creek, Oregon, USA

AbstractPacific Northwest (PNW) streams in the United States were impacted by the 20th century development, when removal of instream structure and channelization degraded an aquatic habitat. The lower Kelley Creek in southeast Portland, USA was channelized during the 1930's Works Progress Administration (WPA) projects. Stream restoration reintroduced pool‐riffle sequences and heterogeneous substrates to protect salmonids while mitigating impacts from flooding. We investigated whether the restored pool‐riffle morphology changed substantially following effective discharge events. We examined channel forms for four reaches representing three time periods—pre‐development (two reference reaches), development and restoration. We conducted thalweg profiles, cross‐sections and pebble counts along the reaches to examine how channel geometry, residual pool dimensions and particle size distribution changed following effective discharge events. The effective discharge flows altered the restoration reach more substantially than the reference reaches. The restoration reach decreased in median particle size, and its cross‐sectional geometry aggraded near its margins. However, the residual pool morphology remained in equilibrium. Richardson Creek's reference reach degraded at the substrate level, while Kelley Creek's reference reach remained in equilibrium. The restoration reach's aggradation may have resulted from sedimentation along the nearby Johnson Creek. In contrast, Richardson Creek's degradation occurred as upstream land use may have augmented flows. Stream channels with low gradient pool‐riffle morphologies are ideal for salmonid spawning and rearing and should be protected and restored within urban corridors. The findings of our study suggest that the connectivity of streams and the dynamic fluvial geomorphology of stream channels should be considered for stream restoration projects in humid temperate climates. Copyright © 2008 John Wiley & Sons, Ltd.

A theoretical and experimental analysis of formulation and device parameters affecting solution MDI size distributions

The influence of formulation and device configurations on the initial droplet and residual particle size distribution from solution MDIs was theoretically and experimentally examined. Aerodynamic size distribution tests were conducted to characterize the size distribution of the residual particles formed when a solution MDI is actuated. The measured size distributions were approximately log-normally distributed, and did not show evidence of a secondary large particle mode. Theoretical relationships were developed to relate the residual particle size distribution to the initial size distribution of the atomized droplets. The residual particle size distribution was shown to be proportional to the nonvolatile concentration to the one-third power. Ethanol concentration, propellant type, valve size, and actuator orifice diameter were all shown to affect the initial droplet size distribution. Deposition of drug in the mouthpiece and USP inlet affect the measured size distribution during aerodynamic particle size measurements. Although there is a significant increase in the size of initial droplets as ethanol concentration increases, there is only aminor increase in the size of the residual particles measured when the USP Inlet is used due to size dependent deposition in the USP inlet and actuator mouthpiece. Vapor pressure was shown to explain only part of the differences in the size of the atomized droplets for various formulations. Theoretical and empirical equations were developed that make it possible to predict the residual particle size distribution for solution MDIs.

Cloud Droplet Residual Particle Microphysics in Marine Stratocumulus Clouds Observed during the Monterey Area Ship Track Experiment

Abstract The effect of marine boundary layer pollution level (as determined by the aerosol particle number concentration) on the size distribution of aerosol particles that formed cloud droplets in marine stratiform clouds is examined. In situ measurements of cloud droplet residual particles with a counterflow virtual impactor during the Monterey Area Ship Track experiment are presented. The variation in residual particle size distribution and number concentration in clouds that formed in marine boundary layers with different pollution levels are discussed. The measurements show a constant shape of the residual particle size distributions for the variety of pollution levels encountered, even though the aerosol number concentration varied by up to a factor of 6. The measurements indicate that particles smaller than 0.1-μm radius controlled cloud droplet number concentrations in the clouds investigated. From literature values of the maximum supersaturations encountered in stratocumulus clouds, one can estim...

A physically-based algorithm for estimating the relationship between aerosol mass and cloud droplet number

In this study, we present a relationship between total accumulation mode aerosol mass concentrations and cloud droplet number concentrations (Nd). The fundamental aim with the present method is to arrive at a physically-based conversion algorithm in which each step in the conversion is based on real physical processes that occur and can be observed in the atmosphere, and in which all of the fields involved can be observed or modeled. In the last conversion (the critical part in the algorithm), we use measurements of the size distributions of cloud droplet residual particles for different pollution conditions. This conversion assumes that the size of the residual particles can be described with a lognormal distribution function and uses the Hatch’Choate relationship to convert between residual volume and number. The relatively sparse data set with which we have developed the present algorithm results in a course classification of the aerosol mass field. Consequently, uncertainties need to be recognized when using the algorithm in its present form in model calculations. The algorithm has been used on data from 15 days and the agreement between calculated and observedNd values is, with one exception, within a factor of 2 and for many of these cases also much better than a factor of 2. In addition to the results of the algorithm itself, we also present a least-squares fit to the predicted Nd values. To improve the algorithm in the longer-term requires more data of scavenging fractions, particle chemical composition and density, and residual particle size distributions as a function of aerosol mass loading and cloud type.

Small Ice Crystals in Cirrus Clouds: A Model Study and Comparison with In Situ Observations

Abstract An air parcel model including homogeneous freezing nucleation of ice crystals has been used to study the formation and development of cirrus clouds. In situ measurements taken during March 1994 over southern Germany were used for comparison with model predictions. Typical experimental data were chosen for a base-case model run. Using measured aerosol properties as input values, the model predicts the measured ice crystal size distribution. In particular, both measurements and model results show the presence of numerous small ice crystals (diameter between 1 and 20 μm). Both measurements and model results also show that small aerosol particles (below 0.1 μm diameter) are active in forming cirrus cloud particles. The modeled microphysical properties including ice crystal size distribution, number concentration, and the residual particle size distribution are in good agreement with the experimental data. Based on the measured parameter values, a model sensitivity study considering air parcel updraft...