Particle assessment

The delivery system needs to be discussed. This will include consideration of surface charges of the particles and of the device, the development of charges during filling of the product and during in-use streaming, and any relevant changes in effective particle size. Where the prototype device differs from the production device, additional data may be required. Dose uniformity and fine particle assessments at the relevant air flow rates should be reported. 

A promising start has been made in packed tube CFD simulation, especially at lower Re and for reduced geometries such as unit cells and bed segments. Applications to transport and catalyst particle assessment are active areas of research. We look forward to the insights that these simulations promise, to more streamlined and easier application of the CFD methods, and to wider applications such as two-phase flow in trickle beds. 

Pandis S. (2003) Atmospheric aerosol processes how particles change when suspended in air. In NARSTO Fine Particle Assessment, chap. 2 (available at http //www.cgenv.com/ Narsto). 

Anard D, Kirsch-Volders M, Elhajouji A, Bel-PAEME K and Lison D (1997) In-vitro genotoxic ects of hard metal particles assessed by alkaline sin cell gel and elution assay. Carcinogenesis 18(1) 77-184. 

Diffusion and Mass Transfer During Leaching. Rates of extraction from individual particles are difficult to assess because it is impossible to define the shapes of the pores or channels through which mass transfer (qv) has to take place. However, the nature of the diffusional process in a porous soHd could be illustrated by considering the diffusion of solute through a pore. This is described mathematically by the diffusion equation, the solutions of which indicate that the concentration in the pore would be expected to decrease according to an exponential decay function. 

Microscopy (qv) is appHed when particle identification and, perhaps, shape evaluation ate important in addition to size. Shape characterization is used in the abrasives (qv) industries, pollution or contamination assessment, and forensic studies (see Forensic CHEMISTRY). 

Surface Area and Permeability or Porosity. Gas or solute adsorption is typicaUy used to evaluate surface area (74,75), and mercury porosimetry is used, ia coajuactioa with at least oae other particle-size analysis, eg, electron microscopy, to assess permeabUity (76). Experimental techniques and theoretical models have been developed to elucidate the nature and quantity of pores (74,77). These iaclude the kinetic approach to gas adsorptioa of Bmaauer, Emmett, and TeUer (78), known as the BET method and which is based on Langmuir s adsorption model (79), the potential theory of Polanyi (25,80) for gas adsorption, the experimental aspects of solute adsorption (25,81), and the principles of mercury porosimetry, based on the Young-Duprn expression (24,25). 

For dust-control work, it is recommended that a preliminary quah-tative examination of the dust first be made without a detailed particle count. A visual estimate of particle-size distribution will often provide sufficient guidance for a preliminaiy assessment of reqmrements for collection eqmpment. 

Settling and rainout are important mechanisms of contaminant transfer from the atmospheric media to both surface soils and surface waters. Rates of contaminant transfer caused by these mechanisms are difficult to assess qualitatively however, they increase with increasing soil adsorption coefficients, solubility (for particulate contaminants or those adsorbed to particles), particle size, and precipitation frequency. 

Artifacts may be introduced from the environment or through preparative techniques. When assessing individual tiny particles of material, the risk of loss or contamination is high, so that samples of this nature are handled and prepared for examination in a clean bench or a cleanroom (class 100 or better). 

As described above, the code "SIFTING" requires several microstructural inputs in order to ealculate a failure probability distribution. We are thus able to assess the physieal soundness of the Burchell model by determining the change in the predicted distribution when microstructural input parameters, such as particle or pore size, are varied in the "SIFTING" code. Each microstructural input parameter... 

Airborne particulates include dust, fume and aerosols. Many such particles are invisible to the naked eye under normal lighting but are rendered visible, by reflection, when illuminated with a strong beam of light. This is the Tyndall effect and use of a dust lamp provides a simple technique for the rapid assessment of whether a dust is present, its flow pattern, leak sources, the effects of ventilation, etc. More sophisticated approaches are needed for quantitative data. Whether personal, spot or static sampling is adopted will depend upon the nature of the information required. 

In heterogeneous systems AP must be critically reviewed, especially if the reaction involves a two-phase mixture of liquid and gas, or if the gas flows through a deep bed of catalyst particles as in the FCC systems. AP should be checked early in the design process to assess its influence on the overall plant integrity. 

In densely populated areas, traffic is responsible for massive exhausts of nitrous oxides, soot, polyaromatic hydrocarbons, and carbon monoxide. Traffic emissions also markedly contribute to the formation of ozone in the lower parts of the atmosphere. In large cities, fine particle exposure causes excess mortality which varies between one and five percent in the general population. Contamination of the ground water reservoirs with organic solvents has caused concern in many countries due to the persistent nature of the pollution. A total exposure assessment that takes into consideration all exposures via all routes is a relatively new concept, the significance of which is rapidly increasing. 

Tyndall lamp A parallel light beam pro jected onto a cloud of dust particles gen crated from a process to produce scattering of the light, allowing an assessment of the magnitude and path of the cloud. 

This test uses a cloud of sodium chloride particles. The size distribution is from below 0.1 pm to approximately 2.0 pm and a figure for percentage penetration is obtained. Since the test does not materially load the filter, it can be used to assess the quality of each unit before dispatch. This test forms the basis of Eurovent 4/4, which differs a little in procedure. 

The potential between the Helmholtz double layer of a charged particle. Important for assessing the suitability of polyelectrolyte chemicals because it can be easily measured, unlike some other electrokinetic forces. 

The above model has been successfully used to describe the thermomechanical behaviour of iron-particle reinforced resins. More precisely, the importance of this model is that it provides a quantitative means for assessing the adhesion efficiency between the phases and its effect on the thermomechanical properties of the composite. Moreover, by using this model the thermomechanical behaviour, as well as the extent of the mesophase developed in particulates could be described. The... 

It is seen that, although the dimensions and particle sizes may not be precisely matched, all three columns are of a size closely similar to those commercially available with, perhaps, the exception of the long high efficiency column. The small 3 cm column is excellent for the preliminary assessment of a sample. As a result of its size it does not use large volumes of solvent and can be quickly reconditioned after a separation in readiness for the next run. It is very convenient for choosing the best phase system in method development. The other columns would be chosen on a basis of the efficiency required to separate the critical pair in the reduced chromatogram of the sample for analysis. 

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