Particle size ranges

Internal size classification plays an essential role in the funclion-ing of machines for dry grinding in the fine-size range particles are retained in the grinding zone until they are as small as required in the finished product then they are aUowed to discharge. 

In addition, the PMio NAAQS will continue to place emphasis on quantifying and reducing particulate emissions in the less than 10- Im particle-size range. Particle size-specific emission factors have been developed for many sources, and size-specific emission standards have been developed in a number of states. These standards are addressing concerns related to HAP emissions of hea y metals, which are generaUy associated with the submicron particles. 

Particles less than about 1 /btm (10" cm) in diameter have a significant percentage of their atoms at particle surfaces. At such sizes and smaller (in the colloidal size range), particles have important surface properties, whereas larger particles generally do not. Such surface properties have at least three significant consequences ... 

Mean particle size (range) Particle density Degree of expansion at 300 cm/h Binding capacity, mg/mL adsorbent... 

Before choosing a particle sizing technique, examination of the samples under a microscope is usually wise becau.se the range of sizes and shapes present can then he estimated. Most particle size methods are sensitive to particle shape and all are limited with respect to the particle size range. Particles with approximately spherical shapes are measured most accurately. Needles and other shapes that differ significantly from spherical are often analyzed by microscopy. 

Plutonium deposited on soil surfaces may be resuspended in the atmosphere especially in areas that have low soil moisture levels, such as the Nevada Test Site. In drier areas, the levels of ambient airborne dust are expected to be higher than in areas with normal rainfall (Harley 1980). The highest concentrations of plutonium are likely to be found in the fine silt-clay particle size range. Particles of this size tend to be transported the farthest distance by wind and water (WHO 1983). 

The ash loading and size distribution depend on (I) the extent of grinding and fuel cleaning and (2) the combustion time-temperature history. Regardless of the type of combustion system, much of the ash is in the 1-20 pm size range. Particles down to about 10 pm can be efficiently ranoved by hot cyclone collectors. Particles in the 1-10 pm range can be removed by other advanced methods however, this tends to cause additional pressure drop and heat loss. 

Peeler JPK, Huang JR. Segregation of wide size range particle mixtures in fluidized beds. Chem Eng Sci 44 1113 1119, 1989. 

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