Particulate material, size, shape

Particle size analysis and measurement is an important operation in many industries. The stability, chemical reactivity, opacity, flowability, material strength, and some other properties of many materials are affected by the size distribution and characteristics of the particles within them. There are numerous techniques and instrumentation for all types of particle size analysis and characterization available. Some primary properties of particulate materials, mainly shape, will determine the way the particles are detected or... 

Generally, Httle is known in advance concerning the degree of homogeneity of most sampled systems. Uniformity, rarely constant throughout bulk systems, is often nonrandom. During the production of thousands of tons of material, size and shape distribution, surface and bulk composition, density, moisture, etc, can vary. Thus, in any bulk container, the product may be stratified into zones of variable properties. In gas and Hquid systems, particulates segregate and concentrate in specific locations in the container as the result of sedimentation (qv) or flotation (qv) processes. 

Particulate filtration removes suspended liquid or solid materials whose size, shape, and mass allow them to remain airborne at the air velocity conditions present. Filters are available in a range of efficiencies, with higher efficiency indicating removal of a greater proportion of particles and of smaller particles. Moving to medium efficiency pleated filters is advisable to improve lAQ and increase protection for equipment. However, the higher the efficiency of the filter, the more it will increase the pressure drop within the air distribution system and reduce total airflow (unless other adjustments are made to compensate). It is important to select an appropriate filter for the specific application and to make sure that the HVAC system will continue to perform as designed. Filters are rated by different standards which measure different aspects of performance. 

Since the properties of these particulate materials are basically determined by their mean size, size distribution, external shape, internal structure, and chemical composition, the science in the mechanistic study of particle formation and the fundamental technology in their synthesis and characteristic control may constitute the background for the essential development of colloid science and pertinent industries. Scientists have now learned how to form monodispersed fine particles of different shapes of simple or mixed chemical compositions, and, as a result, it is now possible to design many powders of exact and reproducible characteristics for a variety of uses. These achievements are especially important in the manufacture of high-quality products requiring stringent specification of properties. 

The production of substances with well-defined product properties under consideration of economical and ecological boundary conditions is the objective of many processes. For particulate materials, the product properties depend not only on the chemical composition but also on the dispersity of the material. The dispersity is characterized by the particle size distribution, the particles shape and morphology as well as their interfacial properties. This relation was called property function by Rumpf [1]. The control of the property function is known as product engineering or product design. 

The starting point of any study of particle systems is the characterisation of particles in terms of their size, shape and density. Figure 1 shows the range of sizes of some commonly encountered particulate materials compared with other quantities, such as the wavelengths of electromagnetic radiation and the sizes of molecules. 

This paper is a brief review of original basic engineering research in morphological analysis applied to particle characterization which has been conducted during the last 20 years at the University of Iowa, Center for Particulate Material Processing Sciences. The topics discussed include definitions, theory, instrumental and experimental aspects of size, shape and texture measurements of particulate material. 

Morphological analysis is concerned with particle characterization in the case of particle size, particle shape and particle texture. Particle texture may deal with the particle surface characteristics and also with the particle microstructure. Particle size and shape influence physical and chemical properties of particulate materials. Morphological analysis is being developed in order to facilitate a more accurate description of the properties and behavior of particulate systems from a fundamental knowledge of the characteristics of the particles of the system [1,2]. 

Particle size and distributions can be determined by a number of different methods. The technique described here is light scattering. Different measurement methods produce different results which can be correlated experimentally. The absence of distribution standards for light scattering particle sizing instruments precludes any determination of size accuracy. This is further complicated by particles of non-spherical shape which makes the concept of size very difficult to define. However, for particulate materials encountered in most industrial processes, the assumption that particles are spheres produces quite useful results that are repeatable and relate to important parameters of many processes. 

The behavior and properties of particulate material are, to a large extent, dependent on particle morphology (shape, texture etc.) size and size distribution. Therefore proper measurement, informative data presentation and correct data interpretation are fundamental to an understanding of powder handling and end-use properties. In this chapter the following questions will be addressed ... 

In machines with fixed rolls the optimum compaction force is obtained by adjusting the feed rate and density to the nip. Roller diameter, speed, and gap, as well as characteristics of the raw feed such as friction between material and rolls and particulate size, shape, and brittleness, all greatly influence the respective operating conditions. 

Particulate matter. There is a large variety of such materials in the air, primarily solid matter rather than liquid. The particles come from a variety of sources, they are of different size, shape, color, texture, and chemical composition. They can remain suspen-... 

The size and shape of particles in a particulate product are important for several reasons. The efficiency of any process for production of a particulate material relies on the size, shape, and size distribution. A very small mean size product is difficult to centrifuge, wash, and package. Many products must be dissolved for subsequent use and a broad size range leads to variation in time necessary for dissolution among product crystals. Shape can also be important in applications such as pharmaceuticals wherein different crystal faces have different dissolution rates, leading to variation in bioavailability for crystals of different shapes. Therefore, any comprehensive discussion of crystallization must include the genesis of size and size distribution, as well as its possible measurement and control. 

Deposition in the thoracic region is the sum of aerodynamic and thermodynamic deposition of particulate material. Aerodynamic deposition depends on aerodynamic particle size, total volumetric flow rate, anatomical dead space, tidal volume, functional residual capacity (FRC) (combined residual and expiratory reserve volume or the amount of air remaining in the lungs after a tidal expiration) and diameter of the airways. Thermodynamic deposition depends on anatomical and physical characteristics, such as tidal volume, anatomical dead space, functional residual capacity and the transit time of air within each region. Thermodynamic particle size, which is derived from the diffusion coefficient, particle shape factor and the particles mass density, influence thermodynamic deposition. 

Multiphase flow is encountered in many chemical and process engineering applications, and the behaviom of the material is influenced by the properties of the components, such as their Newtonian or non-Newtonian characteristics or the size, shape and concentration of particulates, the flowrate of the two components and the geometry of the system. In general, the flow is so complex that theoretical treatments, which tend to apply to highly idealised situations, have proved to be of little practical utility. Consequently, design methods rely very much on analyses of the behaviour of such systems in practice. While the term multiphase flows embraces the complete spectrum of gas/liquid, liquid/liquid, gas/solid, liquid/solid gas/liquid/solid and gas/liquid/liquid systems, the main concern here is to illustrate the role of non-Newtonian rheology of the liquid phase on the nature of the flow. Attention is concentrated on the simultaneous co-current flow of a gas and a non-Newtonian liquid and the transport of coarse solids in non-Newtonian liquids. 

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