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Powder Characterization
Published in Mohamed N. Rahaman, Ceramic Processing, 2017
Particle shape influences the flow properties and packing of powders as well as their interaction with fluids (e.g., viscosity of a suspension). Qualitative terms are sometimes used to give an indication of the nature of the particle shape (e.g., spherical, equiaxial, acicular, angular, fibrous, dendritic, and flaky). However, except for the fairly simple geometries such as a sphere, cube or cylinder, the quantitative characterization of particle shape can be fairly complex. The shape of a particle is commonly described in terms of a shape factor, which provides some measure of the deviation from an idealized geometry, such as a sphere or a cube. For elongated particles, the most common way of representing the shape has been in terms of the aspect ratio, defined as the ratio of the longest dimension to the shortest dimension. For powders, the sphere is used as a reference, and the shape factor is defined as:
Thermal Radiation
Published in Anthony F. Mills, Heat and Mass Transfer, 2018
The preceding situations were particularly simple to analyze because all the radiation leaving surface 1 reached surface 2. Now consider radiation exchange between two finite black surfaces A1 and A2, as shown in Fig. 6.6. By inspection, only part of the radiation leaving surface 1 is intercepted by surface 2 and vice versa. We define the shape factor (or view factor) F12 as the fraction of energy leaving A1 that is intercepted by A2; likewise, F21 is the fraction of energy leaving A2 that is intercepted by A1. The shape factor is a geometrical concept and depends only on the size, shape, and orientation of the surfaces. Radiation leaves surface 1 at the rate of Eb\A\ [W]; the portion that is intercepted by surface 2 is then Eb1A1F12. Likewise, the radiation leaving surface 2 that is intercepted by surface 1 is Eb2A2F21. Since both surfaces are black, all incident radiation is absorbed, and the net radiant energy exchange is () Q˙12=Eb1A1F12−Eb2A2F21
Powder Characterization
Published in Mohamed N. Rahaman, Ceramic Processing, 2017
Particle shape influences the flow properties and packing of powders as well as their interaction with fluids (e.g., viscosity of a suspension). Qualitative terms are sometimes used to give an indication of the nature of particle shape (e.g., spherical, equiaxial, acicular, angular, fibrous, dendritic, or flaky). However, except for the fairly simple geometries such as a sphere, cube, or cylinder, the quantitative characterization of particle shape can be fairly complex. The shape of a particle is commonly described in terms of a shape factor, which provides some measure of the deviation from an idealized geometry such as a sphere or a cube. For elongated particles, the most common way of representing the shape has been in terms of the aspect ratio, defined as the ratio of the longest dimension to the shortest dimension. For powders, the sphere is used as a reference, and the shape factor is defined as: Shapefactor=1ψ=surfaceareaoftheparticlesurfaceareaofaspherewiththesamevolume
Effect of fibre cross-sectional shape on bending behaviour of yarns and fabrics; part I
Published in The Journal of The Textile Institute, 2025
Mukesh Kumar Singh, B. K. Behera
The variation in bending rigidity and bending hysteresis of a particular yarn with a typical shape is expected from the viscoelastic properties of the PET fibres as reported by Ly and Denby (1984) in the case of wool fibre. It is evident from bending rigidity data and geometrical aspects (Table 2) that rectangular shape offers the least bending stiffness with a constant area of cross section with other shapes. The hexalobal cross section is the second least stiff fibre. It is evident from different shapes that the mass distribution is concentrated more close to the neutral axis, its bending rigidity reduces. This argument further strengthens by the bending rigidity of double flange fibre, in which the mass distribution is away from its neutral axis and bending rigidity increases. The shape factor is defined as the ratio between diameter equivalents to the perimeter to diameter equivalent to the area. In most of the shapes, the experimental shape factor is less than the theoretical shape factors. Takarada et al. (2001) has explained on the basis that after extrusion from the spinneret, the filament undergoes different hot and cold surfaces, heat transfer and air friction, the sharp edges are suppressed and shape tends towards circularity as shown in Figure 1.
Experimental study of aerodynamic resuspension of RDX residue
Published in Aerosol Science and Technology, 2019
Kalyan Kottapalli, Igor V. Novosselov
To quantify particle morphology, 3D shape factor is used. In aerodynamic resuspension scenario, the balance of moments acting on particles highly depends on the height of the particle as it is used for drag force calculation and the moment of the drag force (Dominik and Tielens 1995). The height estimation cannot be performed by a 2D analysis without the assumption of the particle shape. Using SEM, we characterize the height (S), maximum (L), and minimum (I) chord lengths for 50 representative particles. Optical profilometry (VK-X250, Keyence Corporation, Itasca, IL, USA) with the submicrometer lateral resolution is used to confirm the height measurements for similarly prepared samples; these measurements cannot be used to evaluate the morphology of the particle near the surface. Thus, the method is only used to validate the height measurement obtained by the angled SEM method. Figure 5 shows the comparison of particle heights calculated using both techniques. Glass microsphere calibration shows particle diameter to be equal to the height for both techniques. The height of RDX particles in the 10–25 µm region increases with their equivalent 2D diameter. The SEM data is in good agreement with the profilometer measurements.