High-density particles

Figure 2.16 Idealized arrangements of particles on a shaking table a = smaller, higher-density particples b = high-density particles, large in size and low-density particles, small in size c = lesser, low-density particles.

Overall gas holdup increases with gas velocity in the dispersed bubble regime for both low and high density particle systems (Davison, 1989 Tang and Fan, 1989 Bly and Worden, 1990 Nore et al., 1992 Pottboff and Bohnet, 1993). As gas velocity increases and the system enters the coalesced and slugging regimes, the rate of increase in the overall gas holdup decreases (Bly and Worden, 1990). 

Density separation processes exploit the differences in densities (p) of the particles to be separated. Fly ash is comprised primarily of two components aluminosilicate ash particles (p 2.1-2.4g/cm3) and unbumed carbon particles (p 1.8-2.0 g/cm3) with minor amounts of iron-rich spinel, commonly referred to as magnetite (p 3.0-4.5 g/cm3). Under ideal conditions, particles can be efficiently separated based on differences in particle densities alone. However, in continuous density separation processes, particle size differences induce separation inefficiencies that is, smaller, high-density particles behave similarly to larger, low-density particles. For this reason, narrowing the size... 

Axial mixing in the liquid, induced by the upflow of the gas bubbles, can be substantial in commercial-scale bubble columns, especially in the chum turbulent regime. Due to typically small particle size, the axial dispersion of the solid catalyst in slurry bubble columns is expected to follow closely that of the liquid exceptions are high-density particles. The liquid axial mixing can be represented by an axial dispersion coefficient, which typically has the form... 

As also found in bubble columns, the concept of the effective viscosity fails for relatively high-density particles in low-viscosity liquids [87] for a relative increase of /iefr below 1.3. Nevertheless, eq 41 is a very remarkable result. Its accuracy is claimed to be within 15%, provided that ... 

Particle density Below 2-3 g/cm Good fluidization Unsatisfactory fluidization when high density particles are used Blending with low-density particles Installation of internals... 

Methods, Fig. 1 A frame from a continuous flow of particles in a leactimi chamber, (a) Flow of particles under a pressure gradient (the arrows at the inlet and outlet show the flow), (b) Flow front of high-density particles, showing a parabolic velocity profile. Note that the particles in the middle travel at a high velocity, thereby showing a low density, and the particles at the sides travel at a low velocity, thereby showing a high density... 

Fig. 16.3 Comparison of SEM images of low and high-density particles of LiNiO ...

Values of S in Zwietering s (1958) correlation are given and compared with high density particles... 

Garcia-Ochoa J, Khalfet R, Poncin S, Wild G. (1997) Hydrodynamics and mass transfer in a suspended sohd huhhle column with polydispersed high density particles. Chem. Eng. Sci.,... 

Figure 1.16 Growth sequence observed by cryo-TEM for particles prepared from a solution of 0.17 M tetraethoxysilane (TEOS), 1.0 M H2O, and 1.0 M NH3 in n-propanol (a) sample frozen 6 min into reaction, no particles visible (b) sample frozen 16 min into reaction (arrow indicates low-density particle), average particle size 26 nm (c) sample frozen 24 min into reaction (arrow indicates high-density particle), average particle size 20 nm and (sample frozen 66 min into the reaction, average particle size 48 nm. (From Bailey and Mecartney. ... 

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