Geldart Group

Geldanamycins Geldanazines Geldanoxazines Geldart group Gel dyeing Gel electrophoresis Gelfoam... 

Particle Regimes. In 1973, particles were classified with respect to how they fluidize in air at ambient conditions into Geldart groups (6) (Fig. 4). Particles that formed bubbles immediately after the gas superficial velocity exceeded were designated as Group B particles. For these particles, the... 

Fig. 4. Geldart group particle classification diagram for air at ambient conditions (6). Group A consists of fine particles B, coarse particles C, cohesive,...

FIG. 17-40 Effect of inlet loading on collection efficiency for Geldart Group A and Group C particles. (Couttesy of PSRI, Chicago.)... 

Figure 49 shows a set of bed collapsing curves for a Geldart Group A-A (for Geldart s classification of solid particles, see Geldart, 1972, 1973) binary solids mixture, two closely sized alumina powders, of average particle diameter 104 and 66 microns, respectively. The curve on the extreme left with 0% fines represents the pure coarse component, which is... 

Particulate Fluidization Fluid beds of Geldart group A powders that are operated at gas velocities above the minimum fluidizing velocity (U ) but below the minimum bubbling velocity (U ) are said to be particulately fluidized. As the gas velocity is increased above Umf, the bed further expands. Decreasing (ps - py), dp and/or increasing if increases the spread between Umf and U. Richardson and Zaki [Trans. Inst. Chem. Eng., 32, 35 (1954)] showed that U/Ut = n, where n is a function of system properties, 8 = void fraction, U = superficial fluid velocity, and Ut = theoretical superficial velocity from the Richardson and Zaki plot when 8 = 1. 

Minimum bubbling velocity timb is defined as the gas velocity at which bubbles first appear in aggregative fluidization. For coarse uniformly-sized particles, for example those in Geldart group B, it is usually the case that M i, = u /- However, very fine non-uniformly sized particles such as those in group A exhibit smooth bed expansion and no bubbling until a gas velocity considerably in excess of the minimum... 

As mentioned above, particle clustering can also reduce entrainment rates from Geldart Group A systems. The larger clusters will be entrained at lower rates than the individual particles comprising the clusters, as suggested in Figure 11.3. 

It is clear that the flow regime and the particle Geldart Group should be the same in both sizes of beds, if a successful scale-up is to be performed. 

Figure 5 Effect of grid resolution (A.) on the time-averaged dimensionless slip velocity (us/uT). Geldart group A particles are used. The ordinate is scaled with the terminal velocity of single particles (uT 21.84 cm/s) and the abscissa is scaled with the particle diameter dp. The domain size is 1.5 x 6 cm2, comparable to the coarse-grid used in normal simulations.

It has been shown earlier that the fluidisation properties of a powder in air at ambient conditions may be predicted by establishing in which Geldart group it lies. Table 8 shows that most fluidised bed industrial processes are operated at temperatures and pressures well above ambient. It is important to note that at operating temperatures and pressures... 

---