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Geldart Group A powders

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. [Pg.6]

What differentiates a Geldart Group A powder from a Geldart Group B powder ... [Pg.205]

Abrahamsen and Geldart (1980) defined Group A powders as those in which UmbIUm > 1, and Group B powders as those where Umb mf = 1 They developed the following equation to predict UmbIUm. ... [Pg.120]

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... [Pg.562]

An axial Pe number of 5 was estimated for the FFB unit, corresponding to a DA of 30 cm2/s. This estimate was based on dispersion data reported by Zenz (25) on Geldart s Group A powders. [Pg.168]

For Geldart s Group B and Group D powders, the bed transfers from the fixed bed into a bubbling fluidized bed when the gas velocity is increased beyond the minimum fluidization velocity of the system. For Group A powders, no bubbles will be observed, instead the bed will expand homogeneously. The bubbles only appear when the gas velocity is increased beyond the minimum bubbling velocity. Thus the transition point from the... [Pg.68]

It is curious that the influence of bed size appeared to hold even when the bubble was much smaller than the bed diameter. This may be tied to the local concentration of bubbles within certain sections of the bed. The increased local bubble flow led to higher coalescence rates and higher local bubble velocities. There was a distinction in bubble velocity between Geldart group A and B powder while the ratio of visible bubble flow to M-Mmf seems to be independent of the... [Pg.353]

For Geldart s group A powders, the bed expands homogeneously even above the minimum fluidization veloeity, until the minimum bubbling veloeity The Mnib is another good index of high emulsion phase expansion, as shown in Fig. 51. This figure also illustrates how Mnib is determined. [Pg.693]


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See also in sourсe #XX -- [ Pg.119 ]




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