Group D powders

Group D powders They are large particles that are distinguished by their ability to produce deep spouting beds (spurt or jet of gas through the bed). Roasted coffee beans, lead shot, and some roasted metal ores are examples of group D materials. 

The hardest to fluidize are the Group D powders. They are coarse particles such as wheat or soybeans. They can better be spouted than fluidized, and... 

Group D powders are difficult to fluidize—gas will channel through the bed and so shallow beds are common to minimize flow maldistribution. 

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... 

For Group D powders, is about 0.1. For Group A solids, it is 1.0. Geldart (1986) correlated the wake and drift fractions with the Archimedes number, as shown in Fig. 25. 

Increasing temperature has two effects (1) by decreasing gas density, the gas convective component of heat transfer is decreased slightly, and (2) by increasing the thermal conductivity of the gas, the effectivness of packets of emulsion phase in contact with the transfer surface is increased. The overall effect for Group A and B powders is to increase the convective transfer coefficient as was shown by Botterill and Teoman (1980). In the case of Group D powders where the gas convective... 

The validity of extrapolating the data obtained in a semicircular model to a circular one is also of concern. Not much research has been carried out in this area. Preliminary research results by Whiting and Geldart (1980) indicated that, for coarse, spoutable solids (Geldart s group D powders), semicircular columns could provide information very similar to that from the circular ones. 

Group D powders are the largest (in excess of about 1 mm), are generally of lower density (typically seeds, such as wheat, etc.), and are difficult to... 

The above discussion identifies predicted values of Smb as a measure of relative instability, and hence of fluidization quality, in bubbling systems. In the following section the significance of this relation to perturbation propagation in fluidized beds will be examined. For the moment it is sufficient to point out that predicted Smb values lower than about 0.1 correspond approximately to the Group D powders of the Geldart map the predicted B/D boundary, shown in Figure 10.1, represents the locus of dp, Pp) combinations which result in computed values of Smb of exactly 0.1. 

Many typical Group D products (e.g., wheat, rice, sugar, plastic pellets, cereals, barley, malt, agglomerated milk powder) have relatively narrow... 

Oxidation Products of the Elements of Group V. Treat 0.5 gram each of (a) red phosphorus, (b) powdered arsenic, (c) powdered antimony, and (d) powdered bismuth with... 

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