Geldart diagram

Figure 3. Geldart diagram (boundaries according to Molerus [24]).

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, 17-1 Powder-classification diagram for fluidization by air (ambient conditions). [From Geldart, Powder TecbnoL, 7, 285-292 (1973).]... 

Modifications to the Geldart (1973) fluidization diagram have been proposed by Molerus (1982) and Zenz (1984), but are not considered here as they require some knowledge or measurement of particle adhesion forces and bulk surface tension, respectively. That is, detailed investigations into evaluating and/or developing such fluidization diagrams are beyond the present scope of work. 

Note the mean diameter used by Geldart (1973) is actually a surface volume mean diameter dsvm, based on Eq. (3). However, comparing the fluidization curves of several materials with the Geldart (1973) diagram (e.g., fly ash, pulverized coal, coarse ash, PVC powder and screened coke), Wypych (1989b) found the following ... 

Note that a similar problem was described earlier for the Geldart (1973) diagram. Also, it is quite possible that differences in particle shape could contribute to this effect. 

To emphasize some of the above comments and suggestions (as well as some of those presented earlier in relation to the Geldart [1973] diagram), the PVC powder results (Wypych, 1989b) are summarized below. 

Fig. 63. Geldart s powder classification chart, (a) Geldart s original diagram for air (b) Grace s improvement on Geidart s diagram, 1986.

The general flow regime diagram shown i Fig 10.2 illustrates the progression of changes in behavior of a bed of solids as the gas velocity is progressively increased. The letters A, B, C and D refer to the Geldart classification of solids. 

Classes 3 and 4 correspond roughly to group B materials on Geldart s diagram, 5 and 6 to group A and 7 to group C. 

Figure 7.6 Simplified diagram showing Geldart s classification of powders according to their fluidization behaviour in air under ambient conditions (Geldart, 1973)...

Equation (5) is the demarcation between Group B and D powders. The powder classification diagram for the fluidization by air at ambient conditions was presented by Geldart, as shown in Fig. 2. 

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