Voidage local average

Optical fiber measurement of local solids concentrations of FCC catalyst fluidized in a 9-cm-i.d. column gave the results shown typically in Fig. 26. Analysis of these data showed that the radial voidage profile could be described solely by the cross-section-average voidage e, calculated as shown in Sec. 5.1, and the reduced radial coordinate r/R ... 

In the above processes, the cluster diameter is one of the key parameters for EMMS prediction. There are some empirical or semi-empirical expressions proposed for the cluster diameter (say, the review of Harris et al, 2002). Most of these cluster diameters are functions of local voidage or cross-sectionaUy averaged voidage. Li and Kwauk (1994) proposed to correlate the cluster diameter with Nst min, that is. 

The axial pressure gradient, expressed as local bed density under different gas velocities and catalyst inventories, is shown in Fig. 11. It diminishes gradually from the bottom to the top. The average bed density of the lower 3 m section is 100 to 160 kg/m3 (corresponding to a voidage e = 0.87 to... 

We have considered reactors operating at low current densities. At higher values when bubble motion is hindered and coalescence occurs, the rise velocity is likely to be affected by the local rate of gas generation at the electrode. The ability of the electrolyte to circulate between the electrodes will influence the distribution of gas voidage. Hine has addressed this problem and has obtained expressions for the average gas void fraction. 

Figure 19. Variation of the instantaneous local heat transfer coefficient and the point voidage with time on the wall of the cold model circulating fluidised bed combustor. The signals are seen to be strongly cross-correlated. The cross sectionally area averaged suspension densities are from top to bottom, 46.7 kg/m3, 32.0 kg/m3,15.3 kg/m3, (Wu et al, 1991).

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