Fluidization voidage

Rowe (1984) used Eq. (15) to show how pressure would be expected to affect u f for particles with a density of 1250 kg/m and a range of sizes (Fig. 1). In these calculations the minimum fluidization voidage was set at 0.5 and the shape factor at unity it is clear that for particles below about 100 pm in diameter... 

Fig. 3. Zenz plot. Correlation of bed voidage, S, the volume fraction of the fluidized bed that is occupied by gas, for values of S from 1.0 to 0.5, and dimensionless velocity and particle properties, where p — p )/(3 PgU ). The horizontal lines represent the different values of e = 0.5...

Eor turbulent and fast-fluidized beds, bubbles are not present as distinct entities. The following expression for bed voidage, bed occupied by gas, where U is in m/s, has been suggested (17) ... 

Before the bed can become fluidized, however, the particles must dislodge from their packed state, which expands the bed. Thus, the porosity (s) in Eqs (14-5) and (14-9) is not the initial packed bed porosity but the expanded bed porosity at the point of minimum fluidization ( ml ), i.e., the minimum bed voidage in the bed just prior to fluidization. Actually, the values of C and C2 in Eq. (14-8) that give the best results for fluidized beds of uniform spherical particles have been found from empirical observations to be ... 

Horio s scaling law derivation was based on the requirement that two similar circulating fluidized beds have equal values of voidage distribution, dimensionless core radius, gas splitting to core and annulus, solid splitting to core and annulus, and cluster voidage. The CAFM equations were then examined to determine how these requirements could be met. 

Daw, C. S., and Harlow, J. S., Characteristics of Voidage and Pressure Signals from Fluidized Beds using Deterministic Chaos Theory, Proc. 11th Int. Conf. FluidizedBedComb., 2 777 (1991)... 

Zhang, W., Tung, Y., and Johnsson, F., Radial Voidage Profiles in Fast Fluidized Beds of Different Diameters, Chem. Eng. Sci., 46(12) 3045 (1991)... 

The fluidized-bed voidage at minimum bubbling conditions (emb) also has been shown to increase with increasing temperature (Fig. 7) and increasing pressure (Fig. 8). 

The Hydrodynamic Theory of fluidized bed stability was proposed by Foscolo and Gibilaro who adapted the stability principle of Wallis. They postulated that a fluidized bed is composed of two interpenetrating fluids. One fluid is the gas phase, and the solids phase is also considered as a continuous fluid phase. In this theory, voidage disturbances in the bed propagate as dynamic and kinetic waves. The stability of the fluidized bed depends upon the relative velocities of these two waves. The velocities of the kinetic wave (ue) and the dynamic wave (nj are ... 

Louge, M., Lischer, J., and Chang, H., Measurements of Voidage Near the wall of a Circulating Fluidized bed Riser, Powder Tech., 62 269-276 (1990)... 

Silva, E. M. V., Ferreira, M. C., and Freire, J. T., Mean Voidage Measurements and Fluid Dynamics Analysis in a Circulating Fluidized Bed with a Spouted Bed Type Solids F eeding System, Proc. of2nd European Thermal-Sciences and 14th UIT National Heat Transfer Conference, Rome (1996)... 

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