Bubble in gas-fluidized bed

Fig. 10. Formation, growth, and splitting of bubbles in gas-fluidized beds, where (—) is theory (e > 0.8) and (----) is experiment.

Verloop J, Heertjes PM. On the origin of bubbles in gas-fluidized beds. Chem Eng Sci 29 1101-1107, 1974. 

This conclusion provided an emphatic justification for the phenomenon of bubbles in gas-fluidized beds. As these beds represented the most widespread and important industrial applications of fluidization technology, it is not difficult to appreciate the considerable interest generated in the mid-1960s by the diverse analyses (by different authors, employing different fluid-particle interaction force expressions) that arrived at essentially the same conclusion. The inconvenient fact that liquid-fluidized beds appeared to manifest stable, homogeneous behaviour did little to detract from its almost universal acceptance. 

Colver, G. M., Bubble control in gas-fluidized beds with applied electric fields, Powder Technol., 17 9-18(1977)... 

The bubbles in a fluidized bed have a distinct shape and there is a distinct boundary between the gas in the bubble and the... 

Interaction by diffusion will seldom occur in two-phase systems, but may be of importance between gas bubbles in a fluidized bed, especially when the fluidized solid is not a catalyst but only a heat carrier. In homogeneous systems, this type of interaction is the normal kind of interaction. 

Derive the cloud thickness and volume ratio of cloud to bubble for a single bubble in a fluidized bed in terms of the Davidson-Harrison (1963) model. Since the cloud is the region established by the gas circulating in a closed loop between the bubble and its surrounding, the following assumptions can be employed (1) zero radial gas velocity outside the surface of the cloud sphere (r = Rc) (2) uniform gas velocity at far distance from the bubble, i.e., Uboo... 

The attrition of solid particles is an unavoidable consequence of the intensive solids motion resulting from the presence of bubbles in the fluidized bed. The attrition problem is especially critical in processes where the bed material needs to remain unaltered for the longest possible time, as in fluidized-bed reactors for heterogeneous catalytic gas-phase reactions. Catalyst attrition is important in the economics of such processes and may even become the critical factor. 

Figure 9-1 The relationship between Cd and Re for gas bubbles in water-fluidized beds (after Darwn and Harrison20).

Sit, S.P. Grace, J.R. Effect of bubble interaction on interphase mass transfer in gas fluidized beds, Chem. Eng. Sci. 1981, 327. 

Fung A.S., Hamdullahpur F, (1993) Effect of bubble coalescence on entrainment in gas fluidized beds. Powder Technology. 77, pp 251-265 Zenz F.A. et al (1958) A Theoretical-Empirical Approach to the Mechanism of Particle Entrainment from Fluidized Beds. American InstitiUe of Chemical Engineering Journal, 4, pp. 472-479... 

It was observed that like a single bubble in liquid, a rising bubble in a fluidized bed drags a wake of material consisting of a gas-solid mixture up the bed behinds it. Close to the bottom of the bed, just above the gas distributor, solids are entrained by the rising bubbles to form the bubble wake. There is... 

Km emulsion and bubble phases in gas-fluidized bed Michaelis constant mol m 12.2... 

Colver, G. M., Bubble Control in Gas-Fluidized Beds with Applied Electric Fields, J. Powder Tech., 17, 1977, pp. 9-18. 

Through a stirring effect and the convective mass transfer caused by the rising bubbles in a fluidized bed, intensive particle motion is observed. This is favorable for the mass and heat transfer between the gas and product and for the heat transfer between product and heat exchanger. Due to good solid mixing an almost uniform tempera-... 

Lockett, M. J. and Harrison, D. The distribution of voidage fraction near bubbles rising in gas-fluidized beds. Proc. Int. Symp. on Fluidization, Drinkenberg. Netherland Univ. Press, Amsterdam, 1967. 

Powders of small particle size and low density are difficult to fluidize initially, but once they reach the fluidized state they can give origin to beds that can be expanded over a wide range before bubbling occurs. The formation of large bubbles in gas-fluidized systems is often prevented by introducing standard tower packings into the bed to produce what is known as a packed-fluidized bed. 

While it is often helpful to consider the analogy between bubbles in liquids and in gas-fluidized beds, for example, affecting bubble rise velocities, shapes, and coalescence dynamics, one needs to recognize some very significant differences between gas-solid and gas-liquid systems, with profound impact ... 

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