Slugging regime

Crowley, C. J., G. B. Wallis, and J. J. Barry, 1992, Validation of One-Dimensional Wave Model for the Stratificd-to-Slug Regime Transition, lnt. J. Multiphase Flow 18 249 271. (3)... 

Figure 32. Comparison of dynamic pressure variance for three properly scaled beds and two mis-scaled beds in slugging regime (DiFelice et al., 1992a). Properly scaled Cflaposorb A, sand O, bronze. Intentionally mis-scaled +, iron , sand.

Overall gas holdup increases with gas velocity in the dispersed bubble regime for both low and high density particle systems (Davison, 1989 Tang and Fan, 1989 Bly and Worden, 1990 Nore et al., 1992 Pottboff and Bohnet, 1993). As gas velocity increases and the system enters the coalesced and slugging regimes, the rate of increase in the overall gas holdup decreases (Bly and Worden, 1990). 

The fu st term is a modified Archimedes number, while the second one is the Froude number based on particle size. Alternatively, the first term can be substituted by the Reynolds number. To attain complete similar behavior between a hot bed and a model at ambient conditions, the value of each nondimensional parameter must be the same for the two beds. When all the independent nondimensional parameters are set, the dependent parameters of the bed are fixed. The dependent parameters include the fluid and particle velocities throughout the bed, pressure distribution, voidage distribution of the bed, and the bubble size and distribution (Glicksman, 1984). In the region of low Reynolds number, where viscous forces dominate over inertial forces, the ratio of gas-to-solid density does not need to be matched, except for beds operating near the slugging regime. 

Satija, S. and Fan, L.-S. (1985). Characteristics of the Slugging Regime and Transition to the Turbulent Regime for Fluidized Beds of Large Coarse Particles. AIChE J., 31, 1554. Stewart, P. S. B. (1968). Isolated Bubbles in Fluidized Beds Theory and Experiment. Trans. Instn. Chem. Engrs., 46, T60. 

Satija, S. and Fan, L.-S. (1985). Characteristics of Slugging Regime and Transition to Turbulent Regime for Fluidized Beds of Large Coarse Particles. AIChE J., 31,1554. 

What Kehoe and Davidson witnessed, at the transition to turbulence in a tube of relatively small diameter, was a breakdown of a slugging regime into a state of continuous coalescence—virtually a channelling state with tongues of fluid darting in zig-zag fashion through the bed. The point of breakdown of slugging was not sharp. For several powders with particles sizes below 90 /on, Kehoe and Davidson placed the transition between 1... 

For db/dt > 0.6, the bed operates in the slugging regime which is not very interesting from a chemical reactor engineering point of view. 

When the diameter of the bubble (gas) has a value of the same order of magnitude as the diameter of the tube, the fluidized bed will operate in slugging regime, where the bubble occupies the entire cross section of the bed. Depending on the size of the bubble, we might have preferred paths in bed. These cases do not contribute to a good contact of the gas with the suspended particles in the bed, therefore, they should be avoided. The most suitable solution is the choice of a particular type of gas distributor in the inlet of the reactor. 

Nakoryakov, V.E. Pokusaev, B.G. Pribaturin, N.A. Lezhnin, S.I. Press l e Ware Dsmamics in slug regime of gas-liquid flow. Int. Seminar "Transient Phenomena in Multiphase Plow". Dubrovnik, Yugoslavia, 1987. 

Uno and Kintner (1956) measured the rising velocity of gas bubbles in liquid contained in tubes of various diameters and found that the wall effect predominates when Z>e is more than 1/3 of the bed diameter. The wall effect becomes negligible only when Z>e is less than 0.1 of the bed diameter. The regime where the wall effect is dominant is generally called the slugging regime. 

Satifa S, Fan LS. Characteristics of slugging regime and transition to turbulent regime for fluidized beds of large coarse particles. AIChE. J, 31 1554-1562, 1985. 

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