Mechanism of flow regime transition from bubbling to turbulent fluidization

Cai, Pengfei; Ye, Jin; Yu, Z.M.; Wang, Z.-W.

doi:10.1002/aic.690360619

Cited by 76 publications

(55 citation statements)

References 2 publications

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“…According to the experimental evidence available in the literature so far, a common way to classify the flow regimes is to determine the transition velocities by some measurement techniques and interpretation methods (Bai et al, 1996(Bai et al, , 1999Smolders and Baeyens, 2001). The transition velocities have been found to be influenced by many factors such as particle properties (Cai et al, 1990;Grace and Sun, 1991;Gauthier et al, 1999), solids inventory (Chen et al, 1993), column diameter (Kim et al, 2004), distributor design (Svensson et al, 1996;Ellis et al, 2004), operating temperature and pressure (Choi et al, 1998;Sathiyamoorthy and Horio, 2003), the measuring techniques and data analysis methods (Cui and Chaouki, 2004). Therefore one should be very careful when comparing the regime transition velocities obtained with different flow systems and different measurement techniques.…”

Section: Introductionmentioning

confidence: 99%

“…Rhodes and Geldart (1986) even suggested that the transition characterized by U k is actually a transfer of solids from the fluid bed to the freeboard instead of a fundamental change in the flow structures in the bed. Some other researchers suggested that the turbulent regime starts at U c (Sun and Chen, 1989;Cai et al, 1990;Rhodes, 1996). Chehbouni et al (1994) carried out a comprehensive study on flow regime transitions and used both pressure fluctuations and voidage fluctuations to characterize U c .…”

Section: Introductionmentioning

confidence: 99%

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New investigation in regime transition from bubbling to turbulent fluidization

He-hua¹,

Zhu²

2008

Can J Chem Eng

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The regime transition velocity from bubbling to turbulent fluidization was investigated in a 0.267 m diameter fluidized bed with FCC particles. Different transition velocities and processes are found from the measurements of differential pressure fluctuations and local solids concentration. The measurements of differential pressure fluctuations shows a relatively quicker global regime transition, while the local regime transition obtained from the local solids concentration presents a more gradual process marked by two transition velocities. These transition velocities increase with initial static bed height. For the same initial static bed height, increasing the spacing between two pressure taps leads to lower pressure fluctuations and the appearance of two transition velocities.On aétudié la vitesse de transition de régime entre la fluidisation bullante et turbulente dans un lit fluidisé de 0,267 m de diamètre garni de particules de FCC. Différentes vitesses de transition associéesà des processus différents ontété obtenuesà partir des mesures de fluctuations de pression différentielle et de concentration des solides. Les mesures de fluctuations de pression différentielle montrent la présence d'une transition de régime globale plus rapide, tandis que la transition de régime local obtenueà partir de la concentration de solides locale présente un processus graduel marqué par deux vitesses de transition. Ces vitesses de transition augmentent avec la hauteur de lit statique initiale. Pour la même hauteur de lit statique initiale, le fait d'augmenter l'espacement entre les deux prises de pression entraîne des fluctuations de pression plus faibles et l'apparence de deux vitesses de transition.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

New investigation in regime transition from bubbling to turbulent fluidization

He-hua¹,

Zhu²

2008

Can J Chem Eng

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“…6 Goldschmidt 29 reported that a strong intensity in pressure drop fluctuations indicates more vigorous bubbling of the fluidized bed. Different fluidization regimes are identified with a change in characteristics of the pressure fluctuations (Cai et al 30 ). Figure 1 shows the pressure drop (across the whole bed) fluctuations, averaged over the cross-section of a fluidized bed at different operating pressures.…”

Section: ■ Parameter Settingsmentioning

confidence: 99%

Numerical Investigation on the Effect of Pressure on Fluidization in a 3D Fluidized Bed

Verma

Padding

Deen

et al. 2014

Ind. Eng. Chem. Res.

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We apply a two-fluid model to investigate hydrodynamic differences in a three-dimensional fluidized bed operating at pressures of 1, 2, 4, 8, 16, 20, and 32 bar. The simulation results are compared with experimental results from the literature and show very good agreement. A detailed investigation is carried out on pressure fluctuations, porosity distribution, and bubble and solids flow characteristics. At high pressure, the porosity distribution is homogeneous and fluidization is smooth. The bubble size depends upon the location in the 3D bed, showing different trends at different pressures. The average bubble size is reduced with an increase in pressure, caused by a difference in coalescence and splitting of bubbles. An initial increase in pressure from 1 to 2 bar shows an increase in bubble rise velocity, but a further increase in pressure causes bubbles to rise more slowly. High up-flow of solids is observed in the center at high pressures, with pronounced differences in solids circulation vortices.

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“…[10,11] developed a few correlations for prediction of 'U c ' for binary solids systems in fluidized beds with mono-density particles with relatively narrow size distribution. Buyevich and Kapbasov [12] studied the momentum equations governing vertical distribution of particles of different sizes and densities in a homogeneous fluidized bed and concluded that the conventional kinetic theory of gaseous mixtures, in which such force differences are usually not taken into account and the relative motion is conceived as a phenomenon of purely diffusional origin, is sufficient for expressing mean forces of interaction between the particulate components in terms of observable variables.…”

Section: Introductionmentioning

confidence: 99%

Effect of promoters and secondary fluidizing medium on mixing: statistical and ANN approaches

Mohanty¹,

Mohanty²,

Roy

et al. 2008

Asia-Pacific J Chem Eng

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Factorial design (statistical approach) and artificial neural network (ANN) models have been developed for the prediction of mixing the index with four system parameters, such as static bed heights, average particle densities, average particle sizes and gas velocities, under four different experimental conditions, viz., only primary air, simultaneous primary and secondary air, disc promoter and rod promoter. The values of the mixing index obtained through the developed models are found to agree well with their experimental counterparts. It has also been found from these investigations that under simultaneous primary and secondary air supply conditions the best mixing performance is achieved, i.e. I M ≈ 1.0, as compared to rod promoter, disc promoter, and only primary air supply. 

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Mechanism of flow regime transition from bubbling to turbulent fluidization

Cited by 76 publications

References 2 publications

New investigation in regime transition from bubbling to turbulent fluidization

New investigation in regime transition from bubbling to turbulent fluidization

Numerical Investigation on the Effect of Pressure on Fluidization in a 3D Fluidized Bed

Effect of promoters and secondary fluidizing medium on mixing: statistical and ANN approaches

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