Local bubble behavior in three‐phase fluidized beds

Abstract

Bubble behavior, including bubble Sauter diameter, bubble rise velocity, bubble frequency and local gas holdup in different radial and axial positions, was measured using a dual electro-conductivity probe in air-water-glass beads fluidization systems. It has been found that the bubble characteristics differ significantly in various flow regimes, depending on the operating conditions; the radial distribution of bubble parameters also changes from one flow regime to another. Thus, it is necessary to employ local bubble behavior in the modeling of three-phase fluidized beds.Le comportement des bulles, et notamment le diametre des bulles de Sauter, la vitesse d'ascension des bulles et la retention de gaz locale dans des positions radiales et axiales differentes, a ete mesure a I'aide d'une sonde d'electroconductivite duale dans des systemes de fluidisation a billes air-eau-verre. On a trouve que les caracteristiques des bulles variaient de faqon significative dans divers regimes d'ecoulement selon les conditions de fonctionnement; la distribution radiale des parametres des bulles change avec le regime d'ecoulement. C'est pourquoi le comportement des bulles local est a inclure dans la modelisation des lits fluidises triphasiques.Keywords: bubble behavior, fluidization, three-phase fluidized bed, flow regime.n the modeling of three-phase fluidized-bed reactors, bub-I ble characteristics such as bubble size, bubble rise velocity and local gas holdup, are of fundamental importance. On the other hand, bubbles play a major role on the flow structure and phase holdups in the beds. Investigation of bubble behavior would provide a basic knowledge for the analysis of hydrodynamic phenomena of the fluidized beds. Therefore, many researchers have recently paid attention to this aspect (Fukuma et al., 1987; Han and Kim, 1990), though the effect of flow regimes has not been discussed in their work.Moreover, it has been found that flow regimes in a threephase fluidized bed depend mainly upon operating conditions (Muroyama et al., 1985;Fan et al., 1986;Chen et al., 1995a), and the bubble behavior is significantly different in different flow regimes. However, surprisingly little work has been found in the literature concerning the effect of flow regimes on bubble behavior.The present work is aimed at an investigation into local bubble behavior in different flow regimes under various operating conditions by means of a dual electro-conductivity probe. The effect of flow regimes on the bubble behavior is discussed. ExperimentalExperiments were carried out in a Plexiglas column with a 0.285 m inside diameter and a 4.1 m height in air-tap water-glass beads systems. The distributor is shown in Figure 1. It was found that the orifice size of gas passageway on the distributor has a remarkable effect on the flow pattern: the large diameter of the orifices would result in an early onset of the turbulent bubble regime (TBR) without undergoing the homogeneous bubble regime (HBR) or the *Author to whom correspondence should be addressed. transiti...

Bubble Size in a Cocurrent Fiber Slurry

“…This distribution type has also been used by others in similar systems. 15,20,21 Although a lognormal bubble diameter distribution appears to be the most commonly used distribution to describe bubble sizes in bubble columns, 22 other distributions have also been used. 22,23 When the solid phase in a gas-liquid-solid system is composed of a fibrous material, additional complications arise because the fibers typically make the system opaque and they may form entanglements around any probe tip and modify the acquired signal.…”

“…Matsuura and Fan determined that bubble diameter distributions in an air−water−glass bead system followed log-normal distributions. This distribution type has also been used by others in similar systems. ,, Although a log-normal bubble diameter distribution appears to be the most commonly used distribution to describe bubble sizes in bubble columns, other distributions have also been used. , …”

Characterization of Bubbly Flow Systems: A Review

“…The impedance probe has been applied to measure the bubble volume fraction, bubble length and bubble rise velocity in three-phase fluidized beds utilizing the difference in conductivity between the liquid and the gas phase. 18,19 Similarly, the dual electrical resistivity probe has been used to study the bubble size, [20][21][22] bubble rise velocity [22][23][24] and gas volume. 21,24 To discern the local flow structures in fluidized beds, the conductivity probe signal can be analyzed based on the statistical, fractal, chaos and wavelet analyses.…”

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“…18,19 Similarly, the dual electrical resistivity probe has been used to study the bubble size, [20][21][22] bubble rise velocity [22][23][24] and gas volume. 21,24 To discern the local flow structures in fluidized beds, the conductivity probe signal can be analyzed based on the statistical, fractal, chaos and wavelet analyses.…”