Mixing and segregation in a bidisperse gas–solid fluidised bed: a numerical and experimental study

Bokkers, GA; Annaland, van M Martin Sint; Kuipers, J.A.M.

doi:10.1016/j.powtec.2004.01.018

Cited by 282 publications

(160 citation statements)

References 12 publications

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“…Nevertheless non tracking techniques have also been employed to collect data of the motion at a particular position in the bed (Ibsen et al, 2002). On the other hand, when analyzing objects motion in a 2 D bed, visualization techniques (Shen et al, 2004;Bokkers et al, 2004) have been employed. Kunii and Levenspiel (1991) reviewed the first studies intended to characterize the motion of large objects immersed in a fluidized bed.…”

Section: Introductionmentioning

confidence: 99%

Buoyancy effects on objects moving in a bubbling fluidized bed

Soria-Verdugo

García-Gutiérrez

García-Hernando

et al. 2011

Chemical Engineering Science

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a b s t r a c tThe effect of buoyant forces on the motion of a large object immersed in a bubbling fluidized bed (BFB) was experimentally studied using digital image analysis. The experiments were performed in a 2 D bubbling fluidized bed with glass spheres as bed material and cylindrical objects with different densities and sizes. The object motion was measured using non intrusive tracking techniques. The effect of gas velocity was also analyzed.The circulation of an object in a BFB is defined by several parameters. The object might be able to circulate homogeneously throughout the bed or stay in preferred regions, such as the splash zone or the bottom zone. While circulating, the object moves back and forth between the surface of the bed and the inner regions, performing a series of cycles. Each cycle is composed by sinking and rising paths, which can be one or several, depending on whether a passing bubble is able to lift the object to the surface or the object is detached from it or its drift at an intermediate depth. Therefore, the number of rising paths or number of jumps that the object undergo in a cycle, interleaved with sinking paths, and the maximum attained depth characterize each cycle, together with the mean sinking and rising velocities of the object. In this work, experimental measurements of the probability distributions of the number of jumps and the maximum attained depth, the axial homogeneity of object motion and rising and sinking object velocities are presented for objects with different sizes and densities. The results show a coherent behavior, independent of density and size, for the probability distributions of the number of jumps. This is also true for the maximum attained depth, but only when a proper circulation throughout the bed is ensured. Such a proper circulation and axial homogeneity is, on the other hand, much affected by object density, size and gas velocity. Rising and sinking velocities are highly dependent on gas velocity, as established in well known models of bubble and dense phase velocities. Nevertheless, rising velocities are practically unaffected by object density or size, while sinking velocities show a low dependence on density and a steeper one on size. These results suggest that buoyant forces are relevant during the sinking process, and almost neutral during the rising path.

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Section: Introductionmentioning

confidence: 99%

Buoyancy effects on objects moving in a bubbling fluidized bed

Soria-Verdugo

García-Gutiérrez

García-Hernando

et al. 2011

Chemical Engineering Science

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“…With the development of CCD cameras and Particle Image Velocimetry (PIV) or other velocimetry techniques, there are several studies showing experimental information on particle velocity in very thin, fluidized beds, whose behaviour can be considered two or quasi two dimensional (e.g. Bokkers et al, 2004;Liu et al, 2005;Santana et al, 2005;Almendros Ibá ñ ez et al, 2006;Laverman et al, 2008;Sá nchez Delgado et al, 2010). At this regard, reported mean particle velocities are clearly smaller than the characteristic bubble velocity in two dimen sional beds working with Geldart B particles and superficial velocity around 2 times the minimum fluidisation velocity U mf .…”

Section: Introductionmentioning

confidence: 99%

Comparison between two-fluid model simulations and particle image analysis & velocimetry (PIV) results for a two-dimensional gas–solid fluidized bed

Hernández-Jiménez

Sánchez-Delgado

Gómez-García

et al. 2011

Chemical Engineering Science

108

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a b s t r a c tThis work compares simulation and experimental results of the hydrodynamics of a two dimensional, bubbling air fluidized bed. The simulation in this study has been conducted using an Eulerian Eulerian two fluid approach based on two different and well known closure models for the gas particle interaction: the drag models due to Gidaspow and Syamlal & O'Brien. The experimental results have been obtained by means of Digital Image Analysis (DIA) and Particle Image Velocimetry (PIV) techniques applied on a real bubbling fluidized bed of 0.005 m thickness to ensure its two dimensional behaviour. Several results have been obtained in this work from both simulation and experiments and mutually compared. Previous studies in literature devoted to the comparison between two fluid models and experiments are usually focused on bubble behaviour (i.e. bubble velocity and diameter) and dense phase distribution. However, the present work examines and compares not only the bubble hydrodynamics and dense phase probability within the bed, but also the time averaged vertical and horizontal component of the dense phase velocity, the air throughflow and the instantaneous interaction between bubbles and dense phase. Besides, quantitative comparison of the time averaged dense phase probability as well as the velocity profiles at various distances from the distributor has been undertaken in this study by means of the definition of a discrepancy factor, which accounts for the quadratic difference between simulation and experiments The resulting comparison shows and acceptable resemblance between simulation and experiments for dense phase probability, and good agreement for bubble diameter and velocity in two dimensional beds, which is in harmony with other previous studies. However, regarding the time averaged velocity of the dense phase, the present study clearly reveals that simulation and experiments only agree qualitatively in the two dimensional bed tested, the vertical component of the simulated dense phase velocity being nearly an order of magnitude larger than the one obtained from the PIV experiments. This discrepancy increases with the height above the distributor of the two dimensional bed, and it is even larger for the horizontal component of the time averaged dense phase velocity. In other words, the results presented in this work indicate that the fine agreement commonly encountered between simulated and real beds on bubble hydrodynamics is not a sufficient condition to ensure that the dense phase velocity obtained with two fluid models is similar to that from experimental measurements on two dimensional beds.

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“…Additionally, digital images are analyzed using a newly developed digital image analysis algorithm (DIA) to determine the local particle volume fraction. Several workers applied PIV to study 2D granular flows, such as gas-fluidized beds (Bokkers et al [2], Laverman et al [3] and Dijkhuizen et al [4]), spout fluidized beds (Link et al [5]), spouted beds (Liu et al [6]), but also vibrated granular beds (Zeilstra et al [7] and Deng et al [8]), rotating drums (Jain et al [9]) and silos or hoppers (Medina et al [10] and Steingart et al [11]). Through these applications, PIV has proven to be a powerful tool for 2D granular flow field measurement.…”

Section: Introductionmentioning

confidence: 99%

An experimental study of the effect of collision properties on spout fluidized bed dynamics

et al. 2011

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In this paper we experimentally study the effect of collision properties of different particle systems on the bed dynamics of a spout fluidized bed. This is done in different flow regimes: the spout-fluidization regime (case A), the jet-in-fluidized-bed regime (case B) and the spouting-with-aeration regime (case C). The considered particle systems comprise glass beads, γ-alumina oxide and zeolite 4A particles, which are all classified as Geldart D. A non-intrusive measurement technique is used, viz. particle image velocimetry (PIV) to measure the particle flow field in a pseudo two-dimensional (2D) spout fluidized bed. Additionally, digital images are analyzed using a newly developed digital image analysis (DIA) algorithm to evaluate the particle volume fraction. It is demonstrated that the new proposed DIA algorithm provides reliable information on the particle volume fraction, showing that it is a powerful tool when combined with PIV. The added value of DIA is confirmed by comparing the particle velocity fields and volumetric particle fluxes. The particle fluxes display only small differences between the particle systems for each of the examined flow regimes, with the largest difference in the jet-in-fluidized bed regime. In this regime, the flow behaviour of the zeolite 4A particles does not show any features of the spout fluidized bed anymore, but behaviour of an ordinary fluidized bed. This is due to the direct bubble formation above the bottom plate, which results in a large disturbance near the spout entrance. It seems that zeolite 4A particles -because of their small restitution coefficient-tend to cluster in a more pronounced way, producing more bubbles compared to glass beads and γ-alumina oxide particles.

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Mixing and segregation in a bidisperse gas–solid fluidised bed: a numerical and experimental study

Cited by 282 publications

References 12 publications

Buoyancy effects on objects moving in a bubbling fluidized bed

Buoyancy effects on objects moving in a bubbling fluidized bed

Comparison between two-fluid model simulations and particle image analysis & velocimetry (PIV) results for a two-dimensional gas–solid fluidized bed

An experimental study of the effect of collision properties on spout fluidized bed dynamics

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