Initial particle velocity spatial distribution from 2-D erupting bubbles in fluidized beds

Santana, D.; Nauri, Sara; Acosta, A. J.; García, Nelson Afanador; Macías-Machín, A.

doi:10.1016/j.powtec.2004.11.013

Cited by 48 publications

(39 citation statements)

References 18 publications

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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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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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“…The experimental facility employed is similar to the one described in more detail in [11]. A 2D fluidized bed (1.1 m wide, 0.6 m high and 0.005 m thick) was used with the front and the rear walls made of glass.…”

Section: Experimental Set-up and Calibrationmentioning

confidence: 99%

Voidage distribution around bubbles in a fluidized bed: Influence on throughflow

et al. 2010

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a b s t r a c tIn this work, a new method for measuring void fraction distribution around endogenous bubbles in a 2D fluidized bed is presented. The technique is based on illuminating a transparent wall 2 dimensional bed with diffuse light from the rear and recording the distribution of light that penetrates the bed. The recording is made with a high speed video camera, which gives frames with grey level corresponding to the light penetration and from which the voidage distribution around the bubbles can be determined. In this way, voidage distribution in the region very close to the bubble contour (r/R b ≲ 1.2) is obtained, which was not possible in previous studies due to limitations in spatial resolution. A correlation is proposed for the voidage at the contour of the bubble, with the voidage depending on the radial position and the polar angle ε(r, θ). In addition, the effect of the voidage distribution on the throughflow crossing the bubbles was studied and an increase of 20% was determined for the average bubble geometry of the more than 100 bubbles analysed.

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“…Müller et al [26] defined the eruption instant as the time when the vertical velocity of the dome nose reaches its maximum, which corresponds approximately to a ratio between the dome thickness and the particle diameter of ı/d p ∼ 3 under their experimental conditions. Santana et al [12] and Almendros-Ibáñez et al [13,25] defined the eruption instant as the time when the bubble dome is broken and the bubble interior and the freeboard become connected. The same criteria will be followed in this work.…”

Section: Isolated Bubble Eruption: the Stalactite Effectmentioning

confidence: 99%

“…Different works can be found in the literature using PIV in granular flows [32], silo discharge [33][34][35] and fluidized beds [26,12]. The same PIV software used by Müller et al [26](MATPIV 1.6.1 [36]) and the same iterative process and filters of this work were followed.…”

Section: Jet Spike Mechanismmentioning

confidence: 99%

“…At the bed surface, the initial flux of ejected particles E 0 depends on the mean density at that level, which can be approximated as i0 = (1 − mf ) p [7][8][9], and on the particle ejection velocity v 0 , which is related with the bubble velocity [10][11][12][13]. There are fewer experimental studies in the literature about E 0 because of the difficulty of accurately measuring this flux.…”

Section: Introductionmentioning

confidence: 99%

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Experimental observations on the different mechanisms for solid ejection in gas-fluidized beds

Almendros-Ibáñez

Sánchez-Delgado

Sobrino

et al. 2009

Chemical Engineering and Processing: Process Intensification

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a b s t r a c tThis work presents an experimental study of the ejection velocity for different mechanisms of solid ejection in fluidized beds. The experiments were carried out in a 2D fluidized bed, where the bubble eruptions were recorded with a frequency of 250 frames per second using a high speed video camera with a resolution of 1.3 Megapixels.The results show that in isolated bubble eruption, the dome velocity is significantly reduced by the effect of a group of raining particles in the form of stalactites within the bubble. Higher velocities are observed when bubble coalescence takes place. If bubbles coalesce before the leading bubble breaks, the momentum of the trailing bubble together with the increase in the throughflow accelerate the dome of the leading bubble. In contrast, when coalescence occurs after the breakage of the leading bubble, the wake of the trailing bubble is projected into the freeboard with a very high velocity (wake spike mechanism). The last observed mechanism, the jet spike mechanism, occurs when a stream of bubbles reaches the bed surface following the path opened by the previous bubbles. A cloud of particles moving upward is observed, although their velocities are not as high as in the wake spike mechanism due to the interchange of momentum during the collisions with other particles.Finally, an explanation for some of the patterns of gas release from erupting bubbles recently observed by Hartung et al.

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Initial particle velocity spatial distribution from 2-D erupting bubbles in fluidized beds

Cited by 48 publications

References 18 publications

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

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

Voidage distribution around bubbles in a fluidized bed: Influence on throughflow

Experimental observations on the different mechanisms for solid ejection in gas-fluidized beds

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