The role of contact stresses and wall friction on fluidization

Loezos, Peter N.; Costamagna, Paola; Sundaresan, Sankaran

doi:10.1016/s0009-2509(02)00421-9

Cited by 71 publications

(75 citation statements)

References 19 publications

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“…(4) (8) suggest that hysteresis and overpressure will be observed due to wall effects in fluidized beds with small diameters, as observed in previous studies [38 40]. For instance, wall effects were observed by Srivastava and Sundaresan [38] and Loezos et al [39], who studied fluidized particles in cylindrical beds with internal diameters of 10 and 50 mm. In addition, wall effects were also observed by Liu et al [40] , who used microfluidized beds with internal diameters ranging from 12 and 32 mm.…”

Section: Wall Effects During the Defluidization Fluidization Processsupporting

confidence: 58%

“…In this way, the value of the coefficient n was fitted to the experi mental data using the methodology of Srivastava and Sundaresan [38] and Loezos et al [39]. The value of ϕ min was assumed to be equal to the average particle concentration under minimum fluidization condi tions, ϕ mf , which was estimated by measuring the mass of the particles in the bed and the fixed bed height.…”

Section: Wall Effects During the Defluidization Fluidization Processmentioning

confidence: 99%

“…The value of ϕ min was assumed to be equal to the average particle concentration under minimum fluidization condi tions, ϕ mf , which was estimated by measuring the mass of the particles in the bed and the fixed bed height. According to the work of Srivastava and Sundaresan [38] and Loezos et al [39], two different J values were used in the present study. Namely, J df , was used for the defluidizaton curve, and J f was used for the fluidization process.…”

Section: Wall Effects During the Defluidization Fluidization Processmentioning

confidence: 99%

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On the minimum fluidization velocity in 2D fluidized beds

et al. 2011

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a b s t r a c tIn the present study, a new correlation for the determination of the minimum fluidization velocity in 2D fluidized beds was developed. The proposed correlation was based on the experimental results obtained in 2D fluidized beds with different particle sizes, bed thicknesses and bed heights. Thus, the proposed correlation depends only on the nondimensional variable t/d p , where t is the bed thickness and d p is the particle size. The proposed correlation was compared with other experimental results that can be found in the literature, and two different trends were observed. Namely, one set of experimental results was in accordance with the proposed correlation, while the other set deviated from the theoretical results. In particular, the minimum fluidization velocities of the experimental results were greater than the predicted values of the proposed correlation. In view of the differences in the experimental conditions, the observed discrepancies may be attributed to the effects of electrostatic charge and particle shape. In addition, the experimental fluidization defluidization curves were compared to the theoretical results of Jackson's model, and the parameters were fitted to the experimental data. However, Jackson's model is based on a 1D bed; thus, general parameters could not be obtained for a bed with a fixed particle size and thickness due to the two dimensional voidage distribution in the bed and bed cohesion effects, which are a result of electrostatic forces and are not considered in Jackson's model.

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Section: Wall Effects During the Defluidization Fluidization Processsupporting

confidence: 58%

Section: Wall Effects During the Defluidization Fluidization Processmentioning

confidence: 99%

Section: Wall Effects During the Defluidization Fluidization Processmentioning

confidence: 99%

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On the minimum fluidization velocity in 2D fluidized beds

et al. 2011

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“…5 times higher than in the case of smooth columns. Loezos et al (2002) performed gas fluidisation in sand columns. They noted that wall friction is the main cause of pressure overshoot and that it increases with decreasing diameter of the column.…”

Section: Plane-type Experimentsmentioning

confidence: 99%

Initiation of backward erosion piping in uniform sands

Beek¹,

Bezuijen²,

Sellmeijer³

et al. 2014

Géotechnique

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The process of backward erosion piping poses a threat to dams and dikes on foundations of nonplastic sands and silts. The available models for design and predictions focus predominantly on the progression of the pipe. However, sand boils in the field will occur as a result of the initiation of sand transport. Although criteria are available for predicting sand boiling and heaving in columns, there is no model describing the initiation of piping in situations where the exit flow is not uniform, as is the case in most backward erosion experiments and situations in the field. This study compared laboratory experiments in which the process of initiation leads directly to failure with analytical and numerical groundwater flow calculations and heave criteria. The aim was to develop a model for the onset of pipe formation. It emerged that the sand bed needs to be fluidised over a distance of at least 20 times the grain diameter from the toe of the structure for a pipe to initiate. The proposed model explains the scale effects of grain size and configuration on a critical gradient. This approach clarifies the processes governing pipe initiation and progression and it can be used to establish a conservative estimate of the critical head in uniform sands, which is essential for laboratory work on this topic and for the appraisal of sand boils in practice.

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“…This is believed to be caused by the existence of yield stresses caused, for example, by friction due to particles contact with the walls of the column [22,23], which reportedly resulted in plugging or channelling of the nanoparticle agglomerates at low velocities. Similarly, in this work, typical hysteresis effects to different degrees were observed in the bed expansion measurement for all three types of silica nanoparticles.…”

Section: Hysteresis Effectmentioning

confidence: 99%

Fluidisation behaviour of silica nanoparticles under horizontal vibration

Zhang¹,

Zhao²

2010

Journal of Experimental Nanoscience

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In present study, fluidization behaviour of silica nanoparticles with primary size between 7 and 16nm under horizontal vibration was investigated. Fluidization characteristics were assessed by observing pressure drop, bed expansion and bed collapse behaviour at the vibration frequencies between 0 and 34 Hz. Horizontal vibration is demonstrated to be as effective as the vertical configuration reported previously in terms of fluidization improvement. In all cases, smooth agglomerate particulate fluidization was observed at vibrational frequencies greater than 16.7 Hz as long as the vibrational amplitude is set to be more than 1. This is much lower than previous reported value, and suggests that fluidization assisted with horizontal vibration is a promising technique for the large scale processing of nanomaterials (e.g. reacting, dispersing, or coating).

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The role of contact stresses and wall friction on fluidization

Cited by 71 publications

References 19 publications

On the minimum fluidization velocity in 2D fluidized beds

On the minimum fluidization velocity in 2D fluidized beds

Initiation of backward erosion piping in uniform sands

Fluidisation behaviour of silica nanoparticles under horizontal vibration

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