The effect of frictional pressure, geometry and wall friction on the modelling of a pseudo-2D bubbling fluidised bed reactor

Cloete, Schalk; Johansen, Stein Tore; Zaabout, Abdelghafour; Annaland, Martin van Sint; Gallucci, Fausto; Amini, Shahriar

doi:10.1016/j.powtec.2015.04.060

Cited by 12 publications

(9 citation statements)

References 21 publications

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“…A major limitation of the TFM is that it requires the solid clusters and gas bubbles, which are typical of fluidization and can occur on lengths scales as small as several particle diameters, to be resolved (Cloete et al, 2011;Cloete et al, 2015aCloete et al, , 2016c. This requires restrictively small grid cells to be used for accurate results, therefore studies using the TFM are generally limited to lab-scale studies (Bakshi et al, 2016;Cloete et al, 2016a;Cloete et al, 2015b;Cloete et al, 2013;Ellis et al, 2011;Hamidouche et al, 2019;Ostermeier et al, 2017;Tricomi et al, 2017).…”

Section: Introductionmentioning

confidence: 99%

On the choice of closure complexity in anisotropic drag closures for filtered Two Fluid Models

Cloete

Radl

et al. 2019

Chemical Engineering Science

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Filtered Two Fluid Models (fTFMs) aim to enable accurate industrial-scale simulations of fluidized beds by means of closures accounting for the effects of bubbles and clusters. The present study aims to improve anisotropic closures for the drift velocity, which is the primary sub-grid effect altering the filtered drag force, by deriving increasingly complex closures by considering additional independent variables (markers). Three different anisotropic closures, as well as an isotropic closure, are evaluated. A priori tests revealed a significant increase in the predictive capability of the closures as the complexity, in terms of the number of markers considered, increases. However, this improvement is relatively small when compared to the effect of considering anisotropy. Next, a posteriori tests were completed by comparing coarse-grid simulations of bubbling, turbulent and core-annular fluidization against benchmark resolved TFM simulations. This analysis shows good performance of all anisotropic closures, with negligible to minor effects of increasing the drag closure's complexity by considering additional markers. On the other hand, the isotropic closure lacks generality and shows poor grid independence behaviour. It is therefore concluded that it is essential to include important physical effects, such as anisotropy, in fTFM closures, while complexity in terms of the number of markers considered is of lesser importance.

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Section: Introductionmentioning

confidence: 99%

On the choice of closure complexity in anisotropic drag closures for filtered Two Fluid Models

Cloete

Radl

et al. 2019

Chemical Engineering Science

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“…However, it should again be emphasized that this near free-slip implementation is not generally applicable. For example, previous work conducted by the authors in a pseudo-2D setup [37,38] showed that high wall friction on the large front and back walls must be included to reasonably predict experimentally measured solids velocity profiles. The primary advantage of the Schneiderbauer approach is that it can deliver reasonable results in fast and dilute flows with settings which can also achieve reasonable results in slow and dense flows.…”

Section: Simulation Resultsmentioning

confidence: 99%

Evaluation of wall friction models for riser flow

Cloete

Radl

et al. 2016

Powder Technology

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Two different approaches for modelling the particle-wall collisions, the frequently employed Johnson & Jackson model and the recently proposed Schneiderbauer model, were evaluated in a fluidized bed riser by comparing simulation results to experimental data over a range of fluidization velocities and solids fluxes. For the Johnson & Jackson model, it was shown that partial slip settings recommended for denser fluidization conditions (a specularity coefficient in the order of 0.1) failed to predict cluster formation at the walls at higher gas flow rates due to unrealistically large granular temperature generation in the near-wall regions. By reducing wall friction to settings approaching a free-slip condition (specularity coefficient in the order of 0.001), this problem is overcome by eliminating excessive granular temperature generation from over-predicted strain rates at the walls. However, this approach results in an overestimation of the downward velocity of the clusters at the wall in dense cases. Despite this shortcoming, predictions are remarkably accurate for most of the cases. The Schneiderbauer model, with model parameters close to recommended settings, performs similarly well for most of the cases, slightly under-predicting cluster formation at the walls in the dilute cases. Generally, it also predicts more realistic flow behaviour since it prevents dense clusters from falling rapidly at the walls. The Schneiderbauer wall friction model is therefore recommended for use in future studies of risers, since it is able to deliver reasonable results over a wider range of flow conditions than the Johnson and Jackson model, using a single set of friction parameters. Furthermore, it has the benefit of using experimentally measurable quantities as input.

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“…While bubbles move in the bed, they also break due to the strong downward movement of the solid phase. Such an unsteady change in the size and number of the bubbles in the bed influences heat and mass transport properties in the fluidized bed and hence the reactor performance . The prediction of time-averaged flow behavior in gas–solid fluidized beds with reasonable accuracy is now possible, but the prediction of bubbling behavior or instantaneous phase distributions using the Eulerian two-fluid model (TFM) is still a challenge.…”

Section: Introductionmentioning

confidence: 99%

“…However, the predictions of TFM are known to depend on the closure equations and eventually the ability of the latter to describe the underlying flow physics into the TFM. Bubbling characteristics (i.e., bubble size and bubbling frequency) in a fluidized bed and the formation of large bubbles/slugs are known to be governed by the interfacial forces (e.g., drag force), solid shear stresses, − and particle–particle collisions and also due to variations in wall boundary conditions , for particular flow conditions and particle properties.…”

Section: Introductionmentioning

confidence: 99%

“…The solid frictional viscosity models (e.g., Srivastava and Sundaresan, Johnson and Jackson, and Syamlal et al), which are derived on the basis of Schaeffer or Coulomb frictional law, depend on the critical solid pressure or frictional solid pressure. The effect of different solid frictional viscosity models was investigated by a few researchers. ,,,,, An increase in the solid frictional viscosity values led to an increase in the size of the bubbles due to an increase in the compactness of the solid phase around the bubble. A comparison of bubbling characteristics predicted using the constant viscosity model and kinetic theory of granular flow (KTGF)-based solid frictional models was reported. ,, In the frictional viscosity models proposed by Srivastava and Sundaresan, Johnson and Jackson, and Syamlal et al., the frictional contribution of the solid pressure is added to the granular pressure when the solid volume fraction exceeds a threshold value.…”

Section: Introductionmentioning

confidence: 99%

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Eulerian Simulations of Bubbling Behavior in a Gas–Solid Fluidized Bed: Role of Solid Frictional Viscosity

Singh

Roy

Buwa

2021

Ind. Eng. Chem. Res.

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Eulerian computational fluid dynamics (CFD) models that can predict bubbling behavior accurately are important to predict solids mixing, transport processes, and reactions in fluidized beds. In the present work, Eulerian two-fluid simulations are performed to understand the role of solid-phase viscosity in bubbling behavior for different Geldart Group particles and in the entire bubbling regime. The predictions are validated with temporally and spatially resolved measurements performed using electrical capacitance tomography (ECT). In dense conditions, the solid frictional viscosity around the bubbles was higher and the gas tends to accumulate in the bubbles, leading to the formation of larger bubbles. However, under dilute conditions, smaller bubbles are formed due to the marginal influence of the frictional viscosity. Further, the bubbling frequency and bubble chord length distribution predicted using the Johnson−Jackson frictional pressure model with a critical solid volume fraction of 0.55 and the Schaffer frictional viscosity model are in good agreement with the corresponding ECT measurements.

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The effect of frictional pressure, geometry and wall friction on the modelling of a pseudo-2D bubbling fluidised bed reactor

Cited by 12 publications

References 21 publications

On the choice of closure complexity in anisotropic drag closures for filtered Two Fluid Models

On the choice of closure complexity in anisotropic drag closures for filtered Two Fluid Models

Evaluation of wall friction models for riser flow

Eulerian Simulations of Bubbling Behavior in a Gas–Solid Fluidized Bed: Role of Solid Frictional Viscosity

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