Modeling and analysis of local hot spot formation in down-flow adiabatic packed-bed reactors

Agrawal, Rachana; West, David; Balakotaiah, Vemuri

doi:10.1016/j.ces.2006.11.057

Cited by 35 publications

(20 citation statements)

References 18 publications

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“…The fluid interface is compressed and stretched at the flow stagnation points at a stretching and compression rates = q x ∕ x = − q z ∕ z. This forms hot spots, i.e., regions where mixing and reaction are maximum [Agrawal et al, 2007;Gérard et al, 2012], which follow the strain rate distribution (Figures 2a-2c). The hot spots appear on either side of the stagnation points (Figures 2d) where the compression of the boundary layer is highest.…”

Section: Mixing and Dissolution Patternsmentioning

confidence: 99%

Dissolution patterns and mixing dynamics in unstable reactive flow

Hidalgo

Dentz

Cabeza

et al. 2015

Geophysical Research Letters

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We study the fundamental problem of mixing and chemical reactions under a Rayleigh‐Taylor‐type hydrodynamic instability in a miscible two‐fluid system. The dense fluid mixture, which is generated at the fluid‐fluid interface, leads to the onset of a convective fingering instability and triggers a fast chemical dissolution reaction. Contrary to intuition, the dissolution pattern does not map out the finger geometry. Instead, it displays a dome‐like, hierarchical structure that follows the path of the ascending fluid interface and the regions of maximum mixing. These mixing and reaction hot spots coincide with the flow stagnation points, at which the interfacial mixing layer is compressed and deformed. We show that the deformation of the boundary layer around the stagnation points controls the evolution of the global scalar dissipation and reaction rates and shapes the structure of the reacted zones. The persistent compression of the mixing layer explains the independence of the mixing rate from the Rayleigh number when convection dominates.

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Section: Mixing and Dissolution Patternsmentioning

confidence: 99%

Dissolution patterns and mixing dynamics in unstable reactive flow

Hidalgo

Dentz

Cabeza

et al. 2015

Geophysical Research Letters

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“…Previous studies were focused on linear analysis of the first four modes (see Figure 1 with the corresponding μ mn ) in either 3D16, 27, 28 or shallow reactor models15, 16, 29, 30 and did not simulate patterns. Linear analysis suggests formation of moving nonrotating patterns of the form (2) while the unstable domains of certain modes were quite similar in 3D and SR models.…”

Section: Introductionmentioning

confidence: 99%

Transversal patterns in three‐dimensional packed bed reactors: Oscillatory kinetics

Nekhamkina¹,

Sheintuch²

2010

AIChE Journal

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in Wiley Online Library (wileyonlinelibrary.com).Formation of transversal patterns in a 3D cylindrical reactor is studied with a catalytic reactor model in which an exothermic first-order reaction of Arrhenius kinetics occurs with a variable catalytic activity. Under these oscillatory kinetics, the system exhibits a planar front (1D) solution with the front position oscillating in the axial direction. Three types of patterns were simulated in the 3D system: rotating fronts, oscillating fronts with superimposed transversal (nonrotating) oscillations, and mixed rotating-oscillating fronts. These solutions coexist with the planar front solution and require special initial conditions. We map bifurcation diagrams showing domains of different modes using the reactor radius as a bifurcation parameter. The possible reduction of the 3D model to the 2D cylindrical shell model is discussed.

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“…fully developed or simultaneously developing boundary layers) but are independent of channel geometry. For the case of shallow packed-beds, the form of the second term is different, where the exponents are different on the velocity (or Reynolds number) and diffusivity (or Schmidt/Prandtl number), see for example, Agrawal et al [28]. Again, this new form does not alter any of qualitative bifurcation features studied here].…”

Section: Model Developmentmentioning

confidence: 83%

“…Regarding the accuracy (and validity) of the present model with respect to simpler or more complex models, the following comments (which are substantiated in references [22][23][24][25][26][27][28][29][30][31][32]) are appropriate: (i) The simplest of the models, namely the one dimensional pseudo-homogeneous plug flow model is structurally unstable and does not show ignition/extinction but only parametric sensitivity (ii) The pseudo-homogeneous model with no axial gradients (which is included as a special case of our model when interphase gradients are negligible) is robust but is good only for very small axial length scales and hydraulic diameters (micro-channels) [Remark: Structural stability or robustness here implies that the bifurcation and/or qualitative features do not change when the model is perturbed by including spatial gradients or other phenomena as long as the perturbations are small, see [30]] (iii) The 2-D boundary layer models (of parabolic type) that ignore axial diffusion (conduction) are structurally unstable, index infinity differential-algebraic system (and are not initial value problems). Further, as explained in the literature articles [23,26], most computational codes do not consider the Gibbs' phenomenon (which does not disappear even for arbitrarily small mesh size and leads to incorrect fluxes and temperature overshoot at the point of ignition) and compute only a single solution.…”

Section: Model Developmentmentioning

confidence: 98%