Numerical investigation and modeling of reacting gas-solid flows in the presence of clusters

Capecelatro, Jesse; Pepiot, Perrine

doi:10.1016/j.ces.2014.10.005

Cited by 29 publications

(11 citation statements)

References 57 publications

(67 reference statements)

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“…Turbulent disperse two-phase flows with strong momentum coupling exhibit a wide range of important phenomena that directly impact the overall fluid dynamical system. Such mechanisms include the production of fluid-phase turbulent kinetic energy (TKE) via wakes past particles, 7,13,31 the accumulation of particles in high-strain regions of the flow, 3,11,17,24 and the spontaneous generation of densely packed particles, 1,[6][7][8]14,18 i.e., clusters, that have been observed to hinder mixing between the phases 9,25 and amplify the aforementioned two-way-coupled effects. In wall-bounded flows, non-trivial coupling between the phases leads to additional inhomogeneities in particle concentration that feed back to the underlying turbulence.…”

Section: Introductionmentioning

confidence: 99%

Strongly coupled fluid-particle flows in vertical channels. I. Reynolds-averaged two-phase turbulence statistics

2016

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Simulations of strongly coupled (i.e., high-mass-loading) fluid-particle flows in vertical channels are performed with the purpose of understanding the fundamental physics of wall-bounded multiphase turbulence. The exact Reynolds-averaged (RA) equations for high-mass-loading suspensions are presented, and the unclosed terms that are retained in the context of fully developed channel flow are evaluated in an Eulerian-Lagrangian (EL) framework for the first time. A key distinction between the RA formulation presented in the current work and previous derivations of multiphase turbulence models is the partitioning of the particle velocity fluctuations into spatially correlated and uncorrelated components, used to define the components of the particle-phase turbulent kinetic energy (TKE) and granular temperature, respectively. The adaptive spatial filtering technique developed in our previous work for homogeneous flows [ J. Capecelatro, O. Desjardins, and R. O. Fox, "Numerical study of collisional particle dynamics in cluster-induced turbulence," J. Fluid Mech. 747, R2 (2014)] is shown to accurately partition the particle velocityfluctuations at all distances from the wall. Strong segregation in the components of granular energy is observed, with the largest values of particle-phase TKE associated with clusters falling near the channel wall, while maximum granular temperature is observed at the center of the channel. The anisotropy of the Reynolds stresses both near the wall and far away is found to be a crucial component for understanding the distribution of the particle-phase volume fraction. In Part II of this paper, results from the EL simulations are used to validate a multiphase Reynolds-stress turbulence model that correctly predicts the wall-normal distribution of the two-phase turbulence statistics.

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Section: Introductionmentioning

confidence: 99%

Strongly coupled fluid-particle flows in vertical channels. I. Reynolds-averaged two-phase turbulence statistics

2016

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“…We found that the mean scalar gradient is unable to reproduce the unclosed scalar flux profiles shown in Figure , and thus more sophisticated models are needed. In Capecelatro et al, an equation for

\overset{true˜}{ɛ_{p}^{'} Y_{VOL}^{'}}

was derived for a zero‐dimensional system. However, it was ultimately found that obtaining closures for the unclosed terms that appear in this equation for

\overset{true˜}{ɛ_{p}^{'} Y_{VOL}^{'}}

is challenging.…”

Section: Reduced‐order Modelingmentioning

confidence: 99%

“…Recent work has demonstrated that two‐dimensional simulations are only capable of capturing qualitative features of particle clustering, and a fully three‐dimensional description is required to accurately capture the quantitative flow behavior in CFB risers. Capecelatro et al performed three‐dimensional EL simulations of catalytic particles in a periodic pipe flow. Those simulations showed that the presence of clusters delayed the conversion process by up to 85% compared to a corresponding homogeneous flow.…”

Section: Introductionmentioning

confidence: 99%

“…Local regions of densely packed catalytic particles, referred to as clusters, develop in the flow and fall at the walls of the reactor, while dilute suspensions of particles rise in the central region . Clusters have been observed to reduce mixing and interaction of particles with the transport gas, potentially lowering operating efficiencies significantly. Meanwhile, detailed studies demonstrating the quantitative impact of particle clustering on chemical processes occurring in such flows remain elusive.…”

Section: Introductionmentioning

confidence: 99%

“…With EL, individual particle trajectories are solved using Newton's laws of motion, and models are required for interphase exchange and particle collisions. Due to the added computational expense of tracking individual particles, EL methods coupled with a kinetic model have only recently been applied in three dimensions, and are generally limited to the dense granular flow regime near the inlet of the reactor. Most EL studies to date consider two‐dimensional flows with a relatively small number of particles (e.g., Refs.…”

Section: Introductionmentioning

confidence: 99%

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A computational study of the effects of multiphase dynamics in catalytic upgrading of biomass pyrolysis vapor

2018

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A recurring challenge among the variety of existing biomass-to-biofuel conversion technologies is the need to ensure optimal and homogeneous contact between the various phases involved. The formulation of robust design rules from an empirical standpoint alone remains difficult due to the wide range of granular flow regimes coexisting within a given reactor. In this work, a volume-filtered Eulerian-Lagrangian framework is employed that solves chemically reacting flows in the presence of catalytic particles. The simulation strategy is used to quantify the role of the particle clustering on catalytic upgrading of biomass pyrolysis vapor in risers. It is shown that particle clustering can reduce the catalytic conversion rate of biomass pyrolysis vapors by up to about 50%. The simulation results are also compared with an engineering model based on continuously stirred tank reactor (CSTR). A one-dimensional Reynolds-averaged transport equation is derived, and the unclosed terms that account for the heterogeneity caused by clusters are evaluated.

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Meso‐scale statistical properties of gas–solid flow—a direct numerical simulation (DNS) study

Liu

Wang

2016

AIChE Journal

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Statistical properties of particles in heterogeneous gas–solid flow were numerically investigated based on the results of a three‐dimensional large‐scale direct numerical simulation (DNS). Strong scale‐dependence and local non‐equilibrium of these properties, especially the particle fluctuating velocity (PFV) or granular temperature, were observed to be related to the effect of meso‐scale structures formed by the compromise in competition between fluid and particle dominated mechanisms. To quantify such effects, the heterogeneous structures were partitioned into a gas‐rich dilute phase and a solid‐rich dense phase according to the particle‐scale voidage defined through the Voronoi tessellation. Non‐equilibrium features, such as the deviation of PFV from Gaussian distribution and anisotropy, were found even in phase‐specific properties. A new distribution function for the PFV well characterizing these features was obtained by fitting the DNS results, which takes a typical bi‐disperse mode, with phase‐specific granular temperatures. The implications of these findings to the kinetic theory of granular flow and traditional continuum models of gas–solid flow were also discussed. © 2016 American Institute of Chemical Engineers AIChE J, 63: 3–14, 2017

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Numerical investigation and modeling of reacting gas-solid flows in the presence of clusters

Cited by 29 publications

References 57 publications

Strongly coupled fluid-particle flows in vertical channels. I. Reynolds-averaged two-phase turbulence statistics

Strongly coupled fluid-particle flows in vertical channels. I. Reynolds-averaged two-phase turbulence statistics

A computational study of the effects of multiphase dynamics in catalytic upgrading of biomass pyrolysis vapor

Meso‐scale statistical properties of gas–solid flow—a direct numerical simulation (DNS) study

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